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3.1 Biological molecules

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How does the structure of carbohydrates relate to their function?

Monosaccharides are the monomers from which larger carbohydrates are made. Glucose, galactose and fructose are common monosaccharides. A condensation reaction joins two monosaccharides to form a disaccharide and forms a glycosidic bond. Polysaccharides are formed by the condensation of many glucose units. The relationship between the structure of glycogen, starch and cellulose and their functions, plus biochemical tests for reducing sugars, non-reducing sugars and starch.
A focused answer to the AQA A-Level Biology 3.1 specification points on carbohydrates. Covers monosaccharides, condensation and glycosidic bonds, the structure-function relationships of starch, glycogen and cellulose, and the Benedict's and iodine biochemical tests.
11 min answer →

How do enzymes lower activation energy, and what changes their rate of reaction?

Enzymes as catalysts lowering activation energy through formation of enzyme-substrate complexes. The induced-fit model of enzyme action. The effects of temperature, pH, enzyme and substrate concentration, and competitive and non-competitive inhibitors on the rate of enzyme-controlled reactions.
A focused answer to the AQA A-Level Biology 3.1.4 dot point on enzymes. Explains the induced-fit model, how enzymes lower activation energy, the enzyme-substrate complex, and how temperature, pH, concentration, and competitive and non-competitive inhibitors affect reaction rate.
11 min answer →

How does the structure of triglycerides and phospholipids relate to their functions?

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid. A condensation reaction between glycerol and a fatty acid forms an ester bond. The R group of a fatty acid may be saturated or unsaturated. In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group. The different structures of triglycerides and phospholipids relate to their different roles in living organisms. The emulsion test for lipids.
A focused answer to the AQA A-Level Biology 3.1 specification points on lipids. Covers triglyceride and phospholipid structure, ester bonds and condensation, saturated versus unsaturated fatty acids, the structure-function relationship, and the emulsion test.
9 min answer →

How is genetic information stored in DNA and RNA, and how is energy carried by ATP?

The structure of DNA and RNA as polymers of nucleotides joined by phosphodiester bonds. Semi-conservative replication of DNA. The structure of ATP and its hydrolysis to release energy.
A focused answer to the AQA A-Level Biology 3.1.5 and 3.1.6 dot points on nucleic acids. Covers nucleotide structure, the DNA double helix, RNA, phosphodiester bonds, the rules of base pairing, semi-conservative replication, and the structure and hydrolysis of ATP.
12 min answer →

How does the structure of proteins determine their function?

Amino acids are the monomers from which proteins are made. The general structure of an amino acid as RCH(NH2)COOH. A condensation reaction between two amino acids forms a peptide bond. The relationship between primary, secondary, tertiary and quaternary structure, and protein function. The biuret test for proteins.
A focused answer to the AQA A-Level Biology 3.1 specification points on proteins. Covers amino acid structure, peptide bonds and condensation, the primary, secondary, tertiary and quaternary levels of structure, how structure determines function, and the biuret test.
11 min answer →

Why is water essential to life, and what roles do inorganic ions play in organisms?

Water as a polar molecule with hydrogen bonding, and its importance as a metabolite, solvent and in its high heat capacity, latent heat of vaporisation and cohesion. The roles of inorganic ions including hydrogen ions, iron ions, sodium ions and phosphate ions.
A focused answer to the AQA A-Level Biology 3.1.8 and 3.1.9 dot points on water and inorganic ions. Explains why water is a polar molecule, how hydrogen bonding gives water its key properties, and the biological roles of hydrogen, iron, sodium and phosphate ions.
10 min answer →