An eukaryotic gene contains two kinds of base sequences. Which of these plays an important role in protein synthesis?

Options

A. Introns are present in mRNA and exons are present in rRNA
B. Exons
C. Both (1) & (2)
D. None

Answer

To answer the question regarding which kind of base sequences in a eukaryotic gene plays an important role in protein synthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Eukaryotic Genes**: Eukaryotic genes consist of two types of base sequences: introns and exons.

2. **Transcription Process**: The first step in gene expression is transcription, where the DNA sequence of a gene is transcribed into a primary RNA transcript. This primary transcript is also known as heterogeneous nuclear RNA (hnRNA).

3. **Identifying Introns and Exons**:
- **Introns**: These are non-coding sequences that do not contribute to the final protein product. They are present in the primary RNA transcript but are not included in the mature mRNA.
- **Exons**: These are coding sequences that contain the information necessary to produce proteins. They are retained in the mature mRNA after splicing.

4. **RNA Maturation**: The primary RNA transcript undergoes several modifications to become mature mRNA:
- **Splicing**: Introns are removed from the primary transcript, and exons are joined together. This process is essential because it ensures that only the coding sequences are present in the mature mRNA.
- **Capping and Methylation**: Additional modifications, such as the addition of a 5' cap and a poly-A tail, occur to protect the mRNA and facilitate its translation.

5. **Role in Protein Synthesis**: The mature mRNA, which consists only of exons, is then translated into a protein. Therefore, exons play a crucial role in protein synthesis as they contain the coding information.

### Conclusion:
In summary, **exons** are the sequences that play an important role in protein synthesis in eukaryotic genes, as they are the coding regions that are retained in the mature mRNA after the introns have been removed.