The two sub-units of ribosome remain united at a critical ion level of

Options

A. Calcium
B. Copper
C. Manganese
D. Magnesium

Answer

To solve the question regarding the critical ion level at which the two sub-units of ribosomes remain united, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ribosome Structure**:
- Ribosomes are essential cellular structures involved in protein synthesis. They consist of two sub-units: the larger and the smaller sub-unit. In prokaryotes, these are referred to as 70S ribosomes (50S and 30S sub-units), while in eukaryotes, they are known as 80S ribosomes (60S and 40S sub-units).

**Hint**: Remember that ribosomes are made of two sub-units and their classification differs between prokaryotes and eukaryotes.

2. **Function of Ribosomes**:
- The two sub-units of ribosomes do not remain united at all times. They come together specifically during the process of translation or protein synthesis.

**Hint**: Focus on the role of ribosomes during protein synthesis to understand when the sub-units unite.

3. **Importance of Ions**:
- The binding of the ribosomal sub-units is facilitated by certain inorganic ions. Among the options provided (calcium, copper, manganese, magnesium), one specific ion is crucial for this binding.

**Hint**: Think about which ions are commonly associated with ribosomal function and binding.

4. **Identifying the Critical Ion**:
- The critical ion that is essential for the binding of ribosomal sub-units is magnesium (Mg²⁺). It is required in specific concentrations: approximately 0.0001 moles in eukaryotes and 0.0005 moles in prokaryotes.

**Hint**: Recall that magnesium is often involved in many biological processes, including enzyme activity and structural stability.

5. **Conclusion**:
- Based on the information, the answer to the question is that the two sub-units of ribosomes remain united at a critical ion level of magnesium.

**Final Answer**: The correct option is **D) Magnesium**.