AIEM — ICSE Exam Prep

Biomolecules

The chemical composition of living and non-living matter is qualitatively similar, but the relative abundance of carbon, hydrogen and oxygen is higher in living systems. Water is the most abundant chemical in living organisms (70-90% of cellular mass).

Analysing chemical composition

A tissue is ground in trichloroacetic acid and strained, giving an acid-soluble pool (filtrate, micromolecules, 18-800 Da) and an acid-insoluble fraction (retentate, macromolecules). Burning the tissue leaves ash (inorganic elements).

Primary vs secondary metabolites

Primary metabolites (amino acids, sugars, fatty acids) have identifiable functions; found in animal tissues.
Secondary metabolites (alkaloids, pigments, rubber, toxins, essential oils) have roles not always understood; many are useful to humans.

The four biomacromolecules

The acid-insoluble fraction has only proteins, nucleic acids, polysaccharides and lipids. Except for lipids, these are polymers. Lipids are not strictly macromolecules but separate here as water-insoluble membrane vesicles.

Proteins

Heteropolymers of 20 amino acids joined by peptide bonds. Structure has four levels - primary (sequence), secondary (right-handed helix / pleated sheet), tertiary (3D folding), quaternary (subunit arrangement, e.g. haemoglobin = 2 alpha + 2 beta). Collagen is most abundant in animals; RuBisCO most abundant in the biosphere.

Carbohydrates, lipids, nucleic acids

Monosaccharides (glucose, ribose) -> polysaccharides (starch, glycogen, cellulose, chitin). Lipids include fatty acids, glycerol, glycerides and phospholipids. Nucleic acids (DNA, RNA) are polynucleotides; each nucleotide = base + sugar + phosphate.

Enzymes

Mostly proteins (ribozymes are catalytic RNA). They lower activation energy, act through an active site, form an ES complex, are affected by temperature, pH and substrate concentration, fall into 6 classes, and may need cofactors (prosthetic groups, coenzymes, metal ions).