Which one of the following is the diagrammatic representation of a nucleotide?

Options

A.
B.
C.
D.

Answer

To determine which option represents a nucleotide, we need to understand the structure of a nucleotide itself. Here’s a step-by-step breakdown:

### Step 1: Understand the Components of a Nucleotide
A nucleotide is composed of three main components:
1. **Pentose Sugar**: This is a five-carbon sugar. There are two types of pentose sugars in nucleotides: ribose (found in RNA) and deoxyribose (found in DNA).
2. **Nitrogen Base**: This can be one of five different bases: adenine (A), guanine (G), cytosine (C), thymine (T), or uracil (U).
3. **Phosphate Group**: This is attached to the 5' carbon of the pentose sugar.

### Step 2: Identify the Structure of the Pentose Sugar
- The pentose sugar has five carbon atoms.
- In ribose, there is a hydroxyl (-OH) group on the 2' carbon, while in deoxyribose, this hydroxyl group is absent.

### Step 3: Locate the Nitrogen Base and Phosphate Group
- The nitrogen base is attached to the 1' carbon of the pentose sugar.
- The phosphate group is attached to the 5' carbon of the pentose sugar.

### Step 4: Analyze Each Option
Now, we need to analyze the provided options to see which one correctly represents these components:
1. **Option 1**: Contains a nitrogen base on the 1' carbon but lacks a phosphate group on the 5' carbon. This represents a nucleoside, not a nucleotide.
2. **Option 2**: Shows a nitrogen base on the 2' carbon and a phosphate group on the 3' carbon, which is incorrect. The nitrogen base should be on the 1' carbon, and the phosphate group should be on the 5' carbon.
3. **Option 3**: Displays a purine structure, which is just a nitrogen base and does not include the sugar or phosphate group, thus not representing a nucleotide.
4. **Option 4**: Correctly shows a pentose sugar with a nitrogen base on the 1' carbon and a phosphate group on the 5' carbon.

### Step 5: Conclusion
Based on the analysis, **Option 4** is the correct representation of a nucleotide.

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