Lecture on Proteins and Their Functions

Overview of Protein Functions

• Proteins have diverse roles:
  • Transporting nutrients
  • Catalyzing chemical reactions
  • Building structures in living organisms

Amino Acids: Building Blocks of Proteins

• Proteins are made of 21 amino acids
• Composed of carbon, oxygen, nitrogen, hydrogen
• Some contain sulfur; selenocysteine contains selenium
• Structure:
  • Amino group, carboxyl group, side chain
  • Side chain varies and determines properties:
    • Hydrophobic: Carbon-rich, non-interactive with water
    • Hydrophilic/Polar: Interact well with water
    • Charged: Interact with opposite charges

Protein Structures

Primary Structure

• Linear sequence of amino acids encoded by DNA
• Amino acids linked by peptide bonds, releasing water
• Forms protein backbone

Secondary Structure

• Folding of protein chains into:
  • Alpha helices: Right-handed coil, stabilized by hydrogen bonds
  • Beta sheets: Stabilized by hydrogen bonds between strands

Tertiary Structure

• Three-dimensional shape determined by amino acid characteristics
• Globular proteins: Hydrophobic side chains inside, away from water
• Membrane proteins: Hydrophobic residues outside, interacting with lipids
• Charged amino acids: Enable interaction with complementary molecules

Quaternary Structure

• Multiple polypeptide chains form functional molecules (e.g., hemoglobin)
• Hemoglobin:
  • Four subunits cooperatively bind and release oxygen

Visual Representations of Proteins

• Space-filling diagrams: Show all constituent atoms
• Ribbon diagrams: Highlight organization, alpha helices
• Surface representations: Indicate water-accessible areas

Protein Functionality

• Function determined by 3D shapes
• Hemoglobin: Oxygen transport, 6.5 nm, 280 million molecules in red blood cells
• Antibodies: Bind pathogens, initiate immune response
• Insulin: Regulates blood glucose, stable during transport
• Alpha Amylase: Begins starch digestion in saliva
• Calcium Pump: Uses ATP to move calcium ions post muscle contraction
• Ferritin: Stores iron in non-toxic form, spherical with channels, hollow interior
• Collagen: Triple helix for structural support, forms fibrils and fibers

Further Resources

• Learn more at the RCSB Protein Data Bank