The association of two subunits of the ribosome in translation is governed by the concentration of

Options

A. `Mg^(2+)`
B. `Ca^(2+)`
C. `ATP`
D. `H^+`

Answer

To solve the question regarding the association of the two subunits of the ribosome in translation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ribosome Structure**:
- Ribosomes are composed of two subunits: a large subunit and a small subunit. These subunits come together during the process of translation to synthesize proteins.

**Hint**: Remember that ribosomes are made of RNA and proteins and consist of two distinct subunits.

2. **Role of Ions in Ribosome Function**:
- The association of ribosomal subunits is influenced by various ions. Among the options given (magnesium ion, calcium ion, ATP, hydrogen ion), we need to identify which one is crucial for the binding of these subunits.

**Hint**: Think about which ions are commonly known to stabilize ribosomal structures and facilitate their function.

3. **Magnesium Ion Concentration**:
- It is known that magnesium ions (Mg²⁺) play a significant role in ribosomal function. They are essential for the binding of the ribosomal subunits during translation. The optimal concentration of magnesium ions for eukaryotic ribosomes is around 1 to 2 millimoles, while for prokaryotic ribosomes, it is about 0.5 millimoles.

**Hint**: Consider the physiological concentrations of ions that are required for biological processes.

4. **Disassociation of Ribosomal Subunits**:
- If the concentration of magnesium ions falls below a certain threshold (0.5 millimoles for eukaryotes and 0.3 millimoles for prokaryotes), the ribosomal subunits will disassociate. This indicates that magnesium ions are crucial for maintaining the integrity of the ribosome during translation.

**Hint**: Reflect on how ion concentration can affect the stability of molecular complexes.

5. **Conclusion**:
- Based on the information gathered, we conclude that the association of the two subunits of the ribosome in translation is primarily governed by the concentration of magnesium ions.

**Final Answer**: The correct option is **magnesium ion**.