Which of the following is a non-sense codon?

Question

Which of the following is a non-sense codon?

1. A. UAA (Correct answer)
2. B. AUG
3. C. UUU
4. D. UGC

Correct Answer

Option A — UAA

Detailed Solution & Explanation

The correct answer is UAA.

Key Points

• UAA is a non-sense codon, also known as a stop codon or termination codon.
• The three non-sense codons in the genetic code are UAA, UAG and UGA, traditionally nicknamed ochre, amber and opal respectively.
• These codons do not code for any amino acid.
• Instead, they signal the termination of translation, causing the ribosome to release the completed polypeptide chain with the help of release factors.
• By contrast, AUG is the initiation (start) codon, which codes for methionine in eukaryotes and formyl-methionine in prokaryotes, and thus has a dual function. UUU codes for phenylalanine — historically the first codon ever deciphered, by Marshall Nirenberg in 1961 — and UGC codes for cysteine.
• The genetic code has 64 codons in total: 61 sense codons and 3 non-sense codons.
• It is described as degenerate (one amino acid may have several codons), unambiguous, non-overlapping and nearly universal.

Exam Tip

• memorise the start and the three stop codons.

प्रश्न (हिन्दी में)

निम्नलिखित में से कौन–सा एक नॉन–सेंस कोडन है?

1. A. UAA
2. B. AUG
3. C. UUU
4. D. UGC