Deoxyribonucleoside triphosphate serve dual purposes. The purposes are
I. acting as substrate
II. acting as enzymes
III. provide energy for polymerisation
IV. Increase the rate of reaction.
Choose the correct option.

Options

A. I and II
B. II and III
C. III and IV
D. I and III

Answer

To solve the question regarding the dual purposes of deoxyribonucleoside triphosphate (dNTP), we will analyze each of the given options step by step.

### Step 1: Understanding the Role of dNTP
Deoxyribonucleoside triphosphate (dNTP) is a building block of DNA. It is composed of a deoxyribose sugar, a nitrogenous base, and three phosphate groups.

### Step 2: Analyzing Each Purpose
1. **Acting as substrate**:
- dNTP serves as a substrate in DNA synthesis. It provides the necessary components for the formation of DNA strands.
- **Conclusion**: This statement is correct.

2. **Acting as enzymes**:
- dNTP does not function as an enzyme. Enzymes are typically proteins that catalyze biochemical reactions. dNTP is not an enzyme itself; instead, it is utilized by enzymes like DNA polymerase during DNA replication.
- **Conclusion**: This statement is incorrect.

3. **Provide energy for polymerization**:
- The triphosphate groups in dNTP release energy when they are cleaved during the polymerization process, which is essential for forming the phosphodiester bonds in DNA.
- **Conclusion**: This statement is correct.

4. **Increase the rate of reaction**:
- While dNTPs are involved in the reaction, they do not act as catalysts to increase the rate of the reaction. This role is fulfilled by enzymes like DNA polymerase.
- **Conclusion**: This statement is incorrect.

### Step 3: Selecting the Correct Options
Based on the analysis:
- Correct statements: I (acting as substrate) and III (provide energy for polymerization).
- Incorrect statements: II (acting as enzymes) and IV (increase the rate of reaction).

### Final Answer
The correct option is: **I and III**.

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