Essential NEET Facts — Biomolecules — Summary

Glucose vs fructose: Both are $C_6H_{12}O_6$ isomers. Glucose = aldohexose (CHO group). Fructose = ketohexose (C=O at C2).
Anomers: $\alpha$ -D-glucose has C1-OH axial (below the ring in Haworth). $\beta$ -D-glucose has C1-OH equatorial (above the ring). Mutarotation = interconversion via open-chain form.
Non-reducing sugar: Sucrose only. Glycosidic bond at C1 of glucose AND C2 of fructose — both anomeric carbons blocked. Cannot open to free aldehyde/ketone.
Reducing disaccharides: Lactose (glucose–galactose, $\beta$ -1,4) and maltose (glucose–glucose, $\alpha$ -1,4) — each has one free anomeric carbon.
Polysaccharide linkages: Amylose = $\alpha$ -1,4 linear. Amylopectin = $\alpha$ -1,4 + $\alpha$ -1,6 branched. Cellulose = $\beta$ -1,4 linear (indigestible). Glycogen = $\alpha$ -1,4 + $\alpha$ -1,6, most branched.
Peptide bond: Formed by condensation (loss of H $_2$ O) between –COOH and –NH $_2$ . Covalent. Partial double-bond character.
Protein denaturation: Breaks H-bonds, disulfide bonds, hydrophobic interactions. Does NOT break peptide bonds. Primary structure preserved.
Protein secondary structure: $\alpha$ -helix = intramolecular H-bonds between C=O and N-H of every 4th residue. $\beta$ -sheet = intermolecular H-bonds.
Haemoglobin: Quaternary structure — 4 subunits (2 $\alpha$ + 2 $\beta$ ). Example of protein with all four structural levels.
Fat-soluble vitamins ADEK: A = retinol (night blindness). D = calciferol (rickets/osteomalacia). E = tocopherol (infertility). K = phylloquinone (delayed clotting).
Water-soluble vitamin deficiencies (high-yield pairs): B1 → beriberi. B3 → pellagra. B9 → megaloblastic anaemia. B12 → pernicious anaemia. C → scurvy.
DNA base pairing: A–T = 2 H-bonds. G–C = 3 H-bonds. Higher G–C → higher $T_m$ .
DNA vs RNA sugar: DNA = deoxyribose (no 2'-OH). RNA = ribose (has 2'-OH). RNA also has uracil instead of thymine.
Three RNA types: mRNA (genetic code carrier), tRNA (amino acid transporter, cloverleaf), rRNA (ribosome structural component).
Isoelectric point: At pI, amino acid is a zwitterion ( $^+H_3N$ –CHR–COO $^-$ ), net charge zero, no migration in electric field.