Choose the correct Statement about DNA packaging from the following.

Options

A. The beads-on-string structure in chromatin is packaged to from chromatin finers that are further coiled and condensed during metaphase.
B. A typical nucleosome contains 300 bp of DNA helix
C. Histones are rich in the basic amino acid residues glycine and arginine , both of which carry a oha positive charge .
D. In a typical nucleus , the region of chromatin which stains light is referred to as heterochromatin.

Answer

To solve the question about DNA packaging, we need to analyze the statements provided and determine which one is correct. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand DNA Packaging
DNA is a long molecule that needs to be efficiently packaged to fit within the nucleus of a cell. This packaging is achieved through the formation of nucleosomes, where DNA wraps around histone proteins.

### Step 2: Identify the Role of Histones
Histones are basic proteins that have a positive charge due to their amino acid composition. This positive charge allows them to bind to the negatively charged DNA, facilitating the packaging process.

### Step 3: Analyze the Statements
1. **Statement A**: "During the metaphase, the structure of the beads-on-string chromatin coils and condenses."
- This statement is correct. During metaphase, chromatin condenses into visible chromosomes, and the beads-on-string structure (nucleosomes) is not visible.

2. **Statement B**: "In a typical nucleosome, there are 300 base pairs of DNA."
- This statement is incorrect. A typical nucleosome contains about 200 base pairs of DNA, not 300.

3. **Statement C**: "Histones are rich in basic amino acids residues like Glycine and Arginine and have a positive charge."
- This statement is partially incorrect. While histones are rich in basic amino acids, Glycine is not one of the primary basic amino acids; instead, Lysine and Arginine are more prevalent.

4. **Statement D**: "In a typical nucleus, the light region of chromatin is called heterochromatin."
- This statement is incorrect. The light-staining region of chromatin is called euchromatin, while heterochromatin is the densely packed and dark-staining region.

### Step 4: Conclusion
Based on the analysis, the correct statement about DNA packaging is **Statement A**: "During the metaphase, the structure of the beads-on-string chromatin coils and condenses."