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DNA

DNA. Evidence That Viral DNA Can Program Cells:. To reproduce, a virus must infect a cell and take over the metabolic machining of the cell. Viruses are a tool for molecular genetics – these viruses are called bacteriophages (bacteria eaters).

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DNA

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  1. DNA

  2. Evidence That Viral DNA Can Program Cells: • To reproduce, a virus must infect a cell and take over the metabolic machining of the cell

  3. Viruses are a tool for molecular genetics – these viruses are called bacteriophages (bacteria eaters)

  4. T2 is one phage that infects Escherichia Coli (E. Coli). • T2 is almost entirely composed of DNA and Proteins. • T2 is capable of turning E. Coli into a T2 producing factory.

  5. Hershey and Chase- concluded that DNA (not the protein) was injected into the host cell using this experiment…

  6. In 1947, Chargaff discovered that DNA composition varies from one species to another. • Amounts of the four bases are not equal but in characteristic ratios of A-T and C-G.

  7. Replication • Begins at sites called the “origin of replication”

  8. The circular bacterial chromosome has a single origin identified by a specific sequence of nucleotides. • Proteins attach and open a replication bubble where replication proceeds in both directions. • At each end of a replication bubble is a replication fork (Y region where new DNA strands are elongated). • Elongation of a new DNA is catalized by enzymes called DNA polymerases. (rate is 500 nucleotides/second in bacteria and 50 p/second in humans)

  9. DNA polymerase – (nucleoside triphosphate), a nucleotide with three phosphate groups • ATP has ribose as the sugar and is the substrate for RNA synthesis. • Hydrolysis of the phosphate is the exergonic reaction that drives the polymerization of nucleotides to form DNA.

  10. Two strands of DNA are antiparallel. • Carbon atoms of the sugar are numbered (prime ‘ indicates carbon of the sugar) • The phosphate of the nucleotide is attached to 3’ and to the 5’ of the adjacent nucleotide • OH is attached to the terminal nucleotide. • Gives DNA distinctive polarity

  11. The polymerase simply nestles in the replication fork and moves along the template strand as the fork progresses. The DNA strand made by this mechanism is called the leading strand. • To elongate the other new strand of DNA, polymerase must work away from the replication fork. This is the lagging strand.

  12. As a replication bubble opens, polymerase can work its way from a replication fork and synthesis a short piece of DNA. • These pieces are called Okazaki fragments. • DNA ligase joins the fragments into a single strand of DNA

  13. Priming DNA synthesis • DNA polymerases can not initiate synthesis of a polynucleotide; they can only add nucleotide to the end of an existing chain. • The primer is RNA • Only one primer is required for a DNA polymerase to begin synthesizing the leading strand of a new DNA

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