Structure and Function of Proteins

Overview

• Focus on:
  • Amino acids
  • Di- and polypeptides
  • Levels of protein structure
  • Types of proteins
  • Denaturation of proteins

Key Elements of Proteins

• Contain:
  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Small amount of Sulfur

Roles of Proteins

• Enzymatic Activity:
  • Example: Amylase (digestive enzyme for starch)
  • Example: DNA polymerase (DNA replication)
• Structural Support:
  • Example: Collagen in bones
  • Microtubules within cells
• Transport:
  • Example: Hemoglobin in red blood cells
  • Carrier proteins in plasma membranes
• Defense Against Infection:
  • Example: Antibodies and antimicrobial proteins
• Cell Signaling:
  • Example: Hormones and receptor proteins
• Gene Regulation:
  • Example: Transcription factors

Amino Acids

• Monomers of proteins
• Basic structure:
  • Central carbon (alpha carbon)
  • Hydrogen atom
  • Amine Group: NH2 (gives alkaline properties)
  • Carboxyl Group: COOH (gives acidic properties)
  • R Group: Side group that varies among amino acids
  • 20 different naturally occurring amino acids
    • R groups: hydrophobic (repel water) or hydrophilic (attract water)

Essential vs Non-Essential Amino Acids

• Essential Amino Acids:
  • Cannot be synthesized by the body
  • Must be obtained from diet (9 essential amino acids)
• Non-Essential Amino Acids:
  • Synthesized by the body
  • Can become conditionally essential (e.g., during pregnancy)

Protein Formation

• Amino acids join through peptide linkages via condensation reactions
• Formation of Dipeptides and Polypeptides
  • Dipeptides can be broken apart by hydrolysis

Levels of Protein Structure

1. Primary Structure:
   • Specific sequence of amino acids
2. Secondary Structure:
   • Local folding patterns
   • Common types:
     • Alpha helix
     • Beta pleated sheet
3. Tertiary Structure:
   • 3D arrangement of polypeptide chain
4. Quaternary Structure:
   • Interaction of two or more polypeptide chains

Types of Proteins

• Conjugated Proteins:
  • Contain prosthetic groups (e.g., hemoglobin)
• Non-Conjugated Proteins:
  • Consist solely of amino acids
• Fibrous Proteins:
  • Elongated shapes, provide structural support (e.g., collagen)
• Globular Proteins:
  • Compact, spherical shape, perform metabolic functions (e.g., enzymes like amylase, insulin)

Denaturation of Proteins

• Caused by extreme pH or high temperatures
• Loss of 3D shape impacts function
• Example: Enzyme activity affected by temperature
  • Increased temperature = increased reaction rate until denaturation occurs
  • Proteins have specific pH ranges for stability
  • Deviations from optimal pH can disrupt protein structure

Summary of Key Points

• Proteins contain key elements and have diverse roles in biological processes.
• Amino acids are pivotal, classified as essential and non-essential.
• Peptides are formed through condensation reactions, and protein structure is categorized into primary, secondary, tertiary, and quaternary levels.
• Proteins can be fibrous or globular and can be denatured by environmental changes.