Nucleoside is

Options

A. Sugar + Nitrogenous base
B. Sugar + Phosphate
C. Nitrogenous base + Phosphate
D. Purine + Pyrimidine

Answer

### Step-by-Step Solution:

1. **Understanding Nucleosides**:
- A nucleoside is a molecular structure that consists of two main components: a sugar and a nitrogenous base.

2. **Components of Nucleosides**:
- The sugar can either be ribose (found in RNA) or deoxyribose (found in DNA).
- The nitrogenous base can be classified into two categories: purines and pyrimidines.
- Purines include adenine (A) and guanine (G).
- Pyrimidines include cytosine (C) and thymine (T).

3. **Formation of Nucleotides**:
- When a phosphate group is added to a nucleoside, it forms a nucleotide.
- Therefore, nucleotides are composed of a nucleoside (sugar + nitrogenous base) plus a phosphate group.

4. **Conclusion**:
- Based on the definitions and components discussed, we conclude that a nucleoside is defined as the combination of sugar and nitrogenous base.

### Final Answer:
Nucleoside is defined as **sugar plus nitrogenous base**.

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