Overview of Proteins and Amino Acids

Dec 25, 2024

Lecture on Proteins and Amino Acids

Importance of Proteins

  • Essential for normal cellular function
  • Composed of long chains of amino acids
  • Amino acids are linked by peptide bonds
  • Proteins fold into specific structures

Ingredients and Recipe for Proteins

  1. Ingredients: 20 amino acids
  2. Recipe: How amino acids fold into proteins

Types of Amino Acids

  • 20 amino acids used by humans

Categories of Amino Acids

  1. Dispensable (5): Can be synthesized by the body

    • Alanine
    • Asparagine
    • Aspartic acid
    • Glutamic acid
    • Serine

  2. Conditionally Essential (6): Usually synthesized but not always

    • Arginine
    • Cysteine
    • Glutamine
    • Glycine
    • Proline
    • Tyrosine

  3. Essential (9): Cannot be synthesized, must be obtained from diet

    • Histidine
    • Isoleucine
    • Leucine
    • Lysine
    • Methionine
    • Phenylalanine
    • Threonine
    • Tryptophan
    • Valine

Structure and Properties of Amino Acids

  • Core Structure: Amine group (NH2) and Carboxylic acid group (COOH) bound to an alpha carbon
  • Zwitterions: At physiological pH (7.4), amino acids are charged
  • Side Chains (R group): Determines properties
    • Hydrophobic (non-polar)
    • Hydrophilic (polar)

Hydrophobic Amino Acids

  • Non-polar side chains (alkyl or aromatic)

Hydrophilic Amino Acids

  • Polar side chains
    • Acidic: Lose a hydrogen (e.g., Aspartic acid, Glutamic acid)
    • Basic: Gain a hydrogen (e.g., Lysine, Histidine, Arginine)
    • Neutral: Hydroxyl, sulfhydryl, carboxamide groups

Peptide Bonds and Protein Structure

  • Peptide Bond: Carboxy group of one amino acid binds to the amine group of another
  • Strong and stable due to resonance

Geometric Property: Chirality

  • Amino acids exist as enantiomers (left and right forms)
  • Proteins use left-oriented amino acids

Protein Synthesis

  • Occurs in ribosomes
  • Utilizes messenger RNA (mRNA) as a template

Levels of Protein Structure

  1. Primary Structure: Sequence of amino acids
  2. Secondary Structure: Alpha helix and beta sheets
    • Reliant on hydrogen bonds for stability
  3. Tertiary Structure: Overall 3D shape of the polypeptide
    • Includes disulfide bridges and hydrophobic interactions
  4. Quaternary Structure: Multiple polypeptides form a functional protein
    • Example: Hemoglobin

Recap

  • 20 amino acids: 5 dispensable, 6 conditionally essential, 9 essential
  • Protein structures: Primary, secondary, tertiary, quaternary
  • Bonds: Peptide bonds, hydrogen bonds, disulfide bridges

This lecture provides a comprehensive overview of the structure and synthesis of proteins, which are vital for cellular function. Understanding amino acids and their interactions is crucial for future clinicians.