Question

Histone proteins are rich in
A. Alanine and glycine
B. Arginine and lysine
C. Histidine and serine
D. Tyrosine and cysteine

Answer 1

Hint: The DNA is wrapped around an octamer of histone core to form bead like structures called nucleosomes. The histone proteins are rich in basic amino acids arginine and lysine.

Complete answer: In eukaryotic cells, histones are highly basic proteins around which the DNA molecule is wrapped twice to accommodate very long DNA molecules into the cell nucleus, without histones the unwrapped DNA would be very long. That's how histone provides structural support to a chromosome. Some variants of histones are also associated with the regulation of gene expression.
As we know, DNA is negatively charged and histones are composed of mostly positively charged amino acids, they are abundant in lysine and arginine.. Due to this positive charge on histone, they remain closely associated with the negatively charged DNA through electrostatic force of attraction. Due to neutralizing the charges, the DNA and histone become more tightly packed.
We have four options: Alanine and glycine, Arginine and lysine, Histidine and serine and Tyrosine and cysteine.
Alanine (Ala) and glycine (Gly) both are neutral at pH 7. They exist as a zwitterion. Arginine (Arg) and lysine (Lys) both have positive charge at neutral pH values.
Histidine (His) is positively charged while serine is neutral at neutral pH.
Tyrosine and cysteine both are neutral at pH 7. So, only option B has both positive charged proteins. So, the correct option is B. Arginine and lysine.

Note: The octamer core of histone proteins is made up of two units, each unit is made up of H2A, H2B, H3 and H4. Another protein called H1 is present at the point of entry and exit of DNA from the nucleosome. All these proteins have position charge on them.