Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by `:`

Options

A. base-sugar-phosphate
B. base-sugar-OH
C. `("base-sugar-phosphate")_(n)`
D. sugar -phosphate

Explanation

To answer the question, "Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by:", we can break down the components of a nucleotide step by step.

### Step-by-Step Solution:

1. **Understanding Nucleotides**:
- Nucleotides are the basic building blocks of nucleic acids, which include DNA and RNA.

2. **Components of Nucleotides**:
- Each nucleotide is composed of three main components:
- **Nitrogenous Base**: This can be either a purine (adenine or guanine) or a pyrimidine (cytosine, thymine, or uracil).
- **Sugar**: The sugar component can be deoxyribose in DNA or ribose in RNA.
- **Phosphate Group**: This is a phosphate molecule that is attached to the sugar.

3. **Formation of Nucleotide**:
- The nitrogenous base and the sugar are linked together by an N-glycosidic bond, forming a nucleoside.
- The nucleoside then attaches to the phosphate group through a phosphoester bond, resulting in the formation of a nucleotide.

4. **Summary of Components**:
- Therefore, each nucleotide is a composite molecule formed by:
- **Nitrogenous Base**
- **Sugar**
- **Phosphate Group**

5. **Conclusion**:
- The correct answer to the question is that each nucleotide is formed by a nitrogenous base, a sugar, and a phosphate group.

### Final Answer:
Each nucleotide is a composite molecule formed by a nitrogenous base, a sugar, and a phosphate group.

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