Question

Which of the following is NOT a stop codon?

• A. UAA
• B. UAG
• C. UGA
• D. AUG

Hint:

Mnemonic to remember the three stop codons:
U Are Away (UAA)
U Are Gone (UAG)
U Go Away (UGA)
And remember: AUG = All Users Go (Start).

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks us to identify the codon among the options that does NOT act as a translation termination (stop) codon.
This relates to the properties of the genetic code in molecular biology.

Step 2: Key Formula or Approach:
The genetic code consists of 64 codons, of which 61 code for amino acids and 3 serve as termination signals.
We recall the specific sequences of the three stop codons and the start codon.

Step 3: Detailed Explanation:

• During translation, ribosomes synthesize polypeptide chains based on mRNA sequences.

• Translation termination occurs when the ribosome encounters a stop codon (nonsense codon) on the mRNA.

• No transfer RNA (tRNA) has anticodons complementary to these stop codons; instead, release factors bind to them to release the polypeptide chain.

• The three stop codons in the standard genetic code are:
1. UAA (Ochre)
2. UAG (Amber)
3. UGA (Opal)

• In contrast, the codon AUG is known as the initiation (start) codon.

• AUG serves a dual function: it signals the start of translation and codes for the amino acid methionine (or N-formylmethionine in prokaryotes).

• Since AUG is a start codon, it is not a stop codon.


Step 4: Final Answer:
Therefore, AUG is not a stop codon.