CAPF AC 2020 Q13: Science & Technology – Biology
- (a) DNA only
- (b) DNA and Protein
- (c) DNA and RNA
- (d) RNA and Protein
Answer: (b) DNA and Protein
Explanation
Eukaryotic chromatin
How to think: think of beads on a string.
The string is DNA and the beads are histone proteins.
Chromatin is the thread-like material in the nucleus of a eukaryotic cell.
It is made of DNA wound around proteins called histones.
During cell division it condenses into chromosomes.
| Part of chromatin | Detail |
|---|---|
| DNA | Carries the genetic information |
| Histones | Basic proteins; DNA wraps around them |
| Non-histone proteins | Help in packing and gene control |
| Nucleosome | The repeating unit: DNA around a core of eight histones |
The options checked:
| Option | Verdict |
|---|---|
| (a) DNA only | Incorrect; naked DNA is found in prokaryotes |
| (b) DNA and Protein | Correct |
| (c) DNA and RNA | Incorrect; it leaves out the histone proteins |
| (d) RNA and Protein | Incorrect; that describes a ribosome |
NCERT notes that chromatin also has a small amount of RNA.
The two main parts are still DNA and protein.
Answer: (b) DNA and Protein.
Why each option is right or wrong
- (a) Incorrect. Eukaryotic DNA is not naked; it is packed with histone proteins.
- (b) CORRECT. Chromatin is mainly DNA wound around histone proteins.
- (c) Incorrect. RNA is present only in small amounts; the proteins cannot be left out.
- (d) Incorrect. RNA and protein together make a ribosome, not chromatin.
Key point
Chromatin = DNA + histone proteins (plus non-histone proteins and a little RNA). Repeating unit = nucleosome, DNA around eight histones.
Remember
Chromatin = DNA + histone proteins.
Common mistakes
- Choosing DNA only, forgetting the histone proteins.
- Confusing chromatin with a ribosome, which is RNA and protein.
- Thinking chromatin and chromosomes are different materials; a chromosome is condensed chromatin.
Exam tip
Educated guess: chromatin must have DNA, so (d) is out. DNA alone is the prokaryote case, so (a) is out. Histones decide for (b).
Sources
- NCERT Class XI Biology — Cell: The Unit of Life (nucleus)
- NCERT Class XII Biology — Molecular Basis of Inheritance (packaging of DNA helix)