Why are genes contained in compact chromatin typically not expressed?

• A. Because compact chromatin increases the rate of RNA polymerase activity.
• B. Because compact chromatin enhances the binding of transcription factors.
• C. Because compact chromatin allows for more efficient DNA replication.
• D. Because the DNA is tightly packed, preventing access by transcription machinery.

Answer: (D)

Verified step by step guidance

1. Understand that chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.
2. Recognize that chromatin can exist in two forms: euchromatin, which is less compact and more accessible, and heterochromatin, which is tightly packed and less accessible.
3. Identify that gene expression requires the transcription machinery, including RNA polymerase and transcription factors, to access the DNA.
4. Note that in compact chromatin (heterochromatin), the DNA is tightly packed, which physically restricts the access of transcription machinery to the DNA.
5. Conclude that because the transcription machinery cannot access the DNA in compact chromatin, genes contained in these regions are typically not expressed.