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22 Cards in this Set
- Front
- Back
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Why is DNA replication called semiconservative?
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A parental strand serves as a template for synthesis of a daughter strand. The two copies of DNA formed have one strand from the original DNA and a new daughter strand
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What are the 3 VERY IMPORTANT characteristics of DNA polymerase reaction?
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1. DNA synthesis is primed which means DNA polymerase needs a complementarty primer of RNA or DNA with a free 3'-OH
2. DNA synthesis of both strands ALWAYS proceeds in 5' to 3' direction 3. DNA synthesis is template directed, so dNTP must form a complementary base pair with the template strand before catalysis of the 3' to 5' phosphodiester bond |
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Specify the domains of DNA polymerase I and describe their function in DNA replication in prokaryotes.
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Single protein that consists of:
-5' to 3' exonuclease=primer removal in conjunction with RNaseH -3' to 5' exonuclease=proofreading -5' to 3' polymerase= phosphodiester bond formation at a rate of 10 dNTP/sec and stays on strand of 10-20 dNTP |
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What are the functions of alpha, beta, and epsilon subunits of DNA polymerase III in DNA replication?
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alpha=5' to 3' polymerase activity at a rate of 1000dNTP/sec
beta= sliding clamp that allows keeps the unit on the DNA strand and allows it to move down the strand epsilon= 3' to 5' exonuclease activity for proofreading |
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Describe the structure of DNA polymerase III.
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Its a holoenzyme that is an asymmetric dimer. Each subunit contains an alpha, beta, and epsilon region and the subunits are connected by DNAB helicase and a clamp loader
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How does DNA replication start in prokaryotes?
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An initiator protein binds to the oriC (origin of replication) site Helicase unwinds DNA and Primase synthesizes primers
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Describe the replication fork and identify leading and laggig strands, the template strand, and the direction of fork movement
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The replication fork is created by helicase unwinding the DNA. The leading strand is the synthesis of DNA from 5' to 3' in the direction of the fork while the lagging strand is the synthesis of DNA from 5' to 3' but in okazi fragments. The template strand is the parent strand. Both strands are read from 3' to 5'.
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Compare the size of okazaki fragments in prokaryotes and eukaryotes.
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Prokaryotes have 1000 deoxynucleotides and eukaryotes have 200 deoxynucleotides (same size as nucleosome so it it thought that they make nucleosomes at a time)
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What is the trombone model?
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The lagging strand is looped so both the lagging and leading strands can be synthesized at once. The loop gets longer as Polymerase III adds more nucleoside until it reaches the end of the okazaki fragment. THe sliding clamp then releases and the new RNA primer is made
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What joins the okazaki fragments together?
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DNA ligase catalyzes formation of the 3' 5' phosphodiester bond
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What is the role of single stranded DNA binding proteins?
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Stabilize unwound DNA
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How does prokaryotes prevent overwinding infront of the replication bubble?
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Topoisomerase II Gyrase decreases the LK by forming negative supercoils so the strand doesn't have a chance to positive supercoil
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What is the role of 5' to 3' exonuclease activity of DNA polymerase I?
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removes RNA primers
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What are the 3 main mechanisms that contribute to high fidelity of DNA replication?
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1. Complementary base pairing error is 10^-4
2. Proofreading by 3' to 5' exonuclease activity error is 10^-3 3. DNA repair mechanism |
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How many ori sites do eukaryotes have?
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30,000
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What are the functional counterparts in eukaryotes of the prokaryotic enzymes primase, DNA polymerase I, and DNA polymerase III?
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primase = DNA polymerase alpha/primase
DNA poly 1 =primal removal of combined activity of RNase H and 5'to3' exonucleases associated with replication fork DNA poly 3 = DNA polymerase epsilon and DNA polymerase delta |
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What is PCNA and how does it function?
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PCNA is the sliding clamp prein that enables processivity of DNA polymerase E and D
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What is the function of the telomerase cap?
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It is to prevent important DNA on the lagging strand from not being replicated because DNA polymerase A/primase runs out of room on the lagging strand to synthesis a primer.
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What is the telomere repeat sequence and how long is it?
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TTAGGG which repeats to 5000-15000 bases
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How is telomeres synthesized?
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Telomerase (ribonucleoprotein) has its own RNA template and reverse transcriptase synthesizes DNA from the RNA template on to the strand with 3' overhang (synthesized from 5' to 3'. This process is repeated many times
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What are the functions of telomeres?
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1. protect ends of chromosome from degradation by exonucleases
2. prevent non-homologous end joining of chromosomes by DNA ligase 3. prevent homologous recombination of chromosome ends by recombination enzymes that repair double strand breaks |
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What common antibiotic is used to inhibit prokaryotic gyrase?
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quinolones
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