Question: 146: If the length of a DNA molecule is 1.1 metres, what will be the approximate number of base pairs?
(1) 3.3 \times 10^{6} \mathrm{bp}
(2) 6.6 \times 10^{6} \mathrm{bp}
(3) 3.3 \times 10^{9} \mathrm{bp}
(4) 6.6 \times 10^{9} \mathrm{bp}
Answer: Option (3)
Explanation:
In a DNA double helix, the distance between two successive base pairs is
0.34 \times 10^{-9} \mathrm{~m}.
The total length of the DNA molecule is given as 1.1 \mathrm{~m}.
The number of base pairs is calculated by dividing the total length by the distance per base pair.
Number of base pairs =\dfrac{1.1}{0.34 \times 10^{-9}}.
Number of base pairs \approx 3.23 \times 10^{9}.
Approximating to one significant figure, the number of base pairs is
3.3 \times 10^{9} \mathrm{bp}.
Therefore, the correct option is (3).