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Organization of DNA in Eukaryotes

Organization of DNA in Eukaryotes. By Tibor Cemicky. DNA In Eukaryotes and Prokaryotes. Both Prokaryotes and Eukaryotes use DNA as their genetic material They have the same genetic code but their DNA is organized and used differently

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Organization of DNA in Eukaryotes

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  1. Organization of DNA in Eukaryotes By Tibor Cemicky

  2. DNA In Eukaryotes and Prokaryotes • Both Prokaryotes and Eukaryotes use DNA as their genetic material • They have the same genetic code but their DNA is organized and used differently • Prokaryotes have naked DNA which consists mostly of single copy genes which are translated and transcribed without modification • Situation in eukaryotes is more complex

  3. Replication initiation sites • Replication initiation sites are points where replication of DNA begins • Prokaryotes have only 1 initiation point on their DNA molecule • Eukaryotes have many initiation points

  4. Nucleosomes • DNA is associated with proteins to form nucleosomes • Nucleosomes are globular structures that contain eight histone proteins with DNA wrapped around • Another histone protein • Bonds the structure together • (Histone H1) • DNA is wapped twice • around the nuclesome core

  5. Functions of Nucleosomes • Nucleosomes help to package the DNA during mitosis and meiosis by the process of supercoiling • Supercoiling is the process where a DNA molecule is twisted upon itself • Nucleosomes can be used to mark particular genes to promote gene expression by transcription or translation or to cause silencing of a gene by preventing transcription.

  6. Repetitive Sequences • Most of DNA in eukaryotes consists of repetitive base sequences which are not translated • Highly repetitive sequnces are sequnces between 5-300 bases which may be repeated as many as 10,000 times • These form as much as 45 percent of DNA in eukaryotes • Only a small portion of DNA in eukaryotes consists of single copy or unique genes • Function of repetitive sequences is not known yet

  7. Introns and Exons • Many genes in eukaryotes contain intons and exons • Introns are sequences of bases which are transcribed but not translated • Exons are sequences which are transcribed and actually used during translation • Introns are removed after transcription from the final mRNA in a process called post-transcriptional modification • Prokaryotes do not ussualy have introns

  8. Transcription and post-transcriptional modification

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