Question

Histones are rich in

• A. histidine
• B. alanine and glycine
• C. cysteine and tyrosine
• D. lysine and arginine

Answer 1

The correct option is D

lysine and arginine

The correct option is D.

Explanation for the correct option:

1. Histones are special highly alkaline proteins that are found in the nucleus of the eukaryotic cell.
2. They are responsible to package the DNA (deoxyribonucleic acid) in the compact form called nucleosomes.
3. Histones contain two basic amino acids lysine and arginine.
4. In a eukaryotic cell, the DNA is wound around an octamer of histone core to form bead-like structures called nucleosomes.
5. The octamer core of histone proteins is made of two units each of H₂A, HB, H3, and H4.
6. The histone protein H1 is present at the point of entry and exit of DNA from nucleosomes.
7. The histone proteins are rich in basic amino acids lysine and arginine which give a positive charge to them.
8. The positive charge of histone proteins helps in the winding of negatively charged DNA that is around them.

Explanation for Incorrect option:

Option A:

1. Histidine is also a positively charged basic amino acid.
2. Histidine is the amino acid with the least basic character.
3. Serine is also a polar amino acid but it does not have a charge.
4. Histidine is not present in Histone proteins.

Option B:

1. Glycine is the most simple amino acid as its side chain has only a single H-atom.
2. Alanine is also a non-polar amino acid but it has a hydrophobic side chain.
3. Alanine and Glycine are not present in Histone proteins.

Option C:

1. Tyrosine is a hydrophobic amino acid.
2. Tyrosine is non-polar and has an aromatic group in its side chain.
3. Cysteine is a polar amino acid but does not have a charge.
4. Cysteine is hydrophobic.
5. Cysteine has a sulfur group in its side chain.
6. Tyrosine and Cysteine are not present in Histone proteins.

Final answer: Histones are rich in lysine and arginine.