Biological Molecules - A Level Biology Overview

Introduction

• Lecture covers all of Topic 1: Biological Molecules for A Level Biology.
• Includes key facts and summaries.
• Full set of detailed notes and active recall workbook available for further study.

1. Monomers and Polymers

• Monomers: Small units forming larger molecules.
• Polymers: Made from monomers bonded together.
  • Examples of monomers: Glucose, amino acids, nucleotides (RNA, DNA)
  • Polymers: Starch, cellulose, glycogen (glucose); proteins (amino acids); DNA/RNA (nucleotides).
• Reactions:
  • Condensation Reaction: Joins molecules, forms chemical bonds, loses water.
  • Hydrolysis Reaction: Breaks chemical bonds, uses water.

2. Carbohydrates

Types

• Monosaccharides: Glucose, fructose, galactose.
• Disaccharides: Sucrose, maltose, lactose.
• Polysaccharides: Starch, cellulose, glycogen.

Key Details

• Alpha vs Beta Glucose: Different structure, same formula (isomers).
• Glycosidic Bond: Formed in disaccharides and polysaccharides via condensation.
• Polysaccharide Functions:
  • Starch (plants): Glucose storage for energy.
  • Cellulose (plants): Structural strength in cell walls.
  • Glycogen (animals): Glucose storage in liver/muscles.

Structural Details

• Starch: Amylose (unbranched, helical) & Amylopectin (branched).
• Cellulose: Long, straight chains form fibrils with hydrogen bonds for strength.
• Glycogen: Highly branched, rapid hydrolysis for energy.

3. Lipids

Types

• Triglycerides: Glycerol + 3 fatty acids.
• Phospholipids: Glycerol + 2 fatty acids + phosphate group.

Properties and Functions

• Triglycerides:
  • Energy storage (high ratio of C–H bonds).
  • Metabolic water source.
  • Low mass for energy storage.
• Phospholipids:
  • Form cell membranes (bilayer).
  • Hydrophilic head & hydrophobic tail.

4. Proteins

Structure

• Amino Acids: Monomers of proteins.
• Levels of Protein Structure:
  • Primary: Sequence of amino acids.
  • Secondary: Alpha helix/beta sheet (hydrogen bonds).
  • Tertiary: 3D shape (ionic, hydrogen, disulfide bonds).
  • Quaternary: Multiple polypeptide chains.

Enzymes

• Proteins with unique 3D structure for catalysis.
• Models:
  • Induced Fit: Active site molds around substrate.
• Factors Affecting Enzyme Activity:
  • Temperature, pH, substrate/enzyme concentration, inhibitors.

5. Nucleic Acids

DNA

• Structure: Double helix, sugar-phosphate backbone.
• Base Pairs: Adenine-Thymine, Cytosine-Guanine.
• Replication: Semi-conservative, involves DNA helicase and polymerase.

RNA

• Differences from DNA: Ribose sugar, single-stranded, shorter.
• Functions: mRNA, tRNA, rRNA.

6. ATP (Adenosine Triphosphate)

• Nucleotide derivative, immediate energy source.
• Formed by condensation, releases energy when hydrolyzed.

7. Water

• Properties:
  • High heat capacity and vaporization.
  • Solvent, metabolite, cohesion.

8. Inorganic Ions

• Essential for physiological functions:
  • Hydrogen ions: pH and enzyme activity.
  • Iron ions: Oxygen transport in hemoglobin.
  • Sodium ions: Co-transport and action potentials.
  • Phosphate ions: Found in nucleic acids and ATP.

Conclusion

• Importance of biological molecules in cellular functions.
• Further resources available for in-depth study.