How many nucleotides are used for the synthesis of A chain and B chain of insulin?

Options

A. 90 for A and 63 for B
B. 63 for A and 90 for B
C. 92 for A and 61 for B
D. 60 for A and 61 for B

Answer

To determine how many nucleotides are used for the synthesis of the A chain and B chain of insulin, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Insulin**:
- Insulin is a peptide hormone composed of two polypeptide chains known as the A chain and the B chain.
- The A chain consists of 21 amino acids, while the B chain consists of 30 amino acids.

2. **Amino Acids and Codons**:
- Each amino acid in a protein is encoded by a codon, which is a sequence of three nucleotides.
- Therefore, to find the number of nucleotides required to code for a certain number of amino acids, we multiply the number of amino acids by 3 (since each amino acid corresponds to one codon of three nucleotides).

3. **Calculate Nucleotides for A Chain**:
- For the A chain:
\[ \text{Number of nucleotides} = \text{Number of amino acids} \times 3 = 21 \times 3 = 63 \text{ nucleotides} \]

4. **Calculate Nucleotides for B Chain**:
- For the B chain:
\[ \text{Number of nucleotides} = \text{Number of amino acids} \times 3 = 30 \times 3 = 90 \text{ nucleotides} \]

5. **Summarize the Results**:
- A chain requires 63 nucleotides.
- B chain requires 90 nucleotides.

6. **Final Answer**:
- Therefore, the correct answer is:
- 63 nucleotides for the A chain and 90 nucleotides for the B chain.