Which enzyme catalyzes the elongation of DNA molecules?
Answer: A
Correct answer: DNA polymerase
DNA polymerase is the elongating enzyme: it adds nucleotides one at a time to the 3’ end of a primed strand, choosing each to pair with the template. Helicase unwinds, primase starts the chain, and ligase seals nicks - none of them extends it.
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What is the IUPAC code for an A, C, T ambiguity in a nucleic acid sequence?
Answer: B
Correct answer: H
The IUPAC ambiguity codes for three bases are named by which base is excluded, and they run B, D, H, V after A, C, G, T: B is not A, D is not C, H is not G, V is not T. So A, C or T - everything but G - is H. (S is a two-base code, for C or G.)
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There is a single origin for DNA replication in bacteria. How many origins of replication are found in the much larger genomes of eukaryotes such as mammals?
Answer: C
Correct answer: Thousands and tens of thousands
A mammalian genome is roughly a thousand times the size of a bacterial one, and a single fork would take weeks to copy it. Eukaryotes therefore fire tens of thousands of origins, spaced along every chromosome, so that many replicons are copied at once and an S phase takes hours rather than weeks.
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