The 5' and 3' numbers are related to the
Answer: B
Correct answer: carbon number in sugar
The primes refer to the carbon atoms of the deoxyribose, numbered 1’ to 5’ to distinguish them from the numbering of the base. The phosphate joins the 5’ carbon of one sugar to the 3’ carbon of the next, which is what gives each strand a direction.
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Name the protein, which is responsible for the formation of RNA primer?
Answer: D
Correct answer: Primase
DNA polymerase cannot start a chain, only extend one, so every new strand needs a starter with a free 3’-OH. Primase, an RNA polymerase, lays down a short RNA primer - once on the leading strand and once for each Okazaki fragment. The primers are later removed and replaced with DNA.
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The size of a linear DNA fragment in a gel can be estimated by
Answer: D
Correct answer: comparison with a molecular weight standard such as Hind III digested phage lambda
A gel gives relative mobility, not an absolute size, so the fragment is sized by running a ladder of known fragments alongside it - lambda DNA cut with HindIII is the classic one - and reading the unknown against them. Since mobility varies roughly with the logarithm of length, plotting log(size) against distance gives a usable calibration curve.
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