BMSC 220 Lec 5

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BMSC 220 Lec 5
2013-10-18 17:56:13
BMSC 220

Lecture 5
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  1. Semiconservative DNA Replication
    -means one strand of parental DNA is conserved as one half of each new progeny DNA molecule
  2. Central Enzyme in DNA Replication
    -DNA polymerase
  3. Fundamental Properties of DNA Polymerases
    • -synthesize DNA in only the 5' to 3' end 
    • -means that the new strand created is built from 3' to 5' 
    • -polymerases add a new dNTP(deaoxyribonucleotide triphosphate) only to a preformed primer strand that is H bonded to the template
  4. What Direction do DNA polymerases read the DNA template?
    -3' to 5' direction
  5. Replication Fork
    • -region of DNA synthesis where the parental strands separate and two new daughter strands elongate
    • -location of active DNA replication containing the macromolecular complex
  6. Leading Strand
    -synthesized in a continuous manner in the direction of overall DNA replication
  7. Lagging Strand
    -synthesized in a discontinuous manner in the direction opposite of movement of the DNA fork
  8. Okazaki Fragments
    -small pieces of newly synthesized DNA that are joined to form an intact new DNA strand on the lagging strand
  9. Initiation of Okazaki Fragments
    -short fragments of RNA serve as primers for DNA replication which are added by Primase
  10. Primase
    • -enzyme that makes short RNA primers complementary to lagging strand 
    • -3-10 nucleotides
    • -does not require a 3'OH group be already attached to the chain
  11. Exonuclease
    -enzymes that degrade(hydrolyzes) DNA or RNA molecules from their ends
  12. RNase-H
    -enzyme that degrades the RNA strand(primer) of RNA-DNA hybrids in eukaryotes
  13. DNA Ligase
    • -enyzme that seals breaks in DNA strands following removal of the RNA primer by RNase H and insertion of new DNA base pairs by DNA polymerase 
    • -joins Okazaki fragments together
  14. Clamp Loading Protein
    -loads clamp proteins onto replication fork at primer
  15. Sliding Clamp Proteins
    -load and hold polymerase onto template
  16. Helicases
    -enzymes that catalyze the unwinding of parental DNA (in ATP dependent manner)
  17. Single-Stranded DNA Binding Proteins
    -stabilize the unwound single stranded template DNA
  18. Topoismoerases
    • -enzymes that catalyze the reversible breakage and rejoining of DNA strand to relieve torsion caused by unwinding of DNA by replication fork
    • -like spinning the garden hose when you coil it up
  19. Origins of Replication
    • -ori
    • -DNA sequences that serve as binding sites for the protein complex that initiates the DNA replication process 
    • -single origins can suffice for simple organisms, but humans have about 30,000 ori sequences
  20. ARS
    • -autonomously replicating sequence is an origin of DNA replication in yeast
    • -100 bp with bp common core
  21. ORC
    • -origin recognition complex 
    • -recognizes core sequence and bind to initiate formation of replication bubble
    • -bind to ori/ARS
  22. Telomerase
    • -unique enzyme that maintains the ends of the eukaryotic chromosomes
    • -possesses reverse transcriptase activity
  23. Reverse Transcriptase
    -DNA polymerase that uses RNA template
  24. Telomeres
    • -repeats of a simple sequence DNA that maintain the ends of linear chromosomes 
    • -needed because DNA polymerase cannot replicate the extreme 5' end of linear molecules
  25. Action of Telomerase (diagram)
  26. DNA Fidelity of Replication
    • -free energy differences in H bonding leads to an incorrect base every 100-1000 pairs
    • -polymerase makes a mistake 1 in every 105-106 
    • -proofreading by polymerase improves the fidelity to a mistake in 1 in every 108-109
    • -DNA repair mechanisms increase fidelity further
  27. Proofreading
    • -selective removal of mismatched bases by DNA polymerase 
    • -made possible by fundamental properties of DNA polymerases, that they require primers and only go from 5' to 3'