Cell Biology Quiz: Histones and Nucleosomes

Histone Charges

• Histones are proteins associated with DNA in chromatin, contributing to the structural organization of genetic material.
• The positive charge on histones primarily arises from the presence of amino acids, specifically arginine and lysine, due to their basic side chains.

Nucleosome Structure

• A nucleosome consists of approximately 200 base pairs (bp) of DNA wrapped around a core of histone proteins.
• This structure forms the fundamental unit of chromatin, playing a crucial role in packaging DNA within the nucleus.

Assertion & Reason Concepts

• An assertion regarding nucleosome charge states that the net charge is neutral—this is true due to oppositely charged components: histones (positively charged) and DNA (negatively charged).
• There is a distinction between the attributes of heterochromatin and euchromatin, where heterochromatin is conventionally considered transcriptionally inactive due to its tightly packed state.

Heterochromatin vs. Euchromatin

• Heterochromatin is characterized by dense packing, resulting in reduced transcriptional activity compared to euchromatin, which is loosely packed and transcriptionally active.
• Misconceptions exist regarding the transcriptional state of heterochromatin, as it is not active despite some being loosely packed under certain conditions.