If EcoRI cut the ds. DNA fargment at four places, then what is the ratio of number of hydrogen bonds present at those locations before cleavage by EcoRI and number of hydrogen bonds cleaved by EcoRI at those loactions respectievly ?

Options

A. `8:14`
B. `7:4`
C. `8:2`
D. `6:2`

Answer

To solve the problem, we need to determine the ratio of the number of hydrogen bonds present in the double-stranded DNA before cleavage by EcoRI to the number of hydrogen bonds cleaved by EcoRI at those locations.

### Step-by-Step Solution:

1. **Identify the DNA Sequence**:
Let's consider the DNA sequence where EcoRI cuts. For example, the sequence is:
```
5' - G A A T T C C T T A A G - 3'
3' - C T T A A G G A A T T C - 5'
```

2. **Count Hydrogen Bonds Before Cleavage**:
- In DNA, adenine (A) pairs with thymine (T) via 2 hydrogen bonds, and guanine (G) pairs with cytosine (C) via 3 hydrogen bonds.
- For the sequence above:
- G-C pairs: 3 hydrogen bonds
- A-T pairs: 2 hydrogen bonds
- Count the hydrogen bonds for the entire sequence:
- G (3) + A (2) + A (2) + T (2) + T (2) + C (3) + C (3) + T (2) + T (2) + A (2) + A (2) + G (3) = 14 hydrogen bonds for one side.
- Since EcoRI cuts at 4 places, the total number of hydrogen bonds before cleavage is:
\[ 14 \text{ hydrogen bonds} \times 4 \text{ cuts} = 56 \text{ hydrogen bonds} \]

3. **Count Hydrogen Bonds Cleaved by EcoRI**:
- EcoRI cuts between A and T, and G and C pairs remain intact.
- The number of hydrogen bonds cleaved at each cut:
- Each A-T pair contributes 2 hydrogen bonds.
- If EcoRI cuts at 4 locations, the total number of cleaved hydrogen bonds is:
\[ 2 \text{ hydrogen bonds} \times 4 \text{ cuts} = 8 \text{ hydrogen bonds} \]

4. **Calculate the Ratio**:
- The ratio of the number of hydrogen bonds present before cleavage to the number of hydrogen bonds cleaved is:
\[ \text{Ratio} = \frac{\text{Hydrogen bonds before cleavage}}{\text{Hydrogen bonds cleaved}} = \frac{56}{8} = 7 \]
- Thus, the final ratio is:
\[ 7 : 1 \]

### Final Answer:
The ratio of the number of hydrogen bonds present before cleavage by EcoRI to the number of hydrogen bonds cleaved by EcoRI at those locations is **7:1**.