Introduction to biological macromolecules

Lecture 1

Biological macromolecules

Large molecules essential for life, including carbohydrates, nucleic acids, and proteins; they interact in dynamic networks within cells to support structure, energy storage, information transfer, and catalysis.

Role of carbohydrates

Provide immediate and stored energy, form structural components (e.g., plant and bacterial cell walls), and create protective/signalling coats on cell surfaces that influence motility and adhesion.

Medical relevance of carbohydrates

Glucose homeostasis is vital; dysregulation leads to diabetes. Glycogen storage diseases arise from missing enzymes needed for glycogen synthesis or breakdown, causing weakness, sweating, confusion, kidney stones, and stunted growth.

Monosaccharides

Basic sugar units with multiple hydroxyl groups and either an aldehyde (aldose) or ketone (ketose). They rarely exist in linear form and instead cyclize into ring structures.

Glucose isomers (α and β)

Cyclization of glucose produces α‑ and β‑anomers, which differ at the anomeric carbon. These small structural differences lead to polysaccharides with dramatically different properties (e.g., starch vs cellulose).

Disaccharides

Two monosaccharides linked by a condensation reaction (loss of water). Example: sucrose (glucose + fructose).

Polysaccharides

Long chains of sugars that may be linear or branched. Their sequence is determined by enzymes, not genetic templates.

Reducing end

The end of a sugar chain capable of opening into a linear form and participating in redox reactions.

Glycogen

Highly branched glucose polymer used for rapid energy release. Branching increases the number of accessible ends for enzymatic digestion. In animals, especially active mammals, this supports fast mobilization of glucose during muscle activity.

N‑linked oligosaccharides

Complex carbohydrates attached to proteins via asparagine residues. Built from a core pentasaccharide and elaborated into diverse structures on cell surfaces.

Nucleic acids

DNA and RNA store and transmit genetic information. RNA also performs catalytic and structural roles (e.g., in ribosomes) and serves as the genome for some viruses.

Nucleotide structure

Composed of a sugar (ribose or deoxyribose), a nitrogenous base, and three phosphate groups.

DNA vs RNA bases

DNA uses A, T, G, C; RNA uses A, U, G, C.

Phosphodiester bond

Covalent linkage between nucleotides forming the sugar‑phosphate backbone of nucleic acids.

Base pairing

Hydrogen bonding between complementary bases: A–T (or A–U in RNA) and C–G. Enables double‑stranded DNA formation.

DNA double helix

Two antiparallel strands with bases stacked like ladder rungs; major and minor grooves form binding sites for proteins.

Hairpin loops in RNA

Local base‑paired structures formed when a single RNA strand folds back on itself. Important in tRNA and viral RNA structure.

tRNA structure

Contains four hairpin regions forming a compact 3D shape recognized by the ribosome; essential for accurate translation.

Ribosome

Large RNA–protein complex where RNA forms the catalytic active site. Responsible for protein synthesis.

Proteins

Highly diverse macromolecules that perform structural, catalytic, and regulatory functions. Their function depends on their 3D structure.

Four levels of protein structure !

Primary: amino acid sequence

Secondary: α‑helices and β‑sheets

Tertiary: overall 3D fold

Quaternary: arrangement of multiple polypeptide chains

Amino acid structure

Central carbon with amino group, carboxyl group, hydrogen, and variable R‑group. Natural proteins use L‑amino acids.

Hydrophobic amino acids

Non‑polar side chains that cluster inside proteins or at interaction interfaces. Cysteine can form disulphide bonds or bind metals.

Hydrophilic amino acids

Polar or charged side chains that interact with water; contribute to protein solubility and reactivity.

Peptide bond

Covalent bond linking amino acids via condensation; forms the protein backbone with N‑terminus and C‑terminus.