Question

Chromatin structure must be altered in order for gene expression to occur because:
A. Condensed chromatin is replicated but not transcribed.
B. Condensed chromatin makes most DNA sequences inaccessible to the transcription complex.
C. Decondensed chromatin has more nucleosomes per DNA molecule.
D. Heterochromatin is actively transcribed and euchromatin is not transcribed.

Answer 1

Hint: Chromatin is the mixture of DNA and proteins that form chromosomes which are found in the nucleus of our cell. Chromatin material is a genetic material made up of DNA, RNA and proteins associated with them. Chromatin is a thread-like structure which condenses to form chromosomes during division of cells.

Complete step by step solution:
The main purpose of chromatin is to compact the DNA into a small, less voluminous unit that can fit inside the nucleus. Histone and DNA complexes make up chromatin, which is found in cells. In the nucleus of eukaryotic cells, chromatin, a combination of DNA and proteins, creates chromosomes. In order to fit inside the nucleus, nuclear DNA is extremely compressed and wrapped around nuclear proteins rather than appearing as free linear strands. It is now widely known that the chromatin structure around expressed genes is altered. The hypersensitivity to nucleases that marks locations that no longer carry canonical nucleosomes and to which transcription factors bind is most noticeable in the vicinity of promoters and enhancers. DNA condenses in nucleosomes. In contrast to euchromatin, heterochromatin lacks transcriptional activity.
So, option (B) is correct.

Note:
Chromatin is divided into two categories namely: euchromatin and heterochromatin. Euchromatin is a lightly stained, loosely packed part of chromatin and this can be transcribed as well. Heterochromatin is a darkly stained, tightly packed part of chromatin and cannot be transcribed.