does bacteria have a Hayflick limit (limit of division) like normal human cells do?

Okay, so this is very complicated question to answer and it requires a lot of molecular biology. If any part of my answer is incomprehensible, please let me know. The main difference between our genome and bacterial genome is that our DNA molecules are packed into structures we called chromosomes and they are linear, meaning they have a starting point and an end point. Bacteria don't have chromosomes and their DNA is circular. Due to the mechanism of DNA replication, our DNA isn't completely replicated. That is, "the mother" DNA and "the daughter" DNA (those are not official terms) aren't identical. "The daughter" DNA will always be a bit shorter. What does that mean for us? How much of DNA do we use per one cell division? Well, on the both ends of our linear DNA there are what we call telomeric regions, or telomeres. Those are long repeated sequences that don't code for any protein. Their only purpose (as far as we know) is to save the important part of DNA from being lost during the replication process. Instead of losing important genes, we lose a small part of telomeres in every cell division. After 40 - 60 divisions telomeres reach critical length and they can't be sacrificed anymore. This is where DNA replication and hence cell division stop happening. Because bacteria have circular DNA, they don't have those problems. Their polymerase can replicate an entire genome without losing one single part of it. They don't need telomerases and therefore they don't have any limits in cell division. If a bacterial specie had Hayflick limit they would stop reproducing after some number of divisions and that would be the end of the specie. What you should ask now is: what about cancer cells? They seem to be immortal and divide without any limits. What about single celled eukaryotes, like amoeba? They have chromosomes too (linear DNA) but they don't have Hayflick limit. The answer to those questions is very interesting and rises a lot of possibilities for us. There is an enzyme called telomerase. This enzyme extends telomerases and prevents them from being lost after a number of replication cycles. It works forever in cancer cells, but for some reason it stops working in "normal" cells. Why? We don't know yet, but we're on our way to find that out. This means we could treat cancers with telomerase inhibitors - if we prevent telomerase from extending their telomeres, cancer cells will stop multiplying after reaching Hayflick limit. Could we treat our normal body cells with telomerase and prevent them from reaching the limit? The answer might be yes. Would that mean we could become immortal in such a way? We don't know yet, but we're certainly going to dig deeper into the problem. Thanks for asking such an interesting question! Alex

what is the advantages of prokaryote with absence nucleus

Essentially, prokaryotes are simpler than eukaryotes. This may not sound like an advantage, but it means that it's really easy to make new prokaryotes, which means that prokaryotic cells reproduce much faster than do eukaryotes. Also, this faster reproduction means that these cells can adapt faster as there are faster generations, which can be an advantage.

are the chromosomes in bacterial cells well developed ?

Chromosomes are the genetic material of the cell, and they contain genes that are transcribed into RNA and translated into proteins. Bacterial chromosomes are one long, single molecule of double stranded, helical, supercoiled DNA. They are usually circular and covalently bonded at the ends1. They are not surrounded by a nuclear membrane, but are located in a region called the nucleoid. Bacterial chromosomes are different from human chromosomes, which are linear, arranged in pairs, and enclosed in a nucleus. Bacterial chromosomes do not undergo mitosis or meiosis, but they can exchange genetic material with other bacteria through processes such as conjugation, transformation, and transduction. Therefore, it depends on how you define “well developed”, but bacterial chromosomes are certainly adapted to their environment and function.

where the DNA and the protein is present in the prokaryotic cells?

DNA is found in the cytoplasm of prokaryotic cell and it is not surrounded by a nuclear membrane or proteins.

Can bacteria get cancer if so what happens?

No, bacteria cannot get cancer. Cancer is the uncontrolled growth of cells in a multicellular organism, and bacteria are single cellular.

can eukaryotes have flagella and pilli? or is that only for prokaryotes?

Yes, and the flagella of motile bacteria differ in structure from eukaryotic flagella. However, Eukaryotes do not have pili or fimbriae.

how were the fossil of the prokaryotes found? Here it says that fossils of prokaryotic were found, how was it understood that it was a prokaryotic? i dont think that something so small like a bacteria could actually leave a imprint like a fossil. thank you

Bacteria generally don't leave fossils, and at most we can infer their existence based on evidence of their effects on other fossilized creatures, such as infections. However, some bacteria have been known to create iron or clay sort of shells that survive after the bacteria has died, creating a sort of model of the bacteria. Bacteria have also been found in fossilized amber, and some cyanobacteria can create stromatolites, which are rocks created by cyanobacteria, calcium carbonate, and the surrounding sediments. Stromatolites can be fossilized, and when cut open, there are sometimes layers or fossilized cyanobacteria inside, protected by the stromatolite.

Is nucleoid considered to be an organelle?

Organelles perform a specific, specialized function and are membrane-bound. Nucleoid is an irregularly shaped organelle. Nucleoplasm and Nucleolus are present in the nucleus. Nucleoplasm and Nucleolus are not found in a nucleoid. It is composed of DNA, RNA, enzymes, dissolved ions, histones and other subnuclear bodies. Hope this helps.

Why do eukaryotic cells need organelles, while prokaryotic cells don't?

they both do, just eukaryote cells support multicellular organisms while prokaryote supports single celled. Though most vital organelles dont belong in a prokaryote.

Main content

Course: Biology library > Unit 23

Lesson 1: Prokaryote structure

Prokaryote structure

Google Classroom

Overview of prokaryotes (bacteria and archaea). Structural features of prokaryotic cells.

Key points:

Prokaryotes are single-celled organisms belonging to the domains Bacteria and Archaea.
Prokaryotic cells are much smaller than eukaryotic cells, have no nucleus, and lack organelles.
All prokaryotic cells are encased by a cell wall. Many also have a capsule or slime layer made of polysaccharide.
Prokaryotes often have appendages (protrusions) on their surface. Flagella and some pili are used for locomotion, fimbriae help the cell stick to a surface, and sex pili are used for DNA exchange.
Most prokaryotic cells have a single circular chromosome. They may also have smaller pieces of circular DNA called plasmids.

Introduction

Bacteria often get a bad rap: they’re described as unsafe “bugs” that cause disease. Although some types of bacteria do cause disease (as you know if you've ever been prescribed antibiotics), many other are harmless, or even beneficial.

Bacteria are classified as prokaryotes, along with another group of single-celled organisms, the archaea. Prokaryotes are tiny, but in a very real sense, they dominate the Earth. They live nearly everywhere – on every surface, on land and in water, and even inside of our bodies.

To emphasize that last point: you probably have about the same number of prokaryotic cells in your body as human cells

^{1}

! That may sound gross, but many of our prokaryotic "sidekicks" play important roles in keeping us healthy.

In this article, we'll look at what prokaryotes are and what exactly makes them different from eukaryotes (such as you, a houseplant, or a fungus). Then, we'll take a closer look at the structures these efficient, omnipresent little organisms use to survive.

What are prokaryotes?

Prokaryotes are microscopic organisms belonging to the domains Bacteria and Archaea, which are two out of the three major domains of life. (Eukarya, the third, contains all eukaryotes, including animals, plants, and fungi.) Bacteria and archaea are single-celled, while most eukaryotes are multicellular.

Fossils show that prokaryotes were already here on Earth

3.5

billion years ago, and scientists think that prokaryotic ancestors gave rise to all of the life forms present on Earth today

^{2, 3}

Prokaryotes vs. eukaryotes

Prokaryotes and eukaryotes are similar in some fundamental ways, reflecting their shared evolutionary ancestry. For instance, both you and the bacteria in your gut decode genes into proteins through transcription and translation. Similarly, you and your prokaryotic inhabitants both pass genetic information on to your offspring in the form of DNA.

In other ways, prokaryotes and eukaryotes are quite different. That may be obvious when we're comparing humans to bacteria. But for me at least, it's less obvious when we're comparing a bacterium to a yeast (which is tiny and unicellular, but eukaryotic). What actually separates these categories of organisms?

The most fundamental differences between prokaryotes and eukaryotes relate to how their cells are set up. Specifically:

Eukaryotic cells have a nucleus, a membrane-bound chamber where DNA is stored, while prokaryotic cells don't. This is the feature that formally separates the two groups.
Eukaryotes usually have other membrane-bound organelles in addition to the nucleus, while prokaryotes don't.
Cells in general are small, but prokaryotic cells are really small. Typical prokaryotic cells range from $0.2$ ‍ $-$ ‍ $2$ ‍ $μm$ ‍ in diameter, while typical eukaryotic cells range from $10$ ‍ $-$ ‍ $100$ ‍ $μm$ ‍ in diameter $^{4}$ ‍.

Many prokaryotic cells have sphere, rod, or spiral shapes (as shown below). In the following sections, we’ll walk through the structure of a prokaryotic cell, starting on the outside and moving towards the inside of the cell.

The capsule

Many prokaryotes have a sticky outermost layer called the capsule, which is usually made of polysaccharides (sugar polymers).

The capsule helps prokaryotes cling to each other and to various surfaces in their environment, and also helps prevent the cell from drying out. In the case of disease-causing prokaryotes that have colonized the body of a host organism, the capsule or slime layer may also protect against the host’s immune system.

Remember Griffith's experiment, which demonstrated the existence of a "transforming principle" (DNA) that could turn rough, harmless bacteria into smooth, pathogenic bacteria? The smooth bacteria were smooth (and capable of causing disease) because they had a capsule!

The cell wall

All prokaryotic cells have a stiff cell wall, located underneath the capsule (if there is one). This structure maintains the cell’s shape, protects the cell interior, and prevents the cell from bursting when it takes up water.

The cell wall of most bacteria contains peptidoglycan, a polymer of linked sugars and polypeptides. Peptidoglycan is unusual in that it contains not only L-amino acids, the type normally used to make proteins, but also D-amino acids ("mirror images" of the L-amino acids). Archaeal cell walls don't contain peptidoglycan, but some include a similar molecule called pseudopeptidoglycan, while others are composed of proteins or other types of polymers

^{5, 6}

Some of the antibiotics used to treat bacterial infections in humans and other animals act by targeting the bacterial cell wall. For instance, some antibiotics contain D-amino acids similar to those used in peptidoglycan synthesis, "faking out" the enzymes that build the bacterial cell wall (but not affecting human cells, which don't have a cell wall or utilize D-amino acids to make polypeptides)

^{5, 7}

Gram staining

Although most bacterial cell walls contain peptidoglycan, they can differ in other ways. In fact, these differences are used to classify bacteria using a technique called the Gram stain. Developed by the 19th-century Danish physician Christian Gram, this technique categorizes strains of bacteria into one of two groups: gram-positive or gram-negative.

The staining process involves applying two dyes to a sample of bacteria. First, a violet dye and iodine are applied, which bind together and form a bulky molecule in the cell walls of the bacteria. Alcohol is then used to wash the sample, removing leftover or loosely bound violet dye-iodine complexes, and a red dye is applied to the sample.

The structure of the cell wall of the bacteria determines which dye is visible at the end of the procedure. Gram-positive bacteria have a thick cell wall of peptidoglycan, which traps the bulky violet dye-iodine molecules. (The red dye also binds, but the violet dye covers it up.) Gram-negative bacteria, on the other hand, have a thin layer of peptidoglycan and an additional outer membrane (see image below). The thin peptidoglycan layer only retains the red dye, giving gram-negative bacteria a pinkish hue.

The plasma membrane

Underneath the cell wall lies the plasma membrane. The basic building block of the plasma membrane is the phospholipid, a lipid composed of a glycerol molecule attached a hydrophilic (water-attracting) phosphate head and to two hydrophobic (water-repelling) fatty acid tails. The phospholipids of a eukaryotic or bacterial membrane are organized into two layers, forming a structure called a phospholipid bilayer.

The plasma membranes of archaea have some unique properties, different from those of both bacteria and eukaryotes. For instance, in some species, the opposing phospholipid tails are joined into a single tail, forming a monolayer instead of a bilayer (as shown below). This modification may stabilize the membrane at high temperatures, allowing the archaea to live happily in boiling hot springs.

In addition to consisting of monolayers in some cases, archaeal plasma membranes differ from those of bacteria and eukaryotes in other ways. Below are three other main differences

^{9}

First, archaea have phospholipids with isoprenoid tails instead of fatty acid tails. The isoprenoid tails are branched, and while the fatty acid tails are not.
Second, the bond that joins the glycerol molecule to isoprenoid tails in archaea is an ether linkage. In bacteria (and eukaryotes), by contrast, the glycerol is joined to fatty acid tails by an ester linkage, as shown below.
Third, the glycerol molecules used to make archaeal phospholipids are mirror images of those used to make bacterial and eukaryotic phospholipids (when considered in three-dimensional space). These forms of glycerol are enantiomers of each other and are designated L-glycerol (found in archaea) and D-glycerol (found in bacteria and eukaryotes).

_Image modified from "Archaea membrane," by Fransciscosp2 (public domain)._

Appendages

Prokaryotic cells often have appendages (protrusions from the cell surface) that allow the cell to stick to surfaces, move around, or transfer DNA to other cells.

Thin filaments called fimbriae (singular: fimbria), like those shown in the picture below, are used for adhesion—that is, they help cells stick to objects and surfaces in their environment.

Longer appendages, called pili (singular: pilus), come in several types that have different roles. For instance, a sex pilus holds two bacterial cells together and allows DNA to be transferred between them in a process called conjugation. Another class of bacterial pili, called type IV pili, help the bacterium move around its environment

^{10}

The most common appendages used for getting around, however, are flagella (singular: flagellum). These tail-like structures whip around like propellers to move cells through watery environments.

Chromosome and plasmids

Most prokaryotes have a single circular chromosome, and thus a single copy of their genetic material. Eukaryotes like humans, in contrast, tend to have multiple rod-shaped chromosomes and two copies of their genetic material (on homologous chromosomes).

Also, prokaryotic genomes are generally much smaller than eukaryotic genomes. For instance, the E. coli genome is less than half the size of the genome of yeast (a simple, single-celled eukaryote), and almost

700

times smaller than the human genome

^{13}

By definition, prokaryotes lack a membrane-bound nucleus to hold their chromosomes. Instead, the chromosome of a prokaryote is found in a part of the cytoplasm called a nucleoid.

In addition to the chromosome, many prokaryotes have plasmids, which are small rings of double-stranded extra-chromosomal ("outside the chromosome") DNA. Plasmids carry a small number of non-essential genes and are copied independently of the chromosome inside the cell. They can be transferred to other prokaryotes in a population, sometimes spreading genes that are beneficial to survival.

For instance, some plasmids carry genes that make bacteria resistant to antibiotics. (These genes are called R genes.) When the plasmids carrying R genes are exchanged in a population, they can quickly make the population resistant to antibiotic drugs. While beneficial to the bacteria, this process can make it difficult for doctors to treat harmful bacterial infections.

Antibiotics are vital for treating harmful bacterial infections, such as pneumonia and tuberculosis. However, the extensive use of antibiotics has led to some strains of pathogenic bacteria becoming resistant. How does this happen?

Some bacteria carry genes (or specific versions of genes) that confer antibiotic resistance. These genes may allow the bacteria to combat natural antibiotics released by other organisms for competition or defense. If resistant bacteria happen to be in an environment that is exposed to antibiotics, then they will survive and reproduce more than non-resistant bacteria (that is, they will be favored by natural selection). If the resistant individuals carry their antibiotic-resistance genes on plasmids, they can also transmit the resistance to other individuals in the population.

Through these mechanisms, colonies of resistant bacteria can quickly form and may be very difficult to kill. For this reason, many scientists urge caution regarding the widespread use of antibiotics.

Internal compartments

Prokaryotes aren't "supposed" to have internal compartments like the organelles of eukaryotes, and for the most part, they don't. However, prokaryotic cells sometimes need to increase membrane surface area for reactions or concentrate a substrate around its enzyme, just like eukaryotic cells. Because of this, some prokaryotes have membrane folds or compartments functionally similar to those of eukaryotes.

For example, photosynthetic bacteria often have extensive membrane folds to increase surface area for the light-dependent reactions, similar to the thylakoid membranes of a plant cell. These bacteria may also have carboxysomes, protein-enclosed cellular compartments where carbon dioxide is concentrated for fixation in the Calvin cycle

^{14}

Check your understanding!

You are looking at a recently discovered unicellular organism using a powerful microscope.
How can you determine if the organism is a prokaryote or eukaryote?

Choose 1 answer:
(Choice A)

It is unicellular, so it must be a prokaryote
(Choice B)
If it has membrane infoldings for photosynthesis, it must be a eukaryote
(Choice C)
If it has a cell wall, it must be a prokaryote
(Choice D)

If it has a membrane-bound nucleus, it must be a eukaryote
All prokaryotic cells have a stiff cell wall for protection, but some eukaryotic cells (like those of plants, fungi, and algae) have cell walls too. This means the presence of a cell wall can't conclusively distinguish a prokaryote from a eukaryote.
While all prokaryotes are unicellular (single-celled organisms), some eukaryotes are also single-celled (for example, freshwater amoebas).
Certain prokaryotes have specialized folds in their membranes which provide extra surface area for performing certain processes, such as photosynthesis and other metabolic functions. (Eukaryotes generally carry out photosynthesis in membrane-bound organelles called chloroplasts.)
The DNA of all eukaryotes is held within a membrane-bound nucleus. Prokaryotic DNA is not contained within a nucleus, but floats around in a region of the cytoplasm called the nuceloid.
The lack of a nucleus is the defining feature of a prokaryotic cell, and the presence of a nucleus is the defining feature of a eukaryotic cell.

This article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Abbott, Allison. (2016, January 8). Scientists bust myth that our bodies have more bacteria than human cells. In Nature news & comment. Retrieved from http://www.nature.com/news/scientists-bust-myth-that-our-bodies-have-more-bacteria-than-human-cells-1.19136.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). The first single-celled organisms. In Campbell biology (10th ed., p. 526). San Francisco, CA: Pearson.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). The first eukaryotes. In Campbell biology (10th ed., p. 528-529). San Francisco, CA: Pearson.
Rollins, David M. (n.d.). Comparison between prokaryotic and eukaryotic cells. Retrieved July 30, 2016 from http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/ProkaryoticvsEukaryotic.htm.
OpenStax College, Biology. (2014, March 28). Structure of prokaryotes. In OpenStax CNX. Retrieved from https://cnx.org/contents/nnx1QFeU@11/Structure-of-Prokaryotes.
Albers, Sonja-Verena and Meyer, Benjamin H. (2011). The archaeal cell envelope. Nature Reviews Microbiology, 9, 416-418. http://dx.doi.org/10.1038/nrmicro2576.
Martinez-Rodriguez, S. Martinez-Gomez, A. I., Rodriguez-Vico, F., Clemente-Jimenez, J. M., and Las Heras-Vazquez, F. J. (2010). Natural occurrence and industrial applications of D-amino acids: An overview. Chemistry and Biodiversity, 7, 1534.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Bacteria and archaea. In Campbell biology (10th ed., p. 569). San Francisco, CA: Pearson.
Waggoner, B., and Speer, B. R. (2006). Archaea: Morphology. In Regents of the University of California. Retrieved from http://www.ucmp.berkeley.edu/archaea/archaeamm.html.
Telford, John L., Michèle A. Barocchi, Immaculada Margarit, Rino Rappuoli, and Guido Grandi. "Pili in Gram-positive Pathogens." Nature Reviews Microbiology Nat Rev Micro 4, no. 7 (2006): 511. http://dx.doi.org/10.1038/nrmicro1443. Retrieved from https://med.uth.edu/mmg/files/2014/12/Ton-That_Telford_012215.pdf.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Bacteria and archaea. In Campbell biology (10th ed., p. 570). San Francisco, CA: Pearson.
Bacterial genomes. (2016). In Department of microbiology, Cornell University. Retrieved from https://micro.cornell.edu/research/epulopiscium/bacterial-genomes.
Genome. (2016, July 18). Retrieved July 30, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Genome.
Murat, D., Byrne, M., and Komeili, A. (2010). Cell biology of prokaryotic organelles. Cold Spring Harb. Perspect. Biol., 2, a000422, pp. 8, 12-13. http://dx.doi.org/10.1101/cshperspect.a000422.

References:

Abbott, Allison. (2016, January 8). Scientists bust myth that our bodies have more bacteria than human cells. In Nature news & comment. Retrieved from http://www.nature.com/news/scientists-bust-myth-that-our-bodies-have-more-bacteria-than-human-cells-1.19136.

Albers, Sonja-Verena and Meyer, Benjamin H. (2011). The archaeal cell envelope. Nature Reviews Microbiology, 9, 414-426. http://dx.doi.org/10.1038/nrmicro2576.

Archaea. (2016, March 2). Retrieved March 2, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Archaea#Membranes

Bacterial genomes. (2016). In Department of microbiology, Cornell University. Retrieved from https://micro.cornell.edu/research/epulopiscium/bacterial-genomes.

Bacterial conjugation. (2003, March 18). In Physics forums. Retrieved March 2, 2016 from https://www.physicsforums.com/threads/bacterial-conjugation.129/.

Bacterial growth. (2015, December 31). Retrieved March 2, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Bacterial_growth.

Chromosomes in bacteria: are they all single and circular? (2012, December 13). Retrieved March 2, 2016 from MicrobeWiki: https://microbewiki.kenyon.edu/index.php/Chromosomes_in_Bacteria:_Are_they_all_single_and_circular%3F.

Frazer, J. (2013, January 12). Archaea are more wonderful than you know. In Scientific American. Retrieved from http://blogs.scientificamerican.com/artful-amoeba/archaea-are-more-wonderful-than-you-know/.

Genome. (2016, July 18). Retrieved July 30, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Genome.

Mandal, A. (2013). Chromosomes in prokaryotes. InNews-Medical.net. Retrieved from http://www.news-medical.net/health/Chromosomes-in-Prokaryotes.aspx.

Martinez-Rodriguez, S. Martinez-Gomez, A. I., Rodriguez-Vico, F., Clemente-Jimenez, J. M., and Las Heras-Vazquez, F. J. (2010). Natural occurrence and industrial applications of D-amino acids: An overview. Chemistry and Biodiversity, 7, 1531-1548.

Meyer, R. R. (2003). Chromosome, prokaryotic. In Genetics. Retrieved from http://www.encyclopedia.com/doc/1G2-3406500050.html.

Murat, D., Byrne, M., and Komeili, A. (2010). Cell biology of prokaryotic organelles. Cold Spring Harb. Perspect. Biol., 2, a000422, pp. 8, 12-13. http://dx.doi.org/10.1101/cshperspect.a000422.

OpenStax College, Biology. (2014, March 28). Structure of prokaryotes. In OpenStax CNX. Retrieved from https://cnx.org/contents/nnx1QFeU@11/Structure-of-Prokaryotes.

Pilus. (2016, February 13). Retrieved March 2, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Pilus.

Prokaryotic chromosomes. (2016, January 21). Retrieved March 2, 2016 from WikiLectures: http://www.wikilectures.eu/index.php/Prokaryotic_Chromosomes.

Purves, W. K., Sadava, D., Orians, G. H., and Heller, H. C. (2003). Bacteria and archaea: the prokaryotic domains. In Life: The science of biology (7th ed., pp. 524-542). Sunderland, MA: Sinauer Associates, Inc.

Purves, W. K., Sadava, D., Orians, G. H., and Heller, H. C. (2003). Cells: The basic units of life. In Life: The science of biology (7th ed., pp. 65-66). Sunderland, MA: Sinauer Associates, Inc.

Purves, W. K., Sadava, D., Orians, G. H., and Heller, H. C. (2003). The genetics of viruses and prokaryotes. In Life: The science of biology (7th ed., pp. 257-277). Sunderland, MA: Sinauer Associates, Inc.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Bacteria and archaea. In Campbell biology (10th ed., pp. 567-575). San Francisco, CA: Pearson.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). The first eukaryotes. In Campbell biology (10th ed., p. 528-529). San Francisco, CA: Pearson.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). The first single-celled organisms. In Campbell biology (10th ed., p. 526). San Francisco, CA: Pearson.

Rollins, David M. (n.d.). Comparison between prokaryotic and eukaryotic cells. Retrieved July 30, 2016 from http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/ProkaryoticvsEukaryotic.htm.

Rohde, R. E. (2016) Course notes for intro to microbiology-Bio 2420. In Austin community college. Retrieved from http://www.austincc.edu/rohde/CHP4.HTM.

Structural biochemistry/lipids/ isoprenoids (2011, February 4). Retrieved February 1, 2016 from Wikibooks: https://en.wikibooks.org/wiki/Structural_Biochemistry/Lipids/Isoprenoids.

Telford, John L., Michèle A. Barocchi, Immaculada Margarit, Rino Rappuoli, and Guido Grandi. "Pili in Gram-positive Pathogens." Nature Reviews Microbiology Nat Rev Micro 4, no. 7 (2006): 509-19. http://dx.doi.org/10.1038/nrmicro1443. Retrieved from https://med.uth.edu/mmg/files/2014/12/Ton-That_Telford_012215.pdf.

Waggoner, B., and Speer, B. R. (2006). Archaea: Morphology. In Regents of the University of California. Retrieved from http://www.ucmp.berkeley.edu/archaea/archaeamm.html.

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Junsang
Posted 6 years ago. Direct link to Junsang's post “does bacteria have a Hayf...”
does bacteria have a Hayflick limit (limit of division) like normal human cells do?
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(21 votes)
Answer
- ++§ Αλεκσανδαρ
  Posted 6 years ago. Direct link to ++§ Αλεκσανδαρ's post “Okay, so this is very com...”
  Okay, so this is very complicated question to answer and it requires a lot of molecular biology. If any part of my answer is incomprehensible, please let me know.
  
  The main difference between our genome and bacterial genome is that our DNA molecules are packed into structures we called chromosomes and they are linear, meaning they have a starting point and an end point. Bacteria don't have chromosomes and their DNA is circular.
  
  Due to the mechanism of DNA replication, our DNA isn't completely replicated. That is, "the mother" DNA and "the daughter" DNA (those are not official terms) aren't identical. "The daughter" DNA will always be a bit shorter.
  
  What does that mean for us? How much of DNA do we use per one cell division? Well, on the both ends of our linear DNA there are what we call telomeric regions, or telomeres. Those are long repeated sequences that don't code for any protein. Their only purpose (as far as we know) is to save the important part of DNA from being lost during the replication process. Instead of losing important genes, we lose a small part of telomeres in every cell division. After 40 - 60 divisions telomeres reach critical length and they can't be sacrificed anymore. This is where DNA replication and hence cell division stop happening.
  
  Because bacteria have circular DNA, they don't have those problems. Their polymerase can replicate an entire genome without losing one single part of it. They don't need telomerases and therefore they don't have any limits in cell division. If a bacterial specie had Hayflick limit they would stop reproducing after some number of divisions and that would be the end of the specie.
  
  What you should ask now is: what about cancer cells? They seem to be immortal and divide without any limits. What about single celled eukaryotes, like amoeba? They have chromosomes too (linear DNA) but they don't have Hayflick limit. The answer to those questions is very interesting and rises a lot of possibilities for us. There is an enzyme called telomerase. This enzyme extends telomerases and prevents them from being lost after a number of replication cycles. It works forever in cancer cells, but for some reason it stops working in "normal" cells. Why? We don't know yet, but we're on our way to find that out. This means we could treat cancers with telomerase inhibitors - if we prevent telomerase from extending their telomeres, cancer cells will stop multiplying after reaching Hayflick limit. Could we treat our normal body cells with telomerase and prevent them from reaching the limit? The answer might be yes. Would that mean we could become immortal in such a way? We don't know yet, but we're certainly going to dig deeper into the problem.
  
  Thanks for asking such an interesting question!
  
  Alex
  Comment on ++§ Αλεκσανδαρ's post “Okay, so this is very com...”
  (78 votes)
Izack
Posted 7 years ago. Direct link to Izack's post “Can bacteria get cancer i...”
Can bacteria get cancer if so what happens?
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- Sammy B
  Posted 7 years ago. Direct link to Sammy B's post “No, bacteria cannot get c...”
  No, bacteria cannot get cancer. Cancer is the uncontrolled growth of cells in a multicellular organism, and bacteria are single cellular.
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jennifer sterling
Posted 5 years ago. Direct link to jennifer sterling's post “can eukaryotes have flage...”
can eukaryotes have flagella and pilli? or is that only for prokaryotes?
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(2 votes)
Answer
- Ivana - Science trainee
  Posted 5 years ago. Direct link to Ivana - Science trainee's post “Yes, and the flagella of ...”
  Yes, and the flagella of motile bacteria differ in structure from eukaryotic flagella.
  
  However, Eukaryotes do not have pili or fimbriae.
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  (5 votes)
Ray
Posted 4 years ago. Direct link to Ray's post “how were the fossil of th...”
how were the fossil of the prokaryotes found?
Here it says that fossils of prokaryotic were found, how was it understood that it was a prokaryotic?
i dont think that something so small like a bacteria could actually leave a imprint like a fossil.
thank you
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(2 votes)
Answer
- Hecretary Bird
  Posted 4 years ago. Direct link to Hecretary Bird's post “Bacteria generally don't ...”
  Bacteria generally don't leave fossils, and at most we can infer their existence based on evidence of their effects on other fossilized creatures, such as infections. However, some bacteria have been known to create iron or clay sort of shells that survive after the bacteria has died, creating a sort of model of the bacteria. Bacteria have also been found in fossilized amber, and some cyanobacteria can create stromatolites, which are rocks created by cyanobacteria, calcium carbonate, and the surrounding sediments. Stromatolites can be fossilized, and when cut open, there are sometimes layers or fossilized cyanobacteria inside, protected by the stromatolite.
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  (5 votes)
sonya
Posted 5 years ago. Direct link to sonya's post “What is the difference be...”
What is the difference between the flagella of eukaryotes and prokaryotes?
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(4 votes)
Answer
nadyeol61
Posted 3 years ago. Direct link to nadyeol61's post “what is the advantages of...”
what is the advantages of prokaryote with absence nucleus
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(3 votes)
Answer
- Hecretary Bird
  Posted 3 years ago. Direct link to Hecretary Bird's post “Essentially, prokaryotes ...”
  Essentially, prokaryotes are simpler than eukaryotes. This may not sound like an advantage, but it means that it's really easy to make new prokaryotes, which means that prokaryotic cells reproduce much faster than do eukaryotes. Also, this faster reproduction means that these cells can adapt faster as there are faster generations, which can be an advantage.
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fire55force
Posted a year ago. Direct link to fire55force's post “are the chromosomes in ba...”
are the chromosomes in bacterial cells well developed ?
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(3 votes)
Answer
- Hannah W.
  Posted 8 months ago. Direct link to Hannah W.'s post “Chromosomes are the genet...”
  Chromosomes are the genetic material of the cell, and they contain genes that are transcribed into RNA and translated into proteins. Bacterial chromosomes are one long, single molecule of double stranded, helical, supercoiled DNA. They are usually circular and covalently bonded at the ends1. They are not surrounded by a nuclear membrane, but are located in a region called the nucleoid. Bacterial chromosomes are different from human chromosomes, which are linear, arranged in pairs, and enclosed in a nucleus. Bacterial chromosomes do not undergo mitosis or meiosis, but they can exchange genetic material with other bacteria through processes such as conjugation, transformation, and transduction. Therefore, it depends on how you define “well developed”, but bacterial chromosomes are certainly adapted to their environment and function.
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marvyayoub2
Posted 3 years ago. Direct link to marvyayoub2's post “where the DNA and the pro...”
where the DNA and the protein is present in the prokaryotic cells?
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(3 votes)
Answer
- Hannah W.
  Posted 8 months ago. Direct link to Hannah W.'s post “DNA is found in the cytop...”
  DNA is found in the cytoplasm of prokaryotic cell and it is not surrounded by a nuclear membrane or proteins.
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estherbaffour101
Posted 3 years ago. Direct link to estherbaffour101's post “Is nucleoid considered to...”
Is nucleoid considered to be an organelle?
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(2 votes)
Answer
- Cadmium Antimony
  Posted 3 years ago. Direct link to Cadmium Antimony's post “Organelles perform a spec...”
  Organelles perform a specific, specialized function and are membrane-bound. Nucleoid is an irregularly shaped organelle. Nucleoplasm and Nucleolus are present in the nucleus. Nucleoplasm and Nucleolus are not found in a nucleoid. It is composed of DNA, RNA, enzymes, dissolved ions, histones and other subnuclear bodies. Hope this helps.
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  (3 votes)
owar padilla
Posted 3 years ago. Direct link to owar padilla's post “Why do eukaryotic cells n...”
Why do eukaryotic cells need organelles, while prokaryotic cells don't?
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(2 votes)
Answer
- grayden.gribble
  Posted a year ago. Direct link to grayden.gribble's post “they both do, just eukary...”
  they both do, just eukaryote cells support multicellular organisms while prokaryote supports single celled. Though most vital organelles dont belong in a prokaryote.
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  (2 votes)