A-Level Biology: Topic 1 - Biological Molecules

Introduction

• Overview of biological molecules in A-Level Biology.
• Key points presented; further details in linked videos and notes.
• Upcoming resources like an active recall workbook.

Monomers and Polymers

• Monomers: Small units forming larger molecules.
• Polymers: Large molecules made of bonded monomers.
  • Examples: glucose, amino acids, nucleotides (RNA/DNA).
• Reactions:
  • Condensation Reaction: Joins molecules, forms chemical bonds, releases water.
  • Hydrolysis Reaction: Breaks molecules, uses water.

Carbohydrates

• Types:
  • Monosaccharides: Single sugar units (glucose, fructose, galactose).
  • Disaccharides: Two sugar units (sucrose, maltose, lactose).
  • Polysaccharides: Many sugar units (starch, cellulose, glycogen).
• Glucose Forms: Alpha and beta isomers (different structures).
• Glycosidic Bonds: Formed in condensation reactions; broken in hydrolysis.
• Function & Structure:
  • Starch: Energy storage in plants.
  • Cellulose: Structural strength in plant cell walls.
  • Glycogen: Energy storage in animals.

Lipids

• Types:
  • Triglycerides: Glycerol + 3 fatty acids.
  • Phospholipids: Glycerol + 2 fatty acids + phosphate group.
• Formation: Condensation reactions forming ester bonds.
• Properties:
  • Energy storage (high ratio of C-H bonds).
  • Hydrophobic nature, low mass.
  • Phospholipids form bilayers due to hydrophilic heads and hydrophobic tails.

Proteins

• Polymers of Amino Acids: Monomers with central carbon, hydrogen, R group, amino and carboxyl groups.
• Structure Levels:
  • Primary: Sequence of amino acids.
  • Secondary: Folding into alpha-helices or beta-sheets.
  • Tertiary: Further 3D folding due to bonding.
  • Quaternary: Multiple polypeptide chains.

Enzymes

• Function: Catalyze reactions by lowering activation energy.
• Specificity: Due to the unique active site shape.
• Models:
  • Induced Fit: Active site molds around the substrate.
• Factors Affecting Rate: Temperature, pH, substrate/enzyme concentration, inhibitors.

Biochemical Tests

• Starch: Iodine test (orange-brown to blue-black).
• Reducing Sugars: Benedict's test (blue to green/yellow/orange/brick red).
• Non-Reducing Sugars: Benedict's after boiling with acid.
• Proteins: Biuret test (blue to purple).
• Lipids: Ethanol emulsion test (white emulsion).

Nucleic Acids

• DNA:
  • Structure: Double helix of polynucleotides with complementary base pairing.
  • Replication: Semi-conservative process involving enzymes like helicase and polymerase.
• RNA:
  • Differences: Ribose sugar, uracil instead of thymine, single-stranded.
  • Types: mRNA, tRNA, rRNA.

ATP (Adenosine Triphosphate)

• Structure: Ribose, adenine, 3 phosphate groups.
• Function: Immediate energy source.
• Reactions:
  • Synthesis: ADP + Pi via ATP synthase.
  • Hydrolysis: Releases energy, catalyzed by ATP hydrolase.

Water

• Properties:
  • Metabolite, solvent, high heat capacity, large latent heat of vaporization, cohesion.
  • Importance in thermal regulation, chemical reactions, and transport.

Inorganic Ions

• Roles in Biological Processes:
  • Hydrogen ions affect pH and enzyme activity.
  • Iron ions in hemoglobin for oxygen transport.
  • Sodium ions in co-transport and action potentials.
  • Phosphate ions in DNA/RNA structures and energy transfer.

This summary covers the main points from the lecture on biological molecules, aiming to aid in revision and understanding of A-Level Biology Topic 1.