Question

Which of the following is NOT a non-sense codon?

• A. UAG
• B. UAA
• C. AUG
• D. UGA

Hint:

Remember the stop codons with the mnemonic:
U Are Gone (UAG)
U Are Away (UAA)
U Go Away (UGA)
AUG is the only codon for Methionine and acts as the "Green Light" for translation.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify which of the provided triplet codons does not function as a "non-sense" or "stop" codon in the standard genetic code.

Step 2: Detailed Explanation:

• The Genetic Code: The genetic code consists of 64 possible codons. Out of these, 61 are "sense" codons because they code for specific amino acids. The remaining 3 are "non-sense" or "stop" codons.

• Defining Non-sense Codons: Non-sense codons do not specify any amino acid. Instead, they signal the termination of protein synthesis (translation) by causing the release of the newly synthesized polypeptide chain from the ribosome. The three standard stop codons are:
- UAG (nicknamed "Amber")
- UAA (nicknamed "Ochre")
- UGA (nicknamed "Opal")

• Analysis of Options:
- Option (A) UAG is a stop codon.
- Option (B) UAA is a stop codon.
- Option (D) UGA is a stop codon.

• Role of AUG: AUG is a "sense" codon. It serves two vital functions: first, it acts as the "Start" or "Initiation" codon for the translation process. Second, it codes for the amino acid Methionine (specifically N-formylmethionine in prokaryotes). Because it codes for an amino acid, it cannot be a non-sense codon.
Final Answer:
AUG is a start/sense codon, whereas UAG, UAA, and UGA are stop/non-sense codons. Thus, AUG is the correct choice.