Where is the DNA in a prokaryote in a eukaryotic

Q: Where is the DNA found in eukaryotes?

In eukaryotes, the cells genetic material, or DNA, is contained within an organelle called the nucleus, where it is organized in long molecules called chromosomes.

When comparing prokaryotic cells to eukaryotic cells, prokaryotes are much simpler than eukaryotes in many of their features (Figure 1). Most prokaryotes contain a single, circular chromosome that is found in an area of the cytoplasm called the nucleoid.

Table of Contents Show

Practice Question
Where is the DNA in a prokaryote?
Where is the DNA found in eukaryotes?
How is the DNA in a prokaryotic different from a eukaryote?

Practice Question

Figure 1. A eukaryote contains a well-defined nucleus, whereas in prokaryotes, the chromosome lies in the cytoplasm in an area called the nucleoid.

In eukaryotic cells, DNA and RNA synthesis occur in a separate compartment from protein synthesis. In prokaryotic cells, both processes occur together. What advantages might there be to separating the processes?

Show Answer

What advantages might there be to having them occur together? Compartmentalization enables a eukaryotic cell to divide processes into discrete steps so it can build more complex protein and RNA products. But there is an advantage to having a single compartment as well: RNA and protein synthesis occurs much more quickly in a prokaryotic cell.

The size of the genome in one of the most well-studied prokaryotes, E.coli, is 4.6 million base pairs (approximately 1.1 mm, if cut and stretched out). So how does this fit inside a small bacterial cell? The DNA is twisted by what is known as supercoiling. Supercoiling means that DNA is either under-wound (less than one turn of the helix per 10 base pairs) or over-wound (more than 1 turn per 10 base pairs) from its normal relaxed state. Some proteins are known to be involved in the supercoiling; other proteins and enzymes such as DNA gyrase help in maintaining the supercoiled structure.

Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a different type of packing strategy to fit their DNA inside the nucleus (Figure 2). At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes. The histones are evolutionarily conserved proteins that are rich in basic amino acids and form an octamer. The DNA (which is negatively charged because of the phosphate groups) is wrapped tightly around the histone core. This nucleosome is linked to the next one with the help of a linker DNA. This is also known as the “beads on a string” structure. This is further compacted into a 30 nm fiber, which is the diameter of the structure. At the metaphase stage, the chromosomes are at their most compact, are approximately 700 nm in width, and are found in association with scaffold proteins.

In interphase, eukaryotic chromosomes have two distinct regions that can be distinguished by staining. The tightly packaged region is known as heterochromatin, and the less dense region is known as euchromatin. Heterochromatin usually contains genes that are not expressed, and is found in the regions of the centromere and telomeres. The euchromatin usually contains genes that are transcribed, with DNA packaged around nucleosomes but not further compacted.

Abbott, A. Lyme disease: Uphill struggle. Nature 439, 524–525 (2006) doi:10.1038/439524a (link to article)

Ahnert, S. E., et al. How much non-coding DNA do eukaryotes require? Journal of Theoretical Biology 252, 587–592 (2008)

Bendich, A. J., & Drlica, K. Prokaryotic and eukaryotic chromosomes: What's the difference? Bioessays 22, 481–486 (2000)

Bradley, M. D., et al. Effects of Fis on Escherichia coli gene expression during different growth stages. Microbiology 153, 2922–2940 (2007)

Cairns, J. The chromosome of Escherichia coli. Cold Spring Harbor Symposia on Quantitative Biology 28, 43–46 (1963)

Dürrenberger, M., et al. Intracellular location of the histonelike protein HU in Escherichia coli. Journal of Bacteriology 170, 4757–1768 (1988)

Endy, D., & Brent, R. Modelling cellular behaviour. Nature 409, 391–395 (2001) doi:10.1038/35053181 (link to article)

Ferdows, M. S., & Barbour, A. G. Megabase-sized linear DNA in the bacterium Borrelia burgdorferi, the Lyme disease agent. Proceedings of the National Academy of Sciences 86, 5969–5973 (1989)

Fraser, C. M., et al. Genomic sequence of a Lyme disease spirochaete, Borrelia burgdorferi. Nature 390, 580–586 (1997) doi:10.1038/37551 (link to article)

Hinnebusch, B. J., & Bendich, A. J. The bacterial nucleoid visualized by fluorescence microscopy of cells lysed within agarose: Comparison of Escherichia coli and spirochetes of the genus Borrelia. Journal of Bacteriology 179, 2228–2237 (1997)

Jacob, F., & Monod, J. Genetic regulatory mechanisms in the synthesis of proteins. Journal of Molecular Biology 3, 318–356 (1961)

Lewin, B. Genes IX (Sudbury, MA, Jones and Bartlett, 2007)

Mason, D. J., & Powelson, D. M. Nuclear division as observed in live bacteria by a new technique. Journal of Bacteriology 71, 474–479 (1956) (link to article)

Minsky, A., et al. Nucleosomes: A solution to a crowded intracellular environment. Journal of Theoretical Biology 188, 379–385 (1997)

Murphy, L. D., & Zimmerman, S. B. Isolation and characterization of spermidine nucleoids from Escherichia coli. Journal of Structural Biology 119, 321–335 (1997)

Rice, P. A., et al. Crystal structure of an IHF-DNA complex: A protein-induced DNA U-turn. Cell 87, 1295–1306 (1996)

Robinow, C., & Kellenberger, E. The bacterial nucleoid revisited. Microbiology and Molecular Biology Reviews 58, 211–232 (1994)

Sandman, K., et al. HMf, a DNA-binding protein isolated from the hyperthermophilic archaeon Methanothermus fervidus, is most closely related to histones. Proceedings of the National Academy of Sciences 87, 5788–5791 (1990)

Sandman, K., et al. Diversity of prokaryotic chromosomal proteins and the origin of the nucleosome. Cellular and Molecular Life Sciences 54, 1350–1364 (1998)

Sauvonnet, N., et al. Pilus formation and protein secretion by the same machinery in Escherichia coli. EMBO Journal 19, 2221–2228 (2000) doi:10.1093/emboj/19.10.2221

Sinden, R. R., & Pettijohn, D. E. Chromosomes in living Escherichia coli cells are segregated into domains of supercoiling. Proceedings of the National Academy of Sciences 78, 224–228 (1981)

Snyder, L., & Champness, W. Molecular Genetics of Bacteria, 2nd ed. (Washington, DC, ASM Press, 2003)

Trucksis, M., et al. The Vibrio cholerae genome contains two unique circular chromosomes. Proceedings of the National Academy of Sciences 95, 14464–14469 (1998)

Willenbrock, H., & Ussery, D. W. Chromatin architecture and gene expression in Escherichia coli. Genome Biology 5, 252 (2004)

Yasuzawa, K., et al. Histone-like proteins are required for cell growth and constraint of supercoils in DNA. Gene 122, 9–15 (1992).

Where is the DNA in a prokaryote?

The DNA in prokaryotes is contained in a central area of the cell called the nucleoid, which is not surrounded by a nuclear membrane.

Where is the DNA found in eukaryotes?

In eukaryotes, the cell's genetic material, or DNA, is contained within an organelle called the nucleus, where it is organized in long molecules called chromosomes.

How is the DNA in a prokaryotic different from a eukaryote?

Prokaryotic DNA can be found in the cytoplasm whereas eukaryotic DNA is found in the nucleus, enclosed by the nuclear membrane. Prokaryotic DNA is organized into a single circular chromosome and eukaryotic DNA is organized into several linear chromosomes. The amount of eukaryotic DNA is higher than prokaryotic DNA.