The ratio between undisturbed and distur-bed H bonds in DNA when it is cut by EcoRI in the target site

Options

A. `3:4`
B. `4:3`
C. `1:1`
D. `2:3`

Answer

To determine the ratio between undisturbed and disturbed hydrogen bonds in DNA when it is cut by EcoRI at its target site, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Target Sequence**:
EcoRI recognizes the palindromic sequence GAATTC in DNA.

2. **Understand the Hydrogen Bonds**:
- Between Guanine (G) and Cytosine (C), there are **3 hydrogen bonds**.
- Between Adenine (A) and Thymine (T), there are **2 hydrogen bonds**.

3. **Analyze the Cut Made by EcoRI**:
EcoRI cuts between the G and A in the sequence GAATTC. This means that the hydrogen bonds between A and T are disturbed (broken).

4. **Count the Undisturbed Hydrogen Bonds**:
- The remaining hydrogen bonds after the cut:
- G-C pairs: 3 (undisturbed)
- A-T pairs: 0 (disturbed)
- Total undisturbed hydrogen bonds = 3 (from G-C) + 0 (from A-T) = **3**.

5. **Count the Disturbed Hydrogen Bonds**:
- The hydrogen bonds that are disturbed (broken) due to the EcoRI cut:
- A-T pairs: 2 (disturbed)
- Total disturbed hydrogen bonds = 2 (from A-T) + 0 (from G-C) = **2**.

6. **Calculate the Ratio**:
- The ratio of undisturbed to disturbed hydrogen bonds is:
\[ \text{Undisturbed:Disturbed} = 3:2 \]

7. **Simplify the Ratio**:
- The ratio can be expressed in its simplest form, which remains **3:2**.

### Final Answer:
The ratio between undisturbed and disturbed hydrogen bonds in DNA when it is cut by EcoRI in the target site is **3:2**.