Which chromatin type is generally more accessible to transcription machinery?

Which chromatin type is generally more accessible to transcription machinery?

• A. Euchromatin
• B. Heterochromatin
• C. Nucleosome
• D. Chromatid

Answer: (A)

DNA accessibility for transcription depends on how open chromatin is. Euchromatin is the lightly packed, transcriptionally active form, which allows transcription factors and RNA polymerase II to access promoter and regulatory regions more readily. In this state, histone tails are often acetylated and chromatin remodelers keep nucleosomes more loosely arranged, making initiation and elongation of transcription easier. In contrast, heterochromatin is highly condensed and enriched in repressive marks, so the DNA is largely inaccessible to the transcription machinery and gene expression is suppressed. A nucleosome is the basic unit of chromatin—DNA wrapped around histone proteins—but whether chromatin is open or closed depends on higher-order organization and histone modifications; euchromatin tends to be more permissive due to its open configuration. A chromatid is simply a replicated chromosome and does not describe chromatin accessibility in interphase.

DNA accessibility for transcription depends on how open chromatin is. Euchromatin is the lightly packed, transcriptionally active form, which allows transcription factors and RNA polymerase II to access promoter and regulatory regions more readily. In this state, histone tails are often acetylated and chromatin remodelers keep nucleosomes more loosely arranged, making initiation and elongation of transcription easier. In contrast, heterochromatin is highly condensed and enriched in repressive marks, so the DNA is largely inaccessible to the transcription machinery and gene expression is suppressed. A nucleosome is the basic unit of chromatin—DNA wrapped around histone proteins—but whether chromatin is open or closed depends on higher-order organization and histone modifications; euchromatin tends to be more permissive due to its open configuration. A chromatid is simply a replicated chromosome and does not describe chromatin accessibility in interphase.