The ratio between hydrogen bonds and phosphodiester bonds broken in each palindromic sequence of a DNA when treated with EcoRI during the fomation of cohesive ends

Options

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

Answer

To solve the question regarding the ratio between hydrogen bonds and phosphodiester bonds broken in each 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. This means that the sequence reads the same in both directions.

2. **Determine the Hydrogen Bonds**:
In the DNA double helix, hydrogen bonds form between complementary bases.
- G (Guanine) pairs with C (Cytosine) with 3 hydrogen bonds.
- A (Adenine) pairs with T (Thymine) with 2 hydrogen bonds.
For the sequence GAA TTC:
- G pairs with C: 3 hydrogen bonds
- A pairs with T: 2 hydrogen bonds (for each A, there are 2 A's in the sequence)
- Therefore, the total hydrogen bonds are:
- G-C: 3
- A-T: 2 + 2 = 4
- Total hydrogen bonds = 3 (G-C) + 4 (A-T) = 7 hydrogen bonds.

3. **Determine the Phosphodiester Bonds**:
Phosphodiester bonds are the bonds between the sugar and phosphate backbone of the DNA. In the case of the palindromic sequence GAA TTC, there are two phosphodiester bonds:
- One between the first G and A
- One between the second A and T
- Therefore, there are 2 phosphodiester bonds broken when EcoRI cuts the DNA.

4. **Calculate the Ratio**:
Now, we can calculate the ratio of hydrogen bonds broken to phosphodiester bonds broken:
- Hydrogen bonds = 7
- Phosphodiester bonds = 2
- Ratio = Hydrogen Bonds : Phosphodiester Bonds = 7 : 2

5. **Final Answer**:
The ratio of hydrogen bonds to phosphodiester bonds broken in the palindromic sequence when treated with EcoRI is 7:2.