Question

Molecular weight of $E.coli$ DNA is $3.1\times {10}^{9}g/mol$. The average molecular weight of nucleotide pair is $660g/mol$ and each nucleotide pair contributes of $0.34nm$ to the length of DNA. The length of $E.coli$ DNA molecule will be approximately

• A. $0.8nm$
• B. $1.6nm$
• C. $1.6\mu m$
• D. $1.6mm$

Answer 1

The correct option is D $1.6mm$

Molcular weight of E.coli DNA is 3.1 x 10${}^9$g/mol.

Molecular weight of DNA = Number of base pairs x average molecular weight of nucleotide pair.

Therefore, number of base pairs = molecular weight of DNA / average molecular weight of nucleotide pair = 3.1 x 10${}^9$ / 660 = 4.70 x 10${}^6$.

One base pair contributes of 0.34 nm length.

Hence, 4.70 x 10${}^6$ base pair contributes to 4.70 x 10${}^6$ x 0.34 = 1.6 x 10${}^6$ nm = 1.6 mm.

Thus, the correct answer is option D.