NEET rarely asks you to describe the full Central Dogma in paragraph form. What it does test: can you distinguish the specific biological roles of DNA versus RNA, and can you connect structural features (base pairing, sugar type, strand number) to those functions?
DNA — the information archive. DNA stores the hereditary blueprint of an organism. Its double-stranded helical structure with complementary base pairing (adenine with thymine via 2 hydrogen bonds, guanine with cytosine via 3 hydrogen bonds) provides a built-in mechanism for faithful replication. Each strand serves as a template for copying the other — this is the molecular basis of heredity (NCERT Class 12 Chemistry Chapter 6, Part 2, page 26).
RNA — the functional messenger. RNA is the working copy. Three major types carry out distinct functions:
The function–structure link NEET exploits. Questions test whether you can connect: (1) double-stranded → replication fidelity (DNA), (2) single-stranded → transient functional roles (RNA), (3) deoxyribose → chemical stability for long-term storage (DNA), (4) ribose → sufficient for short-lived functional molecules (RNA), (5) thymine in DNA versus uracil in RNA.
Watch-out: A common confusion is attributing protein synthesis directly to DNA. DNA does not leave the nucleus in eukaryotes — it is mRNA that carries the message to the cytoplasmic ribosome. Another frequent error: stating that all RNA is single-stranded (some viral RNA is double-stranded, though NEET questions stay within the NCERT scope of single-stranded cellular RNA).
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which of the following is the primary biological function of DNA?
Which type of RNA carries the genetic code from DNA to the ribosome for protein synthesis?
The function of tRNA in protein synthesis is to:
The double-stranded structure of DNA with complementary base pairing directly enables which biological process?
A student claims that DNA directly synthesises proteins in the cytoplasm. What is the correct explanation?
Which structural feature of DNA makes it more chemically stable than RNA, suiting its role as the long-term hereditary store?
If rRNA were absent from a cell, which of the following processes would be directly and immediately affected?
Consider the following statements about nucleic acid functions: (i) DNA undergoes semi-conservative replication. (ii) mRNA acts as the template for translation. (iii) rRNA delivers amino acids to the ribosome. (iv) tRNA reads the mRNA codon via its anticodon. Which statements are correct?
Given
- Total base pairs = 200 (exact counting integer) - A–T pairs = 120 (exact counting integer) - G–C pairs = 80 (exact counting integer)
Required
Total number of hydrogen bonds in this DNA segment.
Concept
In Watson–Crick base pairing, each A–T pair is held by 2 hydrogen bonds and each G–C pair is held by 3 hydrogen bonds. The total hydrogen bonds equal the sum across all pairs.
Formula
Total H-bonds = (number of A–T pairs × 2) + (number of G–C pairs × 3)
Substitution
Total H-bonds = (120 × 2) + (80 × 3)
Calculation
Total H-bonds = 240 + 240 = 480 **Note on exact values:** All numbers in this problem are counting integers (number of base pairs). Counting integers are exact and do not limit significant figures.
Final answer
The DNA segment contains **480 hydrogen bonds**.
Common trap
Confusing the hydrogen bond counts: assigning 3 H-bonds to A–T and 2 to G–C (reversed). Remember: **G–C has the higher bond count (3)** because guanine and cytosine have three complementary H-bonding sites.
Similar NEET-style question
A double-stranded DNA molecule has 30% adenine. If the total number of nucleotides is 2000, how many hydrogen bonds are present? *Approach:* If A = 30%, then T = 30% (Chargaff's rule), so A–T pairs = 30% of 1000 base pairs = 300. G + C = 40%, so G–C pairs = 200. Total H-bonds = (300 × 2) + (200 × 3) = 600 + 600 = 1200. ---
DNA: deoxyribose sugar, A-T-G-C bases, double helix. RNA: ribose, A-U-G-C bases, mostly single-strand. Phosphate-sugar backbone. Bases: purines (A, G) and pyrimidines (T/U, C). H-bond pairs A=T (DNA), A=U (RNA), G≡C.
-- NCERT, p. 26Used to compute total H-bonds in a duplex of given GC%/AT% composition.
| Symbol | Quantity | SI Unit |
|---|---|---|
| %GC | GC content | - |
Empirical formula of simple monosaccharides; glucose/fructose are C6H12O6.
| Symbol | Quantity | SI Unit |
|---|---|---|
| n | carbon count | - |
Number of amide (peptide) bonds in a linear polypeptide of N amino acids.
| Symbol | Quantity | SI Unit |
|---|---|---|
| N | residue count | - |
These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Similar Terms
Student writes A=U for DNA or A=T for RNA. DNA: A=T, G≡C. RNA: A=U (no T), G≡C.
Question on base pairing or sugar identity.
DNA: deoxyribose, A-T-G-C bases. RNA: ribose, A-U-G-C bases (uracil instead of thymine). H-bond pairs: A=T (DNA) or A=U (RNA), G≡C (3 H-bonds, both).
Category: Similar Terms
Student claims denaturation breaks peptide bonds. Denaturation only breaks H-bonds, ionic, hydrophobic interactions; primary structure (peptide bonds) intact.
Question about protein denaturation effects.
Denaturation: heat/pH/organic solvents disrupt secondary, tertiary, quaternary structure. Primary structure (covalent peptide bonds) requires hydrolysis to break.
Root cause: concept gap
Denaturation breaks H-bonds, ionic, hydrophobic; preserves peptide bonds. Hydrolysis (acid/base/enzyme) breaks primary structure.
Root cause: concept gap
DNA: deoxyribose, A=T, G≡C. RNA: ribose, A=U (no T), G≡C.
6 questions from NEET 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
The incorrect statement regarding enzymes is
Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.
swapped classes
Tempts surface-level recall.
Test yourself on this topic with real past-paper questions:
Practice this topic →Get a structured 30-day study plan and a complete formula booklet — delivered to your inbox instantly.