An average base pair in DNA is 650 Da. Histone masses are shown in the table. What is the approximate mass of a nucleosome core in kiloDaltons (kDa)? Histone
Mass (Daltons)
Histone H1
21,130
Histone H2A
13,960
Histone H2B
13,774
Histone H3
15,273
Histone H4
11,236

Question

Quizplus · Accepted Answer

The nucleosome core consists of an octamer of two copies of each of the four core histones (H2A, H2B, H3, and H4) wrapped around by 147 base pairs of DNA. The mass of the histone octamer can be calculated as follows:

(2 x 13,960 Da) + (2 x 13,774 Da) + (2 x 15,273 Da) + (2 x 11,236 Da) = 137,264 Da

Dividing this by the average mass of a base pair (650 Da) gives us:

137,264 Da / 650 Da = ~211 base pairs

However, we need to account for the additional mass of the linker DNA, which is present between nucleosomes. The linker DNA is approximately 20-60 base pairs long, with an average length of 40 base pairs. Therefore, the total mass of the nucleosome core plus linker DNA would be:

(211 + 40) x 650 Da = ~155 kDa

Therefore, the best choice is B, which is the option closest to ~155 kDa.

An Average Base Pair in DNA Is 650 Da