What is the basic unit formed when DNA wraps around histone proteins?

What is the basic unit formed when DNA wraps around histone proteins?

• A. Nucleosome
• B. Chromosome
• C. Helix
• D. Gene

Answer: (A)

DNA wraps around histones to form nucleosomes, the fundamental repeating units of chromatin. A nucleosome consists of about 146 base pairs of DNA wrapped around a histone octamer made from two copies each of H2A, H2B, H3, and H4. The linker histone H1 helps stabilize the DNA as it links adjacent nucleosomes, enabling the beads-on-a-string appearance that shortens and compacts the DNA. This packaging is essential for regulating gene access: tightly packed regions are less accessible to transcription machinery, while more open regions allow expression. A chromosome is a higher-order assembly of many nucleosomes condensed during cell division, the DNA double helix is the structural form of the DNA molecule itself, and a gene is a sequence that encodes a product, not the packaging unit described here.

DNA wraps around histones to form nucleosomes, the fundamental repeating units of chromatin. A nucleosome consists of about 146 base pairs of DNA wrapped around a histone octamer made from two copies each of H2A, H2B, H3, and H4. The linker histone H1 helps stabilize the DNA as it links adjacent nucleosomes, enabling the beads-on-a-string appearance that shortens and compacts the DNA. This packaging is essential for regulating gene access: tightly packed regions are less accessible to transcription machinery, while more open regions allow expression. A chromosome is a higher-order assembly of many nucleosomes condensed during cell division, the DNA double helix is the structural form of the DNA molecule itself, and a gene is a sequence that encodes a product, not the packaging unit described here.