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BMSC 220 Lec 5
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Semiconservative DNA Replication
-means one strand of parental DNA is conserved as one half of each new progeny DNA molecule
Central Enzyme in DNA Replication
-DNA polymerase
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
What Direction do DNA polymerases read the DNA template?
-3' to 5' direction
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
Leading Strand
-synthesized in a continuous manner in the direction of overall DNA replication
Lagging Strand
-synthesized in a discontinuous manner in the direction opposite of movement of the DNA fork
Okazaki Fragments
-small pieces of newly synthesized DNA that are joined to form an intact new DNA strand on the lagging strand
Initiation of Okazaki Fragments
-short fragments of RNA serve as primers for DNA replication which are added by Primase
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
Exonuclease
-enzymes that degrade(hydrolyzes) DNA or RNA molecules from their ends
RNase-H
-enzyme that degrades the RNA strand(primer) of RNA-DNA hybrids in eukaryotes
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
Clamp Loading Protein
-loads clamp proteins onto replication fork at primer
Sliding Clamp Proteins
-load and hold polymerase onto template
Helicases
-enzymes that catalyze the unwinding of parental DNA (in ATP dependent manner)
Single-Stranded DNA Binding Proteins
-stabilize the unwound single stranded template DNA
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
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
ARS
-autonomously replicating sequence is an origin of DNA replication in yeast
-100 bp with bp common core
ORC
-origin recognition complex
-recognizes core sequence and bind to initiate formation of replication bubble
-bind to ori/ARS
Telomerase
-unique enzyme that maintains the ends of the eukaryotic chromosomes
-possesses reverse transcriptase activity
Reverse Transcriptase
-DNA polymerase that uses RNA template
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
Action of Telomerase (diagram)
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 10
5
-10
6
-proofreading by polymerase improves the fidelity to a mistake in 1 in every 10
8
-10
9
-DNA repair mechanisms increase fidelity further
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'
Author
jaz584
ID
241414
Card Set
BMSC 220 Lec 5
Description
Lecture 5
Updated
2013-10-18T21:56:13Z
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