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34 Cards in this Set

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