NCERT says '2'-OH group present at every nucleotide in RNA is a reactive group' — Here's how NEET tests it

NCERT line-by-line

1. TITLE

NCERT says '2'-OH group present at every nucleotide in RNA is a reactive group' — Here's how NEET tests it

2. THE NCERT STATEMENT

NCERT EXACT LINE:
"Further, 2'-OH group present at every nucleotide in RNA is a reactive group and makes RNA labile and easily degradable."
— NCERT Class 12, Chapter 5, Page 87

3. WHY THIS LINE MATTERS

• How many times has NEET tested this? This concept has been tested multiple times, both as a direct factual question and hidden inside multi-statement Assertion-Reason questions.
• What makes this statement tricky? Examiners love to swap "2'-OH" with "3'-OH" or "5'-OH". During a high-pressure exam, the brain easily skips over the number "2".
• What do students typically misremember? Students often remember that Thymine provides stability to DNA over Uracil in RNA, but they forget that the primary chemical reason for RNA's instability and reactivity is actually the 2'-OH group on the ribose sugar.

4. MCQ 

According to NCERT, RNA is labile and easily degradable because:
A) Every nucleotide residue has a reactive 2'-OH group in its ribose sugar.
B) Every nucleotide residue has a reactive 3'-OH group in its ribose sugar.
C) RNA mutates at a faster rate due to the presence of Uracil.
D) It lacks the 2'-OH group, making it chemically more reactive.

5. ANSWER + LINE BREAKDOWN

Correct Answer: A

Break down the NCERT line:
- "2'-OH group present at every nucleotide in RNA" means that unlike DNA (deoxyribose), RNA's ribose sugar retains an oxygen atom on its second carbon.
- "is a reactive group and makes RNA labile and easily degradable" means this specific hydroxyl group acts as a catalyst, making the RNA molecule unstable and prone to breaking down quickly.
- The key word is "2'-OH" because it is the exact structural difference that makes DNA chemically less reactive and structurally more stable than RNA, confirming DNA as the better genetic material for storage.

6. HOW NEET TWISTS THIS

Show 3 ways NEET can ask the same fact:
- As direct question: "Why is DNA chemically less reactive than RNA?" (Answer: It lacks the 2'-OH group).
- As assertion-reason:
Assertion: DNA is a better genetic material for the storage of genetic information than RNA.
Reason: RNA is labile and easily degradable due to the presence of a 2'-OH group at every nucleotide residue. (Answer: Both A and R are true, and R is the correct explanation of A).
- As an except question: "All of the following are reasons why DNA is a better genetic material EXCEPT: (Options will include Thymine vs Uracil, double-stranded nature, mutation rates, and a twisted 2'-OH fact)".

7. MEMORY LOCK

MEMORIZE:
DNA lacks 2'-OH = Stable. RNA has 2'-OH = Reactive & Degradable.

Mnemonic: RNA = Reactive OH, Not Always stable.

8. RELATED NCERT LINES

Also remember these from the same page:
- "RNA is also now known to be catalytic, hence reactive."
- "The presence of thymine at the place of uracil also confers additional stability to DNA."

9. NCERT REFERENCE

NCERT Class 12, Chapter 5, Page 87, Paragraph 2

10. CTA

All important NCERT lines from this chapter → Genetics and Evolution Guide