bio lecture notes 3

bio lecture notes 3 - Structure of Nucleic Acids:...

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Structure of Nucleic Acids: nucleotide structure nitrogenous bases * purines (a=adenine, g=guanine) (double ring) * pyrimidines (t=thymine, c=cytosine) (single ring) all species the amount of A=T and G=C but each species has its own ratio of AT/GC model of how nucleotides combine to form a polymer Model for DNA structure: Four nucleotides Complimentary base pairing (hydrogen bonds) Double Helix Antiparallel Mechanism for replication: PROCESS OF REPLICATION: (eucaryotes) Replication begins at the replication origin (up to 1,000 per DNA molecule) Strands must separate and unwind Helicase enzymes – unwinds helix Topoisomerase- relieve stress of unwinding SSB proteins (single strand binding proteins)- holds separated strands apart Add primer to start Primase now builds a short RNA primer (~10 nucleotides) 5' to 3' DNA polymerase enzymes now bind to the strand next to the primer and catalyzes the addition of new nucleotides, one by one The DNA polymerase move only in one direction that is the new strand will always be built from its 5' to its 3' end. DNA ligase- fuses sections Three questions of interest concerning this process 1. What happens if the wrong base is added to the growing strand? Correct base is put in 2. Where does the energy for these reactions come from? Nucleotides bring energy with them 3. Why does DNA polymerase only build the new strand 5' to 3'? so you can proofread and bring energy in DNA Repair there are 50 or more repair enzymes which replace these damaged areas of DNA
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with the appropriate nucleotides.
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bio lecture notes 3 - Structure of Nucleic Acids:...

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