Correct Answer: B and D only

Histones are basic proteins rich in positively charged amino acids like lysine and arginine, which enable them to bind tightly to negatively charged DNA, forming the fundamental structure of chromatin known as nucleosomes.

Option Analysis

A. Histones are rich in acidic amino acids.
False. Histones contain high levels of basic (positively charged) amino acids such as lysine and arginine, not acidic ones like aspartic or glutamic acid, which would repel DNA’s negative phosphate backbone.

B. Histones are rich in basic amino acids.
True. The abundance of lysine and arginine provides a positive charge, essential for interacting electrostatically with DNA during packaging into chromatin.

C. Histones are important for stabilizing single-stranded DNA.
False. Histones primarily package and stabilize double-stranded DNA in eukaryotic chromatin; single-stranded DNA stabilization involves other proteins like RPA during replication or repair.​

D. Histones bind to DNA to form chromatin.
True. Histones form an octamer core around which ~147 bp of DNA wraps, creating nucleosomes—the basic repeating unit of chromatin that compacts the genome.

Histones rich in basic amino acids play a pivotal role in DNA packaging, addressing key questions like their composition and function in forming chromatin. This guide explains histones’ properties for students preparing for exams like NEET or GATE Life Sciences.

Histones Composition

Histones are small, basic proteins dominated by basic amino acids—lysine (Lys) and arginine (Arg)—which constitute up to 20-30% of their sequence. These residues carry positive charges at physiological pH, contrasting with DNA’s negative phosphate backbone for strong ionic binding.

Acidic amino acids are minimal in histones, as they would hinder DNA association; instead, histones H2A, H2B, H3, and H4 form an octamer with linker histone H1.​

Role in Chromatin Formation

Histones bind DNA to form nucleosomes: DNA wraps ~1.65 times around the histone octamer, compacting 2 meters of human DNA into a nucleus. This chromatin structure regulates access for transcription and replication.

They do not stabilize single-stranded DNA, a function reserved for replication protein A (RPA); histones target double-stranded genomic DNA exclusively.​

Exam-Relevant Insights

For competitive exams, remember: histones’ basic nature (Option B) and chromatin-binding (Option D) are correct; acidic richness (A) and ssDNA stabilization (C) are not. This aligns with NCERT Class 12 Molecular Basis of Inheritance.​