How many amino acids will be coded by the mRNA sequence - 5 C C C U C A U A G U C A U A C 3' if a adenosine residue is inserted after `12^(th)` nucleotide ?

Options

A. Five amino acids
B. Six amino acids
C. Two amino acids
D. Three amino acids

Answer

To determine how many amino acids will be coded by the mRNA sequence 5' C C C U C A U A G U C A U A C 3' after inserting an adenosine residue after the 12th nucleotide, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Original mRNA Sequence**:
The original mRNA sequence is 5' C C C U C A U A G U C A U A C 3'.

2. **Count the Nucleotides**:
Count the nucleotides in the sequence. The sequence has 24 nucleotides.

3. **Insert the Adenosine Residue**:
Insert an adenosine (A) after the 12th nucleotide. The sequence will now look like this:
5' C C C U C A U A A G U C A U A C 3'.

4. **Divide the Sequence into Codons**:
Codons are groups of three nucleotides. After the insertion, the sequence can be divided as follows:
- 1st Codon: C C C
- 2nd Codon: U C A
- 3rd Codon: U A G
- 4th Codon: U C A
- 5th Codon: U A C

5. **Identify the Codons and Their Corresponding Amino Acids**:
Using the genetic code:
- C C C codes for Proline (Pro)
- U C A codes for Serine (Ser)
- U A G is a stop codon (does not code for any amino acid)
- U C A codes for Serine (Ser)
- U A C codes for Tyrosine (Tyr)

6. **Determine the Number of Amino Acids**:
The translation will stop at the first stop codon (U A G). Thus, only the first two codons (C C C and U C A) will be translated into amino acids.

7. **Conclusion**:
Therefore, the total number of amino acids coded by the modified mRNA sequence is **2**.

### Final Answer:
**2 amino acids will be coded by the mRNA sequence after the insertion of the adenosine residue.**