IMAT 2012 Q53 [Nucleotides]

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1

Which one of the following labels, i to v, represents a nucleotide?

image

A. i
B. iv
C. v
D. ii
E. iii

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2

The answer to this question is C, where the figure labelled “v” is the nucleotide.

To begin answering this question, you must first be aware that this is a diagram of the DNA structure. It would be useful therefore, to be oriented to what the different shapes mean:

  • Pentagon = the pentose sugar
  • Circle = phosphate group
  • Rectangle = nitrogenous base (purines and pyrimidines)

Next, you will need to be familiar with the difference between nucleo-S-ide and nucleo-T-ide:

  • Nucleo-S-ide: This consists of the pentose sugar + nitrogenous base
  • Nucleo-T-ide: This consists of the pentose sugar + nitrogenous base + phosphate group

Now that you are oriented to what the shapes mean and the different terms involved, let’s interpret the different labels:

  • i: Pentose sugar only
  • ii: Pentose sugar + phosphate group
  • iii: Base pairing between 2 nucleotides
  • iv: Pentose sugar + nitrogenous base = nucleoSide
  • v: Pentose sugar + nitrogenous base + phosphate group = nucleoTide

Thus, the correct answer in this case will be choice C.

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