Q.30 Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Scaffolding proteins are non-histone chromosomal proteins.
Reason R: Scaffolding proteins are abundant in lysine and Arginine.
In the light of the above statements, choose the most appropriate answer from the options given below:
1. Both A and R are correct and R is the correct explanation of A
2. Both A and R are correct but R is NOT the correct explanation of A
3. A is correct but R is not correct
4. A is not correct but R is correct
Scaffolding Proteins Assertion-Reason: Non-Histone Chromosomal Role
Scaffolding proteins maintain mitotic chromosome structure as non-histone chromosomal proteins. The reason about lysine/arginine abundance fits histones, not scaffold proteins, making option 3 correct.
Correct Answer
3. A is correct but R is not correct. Assertion A accurately identifies scaffolding proteins (like Topo IIα, condensin) as non-histone chromosomal proteins forming the chromosome scaffold. Reason R incorrectly attributes lysine/arginine abundance to them—that characterizes basic histones (H2A, H2B, H3, H4).
Option Breakdown
Option 1: Both Correct, R Explains A
Incorrect. While A holds, R misdescribes scaffold composition. Lysine/arginine-richness defines histones’ DNA-binding via positive charge, not scaffold function.
Option 2: Both Correct, R Doesn’t Explain A
Wrong. R fails as scaffold proteins (SMC family, Topo II) lack histone-like basic amino acid dominance; their roles involve enzymatic activity and structural maintenance.
Option 3: A Correct, R Incorrect
Right choice. Scaffolding proteins organize chromatin loops in metaphase chromosomes after histone depletion, forming a proteinaceous axis. Histones provide basicity, scaffolds provide architecture.
Option 4: A Incorrect, R Correct
False. A is factual per classic experiments (H1/H2A-H2B extraction reveals scaffold). R describes histones, not scaffolds.
| Option | A Correct? | R Correct? | R Explains A? | Status |
|---|---|---|---|---|
| 1 | Yes | No | N/A | Wrong |
| 2 | Yes | No | N/A | Wrong |
| 3 | Yes | No | N/A | Correct |
| 4 | No | No | N/A | Wrong |
