There are many differences in the composition and storage of genetic material in prokaryotes and eukaryotes. Chromosomes in prokaryotes consist of a single nucleic acid molecule which can be either DNA or RNA. There is comparatively little genetic material for example E.coli genome is 1200 micrometres while a single human chromosome is between 12000 and 73000 micrometers in size. Unlike in eukaryotes the genetic material in viral prokaryotes can be single or double stranded RNA or DNA. It can also be linear or circular. Only in viruses can the genetic material be RNA. For example in HIV the virus can infect a host cell and use an enzyme transciptase to sequence a DNA molecule which is then incorporated into the genome of the cell to produce viral proteins or genetic material. Like eukaryotic chromosomes bacterial chromosomes are double stranded DNA and can be associated with proteins. These proteins are histones HU and H1 which are positively charged and are attracted to the negative charges on the phosphate molecules of the DNA. Bacterial and viral genetic material is often supercoiled. Bacterial DNA is circular and forms structures called plasmids which condense into structures known as nucleoids. Eukaryotic chromosomes differ in the quantity of genetic material and its organisation. Eukaryotic chromosomes contain a lot more genetic material. They often have more than one chromosome. The chromosomes are separated from the intracellular environment by the nuclear membrane. The genetic material is packaged with proteins known as histones of which there are 5 ; H1 H2A H2B H3 and H4. The DNA and octamer of histones forms a nucleosome. The first level of packing reduces the entire double helix DNA by a third of its length. The further packing of DNA forms solenoid fibres which then form chromatin which packs into a chromatid. Chromosomes have four chromatids. Each chromosome is 1400nm in diameter.
Unlike eukaryotic genes prokaryotic genes are transcribed and...
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