Answer
Question:
Histones are enriched with:
- (1) Lysine & Arginine
- (2) Leucine & Lysine
- (3) Phenylalanine & Leucine
- (4) Phenylalanine & Arginine
Correct Answer:
(1) Lysine & Arginine
Explanation:
Histones are a group of basic proteins that play a crucial role in the packaging of DNA in eukaryotic cells. They are the major protein components of chromatin and act as spools around which DNA winds, forming nucleosomes — the structural units of chromatin.
Histones are rich in the basic amino acids lysine and arginine, which carry a positive charge at physiological pH. This positive charge facilitates strong electrostatic interactions with the negatively charged phosphate backbone of DNA. These interactions help:
- In tightly packing the DNA into the nucleus.
- In regulating gene expression by controlling the accessibility of DNA to transcription machinery.
Why Lysine and Arginine?
- Lysine (K) and Arginine (R) are basic amino acids due to their positively charged side chains.
- These charges allow strong binding with DNA and maintain chromatin structure.
- Post-translational modifications (e.g., acetylation, methylation) on lysine and arginine residues are key to epigenetic regulation.
In contrast, the other options include amino acids that are non-polar or neutral and do not contribute significantly to histone-DNA interaction.
Summary:
Histones are enriched with lysine and arginine due to their positive charges, enabling interaction with the negatively charged DNA. This is crucial for DNA compaction and gene regulation.