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34 Cards in this Set
- Front
- Back
list the 3 main characteristics of the DNA polymerase rxn
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-DNA synthesis is primed- polymerase requires complentary primer with free 3'OH
-synthesis ALWAYS proceeds from 5' phosphate group to 3'OH (adding 3'OH to next 5'P) -synthesis is template directed (dNTP forms complementary bp before catalysis of phosphodiester bond |
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what polymerases are involved in 5'-3' elongation?
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DNA polymerase 1 and 3
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what DNA polymerases are involved in 3' to 5' exonuclease? 5 to 3' exonuclease?
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3-5 exo DNA poly 1 and 3
5-3 exo DNA poly 1 |
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what is the role in DNA synthesis of DNA polymerase I
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removes primer and fills in gaps on lagging strand; also DNA repair
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what is the role in DNA synthesis of DNA polymerase III
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synthesizes both leading and lagging strands
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describe structure of DNA polymerase I
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single protein containing 3 functional domains
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what are the domains on DNA polymerase 1 and their functions?
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5-3 exonuclease- primer removal in conjuction with RNaseH
3-5 exonuclease- proofreading 5-3 polymerase- phosphodiester bond formation |
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what is the structure of DNA polymerase III?
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holoenzyme that consists of 2 core enzymes
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list the subunits and their function in DNA polymerase III
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alpha- 5-3 polymerase activity
beta- forms dimers referred to as sliding clamp e- 3-5 exonuclease activity for proofreading |
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what is the central component of DNA poly 3 and what is its function?
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complex of proteins referred to as clamp loader-holds 2 core enzymes together and a DNA helicase- opens and unwinds strands
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where does initiator protein of DNA synthesis bind in prokyarotes? in eukaryotes?
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specific DNA segment called origin of replication (oriC site)
eukaryotes- ori site, about 30,000 in human genome |
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what occurs after initiator protein binds in prokaryotes?
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helicase unwinds DNA in ATP dependent process then primase synthesizes RNA primers
formation of 2 replication forks and replication proceeds in both directions |
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describe primase in primer synthesis
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synthesizes short RNA primers of approx 4-10 nucleotides, synthesis initiated de novo
-primer is complementary to DNA template strand |
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how does DNA synthesis proceed once RNA primer binds?
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DNA polymerase III adds nucleotides to 3'OH at end of RNA primer
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in prokaryotes, what model allows simultaenous synthesis of both strands?
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DNA poly 3 loops template for lagging strand- until okazki fragment reaches about 1000 nucleotides then sliding camp is released and new RNA primer made and new loop grows
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describe the function of DNA polymerase 1 in prokaryotes
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removes primer by 5-3 exonuclease and fills gaps with DNA
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what joins DNA fragments on lagging strand in prokaryotes?
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DNA ligase by catalyzing formation of 3, 5 phosphodiester bond (ATP dependent)
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in prokaryotes, what topoisomerase is involved ahead of replication fork?
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2- creates neg supercoils ahead of fork to prevent overwinding of DNA
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what are the 5-3 polymerases in eukaryotes?
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alpha, delta, epsilon
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what are the 3-5 exonucleases
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delta epsilon
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what is the DNA primase in eukaryotes?
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alpha
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what DNA polymerases contain PCNA? what is it involved in?
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delta and epsilon- sliding clamp
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what is the function of alpha DNA polymerase
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primer synthesis
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what is the function of delta DNA polymerase
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synthesis of lagging strand; fills gaps between Okazki fragments after primer is removed
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what is the function of epsilon DNA polymerase
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synthesis of leading strand
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how long are okazki fragments in eukaryotes?
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200 nucleotides in length
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what removes primer in eukaryotes?
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RNase H and other 5-3 exonucleases associated with replication fork
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what is the role of type 1 and 2 topiosomerases in eukaryotic DNA replication?
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1- relaxes positive supercoils ahead of replication fork and 2- removes tangles behind fork
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define telomeres, how long are they
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repetitive DNA sequences at ends of linear chromosomes
avg length is 5-15 kilo bases |
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what is the significance of telomeres?
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extend template of lagging strand so that looping can occur when the end of the chromosome is reached, allowing for no loss of DNA
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what is the telomere repeat seq?
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TTAGGG
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what is the function of telomerase
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ribonucleoprotein enzyme with RNA template complementary to telomere repeat and
reverse transcriptase synthesizes DNA from RNA template |
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what direction does the synthesis of repeat seq proceed?
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in 5-3 direction by reading RNA template 3-5
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what is significance of telomere caps?
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protect end of chromosome from degradation by exonucleases, prevents non-homologous end joining of chromosomes by DNA ligases, prevents homologous recombination
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