AQA A Level Biology 3.1 Biological Molecules Exam Questions

About AQA A Level Biology topic 3.1

Topic 3.1 is the foundation of AQA A Level Biology. It covers the structure and function of the molecules every other topic builds on: carbohydrates, lipids, proteins and enzymes, DNA and RNA, ATP, water and inorganic ions. You will use these ideas again in digestion, protein synthesis, respiration and gene technology, so it pays to get them secure early.

What you need to know for 3.1 Biological Molecules

• 3.1.1 Monomers join by condensation reactions, which form a chemical bond and release water. Polymers are broken down by hydrolysis, which uses water.
• 3.1.2 Alpha and beta glucose, glycosidic bonds, the disaccharides maltose, sucrose and lactose, and how the structures of starch, glycogen and cellulose suit their functions. Benedict's test for reducing and non-reducing sugars, and the iodine test for starch.
• 3.1.3 Triglycerides (glycerol and three fatty acids joined by ester bonds), saturated and unsaturated fatty acids, phospholipids, and the emulsion test.
• 3.1.4 Amino acids, peptide bonds and the four levels of protein structure, plus the biuret test. Enzymes lower activation energy; the induced-fit model; the effects of temperature, pH, enzyme and substrate concentration; competitive and non-competitive inhibitors.
• 3.1.5 DNA and RNA nucleotides, phosphodiester bonds, complementary base pairing, and semi-conservative replication using DNA helicase and DNA polymerase.
• 3.1.6 The structure of ATP, its hydrolysis by ATP hydrolase to release energy, and its resynthesis by ATP synthase.
• 3.1.7 Why water is important: a metabolite, a solvent, high specific heat capacity, large latent heat of vaporisation and strong cohesion, all due to hydrogen bonding.
• 3.1.8 The roles of hydrogen ions, iron ions in haemoglobin, sodium ions in co-transport, and phosphate ions in DNA, RNA and ATP.

Common mistakes in 3.1 Biological Molecules

• Saying hydrolysis breaks a bond without mentioning that water is used.
• Mixing up alpha glucose (starch and glycogen) with beta glucose (cellulose).
• Writing that enzymes are killed. They are denatured: the tertiary structure and active site change shape, so fewer enzyme-substrate complexes form.
• Saying a non-competitive inhibitor binds to the active site. It binds to another site and changes the shape of the active site.
• Saying DNA polymerase forms hydrogen bonds. It joins adjacent nucleotides by condensation reactions, forming phosphodiester bonds.

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