Lecture Notes: Proteins

Overview

• Proteins are polymers like carbohydrates.
• Composed of monomers called amino acids.

Amino Acids Structure

• General Structure:
  • Central carbon with four bonds:
    • Simple hydrogen atom
    • Amino group
    • Carboxyl group
    • R group (variable side chain that differentiates amino acids)
• R Side Chains:
  • Determine differences between the 20 amino acids.
  • Influence protein behavior and location (e.g., non-polar R groups imply hydrophobic proteins, possibly membrane-embedded).

Functions of Proteins

• Proteins perform diverse functions in cellular activities and physiology.
• Focus in this lecture: Structural aspects of proteins.

Amino Acids and Protein Structure

• 20 different types of amino acids.
• Importance of R side chain structure:
  • Non-polar R groups make the protein non-polar despite amino and carboxyl groups having polarity.

Naming Conventions

• Peptides and Oligopeptides:
  • Short proteins (<20 amino acids).
  • Important for cell-to-cell communication and non-lipid hormones.
• Polypeptides and Proteins:
  • Longer chains of amino acids.
  • Most proteins in the body are polypeptides.

Peptide Bonds

• Link amino acids through dehydration reactions.
• Bond between carboxyl group of one amino acid and amino group of the next.
• Loss of charge/polarity in these groups after bond formation.

Protein Structure Levels

1. Primary Structure:
   • Chain of amino acids linked by peptide bonds.
   • Polar covalent bonds generate dipoles leading to hydrogen bonding.
2. Secondary Structure:
   • Formed by hydrogen bonds between amino acids.
   • Patterns: Beta pleated sheets and alpha helices.
3. Tertiary Structure:
   • Dependent on R group interactions.
   • Types of interactions: Disulfide bridges, hydrogen bonding, van der Waals, ionic interactions.
4. Quaternary Structure:
   • Formed by interactions between multiple tertiary structures.
   • Not all proteins have quaternary structure.

Protein Folding and Denaturation

• Protein Folding:
  • Formation of tertiary and quaternary structures.
  • Influences protein activity and functionality.
• Denaturation:
  • Unfolding of proteins, losing secondary, tertiary, quaternary structure without breaking peptide bonds.
  • Caused by pH changes, solute changes, temperature changes (e.g., cooking an egg).

Importance of Protein Structure

• Example: Sickle Cell Anemia
  • Single amino acid change in hemoglobin alters protein and red blood cell shape.
  • Leads to clots and potential severe health issues.
  • Highlights importance of precise protein structure for proper function.

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These notes cover key points on protein structure, amino acids, bond formation, and the biological significance of protein folding and denaturation, using sickle cell anemia as an example.