To initiate translation, the mRNA first binds to :

Options

A. the smaller ribosomal sub-unit
B. the larger ribosomal sub-unit
C. the whole ribosome
D. no such specificity exists

Answer

To solve the question "To initiate translation, the mRNA first binds to:", we need to understand the process of translation in protein synthesis.

### Step-by-Step Solution:

1. **Understanding Translation**:
- Translation is the process by which ribosomes synthesize proteins using mRNA as a template. It involves decoding the mRNA sequence to build a polypeptide chain.

2. **Ribosome Structure**:
- Ribosomes are made up of two subunits: a small subunit and a large subunit. In eukaryotes, the small subunit is referred to as the 40S subunit, while the large subunit is the 60S subunit, combining to form an 80S ribosome.

3. **Initiation of Translation**:
- The initiation of translation begins when the small ribosomal subunit binds to the mRNA. This binding is crucial as it sets the stage for the larger subunit to join and for translation to proceed.

4. **Binding Process**:
- The small ribosomal subunit scans the mRNA for the start codon (AUG), which signals the beginning of translation. Once it locates the start codon, the large ribosomal subunit then attaches, completing the formation of the functional ribosome.

5. **Conclusion**:
- Therefore, the correct answer to the question is that mRNA first binds to the **smallest ribosomal subunit** to initiate translation.

### Final Answer:
To initiate translation, the mRNA first binds to the **smallest ribosomal subunit**.