NEET Chemistry — Important Questions & Concepts
Biomolecules & Biochemistry
Q: Explain the structure of DNA and RNA differences.
DNA (Deoxyribonucleic Acid):
Sugar: Deoxyribose (missing -OH at 2' carbon)
Bases: Adenine, Thymine, Guanine, Cytosine
Structure: Double helix (Watson-Crick model)
Location: Nucleus + mitochondria + chloroplasts
RNA (Ribonucleic Acid):
Sugar: Ribose (has -OH at 2' carbon)
Bases: Adenine, Uracil (no Thymine), Guanine, Cytosine
Structure: Single stranded (mostly)
Types: mRNA (messenger), tRNA (transfer), rRNA (ribosomal)
Base pairing (DNA): A=T (2 H-bonds), G≡C (3 H-bonds)
Base pairing (RNA-DNA hybrid): A=U, G≡CQ: Name the enzyme that catalyses DNA replication and describe its action.
DNA Polymerase III (main replication enzyme in prokaryotes)
DNA Polymerase α, δ, ε (eukaryotes)
Key properties:
1. Reads template 3'→5', synthesises new strand 5'→3'
2. Cannot start synthesis de novo — needs RNA primer
3. Adds dNTPs (deoxyribonucleoside triphosphates)
Other enzymes involved:
Helicase: unwinds double helix at replication fork
Primase: makes short RNA primer (starting point)
Ligase: joins Okazaki fragments on lagging strand
Topoisomerase: relieves tension ahead of forkOrganic Chemistry (NEET focus)
Q: What is the difference between Structural and Functional isomers?
Structural isomers: same molecular formula, different structural arrangement
a) Chain isomers: butane vs 2-methylpropane (C₄H₁₀)
b) Position isomers: 1-propanol vs 2-propanol (C₃H₇OH)
c) Functional isomers: ethanol vs dimethyl ether (C₂H₆O)
Stereoisomers: same connectivity, different spatial arrangement
a) Geometric (cis-trans): double bonds or rings
b) Optical: non-superimposable mirror images (chiral carbon)
Important for NEET: aldehydes vs ketones (functional isomers)
alcohols vs ethers (functional isomers)Revision Notes
BIOMOLECULES:
Carbohydrates: (CH₂O)ₙ | Monosaccharides: glucose, fructose
Proteins: amino acids linked by peptide bonds
Lipids: non-polar, soluble in organic solvents
Nucleic acids: nucleotide = base + sugar + phosphate
DNA vs RNA: deoxyribose vs ribose | T vs U | double vs single stranded
REPLICATION: semi-conservative | 5'→3' synthesis | needs primer
TRANSCRIPTION: DNA → mRNA (nucleus) | TRANSLATION: mRNA → protein (ribosome)
MOLE CONCEPT: n = mass/molar mass | Avogadro's = 6.022×10²³
pH = -log[H⁺] | pKa + pKb = 14 at 25°C
Buffer: Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA])