Question

The distance between two consecutive DNA base pairs is 0.34 nm. If the length of a chromosome is 1 mm the number of base pairs in the chromosome is approximately
A) 3 million
B) 1.5 million
C) 30 million
D) 6 million

Answer 1

The nucleus of a cell has a molecule that contains the genetic material of the organisms known as DNA (deoxyribonucleic acid). It consists of four types of nucleotides or chemical bases. They are: adenine, guanine, thymine and cytosine.

Complete answer:
The distance between two consecutive DNA base pairs is

$$= 0.34nm \\\ = 0.34 \times {10^{ - 9}}m \\\ = 0.34 \times {10^{ - 6}}mm \\\$$

Length of chromosomes

= 1mm \\\ = 1 \times {10^{ - 3}}m \\\ $ The total number of base pairs in the chromosomes is $ = \dfrac{{1 \times {{10}^{ - 3}}}}{{0.34 \times {{10}^{ - 9}}}} \\\ = 2.9411 \times {10^6}m \\\ \approx 3 \times {10^6} \\\ $ **Therefore the correct answer is (A) 3 million.** **Note:** DNA is a double helical structure that has two polynucleotide chains that coil around each other resembling a twisted ladder. Each strand is made up of alternating sugar and phosphate groups. The two strands are held together by the hydrogen bonds between the base pairs, that is, adenine with thymine and guanine with cytosine. During replication, the double helical DNA unwinds and each strand is utilized for the synthesis of new DNA.