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Nucleic Acids and Protein Synthesis: Question 4

Syllabus 6.2

Multiple choice AS 1 mark

Which statement about the genetic code is correct?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Working through the options

The genetic code has three key properties worth distinguishing carefully, because they are easy to mix up.

Triplet: each codon consists of three consecutive bases, and each triplet of bases (read on the mRNA) codes for one amino acid (or a start/stop signal). This is a property of how many bases make up one codon. It has nothing to do with genes.

Non-overlapping: once reading starts at a fixed point, the sequence is read in consecutive, non-overlapping groups of three bases. Each individual base belongs to only one codon; it is never re-read as part of the codon before or after it.

Degenerate: there are 64 possible triplet codons but only 20 amino acids (plus start/stop signals), so most amino acids are specified by more than one codon. For example, both GCU and GCC code for alanine. Degeneracy therefore describes a many-codons-to-one-amino-acid relationship. It does not mean a single codon can code for several different amino acids (each codon still specifies only one amino acid, or a stop signal).

Checking each option:

  • A. Correctly states that degeneracy means one amino acid can have more than one codon. Correct.
  • B. Reverses the relationship: a single codon does not specify more than one amino acid. Incorrect.
  • C. Reverses the meaning of non-overlapping: bases are never shared between adjacent codons. Incorrect.
  • D, confuses “triplet” (three bases) with “three genes.” A triplet code refers to three bases per codon, not multiple genes. Incorrect.

Final answers

  • A. The genetic code is degenerate because most amino acids are coded for by more than one codon.