AS and A Level Biology

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• Topoisomerase: – A. Separates the DNA strands at the origin – B. Keeps the single-stranded DNA regions from coming back together – C. Re-coils the DNA into a helix after replication is complete – D. Breaks DNA backbone to remove tension produced by the helicase – E. Breaks hydrogen bonds between DNA and the RNA primers
  D. Topoisomerase breaks the DNA backbone to relieve supercoiling tension
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• What end overhangs?
  The 3' end of the telomere strand typically has a
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• What kind of cells need cell replication of their telomeres?
  Actively dividing cells, such as stem cells, germ cells, and
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• What percent of all human cancers have high levels of telomerase?
  Around 85–90% of human cancers have high telomerase activity. This
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• If the problem of the telomeres were not solved, what would happen?
  If telomeres were not maintained, chromosomes would become progressively shorter
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• A repeating DNA sequence at the end of chromosomes that prevents them from losing base pair sequences at their ends and from fusing together is— – A telomere – A telomerase – A replicon – A primer – A promoter
  A telomere is the repetitive sequence found at the ends
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• All are part of a nucleotide except— – Pentose sugar – Nitrogenous base – Phosphate group – Fatty acid tail – All of the above are parts of a nucleotide
  Fatty acid tail is not part of a nucleotide. Nucleotides
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