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What does it mean to be anti parrallel in nature, speaking of a DNA strand
The two strands of DNA run 5' to 3' in opposite directions
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During what phase is DNA copied
The S phase (DNA Synthesis)
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DNA replication is said to be semi conservative, why
In the end, one rung is new, and one rung is old
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How long is the S phase
A few hours
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What is a replication fork
An area where the DNA into two strands and DNA synthesis occurs
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What is an ORC, and what is its job
ORC stands for Origin Recognition Complex, it binds to origins of replication to begin replication
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What other enzymes does the ORC attract for replication
- Cdc6 (loads MCM with help from Cdt1)
- MCM helicase
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Geminin does what
Inhibits Cdt1 and pre-RC formation
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CDK and DDK become active when and have what role
In late G1, they activate MCM and load the replisome
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What must happen for replication to start even after all the enzyme are in place
The ORC, Cdc6p, and MCM must be phosphorylated
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How does CDK and DDK inhibit the ORC from replicating more than once a cycle
By Phophorilating S1d2, S1d3 proteins, and MCM
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What does the DNA Helicase do
It seperates the DNA helix
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What is used to prevent overwinding of the DNA during replication
Topoisomerase (Gerase), this splices the DNA allowing it to unwind then seals it back up
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What happens to the DNA when part of it is unwound
It creates supercoils further down the line
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SSB's Single Stranded Binding Proteins have what role
They prevent the double helix from reforming temporarily
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What is Camptothecin
It is a Topoisomerase 1 inhibitor, and is used to treat cancer
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What is Etoposide
It is a Topoisomerase 2 inhibitor and is used to treat cancer
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What is the difference between Topo 1 and 2
- Topo 1 cuts just one strand of DNA to release the tension
- Topo 2 cuts both strands
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Inhibitors of DNA replication are most likely to find medical use as
Anti-cancer drugs
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DNA polymerase β functions in
DNA repair
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DNA polymerase α is composed of and does what
- Made of an RNA polymerase and a DNA polymerase
- It builds an RNA primer starting at the 5' end
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What are the main DNA polymerases and they require what
Polymerases δ and ε and need a 3’OH to polymerize more nucleotides
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What is the polymerase that builds the RNA primer at the 5' end of a new DNA strand in Eukaryotes
DNA polymerase Alpha
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Pol ε is assigned to the
Leading strand
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Polymerase delta is assigned to the
Lagging strand
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What does PCNA do
It keeps the DNA polymerase on the DNA
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What is an RNA primer
- It is the primer to the paint, it is the first portion of the new DNA strand which is necessary for the rest of the strand to stick
- Added by polyemerase alpha
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What is the leading strand
- Strand that is making DNA toward the replication fork
- It uses Polymerase epsilon
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How is the lagging strand different
It makes the DNA away from the replication fork and can only do it in short fragments
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DNA is built in what direction
5'-3' ALWAYS!!
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What kind of bonds are formed to make a new strand of DNA
Covalent, Hydrogen bonds between the bases
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What is an ozarki fragment
In the lagging strand, it is the short fragments that are being replicated
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How are the gaps made by the ozarki fragments filled
A DNA ligase finishes the bond after the primer is removed by a phosphodiester bond
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When the gaps on the Ozarki fragments are filled, the ribonucleotides are replaced with
Deoxyribonucleotides
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What enzyme is necessary to seal the phosphodiester backbone and fuse Ozarki fragments together?
Ligase
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What removes the RNA primer from the DNA
RNase H
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The lagging strand of telomeres cannot be replicated by the usual mechanism, the solution is
A special telomere sequence: tandom repeats of TTAGGG
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Telomerase is
- An enzyme that adds nucleotides to telomeres so that the last portion of the DNA that the lagging strang can't normally transcribe is transcribed leaaving only the repeat of TTAGGG on the end.
- Found especially in cancer cells
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What kind of enzyme is telomerase
A RNA-dependant DNA polymerase
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Cells are more susceptible to mutations when
During the S stage
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