Phosphorus (P) is a structural element of

Options

A. cell membranes
B. proteins
C. nucleic acids
D. all of these

Explanation

**Step-by-Step Solution:**

1. **Understanding the Role of Phosphorus in Biological Structures:**
- Phosphorus is an essential element in various biological molecules and structures. It plays a crucial role in the formation of several key components in living organisms.

2. **Analyzing the Options:**
- **Cell Membrane:** Phosphorus is a component of phospholipids, which are fundamental building blocks of cell membranes. Phospholipids have a hydrophilic (water-attracting) phosphate head and hydrophobic (water-repelling) fatty acid tails.
- **Proteins:** While phosphorus is not a direct component of amino acids (the building blocks of proteins), it can be added to proteins through phosphorylation after translation. This process is important for protein folding and function.
- **Nucleic Acids:** Phosphorus is a critical component of nucleic acids (DNA and RNA). It forms part of the sugar-phosphate backbone, which is essential for the structural integrity of these molecules.

3. **Conclusion:**
- Since phosphorus is a structural element in cell membranes (as part of phospholipids), proteins (through phosphorylation), and nucleic acids (as part of the sugar-phosphate backbone), the correct answer is that phosphorus is a structural element of all of these components.

4. **Final Answer:**
- Therefore, the answer to the question is: **All of these.**

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