similarities and differences between prokaryotic and eukaryotic cells essay

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Prokaryotic vs Eukaryotic Cells – Similarities and Differences

Prokaryotic and eukaryotic cells are the basic units of life on Earth. The basic distinction between prokaryotes and eukaryotes is that prokaryotes lack a membrane-bound nucleus and organelles. Instead, genetic material and processes occur within prokaryotic cytoplasm. Both prokaryotic and eukaryotic cells contain cytoplasm that is enclosed by a cell membrane. Both perform protein synthesis using ribosomes.

Prokaryotes

Prokaryotes are unicellular organisms that lack membrane-bound structures, including the nucleus and other organelles. Usually, prokaryotic cells are small and relatively simple in structure compared with eukaryotic cells. Prokaryotes have a single, often circular chromosome that occupies the nucleoid region of the cell. Plasmids carry additional DNA .

Here are key prokaryote features:

• Capsule : layer of carbohydrates that surrounds the cell wall of some bacteria and helps them attach to surfaces
• Cell wall : consists of peptidoglycans that give the cell structure and protection
• Cell membrane : also known as the plasma membrane, which encloses the cytoplasm and separates the cell from the environment
• Cytoplasm : region enclosed by the cell membrane
• Nucleoid : region that contains DNA
• Plasmids : independently reproducing DNA
• Ribosome : performs protein synthesis
• Flagella : thin, tail-like structures that aid movement
• Pili : short, rod-shaped structures involves in attachment to surfaces and DNA transfer
• Fimbriae : thin, hair-like structures used for attachment
• Vesicles : sacs released by the membrane that perform a variety of functions
• Vacuoles : storage sacs found in some bacterial cells

A eukaryotic cell has a true nucleus and membrane-bound organelles . Plant and animal cells are examples of eukaryotic cells. Here are key eukaryote features.

• Nucleus : contains DNA and oversees all cell processes
• Nucleolus : site of ribosome biogenesis; plays role in cell stress response
• Plasma membrane : encloses the cell
• Cytoplasm : region between the nuclear membrane and the plasma membrane
• Cell wall : supports and protects plant, algae, and and fungi cells
• Mitochondria : provide chemical energy to the cell in the form of ATP
• Chloroplasts : traps energy for photosynthesis in some eukaryotic cells
• Ribosomes : perform protein synthesis
• Endoplasmic reticulum : makes and modifies proteins (rough); expresses lipids (smooth)
• Golgi apparatus : sorts, packages, and processes proteins
• Vesicles and vacuoles : membrane-bound storage and transportation sacs

Similarities Between Prokaryotic and Eukaryotic Cells

The most important similarity between prokaryotes and eukaryotes is that they both consist of cells. The lipid bilayer that forms the cell membrane separates the molecular machinery of life from the outside environment, while allowing for transport into and out of the cell. Also, both prokaryotic and eukaryotic cells use 2′-deoxyribonucleic acid (DNA) to code for genes.

• Have cell or plasma membrane
• Contain cytoplasm
• Have ribosomes
• Have vesicles
• Have vacuoles

Differences Between Prokaryotic and Eukaryotic Cells

The identifying difference between prokaryotic and eukaryotic cells is the absence or presence of a membrane-bound nucleus and organelles. However, they also differ in size, complexity, reproduction, and means of locomotion.

• Prokaryote cells lack a membrane-bound nucleus or organelles.
• Prokaryotic cells generally are smaller than eukaryotic cells.
• Eukaryotic cells are more complex.
• Prokaryotic cells are unicellular, while eukaryotic cells may be multicellular.
• A prokaryotic cell has a single haploid (n) chromosome, while eukaryotes have multiple, paired, diploid (2n) chromosomes.
• Both types of cells have ribosomes, but eukaryotic ribosomes are larger.
• Prokaryotic chromosomes are circular or linear. Eukaryotic chromosomes are linear and associated with histone proteins.
• Both types of cells may use flagella, but the composition and structure differs between prokaryotic and eukaryotic cells.
• Both types of cells use asexual and sexual reproduction, but sexual reproduction is more common in eukaryotes.
• Plants and fungi are eukaryotes that have cell walls, but they are chemically simpler than prokaryotic cell walls.

Kingdoms of Life

Learn how prokaryotic and eukaryotic cells relate to the kingdoms of life.

Which Came First?

Cells started forming on Earth at least 3.5 billion years ago. These cells were prokaryotes, but much simpler than prokaryotic cells today. Scientists believe eukaryotes arose from symbiosis between prokaryotic cells. Eventually, an ancestral prokaryote endosymbiosed other cells, which became mitochondria and chloroplasts, The origin of other organelles is less clear.

Prokaryotes vs Eukaryotes Worksheet

This worksheets tests whether you recognize the differences between prokaryotes and eukaryotes, including properties of the cells and representative organisms.

Worksheet [ PDF ][ PNG ]

Answer Key [ PDF ][ PNG ]

• Campbell, N.A.; Williamson B,; Heyden, R.J. (2006). Biology: Exploring Life . Boston, Massachusetts: Pearson Prentice Hall. ISBN 9780132508827.
• Gribaldo, S.; Brochier-Armanet, C. (January 2020). “Evolutionary relationships between archaea and eukaryotes”. Nature Ecology & Evolution . 4 (1): 20–21. doi: 10.1038/s41559-019-1073-1
• Maton, A. (1997). Cells: Building Blocks of Life . New Jersey: Prentice Hall. ISBN 9780134234762.
• Nelson, D.L.; Cox, M.M. (2005). Lehninger Principles of Biochemistry (4th ed.). New York: W.H. Freeman. ISBN 978-0-7167-4339-2.
• Raven, P.H.; Johnson, G.B. (2002). Biology . McGraw-Hill Education. ISBN 9780071122610.

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• Prokaryotic and eukaryotic cells
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Prokaryotes vs. Eukaryotes: Similarities and Differences

All living cells can be classified as either prokaryotic or eukaryotic. Bacteria are prokaryotic or prenuclear organisms (organisms without a true nucleus), while fungi, protozoa, helminths, and other organisms are eukaryotic.

Viruses depend on host cells for survival, so they are not considered cellular organisms but infectious agents. Prions (abnormal infectious proteins) are also not considered living cells.

A notable characteristic of eukaryotic cells is the presence of membrane-enclosed subcellular organelles with specialized cellular functions such as mitochondria (sites of aerobic respiration) and chloroplasts (sites of photosynthesis in green plants).

• Endoplasmic reticulum processes and transport proteins.
• Lysosomes provide an environment for controlled enzymatic degradation of intracellular substances.
• Mitochondria is the powerhouse of the cell; it generates energy (ATP)
• The nucleus provides a membrane enclosure for chromosomes.
• The Golgi body transports substances throughout the cell, including internal delivery and exocytosis or secretion of molecules.

Prokaryotic cells, such as bacteria, do not contain organelles. All functions take place in the cytoplasm or cytoplasmic membrane of the cell. The cell wall composed of peptidoglycan is the notable structure present only in prokaryotic bacterial cells.

Eukaryotic cells have a cytoskeleton that supports cellular structure, organization, and movement. The cytoskeleton plays an essential role in immunology by mediating phagocytosis.

Eukaryotic and prokaryotic cells differ considerably at the macromolecular level, including chromosomal organization, gene expression, and protein synthesis machinery. For example;

• Eukaryotic cells contain a nucleus with a nuclear membrane enclosing multiple chromosomes, while prokaryotic cells have a single chromosome (nucleoid) that is not enclosed in a nuclear membrane.
• Another major difference between bacterial DNA and eukaryotic DNA is that bacterial DNA has no introns, whereas eukaryotic DNA does.
• A key genetic difference between prokaryotes and eukaryotes is that eukaryotes typically contain two copies of each gene and are, thus, genetically diploid.

Prokaryotic and eukaryotic cells differ substantially in many other characteristics, some of which are tabulated here:

• Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson.
• Pelczar Jr., M., Chan, E., & Krieg, N. (2007). Microbiology (5th edition). Tata McGraw-Hill

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Eukaryotic Cell vs. Prokaryotic Cell

The distinction between prokaryotes and eukaryotes is considered to be the most important distinction among groups of organisms. Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Differences in cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomal DNA .

Prokaryotes were the only form of life on Earth for millions of years until more complicated eukaryotic cells came into being through the process of evolution.

Comparison chart

Definition of eukaryotes and prokaryotes.

Prokaryotes (pro-KAR-ee-ot-es) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos , pl. -otes ; also spelled "procaryotes") are organisms without a cell nucleus (= karyon), or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular.

Eukaryotes (IPA: [juːˈkæɹɪɒt]) are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane bound structure is the nucleus. This feature gives them their name, (also spelled "eucaryote,") which comes from the Greek ευ, meaning good/true, and κάρυον, meaning nut, referring to the nucleus. Animals , plants, fungi, and protists are eukaryotes.

Differences Between Eukaryotic and Prokaryotic Cells

The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms.

• The most fundamental difference is that eukaryotes do have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound.

• In eukaryotes, the mitochondria and chloroplasts perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria . In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare.
• The cell walls of prokaryotes are generally formed of a different molecule (peptidoglycan) to those of eukaryotes (many eukaryotes do not have a cell wall at all).
• Prokaryotes are usually much smaller than eukaryotic cells.
• Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organised chromosomes. Although some eukaryotes have satellite DNA structures called plasmids, these are generally regarded as a prokaryote feature and many important genes in prokaryotes are stored on plasmids.
• Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes.

• Prokaryotes also differ from eukaryotes in the structure, packing, density, and arrangement of their genes on the chromosome. Prokaryotes have incredibly compact genomes compared to eukaryotes, mostly because prokaryote genes lack introns and large non-coding regions between each gene.
• Whereas nearly 95% of the human genome does not code for proteins or RNA or includes a gene promoter, nearly all of the prokaryote genome codes or controls something.
• Prokaryote genes are also expressed in groups, known as operons, instead of individually, as in eukaryotes.
• In a prokaryote cell, all genes in an operon(three in the case of the famous lac operon) are transcribed on the same piece of RNA and then made into separate proteins, whereas if these genes were native to eukaryotes, they each would have their own promoter and be transcribed on their own strand of mRNA. This lesser degree of control over gene expression contributes to the simplicity of the prokaryotes as compared to the eukaryotes.

• Wikipedia:Eukaryote
• Wikipedia:Prokaryote

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• Biology Article
• Prokaryotic And Eukaryotic Cells

Difference between Prokaryotic and Eukaryotic Cells

Introduction: prokaryotes and eukaryotes.

Biotic components of the environment include all forms of life from minute bacteria to towering giant Sequoias. However, at the microscopic level, all living organisms are made up of the same basic unit – the cell.

Prokaryotic Cell

Eukaryotic cell.

As a result, the cell is referred to as the structural and functional unit of all living organisms.  The word cell has its origins in Latin, and when translated, it means “small room” and was first observed by Robert Hooke – an English natural philosopher in the year 1665.

He also compared his discovery to the cells in a honeycomb, as they showcase a similar structure.

An image illustrating the difference between Prokaryotic and Eukaryotic Cells. Note that the prokaryotic cell is a complete individual organism

Eventual advancements in science and technology shed more light into the cell, with new findings and discoveries about its structure and cellular components.  During the 1950s, scientists postulated the concept of prokaryotic cells and eukaryotic cells, with earlier groundwork being laid by Edouard Chatton, a French Biologist in 1925.

Anatomically, cells vary with respect to their classification, therefore, prokaryotic cells and eukaryotic cells differ from each other quite drastically. Read on to explore how they differ from each other.

The term “ prokaryote ” is derived from the Greek word “ pro “, (meaning: before) and “ karyon ” (meaning: kernel). It translates to “ before nuclei. “

Prokaryotes are one of the most ancient groups of living organisms on earth, with fossil records dating back to almost 3.5 billion years ago.

These prokaryotes  thrived in the earth’s ancient environment, some using up chemical energy and others using the sun’s energy. These extremophiles thrived for millions of years, evolving and adapting. Scientists speculate that these organisms gave rise to the eukaryotes.

Prokaryotic cells are comparatively smaller and much simpler than eukaryotic cells. The other defining characteristic of prokaryotic cells is that it does not possess membrane-bound cell organelles such as a nucleus. Reproduction happens  through the process of binary fission.

Structurally, prokaryotes have a capsule enveloping their entire body, and it functions as a protective coat. This is crucial for preventing the process of phagocytosis (where the bacteria gets engulfed by other eukaryotic cells, such as macrophages) The pilus is a hair-like appendage found on the external surface of most prokaryotes and it helps the organism to attach itself to various environments. The pilus essentially resists being flushed, hence, it is also called attachment pili. It is commonly observed in bacteria.

Right below the protective coating lies the cell wall, which provides strength and rigidity to the cell. Further down lies the cytoplasm that helps in cellular growth, and this is contained within the plasma membrane, which separates the interior contents of the cell from the outside environment.  Within the cytoplasm, ribosomes exist and it plays an important role in protein synthesis. It is also one of the smallest components within the cell. 

Some prokaryotic cells contain special structures called mesosomes which assist in cellular respiration . Most prokaryotes also contain plasmids, which contain small, circular pieces of DNA. To help with locomotion,  flagella are present, though, pilus can also serve as an aid for locomotion.  Common examples of Prokaryotic organisms are bacteria and archaea. Also, all members of Kingdom Monera are prokaryotes.

Main Article:   Prokaryotic Cells

The term “ Eukaryotes ” is derived from the Greek word “ eu “, (meaning: good) and “ karyon ” (meaning: kernel), therefore, translating to “ good or true nuclei .” Eukaryotes are more complex and much larger than prokaryotes.   They include almost all the major kingdoms except kingdom monera.

Structurally, eukaryotes possess a cell wall, which supports and protects the plasma membrane. The cell is surrounded by the plasma membrane and it controls the entry and exit of certain substances.

The nucleus contains DNA, which is responsible for storing all genetic information. The nucleus is surrounded by the nuclear membrane. Within the nucleus exists the nucleolus, and it plays a crucial role in synthesising proteins. Eukaryotic cells also contain mitochondria, which are responsible for the creation of energy, which is then utilized by the cell.

Present in only plant cells, chloroplasts are the subcellular sites of photosynthesis. The endoplasmic reticulum helps in the transportation of materials. Besides these, there are also other cell organelles that perform various other functions and these include  ribosomes, lysosomes, Golgi bodies, cytoplasm, chromosomes, vacuoles and centrosomes.

Examples of eukaryotes include almost every unicellular organism with a nucleus and all multicellular organisms.

Main Article:  Eukaryotic Cells

Though these two classes of cells are quite different, they do possess some common characteristics. For instance, both possess cell membranes and ribosomes, but the similarities end there. The complete list of differences between prokaryotic and eukaryotic cells is summarized as follows:

Learn more about prokaryotic cell and eukaryotic cell, their differences and other related topics at BYJU’S Biology

Frequently Asked Questions

What is a prokaryotic cell.

A prokaryotic cell is a primitive type of cell that is characterized by the absence of a nucleus. Furthermore, prokaryotes do not possess membrane-bound cellular organelles. Prokaryotes are exclusively unicellular.

What is a Eukaryotic cell?

Eukaryotic cells are cells that possess a true nucleus along with membrane-bound organelles. Eukaryotes can either be unicellular or multicellular.

What is the difference between Prokaryotic and Eukaryotic cells?

The defining characteristic feature that distinguishes between prokaryotic and eukaryotic cell is the nucleus. In prokaryotic cells, the true nucleus is absent, moreover, membrane-bound organelles are present only in eukaryotic cells. Another major difference between prokaryotic and eukaryotic cells is that prokaryotic cells are exclusively unicellular, while the same does not apply to eukaryotic cells.

Define Cell?

The cell is the basic functional and structural unit of life. Cell plays a vital role in all biological activities and include membrane-bound organelles, which perform several individual functions to keep the cell alive and active.

What is Ribosome?

The ribosome is a multi-component cell organelle consisting of RNA and protein. Therefore, it is called the site of protein synthesis. Ribosomes are present both in prokaryotic and eukaryotic cells. Compared to prokaryotes, eukaryotes have larger ribosomes in their cells.

List out the unique features of Animal and Plant Cells.

Both animal and plant cells have several unique features. Listed below are some important features:

• In structure, both animal and plant cells are quite similar.
• Both possess nucleus and plasma membrane, a selectively permeable membrane of the cell.
• Both animal and plant cells include membrane-bound organelles with their specialized functions.
• Animal and plant cells have vacuoles, which serve as the storage unit and maintain the shape of the cell.
• Mitochondria is the powerhouse of the cell. It stores and provide energy for different cellular activities and is found both in both animal and plant cells.

List out the functions of Chloroplasts.

Chloroplasts are the plastids found in all plant cells. These cell organelles comprise the photosynthetic pigment called chlorophyll and are involved in synthesizing food by the process of photosynthesis.

Who discovered Cell and Cell Theory?

The cell was first discovered in the year 1665 by an English natural philosopher Robert Hooke. The Cell Theory was explained by Theodor Schwann and Matthias Jakob Schleiden in the year 1830.

Further Reading:

• Competent Cells
• Difference Between Plasmid DNA And Chromosomal DNA

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describe the physiological difference between eukaryotic celsl and prokaryotic cells

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What is the difference between prokaryotic and eukaryotic cells?

Discover the structural and functional difference between prokaryotic and eukaryotic cells

• Common features
• Major differences

Additional resources

Bibliography.

The main difference between prokaryotic and eukaryotic cells lies in their structure.

Prokaryotic cells and eukaryotic cells are the two types of cells that exist on Earth . There are several differences between the two, but the biggest distinction between them is that eukaryotic cells have a distinct nucleus containing the cell's genetic material, while prokaryotic cells don't have a nucleus and have free-floating genetic material instead. 

What are prokaryotic and eukaryotic cells?

All living things can be divided into three basic domains: Bacteria , Archaea and Eukarya. The primarily single-celled organisms found in the Bacteria and Archaea domains are known as prokaryotes. These organisms are made of prokaryotic cells — the smallest, simplest and most ancient cells.

Organisms in the Eukarya domain are made of the more complex eukaryotic cells. These organisms, called eukaryotes, can be unicellular or multicellular and include animals, plants, fungi and protists . Many people are unclear on whether yeasts or fungi are prokaryotes or eukaryotes. Both are eukaryotes and share similar cell structure to all other eukaryotes.

There is evidence to suggest that eukaryotes are the descendants of separate prokaryotic cells, according to Berkeley University of California.  

Eukaryotes developed at least 2.7 billion years ago, following 1 to 1.5 billion years of prokaryotic evolution , according to the National Institutes of Health (NIH) . Scientists hypothesize that the nucleus and other eukaryotic features may have first formed after a prokaryotic organism swallowed up another, according to the University of Texas . 

It’s also been suggested that tiny organelles in eukaryotic cells – called mitochondria – may also be the descends of prokaryotic living-bacterium which were engulfed by other cells and remained in the cell as a permanent guest, according to Berkeley University. 

What do prokaryotes and eukaryotes have in common?

Although prokaryotic and eukaryotic cells have many differences, they share some common features, including the following:

• DNA : Genetic coding that determines all the characteristics of living things.
• Cell (or plasma) membrane: Outer layer that separates the cell from the surrounding environment and acts as a selective barrier for incoming and outgoing materials.
• Cytoplasm: Jelly-like fluid within a cell that is composed primarily of water, salts and proteins.
• Ribosomes: Organelles that make proteins.

How do prokaryotes and eukaryotes differ?

Eukaryotic cells have a nucleus surrounded by a nuclear envelope that consists of two lipid membranes, according to Nature E d ucation . The nucleus holds the eukaryotic cell's DNA. Prokaryotic cells do not have a nucleus; rather, they have a membraneless nucleoid region (open part of the cell) that holds free-floating DNA, according to Washington University .

The entire DNA in a cell can be found in individual pieces known as chromosomes . Eukaryotic cells have many chromosomes which undergo meiosis and mitosis during cell division, while most prokaryotic cells consist of just one circular chromosome. However, recent studies have shown that some prokaryotes have as many as four linear or circular chromosomes, according to Nature Education . For example, Vibrio cholerae, the bacterium that causes cholera , has two circular chromosomes.

Eukaryotic cells have several other membrane-bound organelles not found in prokaryotic cells. These include the mitochondria (convert food energy into adenosine triphosphate, or ATP, to power biochemical reactions); rough and smooth endoplasmic reticulum (an interconnected network of membrane-enclosed tubules that transport synthesized proteins); golgi complex (sorts and packages proteins for secretion); and in the case of plant cells, chloroplasts (conduct photosynthesis ). All of these organelles are located in the eukaryotic cell's cytoplasm.

Although only eukaryotes carry membrane-bound organelles, recent evidence suggests that both eukaryotes and prokaryotes can produce organelle-like structures that lack membranes, according to a 2020 report published in the journal Proceedings of the National Academy of Sciences (PNAS).

For instance, in the bacterium Escherichia coli , molecules and proteins cluster together to form liquid "compartments" within the cytoplasm, according to the PNAS study. These compartments form similarly to how oil forms droplets when mixed with water, according to a statement from the University of Michigan . Such membraneless structures have been reported in many bacterial species, including Mycobacterium tuberculosis , which causes tuberculosis, and cyanobacteria, a type of photosynthetic bacteria that can also cause disease.

In eukaryotic cells, the ribosomes are bigger, more complex and bound by a membrane. They can be found in various places: Sometimes in the cytoplasm; on the endoplasmic reticulum; or attached to the nuclear membrane (covering on the nucleus).

In prokaryotic cells, the ribosomes are scattered and floating freely throughout the cytoplasm. The ribosomes in prokaryotic cells also have smaller subunits. All ribosomes (in both eukaryotic and prokaryotic cells) are made of two subunits — one larger and one smaller. In eukaryotes, these pieces are identified by scientists as the 60-S and 40-S subunits. In prokaryotes, the ribosomes are made of slightly smaller subunits, called 50-S and 30-S.

– Robert Hooke: English scientist who discovered the cell

– The Human Body: Anatomy, facts & functions

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The difference in types of subunits has allowed scientists to develop antibiotic drugs , such as streptomycin, that attack certain types of infectious bacteria, according to the British Society for Cell Biology . On the downside, some bacterial toxins and the polio virus use the ribosome differences to their advantage; they're able to identify and attack eukaryotic cells' translation mechanism, or the process by which messenger RNA is translated into proteins.

Most eukaryotes also reproduce sexually (although some protists and single-celled fungi may reproduce through mitosis, which is functionally similar to asexual reproduction). Prokaryotes reproduce asexually, resulting in the offspring being an exact clone of the parent. Some prokaryotic cells also have pili, which are adhesive hair-like projections used to exchange genetic material during a type of sexual process called conjugation, according to Concepts of Biology . Conjugation can occur in bacteria, protozoans and some algae and fungi.

Most prokaryotic cells have a rigid cell wall that surrounds the plasma membrane and gives shape to the organism. In eukaryotes, vertebrates don't have a cell wall but plants do. The cell walls of prokaryotes differ chemically from the eukaryotic cell walls of plant cells, which are primarily made of cellulose. In bacteria, for example, the cell walls are composed of peptidoglycans (sugars and amino acids), according to Washington University .

Check out this animated video by the Amoeba Sisters that explains the difference between prokaryotic and eukaryotic cells. To take a more indepth look into all the cells in the world take a look at Looking Inside Cells: Life Science by Kimerberly Fekany Lee. 

Lesli J Favor, “ How Eukaryotic and Prokaryotic Cells Differ (Britannica Guide to Cell Biology) ,” Rosen Publishing, 2014.

Frantisek Baluska et al, “Eukaryotic Cells and their Cell Bodies: Cell Theory Revised”, Annals of Botany, Volume 94, Jukly 2004, https://doi.org/10.1093/aob/mch109  

James Wagstaff & Jan Lowe, “Prokaryotic cytoskeletons: protein filaments organizing small cells”, Nature Reviews Microbiology, Volume 16, January 2018, https://doi.org/10.1038/nrmicro.2017.153  

Avadhesha Surolia & Abhijit Chakrabarti, “ Biochemical Roles of Eukaryotic Cell Surface Macromolecules ”, Springer International Publishing, 2014.

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Scott is a staff writer for How It Works magazine and has previously written for other science and knowledge outlets, including BBC Wildlife magazine, World of Animals magazine, Space.com and All About History magazine . Scott has a masters in science and environmental journalism and a bachelor's degree in conservation biology degree from the University of Lincoln in the U.K. During his academic and professional career, Scott has participated in several animal conservation projects, including English bird surveys, wolf monitoring in Germany and leopard tracking in South Africa. 

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Chapter 3: Introduction to Cell Structure and Function

3.2 Comparing Prokaryotic and Eukaryotic Cells

Learning objectives.

By the end of this section, you will be able to:

• Name examples of prokaryotic and eukaryotic organisms
• Compare and contrast prokaryotic cells and eukaryotic cells
• Describe the relative sizes of different kinds of cells

Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes ( pro – = before; – karyon – = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes ( eu – = true).

Components of Prokaryotic Cells

All cells share four common components: 1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; 3) DNA, the genetic material of the cell; and 4) ribosomes, particles that synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.

A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle . We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid.

Unlike Archaea and eukaryotes, bacteria have a cell wall made of peptidoglycan, comprised of sugars and amino acids, and many have a polysaccharide capsule (Figure 3.6). The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment. Some prokaryotes have flagella, pili, or fimbriae. Flagella are used for locomotion, while most pili are used to exchange genetic material during a type of reproduction called conjugation.

Eukaryotic Cells

In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. For example, birds and fish have streamlined bodies that allow them to move quickly through the medium in which they live, be it air or water. It means that, in general, one can deduce the function of a structure by looking at its form, because the two are matched.

A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles , which have specialized functions. The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.

At 0.1–5.0 µm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10–100 µm (Figure 3.7). The small size of prokaryotes allows ions and organic molecules that enter them to quickly spread to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly move out. However, larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport. Indeed, the large size of these cells would not be possible without these adaptations. In general, cell size is limited because volume increases much more quickly than does cell surface area. As a cell becomes larger, it becomes more and more difficult for the cell to acquire sufficient materials to support the processes inside the cell, because the relative size of the surface area across which materials must be transported declines.

Section Summary

Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1–5.0 µm.

Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. Eukaryotic cells tend to be 10 to 100 times the size of prokaryotic cells.

eukaryotic cell: a cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs

organelle: a membrane-bound compartment or sac within a cell

prokaryotic cell: a unicellular organism that lacks a nucleus or any other membrane-bound organelle

Concepts of Biology - 1st Canadian Edition Copyright © 2015 by Charles Molnar and Jane Gair is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Prokaryotic vs Eukaryotic Cells – Similarities & Differences

Introduction to similarity and difference between  prokaryotic and eukaryotic cell.

First of all, all the living things consist of cells.  In a living thing, two types of cells exist that are Eukaryotic and Prokaryotic. Most noteworthy, there is similarity and difference between prokaryotic and eukaryotic cell.

The organisms with single cell come under prokaryotes while animal and plant cells come under eukaryotes. The cells are responsible for all various activities of the living being. Cells are the structural as well as a working unit of life.

Prokaryotic Cells

According to facts, these cells are the oldest cells. They do not have a proper nucleus. Also, organisms of single cell have these cells. These cells share four parts in common that are plasma membrane, cytoplasm, DNA and ribosomes.

Such a cell does not have any proper structure within it. Nevertheless, DNA exists in the central part of the cell.

Bacteria have a cell wall that acts as an extra layer of protection. This wall maintains shape and prevents the shortage of water.

Eukaryotic Cells

It is a popular fact that the evolution of these cells has taken place from the prokaryotes. These cells have a membrane nucleus. They have proper structures within them.

Also, they contain a definite nucleus. Such a cell is larger in size with a true nucleus. Also, a nuclear layer encloses the chromatin bodies. Both asexual and sexual division occurs in such cells.

Furthermore, these cells are larger in size than the other type. Hence, they show better structural organization and functional efficiency than prokaryotes. Their name means true nucleus.

Organelles have special cellular functions. This is similar to the special functions of the human body have.

Similarities between Prokaryotic vs Eukaryotic Cells

The following are the similarities between these two cells:

• Firstly, both the cells have ribosomes that influence the process of protein synthesis.
• In both types of cells, DNA exists that relates to genes.
• The cell wall is present in both.
• In both, there are four types of major molecules that are common to both.
• The process of DNA copying is similar in both.
• Some major metabolic pathways are common in both.
• The process of photosynthesis is similar in both.
• In both cells, there are twenty standard amino acids.
• Genetic code is identical in both.
• In both cells, ATP is the energy of source.

The Difference between Prokaryotic and Eukaryotic Cell 

This difference between Prokaryotes and Eukaryote cell is very important. Both these cells vary in their roles, but both roles are very important. Following are the differences between these two cells:

• Firstly, eukaryotes do have “true” nuclei containing the DNA. The prokaryotes, on the other hand, do not.
• In Eukaryotes, the chloroplasts and mitochondria perform various metabolic processes. On the other hand, in Prokaryotes, similar processes occur across the cell membrane.
• The formation of the cell walls of Prokaryotes is from a different molecule than Eukaryotes.
• Prokaryotes have a higher metabolic rate.
• Prokaryotes have a larger surface area.
• Eukaryotic cells are larger in size.

Solved Question for You

Q. Many years ago what type of cells were the only form of life on Earth?

Ans: Millions of years ago prokaryotes were the only form of life on the earth. Afterwards, through the process of evolution, another type of cells came into existence.

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Cell the Unit of Life

• Isotonic Solutions – Definition and Examples
• Discovery of Mitochondria – Who Discovered Mitochondria?
• Oedogonium – Importance and Life Cycle
• What Is Nadph in Photosynthesis?
• Hyphae – Definition, Functions, and Structure
• DNA Replication in Prokaryotes & Eukaryotes
• Chloroplast – Definition, Structure, Functions
• Nucleus – Definition, Structure & Function (with Diagram)
• Endoplasmic Reticulum – Structure & Function (With Diagram)
• What is Lysosome – Definition, Functions, Structure

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Prokaryotes Vs. Eukaryotes | Difference Between Cells & Examples

Prokaryotic and eukaryotic cells

Eukaryotic cells  contain a nucleus and organelles bound by plasma membranes. Fungi, plants, and animals are made of eukaryotic cells (eukaryotes).  Prokaryotic cells  do not have a membrane-bound nucleus or organelles. All bacteria and members of Archaea are made of prokaryotic cells (prokaryotes).

Difference between eukaryotic and prokaryotic cells

The most obvious difference between them is that prokaryotes have no nuclei, but there are four major differences between a eukaryotic and prokaryotic cell:

No prokaryotic cell has a nucleus; every eukaryotic cell has a nucleus.

Prokaryotic cells have no mitochondria; nearly every eukaryotic cell has mitochondria.

Prokaryotic cells have no organelles enclosed in plasma membranes; every eukaryotic cell has a nucleus and organelles, each enclosed in plasma membranes.

Prokaryotic cells have circular strands of DNA; eukaryotic cells have multiple molecules of double-stranded, linear DNA.

Similarities between prokaryotic and eukaryotic cells

For all their differences, prokaryotes and eukaryotes have a few similarities share some common structures (due to physics and evolution), and though their DNA is different, they even share some genetic features.

Both types of cells have five similarities:

Both types of cells carry on all the necessary functions of life (adaptation through evolution, cellular organization, growth and development, heredity, homeostasis, reproduction, metabolism, and response to stimuli). However, they do these things in different ways.

Both cells carry DNA and rDNA (ribosomal DNA)

Both prokaryotic cells and eukaryotic cells have vesicles.

Both prokaryotes and eukaryotes may be single-celled organisms. Amoebas, paramecia, and yeast are all single-cell eukaryotes.

Both types of cells have vacuoles, storage units for food and liquid.

Structures found in prokaryotic and eukaryotic cells

All living organisms use cellular organization to create structures to conduct life processes. Cells organize into tissues, which organize into organs, which organize into amazing life forms like plants, fungi, dogs, ducks, and people.

Intracellular structures are common to both types of cells. Both prokaryotic and eukaryotic cells have:

Plasma membrane

Prokaryotes

An organism with prokaryotic cells is a  prokaryote . Prokaryotic organisms get their names from the Greek roots,  pro  (before) and  karyon  (nut or kernel). This roughly means they are cells with structures so simple that they came from a time before a cell's nucleus existed.

The three domains of life, Eukaryota, Bacteria, and Archaea, include two branches that are prokaryotes:

Bacteria – The first prokaryotes were discovered in 1676. Bacteria have bacterial rRNA (Ribosomal RNA), no nuclear membrane, and cell membranes composed primarily of diacylglycerol diester lipids (ester-linked lipids).

Archaea – Single-cell organisms. They have no nuclear membrane and share some qualities with bacteria (rDNA, circular chromosomes, asexual reproduction) but are set apart from bacteria by their unique rDNA and ether-linked lipids in their cell membranes.

Only the domain, Eukaryota, has eukaryotic cells.

Examples of archaea include  Crenarchaeota  (living in extreme acidity or temperatures) and  Euryarchaeota  (living in salty water or producing methane).

Prokaryotic cells

Prokaryotic cells are extremely small, much smaller than eukaryotic cells. A typical prokaryotic cell is of a size ranging from 0.1 microns ( mycoplasma  bacteria) to 5.0 microns.

1 micron or  micrometer ,  μ m \mu m μ m , is one-thousandth of a millimeter or one-millionth of a meter.

Anywhere from 200 to 10,000 prokaryotic cells could fit on the head of a pin.

Their small size makes prokaryotic cells just one-half to one-thousandth the size of a eukaryotic cell, which is typically between 10 and 100 microns.

One amazing prokaryotic outlier is  Thiomargarita namibiensis , the largest bacterium ever discovered, coming in at a whopping 100 to 300 microns. That is large enough to see in a light microscope.

Prokaryotic Organelles

Prokaryotes have  no organelles  in their cells! All the equivalent functions of eukaryotic cells are performed by four structures: a plasma membrane, cytoplasm, ribosomes, and genetic material (both rDNA and DNA).

Facts about prokaryotic cells

Prokaryotes help recycle nutrients by decomposing dead organisms.

Bacteria in the intestines and mouths of all higher animals help with the digestion of food.

The DNA of a prokaryotic cell is tightly coiled in a ‘nucleoid,’ which is not a true nucleus since it has no membrane.

Prokaryotic rDNA is a single ring of DNA and is only about 0.1 percent of the amount of DNA in a eukaryotic cell.

Prokaryotic cells have many more ways to obtain and use energy than eukaryotic cells, performing photosynthesis, respiration in common with eukaryotes but also using nitrogen fixation, denitrification, sulfate reduction, and methanogenesis.

Roughly half of all bacteria have flagella, little whip-like external structures that all them to move.

Prokaryotic cells can use pili and fimbriae; also types of external growths, to stick to other cells or surfaces they make their home.

Prokaryotic cells can perform binary fission roughly every 24 hours, meaning they can reproduce exponentially fast.

All adult humans have about 0.2 kg of bacteria in their digestive systems and on their skin; recent studies  put the number of bacteria in our bodies as just about equal to the number of eukaryotic cells.

Prokaryotic cells are the oldest life forms on earth, dating back 3.5 million years.

Fungi, plants, protista, and all animals (including humans) are  eukaryotes . We are all built with eukaryotic cells. The word  eukaryote  comes from two Greek roots,  eu  (good, well), and  karyon  (nut, kernel), so a eukaryote has a well-defined or “good” nucleus (kernel) in its cells.

Eukaryotes cells

Eukaryotic cells have nuclei and organelles, which sets them apart from prokaryotic cells.

The organelles in eukaryotic cells act as tiny membrane-bound compartments performing all the functions of life in the cell: energy acquisition and transfer, digestion, waste management, reproduction, and cellular respiration.

Some of these eukaryotic cell organelles are:

Mitochondria (cell powerhouses)

Chloroplasts (in plants and some algae, for photosynthesis)

Endoplasmic reticulum (the cell transport system)

Golgi apparatus (protein packagers)

Ribosomes (protein synthesis)

Vacuoles (water and food storage)

Lysosomes (digestive processes)

Peroxisomes (metabolic processes)

Nucleus (the mind and brain of the cell)

Size of eukaryotic cells

In general, eukaryotic cells are much bigger than prokaryotic cells. One eukaryotic cell could be double to 1,000 times the size of a prokaryotic cell. Eukaryotic cells measure between 10 and 100 microns, which means you could  barely  see them with a standard school light microscope.

Eukaryote Characteristics

Eukaryotes can be single-celled organisms (like protozoa or paramecia) or multicellular organisms (like you or an elephant)

The largest organism on earth is a eukaryote nicknamed the Humongous Fungus, a specimen of Armillaria ostoyae that covers almost four square miles under the ground of Malheur National Forest in Oregon.

Eukaryotes have linear chromosomes, contrasting with the single ring of rDNA in prokaryotes.

Eukaryotes include animal and plant cells, differentiated in many ways but most obviously by the plasma membrane of animal cells and synthesis cell walls in plants.

Eukaryotic cells store chromatin (DNA and proteins) in a gel-like fluid called the nucleoplasm inside the nucleus.

Mitochondria, found only in eukaryotic cells, have their own DNA chromosome, which may indicate they were once freely existing, independent prokaryotic cells “captured” by eukaryotic cells.

In contrast with the mind-blowing miniature prokaryotic cells, eukaryotic cells are so large, even some of their organelles are visible under the light microscope of a high school science laboratory.

The oldest eukaryote, Grypania , dates back around 1.874 billion years ago; fossils of this eukaryote were discovered in a Michigan iron mine.

Eukaryotes mostly reproduce sexually, though some do use cell division.

Adult humans have around 3 ⋅ 10 13 3\cdot {10}^{13} 3 ⋅ 10 13 human (eukaryotic) cells in their bodies and a roughly equal number of bacteria (prokaryotes).

Prokaryotes and eukaryotes quiz

Cell biology can be tricky stuff, so check your understanding by answering these questions.

Are animal cells prokaryotic or eukaryotic?

Name two locations of prokaryotic cells in the human body.

Are mitochondria found in prokaryotic cells?

Name one feature of eukaryotic cells that is not found in prokaryotic cells.

What type of cells are prokaryotic?

List three similarities between prokaryotic and eukaryotic cells.

Do prokaryotes have organelles?

Review the reading and review your answers before you review our answers!

Animal cells are eukaryotic.

Two locations of prokaryotic cells in the human body are in the intestine (where gut bacteria help you digest food) and on your skin (where bacteria thrive).

Mitochondria are not found in prokaryotic cells; they are only in eukaryotic cells.

One feature of eukaryotic cells that is not found in prokaryotic cells is the cell nucleus.

Simple, primitive cells are prokaryotic; they have no nucleus and no organelles encased in plasma membranes.

Three similarities between prokaryotic and eukaryotic cells are that both have vesicles, vacuoles, and the ability to carry out the eight functions of life.

Prokaryotes do not have organelles.

Eukaryotes and Prokaryotes – What are the Similarities, Differences, and Examples

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Every living organism consists of cells. No matter they are unicellular or multicellular, “cells” are the fundamental units of life. All living organisms fall into one of two categories: Eukaryotes or Prokaryotes . Cellular structure determines which type an organism belongs to. In this article, we will show you what prokaryotes and eukaryotes are and outline the similarities and differences between the two.  

[In this figure] Tree of living organisms showing the origins of eukaryotes and prokaryotes. Photo source: wiki.

This article covers

Definition: What is prokaryote?

Prokaryotes (pro-KAR-ee-ot-es) are unicellular organisms that don’t have a membrane-bound nucleus and other organelles. Prokaryotic cells tend to be small, simple cells, measuring around 0.1-5 μm in diameter. Bacteria and archaea are two major branches of prokaryotes.

The name, prokaryote, came from Old Greek: pro-  = before; karyon = nut or kernel, referring to the cell nucleus; suffix  -otos , pl.  -otes).

[In this figure] Diagram of a bacterium. The key structures in a prokaryote cell are shown.

Prokaryotic cell structure

While prokaryotic cells do not have membrane-bound organelles, they do have distinct cellular structures. Below is a breakdown of what you might find in a prokaryotic bacterial cell.

Examples of prokaryotes

[In this figure] Prokaryotic cells comprise bacteria and archaea. They typically have a diameter of 0.1–5 μm, and their DNA is not contained within a nucleus. Instead, their DNA is circular and can be found in a nucleoid region, which floats in the cytoplasm. Cyanobacteria, also known as “blue-green algae,” are prokaryotes consisting of photosynthetic bacteria. Photo source: wiki.

Definition: What is eukaryote?

The name “Eukaryote” literally means to possess a “true nucleus.” Eukaryotes are organisms whose cells have a membrane-enclosed nucleus and other organelles. These membranes are similar to the cell membrane, which is a flexible film of lipid bilayers. Organelles are internal structures responsible for a variety of functions, such as energy production and protein synthesis.

Eukaryotic cells are relatively larger (around 10-200 μm) and more complex. Eukaryotic cells can be free-living as single-cell microorganisms (like paramecium and amoeba ) or become parts of multicellular organisms.

[In this figure] Diagram of an animal cell. The key structures in a eukaryote cell are shown.

Eukaryotic cell structure

An organelle is a tiny cellular structure that performs specific functions within a cell. You can think of organelles as a cell’s internal organs. For example, the nucleus is the cell’s brain, and the mitochondria are the cell’s hearts. Organelles are often enclosed by their own membranes, which divide the cell into many small compartments for different biochemical reactions. Below is an overview of the primary components of eukaryotic cells.

[In this figure] Animals, plants, fungi, algae, and protozoans are all eukaryotes. Most animals and plants are multicellular organisms, while algae and protozoans are unicellular. Fungi consist of both unicellular (yeasts) and multicellular (molds and mushrooms) organisms.

Prokaryotes vs. Eukaryotes – key similarities

I. both prokaryotic and eukaryotic cells follow the “cell theory”.

In biology, cell theory is the historic scientific theory, now universally accepted. The three principles of the cell theory are as described below:

• All living organisms are composed of one or more cells.
• The cell is the basic unit of structure and function in organisms.
• Cells arise from pre-existing cells.

Both prokaryotic and eukaryotic cells meet the description of cell therapy. On the other hand, “viruses” – tiny structures that can only reproduce inside host cells, are not generally considered to be living cells.

II. Both prokaryotic and eukaryotic cells have similar chemical compositions

Prokaryotic and eukaryotic cells differ structurally in many ways. However, it’s important to note that the chemical compositions of these cellular structures and organelles are the same.

For example, both types of cells use and/or contain:

• Carbohydrates
• Proteins (long chains of amino acids)
• DNA and RNA (long chains of nucleic acids)

[In this figure] The composition of a bacterial cell. Most of a cell is water (70%). The remaining 30% contains various proportions of structural and functional molecules. Photo source: Scitable by nature education.

III. Both prokaryotic and eukaryotic cells share similarities in biochemical reactions that are fundamental to all lives

The biomolecules and biochemical reactions that enable cell life are common in both life forms. All types of cells must make and store energy to survive. Whether autotrophic or heterotrophic, cells need the energy to maintain the structure and carry out a range of functions that include cell replication. For example, both cells use adenosine triphosphate (ATP) as the “molecular unit of currency” to provide energy.

IV. Both prokaryotic and eukaryotic cells obey the central dogma of molecular biology

The central dogma of molecular biology explains the flow of genetic information within a biological system. It is often stated as “DNA makes RNA, and RNA makes protein.”

The same system was conserved from prokaryotes to eukaryotes. Both use DNA polymerases to replicate DNA, RNA polymerases for mRNA transcription, and ribosomes for protein translation.

[In this figure] An overview of the central dogma of molecular biochemistry.

V. Similar cell structures in both prokaryotic and eukaryotic cells

All cells, whether prokaryotic or eukaryotic, share these four features:

• Chromosomal DNA
• Plasma membrane

Prokaryotes vs. Eukaryotes – major differences

[In this figure] The differences and similarities of eukaryotic and prokaryotic cell structures.

The most striking difference between prokaryotes and eukaryotes is that membrane-bound nucleus is only existing in eukaryotic cells. Other than that, we summarize the major differences in this table.

From prokaryotes to eukaryotes: endosymbiosis and eukaryotic cell evolution

The hypothesis that eukaryotic cells evolved from a symbiotic association of prokaryotes is particularly well supported by studies of mitochondria and chloroplasts, which are thought to have evolved from bacteria living in large cells. This is called “endosymbiosis theory.” Around 1.5 billion years ago, some prokaryotic cells engulfed other prokaryotes into their cells. These engulfed cells were not digested; instead, they stayed in a symbiotic relationship. These incorporated prokaryotes then lost their ability to live independently and become integrated as part of the hosts. They later became specialized in specific functions, such as energy production in both mitochondria and chloroplasts. The host cell provides physical protection and a constant supply of food and oxygen in return. Mitochondria appear to be related to  Rickettsiales proteobacteria , and chloroplasts appear to be related to nitrogen-fixing filamentous  cyanobacteria . Both mitochondria and chloroplasts still keep their own DNA to make some of their proteins, but most of their proteins still require nuclear DNA from the host cells. The double layers of mitochondrial membranes are another evidence of endosymbiotic origin. The inner mitochondrial membrane could be the original membrane of the engulfed bacterium. The outer mitochondrial membrane was the remained vesicle when the host cell incorporated the bacterium.

[In this figure] Evolution of the eukaryotic cells. The loss of a rigid cell wall allowed the cell membrane to fold inward and create more surface area (forming endoplasmic reticulum), which facilitated the evolution of larger cells. As cells grew larger, cytoskeletal complexity increased, and the cell became increasingly compartmentalized. Endosymbiosis involving bacteria gave rise to mitochondria and chloroplasts. Photo source: macmillan learning.

How to distinguish eukaryotic and prokaryotic cells under a microscope?

You may roughly tell whether a cell is eukaryotic or prokaryotic by its size. Usually, eukaryotic cells are larger (10-200 µm) and prokaryotic cells are smaller (less than 1-5 µm). You can also try to identify the conclusive evidence of eukaryotic cells: the nucleus and organelles. In some protists of large cells, some organelles are visible even without staining. For example, food vacuoles and contractile vacuoles are obvious when viewing amoebas and paramecia under a microscope. Microscopic techniques such as darkfield, phase contrast, and DIC can also make organelles, and cellular structures stand out. The nucleus can be visualized by the staining of its DNA contents by special dyes. Methylene blue is a popular stain for staining animal cells to make nuclei more visible. Methylene blue binds DNA, which is very abundant in the nucleus. The nuclei appear in deep blue color after methylene blue staining. Methylene blue is commonly used by aquarium hobbyists for treating fishes with fungal diseases. You may find useful dyes for microscopic projects at home .

[In this figure]   Check cells stained with Methylene Blue . The left image is at a lower magnification. You can see the nuclei stained with a dark blue (because Methylene Blue stains strongly with DNA). The cell membrane acts like a balloon and holds all the cell parts, like a nucleus, cytosol, and organelles inside. The right image is at a higher magnification. You can also see some small rod-shaped bacteria. Don’t worry; they are normal oral microbes.  You can see our step-by-step guide to “ Look at your cheek cells . “

For fluorescence microscopy, DNA-binding dyes stain nuclei nicely. Common choices include DAPI (4′,6-diamidino-2-phenylindole), Sybr Green, and Ethidium bromide (EtBr).

Q&A: Some frequently asked questions are quickly answered here

Do prokaryotes (bacteria) have a nucleus.

No, prokaryotes don’t have a membrane-bound nucleus. Their DNA is in a region called nucleoid in the cytoplasm. The lack of a nucleus is the major characteristic to separate prokaryotes from eukaryotes. See “ Prokaryotes vs. Eukaryotes – major differences ” to learn more.

Do prokaryotes have organelles?

Prokaryotic cells don’t have the same organelles that eukaryotes have. Generally speaking, prokaryotes don’t have any membrane-bound organelles (including a nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosome, and peroxisome). However, prokaryotic cells have other organelles or cellular structures, such as cell membrane, cell wall, nucleoid, ribosomes, and flagella. See “ prokaryotic cell structure ” to learn more.

Do prokaryotes have ribosomes?

Yes, prokaryotes have ribosomes for protein synthesis. Prokaryotic ribosomes are smaller than eukaryotic ribosomes. Since prokaryotes lack a nucleus, their mRNAs are transcribed in the cytoplasm and can be translated by ribosomes immediately. As a result, in a bacterium cell, you can even see several ribosomes attached to a single RNA molecule. See “ polysomes ” to learn more.

Do prokaryotes (bacteria) have mitochondria?

No, prokaryotes don’t have mitochondria. However, ancient prokaryotes could be the ancestors of mitochondria in current eukaryotic cells. See “ endosymbiosis and eukaryotic cell evolution ” to learn more.

Do prokaryotes have a cell wall?

Yes, all prokaryotic cells are encased by a cell wall. Many also have a capsule or slime layer made of polysaccharides. However, the composition of prokaryotic cell walls is different from the cell walls in eukaryotic plant cells. See “ p lant cell wall ” to learn more.

Do prokaryotes have DNA?

Yes, both prokaryotic and eukaryotic cells use DNA as their genetic materials. Both of them also follow “the central dogma of molecular biology” as “DNA makes RNA, and RNA makes protein” sustain their living.

“What Is a Cell?”

Eukaryotic and Prokaryotic Cells: Key Differences Essay

Introduction.

Differences between the different kingdoms of species might seem obvious at the surface level, yet, inspecting the subject matter closer, one will realize that the line between the two can be drawn at the cellular level. Furthermore, upon the analysis of the differences between eukaryotic and prokaryotic cells, one can develop a proper understanding of the environment that is required for the correct functioning of eukaryotic and prokaryotic cells. Thus, a comparison between the two is required to show that there are two distinct groups of organisms that require different environments and conditions.

The presence of a nucleus is the core difference between eukaryotic and prokaryotic cells, which is even coded in the names thereof. In addition, unlike a eukaryotic cell, a prokaryotic one does not have chromosomes but, instead, contains a substitute called plasmids (Kelly and Callegari 4977). Unlike a chromosome, a plasmid does not have a protein membrane and typically takes a linear shape (Kelly and Callegari 4979). Therefore, the complexity of prokaryotic cells is significantly lower than the one of prokaryotic ones.

In addition, the cellular structure of the two types of cells serves as an important distinction. Prokaryotic cells are typically unicellular, whereas eukaryotic ones are multicellular. The described difference leads to another point of comparison, which is the kingdom that the identified types of cells represent. While prokaryotes typically occur in Bacteria and Archaea, eukaryotic cells can be found in Animals and Plants (“Chapter 4 – Cell Structure”). Thus, a prokaryotic cell can be defined as a simpler life form compared to a more complex eukaryotic one.

Finally, the components that constitute each type of cell are very different, both in their functions and form. It should be noted that there are several organelles that are common for both prokaryotic and eukaryotic cells. However, eukaryotic cells, as more complex mechanisms, contain the organelles that cannot be found in simpler prokaryotic structures. For example, prokaryotic cells do not have lysosomes and peroxisomes, which play the role of conserving and transporting energy and are an important component of eukaryotic cells (“Chapter 4 – Cell Structure”). Similarly, mitochondria and endoplasmic reticulum are not found in prokaryotic cells. Overall, the structure of a prokaryotic cell is less complex than the one of a eukaryotic one.

The DNA as a crucial element in the composition of both prokaryotic and eukaryotic cells also deserves a more detailed analysis as another critical point of difference between the two cell types. In contrast to eukaryotic cells, in prokaryotic ones, the DNA structure is linear due to the arrangement of organelles and, consequently, chromosomes (Kelly and Callegari 4978). At this point, it should be noted that the process of DNA replication is a crucial similarity between eukaryotic and prokaryotic cells. Although the two cell types are distinctively different from each other, the replication of DNA occurs in both cell types according to the same scheme and set of principles.

However, there are some differences in the replication process that allow distinguishing between a prokaryotic and eukaryotic cell based on the DNA replication characteristics. For example, unlike eukaryotic cells, prokaryotic ones have only one point of origin of their replication, which, in turn, occurs only in two directions (Kelly and Callegari 4978). In addition, the entire replication process occurs at a much faster pace than the one in eukaryotic cells and takes approximately 40 minutes (compared to several hours in a complex eukaryotic cell) (Kelly and Callegari 4977).

The described characteristic allows prokaryotic cells to undergo the replication process in an endless cycle, which is impossible in eukaryotic cells due to the presence of telomeres in their chromosomes (“Chapter 4 – Cell Structure”). Thus, the DNA replication process can be regarded as one of the crucial differences between eukaryotic and prokaryotic cells.

The presence of mitochondria in eukaryotic cells as their distinctive feature is the subject of particular interest since the current theories of mitochondria origin allow tracking down the evolution of a prokaryotic cell to a eukaryotic one. According to the theory of endosymbiotic hypothesis, mitochondria were initially prokaryotic cells (). Moreover, like cells, mitochondria could perform the functions of which eukaryotic cells were incapable (“Chapter 4 – Cell Structure”).

However, since the oxidative processes that mitochondria performed were also essential for the proper functioning of eukaryotic cells, the latter acquired mitochondria via endosymbiosis (). As a result, mitochondria are a crucial component of eukaryotic cells nowadays, yet they are completely absent from prokaryotic ones. Providing opportunities for energy conversion, mitochondria in eukaryotes primarily serve to produce ATP, although it also has several other important functions.

Comparing eukaryotic and prokaryotic cells is necessary since it provides insightful results that may prompt a more nuanced understanding of the functioning of cells and tissues, as well as the factors that lead to the disruption in the processes of them. Thus, an improved approach toward treating patients will become possible. While the key distinction between eukaryotic and prokaryotic cells is the nucleus, which is absent in the latter, there are also numerous nuances that allow differentiating between the two cell types.

“Chapter 4 – Cell Structure.” Georgia Highlands College , n.d. Web.

Kelly, Thomas, and A. John Callegari. “Dynamics of DNA Replication in a Eukaryotic Cell.” Proceedings of the National Academy of Sciences , vol. 116, no. 11, 2019, pp. 4973-4982.

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IvyPanda. (2021, June 3). Eukaryotic and Prokaryotic Cells: Key Differences. https://ivypanda.com/essays/eukaryotic-and-prokaryotic-cells-key-differences/

"Eukaryotic and Prokaryotic Cells: Key Differences." IvyPanda , 3 June 2021, ivypanda.com/essays/eukaryotic-and-prokaryotic-cells-key-differences/.

IvyPanda . (2021) 'Eukaryotic and Prokaryotic Cells: Key Differences'. 3 June.

IvyPanda . 2021. "Eukaryotic and Prokaryotic Cells: Key Differences." June 3, 2021. https://ivypanda.com/essays/eukaryotic-and-prokaryotic-cells-key-differences/.

1. IvyPanda . "Eukaryotic and Prokaryotic Cells: Key Differences." June 3, 2021. https://ivypanda.com/essays/eukaryotic-and-prokaryotic-cells-key-differences/.

Bibliography

IvyPanda . "Eukaryotic and Prokaryotic Cells: Key Differences." June 3, 2021. https://ivypanda.com/essays/eukaryotic-and-prokaryotic-cells-key-differences/.

Prokaryotic versus Eukaryotic Gene Expression

To understand how gene expression is regulated, we must first understand how a gene becomes a functional protein in a cell. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different fashions.

Because prokaryotic organisms lack a cell nucleus, the processes of transcription and translation occur almost simultaneously. When the protein is no longer needed, transcription stops. When there is no mRNA present, no protein can be made. As a result, the primary method to control what type and how much protein is expressed in a prokaryotic cell is through the regulation of DNA transcription into RNA. All the subsequent steps happen automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is almost entirely at the transcriptional level.

Eukaryotic cells, in contrast, have intracellular organelles and are much more complex. Recall that in eukaryotic cells, the DNA is contained inside the cell’s nucleus and that is where it is transcribed to produce mRNA. The newly synthesized mRNA is transported out of the nucleus into the cytoplasm, where ribosomes translate the mRNA to produce protein. The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation only occurs outside the nucleus in the cytoplasm. The regulation of gene expression can occur at any stage of the process ( Figure 1 ):

• Epigenetic level : regulates how tightly the DNA is wound around histone proteins to package it into chromosomes
• Transcriptional level : regulates how much transcription takes place
• Post-transcriptional level : regulates aspects of RNA processing (such as splicing) and transport out of the nucleus
• Translational level : regulates how much of the RNA is translated into protein
• Post-translational level : regulates how long the protein lasts after it has been made and whether the protein is processed into an active form

The differences in the regulation of gene expression between prokaryotes and eukaryotes are summarized in Table 1 .

Table 1: Differences in the Regulation of Gene Expression of Prokaryotic and Eukaryotic Organisms

Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax.

OpenStax , Concepts of Biology. OpenStax CNX. May 18, 2016 http://cnx.org/contents/[email protected]

Principles of Biology Copyright © 2017 by Lisa Bartee, Walter Shriner, and Catherine Creech is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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3.2: Comparing Prokaryotic and Eukaryotic Cells

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Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes ( pro - = before; - karyon - = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes ( eu - = true).

Components of Prokaryotic Cells

All cells share four common components: 1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; 3) DNA, the genetic material of the cell; and 4) ribosomes, particles that synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.

A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid (Figure \(\PageIndex{1}\)).

Unlike Archaea and eukaryotes, bacteria have a cell wall made of peptidoglycan, comprised of sugars and amino acids, and many have a polysaccharide capsule (Figure \(\PageIndex{1}\)). The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment. Some prokaryotes have flagella, pili, or fimbriae. Flagella are used for locomotion, while most pili are used to exchange genetic material during a type of reproduction called conjugation.

Eukaryotic Cells

In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. For example, birds and fish have streamlined bodies that allow them to move quickly through the medium in which they live, be it air or water. It means that, in general, one can deduce the function of a structure by looking at its form, because the two are matched.

A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, which have specialized functions. The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.

At 0.1–5.0 µm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10–100 µm (Figure \(\PageIndex{2}\)). The small size of prokaryotes allows ions and organic molecules that enter them to quickly spread to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly move out. However, larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport. Indeed, the large size of these cells would not be possible without these adaptations. In general, cell size is limited because volume increases much more quickly than does cell surface area. As a cell becomes larger, it becomes more and more difficult for the cell to acquire sufficient materials to support the processes inside the cell, because the relative size of the surface area across which materials must be transported declines.

Section Summary

Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1–5.0 µm.

Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. Eukaryotic cells tend to be 10 to 100 times the size of prokaryotic cells.

Contributors and Attributions

Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd ).