KHORANA synthesized two RNAs (a) with repeat sequence of AB and (b) with repeat sequence of ABC the polypeptides code by (a) & (b) are respectively :-

Options

A. Homopolypeptides in both (a) and (b)
B. Heteropolypeptides in both
C. Homopolypeptide in (a) & peptide heteropoly in (b)
D. Heteropolypeptide in (a) & peptide homopoly in (b)

Answer

To solve the question regarding the polypeptides coded by the two RNA sequences synthesized by Khorana, we will analyze each RNA sequence and determine the type of polypeptide they produce.

### Step-by-Step Solution:

1. **Identify the RNA Sequences**:
- RNA (a) has a repeat sequence of **AB**.
- RNA (b) has a repeat sequence of **ABC**.

2. **Determine Codons for RNA (a)**:
- The repeat sequence of AB can be represented as: ABABAB...
- To form codons, we group the sequence into sets of three nucleotides.
- Possible codons from ABABAB... are:
- 1st codon: ABA
- 2nd codon: BAB
- 3rd codon: ABA
- This pattern continues, alternating between ABA and BAB.
- Since there are two different codons (ABA and BAB), this RNA will code for a **heteropolypeptide**.

3. **Determine Codons for RNA (b)**:
- The repeat sequence of ABC can be represented as: ABCABCABC...
- Grouping this into sets of three nucleotides gives us:
- 1st codon: ABC
- 2nd codon: ABC
- 3rd codon: ABC
- This pattern continues with only ABC repeating.
- Since all codons are the same (ABC), this RNA will code for a **homopolypeptide**.

4. **Conclusion**:
- RNA (a) produces a **heteropolypeptide** (due to the presence of different codons ABA and BAB).
- RNA (b) produces a **homopolypeptide** (due to the repeated codon ABC).
- Therefore, the correct answer is: **heteropolypeptide in A and homopolypeptide in B**.

### Final Answer:
The polypeptides coded by the RNAs are:
- RNA (a) - Heteropolypeptide
- RNA (b) - Homopolypeptide