Definition
Monosaccharides (single sugar units, e.g. glucose, fructose) — sweetest taste; Disaccharides (two units joined, e.g. sucrose, from glucose + fructose); Polysaccharides (many units, e.g. starch, cellulose, glycogen) — not sweet.
Main function: quick energy supply, and (as cellulose) structural support in plant cell walls.
Remember
Cellulose is a polysaccharide that gives plant cell walls their strength — it is the most abundant organic molecule on Earth.
Definition
Lipids (fats and oils) are built from fatty acids and glycerol.
Saturated fatty acids: no double bonds between carbons, usually solid at room temperature (animal fats). Unsaturated: have double bond(s), usually liquid at room temperature (plant oils).
Lipids store more energy per gram than carbohydrates and are used for long-term energy storage, insulation, and as part of the cell membrane.
Definition
Proteins are chains of amino acids; each amino acid's unique side chain (R-group) determines its individual properties, and so the protein's overall shape and function.
Functions: structural (keratin), transport (haemoglobin carries oxygen), defence (antibodies), enzymes (catalyse reactions), hormones.
Definition
A nucleotide (the building block of DNA/RNA) has three parts: a sugar, a phosphate group, and a nitrogenous base.
DNA is a double helix, with base pairing A–T and G–C holding the two strands together. RNA is single-stranded and uses uracil (U) instead of thymine (T).
Information flows from DNA (the master copy) to RNA (a working copy, made by transcription) to protein (built by translation) — this is the central pathway of gene expression.
Quick Recap
- ●Carbohydrates: mono/di/polysaccharides — quick energy; cellulose gives plants structure
- ●Lipids: fatty acids + glycerol; saturated (solid, animal) vs unsaturated (liquid, plant); long-term energy + insulation + membranes
- ●Proteins: chains of amino acids; structure, transport, defence, enzymes, hormones
- ●Nucleotide = sugar + phosphate + base. DNA: double helix, A–T/G–C pairing. RNA: single strand, uses U not T
- ●DNA RNA (transcription) protein (translation)
