Term
| What are the differences between prokaryotic and eukaryotic DNA replication? |
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Definition
Prokaryotes
-faster
-one circular chromosome
-one origin of replication
Eukaryotes
-slower
-several pairs of linear chromosomes
-multiple origins of replication
-multiple polymerases working at a replication fork |
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Term
| How do we know there are multiple replication forks in eukaryotes? |
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Definition
-know rate of one replication fork, know the actual rate of replication of eukaryotic DNA
-actual is faster than theoretical, so there must be more than one fork in operation |
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Term
| How many polymerases does eukaryotic DNA replication require? |
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Definition
Three
(alpha, delta, epsilon) |
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Term
| What does alpha polymerase do |
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Definition
| Works with primase to prime & synthesize okazaki fragments |
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Term
| What does delta polymerase do |
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Definition
| extends the RNA/DNA primer on the lagging strand |
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Term
| What does epsilon polymerase do |
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Definition
| replicates the leading strand |
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Term
| What are the steps in DNA replication |
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Definition
1. DNA alpha polymerase synthesizes RNA primer
2. RNA primer is extended with DNA
delta polymerase extends lagging strand
epsilon polymerase extends leading strand
3.RNA primers removed by ribonuclease H1 and FEN-1
4. DNA poly epsilon and delta fill in gaps
5. DNA ligase seals the nicks |
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Term
| What are telomeres and how do they interact with endonucleases? |
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Definition
Ends of chromosomes
Prevent degradation by endonucleases, and fusion with other ends |
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Term
| What are telomeres composed of? |
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Definition
Many repeats of a 6 base pair sequence, followed by a segment rich in Guanosine.
TTAGGG |
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Term
| Describe the T-loop structure of a telomere |
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Definition
| single stranded DNA curls around in a circle. The 3' end disrupts the base pairing in a double-stranded segement, and forms base pairs itself with one strand in this segment. |
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Term
| What is the function of shelterin in telomeres? |
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Definition
| Coat the T-loop, stabilizing the telomere and preventing degradation by endonucleases |
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Term
| What is the end problem with the T-loop structure? |
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Definition
| DNA poly I cannot remove the RNA primer and fill in the gap, which means that each replication would shorten the chromosome by the length of one primer |
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Term
| How is the T-loop structure problem resolved? |
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Definition
| Telomerase enzyme extends the 6 base pair sequence several times using an RNA template, giving DNA primase & DNA delta polymerase room to removed the RNA primer and fill in the gap. Terminal transferase then adds the G repeats to the 3' end. |
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Term
| What enzyme adds the G repeats to the 3' end after telomerase? |
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Definition
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