DNA replication and chromatin remodelling

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Why is DNA replication important?
Maintains inheritance of genetic code from mother to daughter cells, it's proof reads to avoid mutations, but a low level of mutation introduces genetic diversity
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What direction is DNA synthesised in?
5'-3' direction
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What does the new dNTP need to be added?
a free 3'-OH on the prexisting DNA molecule
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Example of DNA damage and mutation
Oxidative deamination of cytosine to uracil. An amine group is lost/
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How many eukaryotic DNA polymerases are there
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What does alpha DNA polymerase do?
Priming of DNA replication
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Beta DNA polymerase
DNA Repair
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Y DNA polymerase
Mitochondrial DNA replication
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Epsilom DNA polymerase
DNA repair/elongation
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delta DNA polymerase
Nuclear DNA replication
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Zeta DNA polymerase
thymine-dimer repair
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What opens the DNA helix in replication
DNA helicase and initator proteins
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What to SSBs do?
stabilise the exposed single stranded DNA and prevent re-annealing
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Why is DNA primase needed
To synthesis a short RNA primer, because DNA polymerase requires a free 3'OH to initiate
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What happens to the short RNA primer after DNA synthesis
It's digested away by RNAse
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Which strand is synthesised as a continuous molecule of DNA?
The leading strand
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What are the lagging strand synthesised as?
Okazaki fragments, joined together by DNA ligase
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prevent tangling by releasing tension, they produce transient breaks in DNA
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Whats the difference between topoisomerase I and topoisomerase II
Topoisomerase I makes single strand breaks, topoisomerase II makes double strand breaks
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What is the mutation rate without DNA polymerase proof reading, and after
before - 10^-3. after - 10^-9
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How does DNA polymerase proofread>
It has 3'-5' exonuclease activity that removes the misincorporated base
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What does the stability of hybrid DNA depend on
the defree od complimentarity between the two strands
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Explain the chromosome end problem
the end of the lagging strand is not synthesised because there is no 3'OH available to add nucleotides to
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What are telomeres
Speicalised ends of the chromosome, they have 500-15000 copies of a simple repear 5' TTAGG 3', so the DNA lost is non-coding.
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What is replicative senescence
When telomeres get to a certain critical length and replication is inhibited
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How is the length of telomeres detected
the amount of TRF1 and TRF2 bound to the TTAGG repeat
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Explain the T loop structure
The g tail with the repeating sequence displaces another sequence away from the end and loops back on itself, disguising the end of the DNA
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What catalyses the formation of T-loop structure
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What is the shelterin complex
A complex known to protect mammilian telomeres from DNA repair mechanisms. and regulate telomerase activity
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How are additional TTAAGGs added to the G-strand
The enzyme telomerase does it, which contains a DNA polymerase and an RNA template CCCUAA
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Where is telomerase expressed?
Germ cells - not somatic cells
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Card 2


What direction is DNA synthesised in?


5'-3' direction

Card 3


What does the new dNTP need to be added?


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Card 4


Example of DNA damage and mutation


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Card 5


How many eukaryotic DNA polymerases are there


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