Question:
Which of the following amino acids are specified by single codons?
Which of the following amino acids are specified by single codons?
Show Hint
Mnemonic: "Met-Trp are the Singletons."
AUG (Methionine) is the most important codon to remember as it signals the start of protein synthesis.
UGG (Tryptophan) is often referred to as the rarest codon in many genomes.
AUG (Methionine) is the most important codon to remember as it signals the start of protein synthesis.
UGG (Tryptophan) is often referred to as the rarest codon in many genomes.
Updated On: Aug 21, 2026
- Tryptophan and histidine
- Methionine and proline
- Methionine and histidine
- Methionine and tryptophan
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question:
This question explores the degeneracy and specificity of the genetic code.
Most amino acids are coded by multiple codons (degeneracy), but a few are unique and coded by only one specific triplet.
Detailed Explanation:
• The Genetic Code:
There are 64 possible codons for 20 standard amino acids.
Because 61 codons specify amino acids (3 are stop codons), many amino acids are "degenerate," meaning they are specified by more than one codon (e.g., Leucine and Arginine have six codons each).
• Single Codon Amino Acids:
Only two amino acids are unique and specified by only a single codon in the standard genetic code:
Methionine (Met): It is coded only by AUG. This codon also functions as the start codon for translation in most organisms.
Tryptophan (Trp): It is coded only by UGG.
• Analyzing other options:
Histidine: Specified by two codons (CAU and CAC).
Proline: Specified by four codons (CCU, CCC, CCA, CCG).
Step 2: Final Answer:
The amino acids specified by single codons are Methionine and Tryptophan.
This question explores the degeneracy and specificity of the genetic code.
Most amino acids are coded by multiple codons (degeneracy), but a few are unique and coded by only one specific triplet.
Detailed Explanation:
• The Genetic Code:
There are 64 possible codons for 20 standard amino acids.
Because 61 codons specify amino acids (3 are stop codons), many amino acids are "degenerate," meaning they are specified by more than one codon (e.g., Leucine and Arginine have six codons each).
• Single Codon Amino Acids:
Only two amino acids are unique and specified by only a single codon in the standard genetic code:
Methionine (Met): It is coded only by AUG. This codon also functions as the start codon for translation in most organisms.
Tryptophan (Trp): It is coded only by UGG.
• Analyzing other options:
Histidine: Specified by two codons (CAU and CAC).
Proline: Specified by four codons (CCU, CCC, CCA, CCG).
Step 2: Final Answer:
The amino acids specified by single codons are Methionine and Tryptophan.
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