Biomolecule Study Notes – Comprehensive overview of carbohydrates, lipids, proteins, and nucleic acids

Carbohydrates

• Monomers: Monosaccharides (C, H, O) with formula Cn H{2n} On (e.g., C6H{12}O6 for glucose, fructose, galactose).

• Functions: Major energy source (glucose, starch, glycogen), structural support (cellulose, chitin).

• Structures: Monosaccharides exist as ring forms; alpha or beta configurations at the anomeric carbon (C1).

• Polymers (Polysaccharides): Formed by dehydration synthesis (glycosidic linkages); broken by hydrolysis.

  • Starch (plants): Amylose (linear, α-1,4) and Amylopectin (branched, α-1,4, α-1,6).

  • Glycogen (animals): Highly branched (α-1,4, α-1,6) for rapid glucose release.

  • Cellulose (plants): Linear β-1,4 linkages, forms strong fibers for cell walls.

  • Chitin (insects/fungi): Structural, polymer of N-acetylglucosamine.

Lipids

• Composition: Glycerol and fatty acids (C, H, O); form triglycerides (glycerol + 3 fatty acids).

• Phospholipids: Glycerol + 2 fatty acids + phosphate head; form cell membranes (hydrophobic tails, hydrophilic heads).

• Fatty Acids:

  • Saturated: No double bonds, straight chain, solid at room temperature.

  • Unsaturated: One or more C=C double bonds, cis bonds cause kinks, fluid at lower temperatures.

• Function: Efficient energy storage.

Proteins

• Monomers: Amino acids (C, H, O, N, S).

• Structure: Central carbon, amino group (–NH_2), carboxyl group (–COOH), H atom, and variable R group (side chain).

• Polymers: Polypeptides linked by peptide bonds (dehydration synthesis).

• Amino Acid Types: Nonpolar, polar uncharged, electrically charged (acidic/basic). Cysteine forms disulfide bridges.

• Protein Folding (Hierarchy):

  • Primary: Linear sequence.

  • Secondary: α-helix, β-pleated sheet (H-bonds).

  • Tertiary: 3D shape (R-group interactions).

  • Quaternary: Multiple polypeptide subunits.

• Example: Sickle-cell disease highlights how a single amino acid substitution alters protein function (hemoglobin).

Nucleic Acids

• Monomers: Nucleotides (C, H, O, N, P).

• Components: Phosphate group, pentose sugar, nitrogenous base.

• Sugars: Deoxyribose (DNA, no OH at 2') vs. Ribose (RNA, OH at 2').

• Bases:

  • DNA: Adenine (A), Cytosine (C), Guanine (G), Thymine (T).

  • RNA: A, C, G, Uracil (U).

• Base Pairing: DNA (A-T, C-G); RNA (A-U, C-G).

• Structures:

  • DNA: Double helix, antiparallel strands (5'→3', 3'→5'), sugar-phosphate backbone, H-bonds between bases.

  • RNA: Usually single-stranded, can fold.

• Functions: DNA stores genetic information; RNA involved in gene expression.

• Processes: Replication (DNA copying), Transcription (RNA synthesis). DNA repair mechanisms (e.g., photoreactivation of thymine dimers).

Connections Across Biomolecules

• Monomers form polymers via dehydration synthesis; hydrolysis breaks them down.

• The specific structure and chemical properties of each biomolecule dictate its function (e.g., energy storage, structural support, genetic information, catalysis).