What is the genetic code?

Question

BlackTom AI · Accepted Answer

The genetic code is the set of rules that relates sequences of three nucleotides (codons) in mRNA to specific amino acids during protein synthesis.

1) Relevant knowledge points and concepts
- Codon: a triplet of nucleotide bases (A, U, G, C in RNA) that is read during translation.
- Translation: ribosomes read mRNA codons and, with tRNA adapters, assemble amino acids into a polypeptide.
- Degeneracy: more than one codon can specify the same amino acid (e.g., GGU, GGC, GGA, GGG → glycine).
- Start and stop codons: AUG commonly codes for methionine and serves as a start codon; UAA, UAG, UGA are stop signals.

2) Step-by-step reasoning
- Proteins are built from amino acids in a sequence determined by mRNA.
- Ribosomes read mRNA in non-overlapping three-base units (codons).
- Each codon corresponds to either an amino acid or a translation stop signal.
- Therefore the essential idea of the genetic code is a mapping from three-base codons to amino acids (or stop signals).

3) Calculations / intermediate steps
- Example mapping: AUG → methionine (start), UUU → phenylalanine, UGC → cysteine.
- Degeneracy example: Leucine has six codons: UUA, UUG, CUU, CUC, CUA, CUG.

4) Why the correct answer is correct
- Option d explicitly states the mapping relationship between a three-base codon sequence and an amino acid, which matches the core definition of the genetic code used in translation.

5) Why the other options are incorrect
- a. “The entire sequence from the promoter to the terminator” describes a gene (DNA region), not the genetic code.
- b. “The entire base sequence of an mRNA molecule” is the mRNA transcript, not the mapping rules.
- c. “The binding of tRNA to mRNA” describes one step in translation, not the code itself.

6) Conclusion
The correct answer is d. The relationship between a three-base codon sequence and an amino acid.

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