Question

Which one of the followings is not a terminator codon?

• A. UAA
• B. UAG
• C. UUC
• D. UGA

Hint:

Termination Codons:
$\bullet$ UAA, UAG, UGA (All three start with 'U' and end translation).
$\bullet$ Initiator Codon: AUG (codes for Methionine).
$\bullet$ UUU and UUC code for Phenylalanine (Phe).

Answer 1

The Correct Option is C

Concept:
During messenger RNA (mRNA) translation, triplet codons specify amino acids. Three of the 64 possible codons do not code for any amino acid and instead act as stop/termination signals.

Step 1: Understanding Terminator (Stop) Codons:
In the standard universal genetic code:
- 61 codons code for the 20 standard amino acids (sense codons).
- 3 codons act as stop/nonsense/terminator codons that signal the termination of polypeptide synthesis.
The three standard terminator codons are:
1. UAA (Ochre)
2. UAG (Amber)
3. UGA (Opal)
When a ribosome encounters any of these three codons in the A-site, release factors bind to them, hydrolyzing the bond between the polypeptide and tRNA, thereby completing translation.

Step 2: Identification of UUC:
The codon UUC is a sense codon.
Both UUU and UUC specify the amino acid Phenylalanine (Phe).
Hence, UUC is an amino-acid coding codon and does not serve as a terminator codon.

Step 3: Final Conclusion:
Among the given options, UUC is not a terminator codon.