Question

How to calculate the molecular mass and length of a segment of B-DNA specifying a 40-kD protein?

Answer 1

QUESTION:

How to calculate the molecular mass and length of a segment of B-DNA specifying a 40-kD protein?

SOLUTION:

Average molecular weight of amino acid = 105.2 dalton

Assume that the 40 kDa protein is composed of 380 amino acids (40000 Da/105.2 Da = 380).

1 amino acid = 3 nucleotides

Number of nucleotides = 380*3 = 1140 nt

Average molecular weight per nucleotide = 499.5 Da

Molecular mass of B-DNA is 5.69*10⁵ Da

In the B-form of DNA, the helix makes a turn every 3.4 nm, and the distance between two neighboring base pairs is 0.34 nm. Hence, there are about 10 pairs per turn.

The contour length of B-DNA = 1140 nt/10 nt * 3.4 nm = 387.6 nm (or 3876 Å).