Biomolecules – Quick Revision Notes

Elemental Composition & Biomolecule Types

• Living and non-living matter share elements, but living tissues have higher C & H proportion.

• All C-containing compounds from living tissue = biomolecules.

• Functional categories: amino acids, fatty acids, nucleotide bases.

Amino Acids

• Protein monomers; elements: C, H, O, N (sometimes S).

• α-carbon bears $\text{–COOH}$, \text{–NH_2}, $\text{H}$, variable $R$.

• Total proteinaceous amino acids: $20$ (e.g., glycine, alanine, serine).

Lipids

• Fats + derivatives; insoluble in water, soluble in organics.

• Elements: C, H >> O.

• Simple: glycerol + $3$ long-chain fatty acids.

• Conjugated: lipid + phosphate/protein/CHO; Derived: products of hydrolysis.

• Roles: energy source, storage.

Nitrogenous Bases, Nucleosides & Nucleotides

• Purines: adenine, guanine (two rings).

• Pyrimidines: cytosine, thymine, uracil (one ring).

• Nucleoside = base + pentose (glycosidic bond).

• Nucleotide = nucleoside + phosphate (ester bond).

• Ribose ⇒ ribonucleotide; deoxyribose ⇒ deoxyribonucleotide.

Metabolites

• Primary: CHO, amino acids, lipids, nucleotides.

• Secondary (plants, fungi, microbes): alkaloids, flavonoids, rubber, essential oils, antibiotics.

Biomacromolecules

• Biomicromolecules: $18{-}800$ Da; Biomacromolecules: $\ge 10\,000$ Da.

• Macromolecules remain in acid-insoluble fraction.

Proteins

• Folded, linear heteropolymers of amino acids (peptide bonds).

• Primary: specific amino-acid sequence (N-terminal → C-terminal).

• Secondary: $\text{H}$-bonds; α-helix/β-sheet (e.g., keratin).

• Tertiary: extensive folding; stabilized by ionic, $\text{H}$, disulphide, hydrophobic bonds.

• Quaternary: multiple subunits (e.g., haemoglobin).

Polysaccharides

• Polymers of monosaccharides via glycosidic linkages.

• Homo- vs heteropolysaccharides.

• Storage: starch (plants), glycogen (animals); Structural: cellulose, chitin.

Nucleic Acids

• High-MW polynucleotides (nucleus, cytoplasm, mitochondria, plastids).

• DNA: deoxyribose; genetic material, regulates metabolism.

• RNA: ribose; mRNA, tRNA, rRNA in protein synthesis; RNA genetic in some viruses (TMV, HIV).

Bonds Linking Monomers

• Peptide: $\text{–NH–CO}$ between $\text{–COOH}$ and \text{–NH_2}.

• Glycosidic: $\alpha$-1,4; $\alpha$-1,6; $\beta$-1,4 between sugar C1 & others.

• Nucleic acids: $3'$, $5'$-phosphodiester; H-bonds (A=T $2$, G≡C $3$).

Metabolism

• Sum of all catalysed reactions; follows definite pathways & flux.

• Anabolism: build-up (e.g., glucose → glycogen); weight ↑.

• Catabolism: breakdown (e.g., glucose → lactic acid); weight ↓.

• Living state = non-equilibrium steady state (continuous work).

Enzymes

• Protein biocatalysts; specific active site binds substrate.

• Lower activation energy by forming transient transition state.

• Optimum temperature & pH (most enzymes $pH\ 6{-}7.5$); denature outside range.

• Rate rises with substrate until saturation (Vmax).

Inhibition

• Competitive: inhibitor at active site.

• Non-competitive: inhibitor at other site.

• Allosteric: pathway end-product inhibits earlier enzyme.

Classification (IUBM)

1. Oxidoreductases

2. Transferases

3. Hydrolases

4. Lyases

5. Isomerases

6. Ligases

Co-factors (conjugated enzymes)

• Prosthetic group (e.g., haem in peroxidase).

• Co-enzyme (organic, e.g., NAD).

• Metal ion (e.g., Zn in carboxypeptidase).