The ratio between phospho esterbonds and hydrogen bonds that are broken in each palindromic sequence of a DNA, when treated with EcoRI is

Options

A. `3:2`
B. `1:2`
C. `2:5`
D. `1:4`

Answer

To solve the question regarding the ratio between phosphoester bonds and hydrogen bonds broken in a palindromic sequence of DNA when treated with EcoRI, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Palindromic Sequence**:
The palindromic sequence recognized by EcoRI is GAA TTC GAA TTC. This means that the sequence reads the same forwards and backwards.

2. **Determine the Phosphoester Bonds Broken**:
EcoRI cuts the DNA at specific sites. For the sequence GAA TTC, EcoRI breaks the phosphoester bonds between the G and A on both strands:
- One phosphoester bond is broken between the G and A on the upper strand.
- One phosphoester bond is broken between the G and A on the lower strand.
- Total phosphoester bonds broken = 2.

3. **Determine the Hydrogen Bonds Broken**:
In the same sequence, we need to analyze the hydrogen bonds:
- The A-T base pairs have 2 hydrogen bonds each.
- In the sequence GAA TTC, there are two A-T pairs (A and T from both strands).
- Each A-T pair contributes 2 hydrogen bonds, so for two A-T pairs, the total is 2 (from one A-T pair) + 2 (from the other A-T pair) = 4 hydrogen bonds.
- Since there are two strands, the total number of hydrogen bonds broken is 4 (from the upper strand) + 4 (from the lower strand) = 8 hydrogen bonds.

4. **Calculate the Ratio**:
Now, we can calculate the ratio of phosphoester bonds to hydrogen bonds:
- Phosphoester bonds = 2
- Hydrogen bonds = 8
- The ratio is 2:8, which simplifies to 1:4.

5. **Final Answer**:
Therefore, the ratio between phosphoester bonds and hydrogen bonds that are broken in each palindromic sequence of DNA when treated with EcoRI is 1:4.