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Molecular Genetics

Molecular Genetics. Eukaryotic and Prokaryotic Chromosomes. Eukaryotic Chromosomes. They are linear and organized in pairs They are replicated at many points along their length simultaneously

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Molecular Genetics

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  1. Molecular Genetics Eukaryotic and Prokaryotic Chromosomes

  2. Eukaryotic Chromosomes • They are linear and organized in pairs • They are replicated at many points along their length simultaneously • Their number varies greatly from one organism to another, but humans have 46 chromosomes; 22 pairs plus an X and either a second X or a Y • Before replication, they are organized as chromatin

  3. Chromatin • DNA is wrapped around collections of proteins called histones • Histones carry a positive charge and DNA carries a negative charge, so they are held together by electrostatic attraction • 9 histones with DNA coiled twice around the 8 histone core is called a nucleosome

  4. Chromatid • Once replication is complete, the chromatin coils and condenses into the familiar chromosome (2 chromatid) that begins mitosis

  5. Prokaryotic Chromosomes • Prokaryotes are single celled organisms that lack membrane bound organelles , including a nucleus • DNA in prokaryotes is in the form of a single, double stranded loop, as opposed to the linear eukaryotic chromosomes • These “naked” loops of DNA attach to the inner membrane of the prokaryote • There are also small, free floating loops of DNA called plasmids

  6. Prokaryotic Replication – Binary Fission • They replicate in one, continuous sweep of polymerase enzymes moving in opposite directions • The bacteria grows to twice its normal size, the DNA loops separate and then the bacteria divides

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