Question

If the length of a double helical DNA is 1.7 meters, then the number of base pairs present in the DNA is
A. $5\times {{10}^{9}}$
B. $1.7\times {{10}^{9}}$
C. $3.4\times {{10}^{9}}$
D. $1.7\times {{10}^{5}}$

Answer 1

DNA is the genetic material present in all living organisms. It is passed from parents to offspring. A eukaryotic DNA is a helical structure twisted around each other. The formula used to calculate base pairs is $Total\text{ }double\text{ }helix\text{ }DNA\text{ }length\text{ }=\text{ }total\text{ }base\text{ }pair\text{ }count\text{ }\times\text{ }gap\text{ }between\text{ }two\text{ }base\text{ }pairs$

Complete answer: DNA can be defined as molecules responsible for transmitting hereditary materials or genetic instructions from parents to offsprings. Eukaryotic DNA is located in the cell nucleus. The term DNA stands for Deoxyribonucleic acid. It is a nucleic acid that consists of a chain of nucleotides. A pentose (deoxyribose), a phosphate group and a base containing nitrogen (adenine, guanine, thymine and cytosine) form a nucleotide. To create a single strand, these nucleotides further bind together. Each chain, therefore, has a backbone that consists of alternating groups of sugar and phosphate groups. As pairs Adenine pairs with Thymine, Guanine with Cytosine. These base pairs are connected by hydrogen bonds. To form a twisted ladder-like structure, the nitrogenous bases of the opposite strands wind around each other. In opposite directions, these two strands move. For solving the given problem, the following method is used. The length between the two base pairs is $0.34nm$
$Total\text{ }double\text{ }helix\text{ }DNA\text{ }length\text{ }=\text{ }total\text{ }base\text{ }pair\text{ }count\text{ }\times\text{ }gap\text{ }between\text{ }two\text{ }base\text{ }pairs$
Here, the total base pair number is unknown. Let's say it's Y:
$1.7\text{ }m=Y\times0.34\times{{10}^{6}}$
$Y=0.34\times{{10}^{6}}/1.7=5\times{{10}^{9}}$
Hence, the correct answer is option A.

Note: There are several distinctions, such as between eukaryotic DNA and prokaryotic DNA. As a covalently closed circular form of DNA is present in prokaryotic cells. Whereas, eukaryotic DNA with two ends occurs as a linear form of DNA. Prokaryotic DNA has no formation of nucleosomes, although certain nucleosomes are formed in eukaryotic DNA. In the cytoplasm of the cell, prokaryotic DNA is contained. Whereas, the nucleus of the cell includes eukaryotic DNA.