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INI-CET 2012 — Biochemistry

Q: In humans, the genetic code is represented by a code of three nucleotides. If one amino acid is coded by more than one triplet, then this is known as?

Degeneracy. ### Explanation **1. Why "Degeneracy" is the Correct Answer:** The genetic code consists of 64 possible codons (triplets) that encode for only 20 standard amino acids. Because there are more codons than amino acids, most amino acids are specified by multiple codons. This phenomenon is termed **Degeneracy** (or Redundancy). * **Mechanism:** Degeneracy primarily occurs at the **third position** of the codon (the 3' end), often explained by the **Wobble Hypothesis**. For example, Leucine is coded by six different codons (UUA, UUG, CUU, CUC, CUA, CUG). This provides a protective mechanism against mutations, as a change in the third nucleotide may still result in the same amino acid (Silent Mutation). **2. Why Other Options are Incorrect:** * **Ambiguity:** This would mean one codon codes for multiple different amino acids. The genetic code is **non-ambiguous**; each specific codon always codes for only one specific amino acid. * **Frame-shift Mutation:** This occurs when the addition or deletion of nucleotides (not in multiples of three) shifts the reading frame, altering all subsequent amino acids. It is a type of mutation, not a property of the code itself. * **Mutation:** This is a general term for any permanent change in the DNA sequence. While degeneracy helps mitigate the effects of mutations, it is not a synonym for the process. **3. High-Yield Clinical Pearls for NEET-PG:** * **Universal Code:** The genetic code is nearly universal across all species. **Exception:** Human mitochondrial DNA (e.g., UGA codes for Tryptophan instead of a Stop codon). * **Non-overlapping & Comma-less:** The code is read sequentially from a fixed starting point without skipping any nucleotides. * **Initiation Codon:** **AUG** (Methionine). In prokaryotes, it codes for N-formylmethionine. * **Stop Codons (Nonsense Codons):** UAA (Ochre), UAG (Amber), UGA (Opal). These do not code for any amino acid. [Practice more Biochemistry PYQs on OnCourse]

2 Previous Year Questions with Answers & Explanations

Questions

All Subjects Biochemistry (2)Forensic Medicine (1)Microbiology (1)Pharmacology (1)Physiology (1)

Q1Easy

Same amino acid is coded by multiple codons due to:

Q2Easy

In humans, the genetic code is represented by a code of three nucleotides. If one amino acid is coded by more than one triplet, then this is known as?