The length of DNA in one chromosome is `510 A^(@)`. It has `20%` of 6-aminopurines. The total number of nucleotides and hydrogen bonds in that chromosome respectively, are

Options

A. 300 & 390
B. 150 & 390
C. 150 & 190
D. 120 & 156

Answer

To solve the problem, we need to calculate the total number of nucleotides and hydrogen bonds in a DNA chromosome that is 510 Å in length and contains 20% of 6-aminopurines (which is adenine).

### Step-by-Step Solution:

1. **Calculate the Total Number of Base Pairs:**
- The length of the DNA is given as 510 Å.
- The distance between two base pairs is 3.4 Å.
- To find the total number of base pairs, we use the formula:
\[ \text{Total Base Pairs} = \frac{\text{Length of DNA}}{\text{Distance between Base Pairs}} = \frac{510 \, \text{Å}}{3.4 \, \text{Å}} \approx 150 \, \text{base pairs} \]

2. **Calculate the Total Number of Nucleotides:**
- Each base pair consists of two nucleotides.
- Therefore, the total number of nucleotides is:
\[ \text{Total Nucleotides} = 2 \times \text{Total Base Pairs} = 2 \times 150 = 300 \, \text{nucleotides} \]

3. **Determine the Composition of Nucleotides:**
- It is given that 20% of the nucleotides are 6-aminopurines (adenine).
- Therefore, the number of adenine (A) nucleotides is:
\[ \text{Number of A} = 20\% \text{ of } 300 = 0.2 \times 300 = 60 \, \text{A} \]
- Since adenine pairs with thymine (T), the number of thymine (T) nucleotides is also 60.

4. **Calculate the Remaining Nucleotides:**
- The total number of nucleotides is 300, and we have 60 adenine and 60 thymine.
- Therefore, the number of guanine (G) and cytosine (C) nucleotides can be calculated as:
\[ \text{Number of G + C} = 300 - (60 + 60) = 300 - 120 = 180 \]
- Since guanine pairs with cytosine, the number of guanine and cytosine nucleotides is equal:
\[ \text{Number of G} = \text{Number of C} = \frac{180}{2} = 90 \]

5. **Calculate the Total Number of Hydrogen Bonds:**
- Adenine and thymine form 2 hydrogen bonds each, and guanine and cytosine form 3 hydrogen bonds each.
- The total number of hydrogen bonds is calculated as follows:
\[ \text{Total Hydrogen Bonds} = (60 \times 2) + (90 \times 3) = 120 + 270 = 390 \]

### Final Answer:
- The total number of nucleotides is **300**.
- The total number of hydrogen bonds is **390**.