AQA Biology A-Level: Topic 1 Biological Molecules

Monomers and Polymers

• Monomers: Small units that form larger molecules (e.g., monosaccharides, amino acids, nucleotides).
• Polymers: Large molecules made from monomers joined together.
  • Formation via condensation reaction (releases water).
  • Breakdown via hydrolysis (adds water).

Carbohydrates

• Composed of carbon, hydrogen, and oxygen.
• Monosaccharides: Single sugar units (e.g., glucose, galactose, fructose).
  • General formula: (CH₂O)n
• Disaccharides: Formed by condensation of two monosaccharides.
  • Examples:
    • Maltose = glucose + glucose
    • Sucrose = glucose + fructose
    • Lactose = glucose + galactose
• Polysaccharides: Multiple monosaccharides.
  • Glycogen: Energy storage in animals; highly branched.
  • Starch: Energy storage in plants; composed of amylose and amylopectin.
  • Cellulose: Component of plant cell walls; composed of beta glucose.

Biochemical Tests for Carbohydrates

• Benedict's Test: Detects reducing sugars.
• Iodine Test: Detects starch.

Lipids

• Composed of carbon, hydrogen, and oxygen.
• Types: Triglycerides and phospholipids.
• Triglycerides:
  • Made of glycerol and three fatty acids.
  • Saturated (no double bonds) vs. Unsaturated (double bonds).
• Phospholipids: One fatty acid replaced by phosphate group.
  • Form cell membranes, involved in cell recognition.

Biochemical Test for Lipids

• Emulsion Test: Detects lipids.

Proteins

• Amino Acids: Building blocks of proteins; 20 different types.
• Protein Structure:
  • Primary: Sequence of amino acids.
  • Secondary: Alpha helices or beta-pleated sheets.
  • Tertiary: 3D structure stabilized by various bonds.
  • Quaternary: Multiple polypeptides interacting.
• Biuret Test: Detects proteins.

Enzymes

• Function as biological catalysts by lowering activation energy.
• Enzyme activity affected by temperature, pH, enzyme concentration, substrate concentration, and inhibitors.

Nucleic Acids (DNA and RNA)

• DNA: Stores genetic information.
• RNA: Transfers genetic information for protein synthesis.
• Made of nucleotides (sugar, phosphate, base).

DNA Replication

• Semi-conservative process: Ensures genetic continuity.

ATP (Adenosine Triphosphate)

• Energy currency of the cell.
• Hydrolysis releases energy.

Water

• Properties: High specific heat capacity, solvent, cohesive, metabolite.

Inorganic Ions

• Important for various biological processes (e.g., pH regulation, oxygen transport, co-transport).