Question

Choose the correct answer from the given alternatives given:
The net electric charge on DNA and histones is
A)Both positive
B)Both negative
C)Negative and positive, respectively
D)Zero

Answer 1

Hint: The DNA present in the chromosome is packed with the help of histones. The net charge on the DNA and histones helps in forming the nucleosomes. The nucleosome is made up of DNA wrapped around eight histone molecules.

Complete answer:
To solve this question, we must know about the packing of DNA in the chromosome.
The DNA is present in the nucleus. In order to fit the long DNA in the nucleus, it is wrapped around histones and gives DNA a compact shape. The DNA coils around histone proteins and forms nucleosomes which appear like beads on a string. Many histones coil into 30-nm fibre consisting of nucleosomes in the compact heterochromatin.

Charge on Histones: A histone is a protein which provides structural support to the DNA. Histones are basic proteins hence positively charged.

Charge on DNA: DNA is made up of deoxyribose sugar, nucleotide bases and phosphate molecules. DNA is negatively charged due to the presence of phosphate backbone. The phosphate group contains negatively charged oxygen atoms. This gives DNA strands negatively charged.

The negative charge on DNA and the positive charge on histone facilitate the binding of histones and DNA. This facilitates the condensation of DNA into chromosomes.

Hence, the correct answer is option (C)

Note: The histones are made up of positively charged amino acids, lysine and arginine. The DNA is negatively charged. These opposite charges give strong attractive force between the DNA and histones.