Haines-4

Haines-4 - DNA Organization in Chromosomes Viral and...

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Unformatted text preview: DNA Organization in Chromosomes Viral and Bacterial Chromosomes Are Relatively Simple DNA Molecules Bacterial and viral chromosomes are usually a single nucleic acid molecule, are largely devoid of associated proteins, and are much smaller than eukaryotic chromosomes. Chromosomes of viruses consist of single- or double-stranded DNA or RNA. Bacterial chromosomes are double- stranded DNA and are compacted into a nucleoid. DNA in bacteria may be associated with HU and H DNA-binding proteins. Supercoiling Is Common in the DNA of Viral and Bacterial Chromosomes Different structures of DNA were realized because of differential sedimentation during ultracentrifugation-3 forms identified-Linear, Underwound, Supercoiled. Supercoiling compacts DNA. Most closed circular DNA molecules in bacteria are slightly underwound and supercoiled. Topoisomerases cut one or both DNA strands and wind or unwind the helix before resealing the ends. Specialized Chromosomes (Present in Eukaryotes) Reveal Variations in Structure Polytene chromosomes (found in various tissues in flies as well as in several protozoans and plants) and lampbrush chromosomes (discovered in the oocytes of sharks, present in most vertebrate oocytes as well as the spermatocytes of some insects) are very large and can be visualized by light microscopy. Polytene chromosomes have distinctive banding patterns, represent paired homologs, and are composed of many DNA strands. The DNA of the paired homologs of polytene chromosomes undergoes many rounds of replication without strand separation or cytoplasmic division....
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Haines-4 - DNA Organization in Chromosomes Viral and...

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