Lecture Notes: Introduction to Proteins

General Structure of Amino Acids

• 20 known amino acids.
• Recognize the general structure in all amino acids.

Condensation Reactions

• Formation of dipeptides and longer amino acid chains.
• Process:
  • Two amino acids join via a condensation reaction.
  • The –OH of the carboxyl group and –H of the amino group form a peptide bond.

Formation of Chains

• Dipeptides: Two amino acids form a dipeptide.
• Oligopeptides: Chains containing up to 20 amino acids.
• Polypeptides: Anything longer than an oligopeptide.
• Proteins: Combination of multiple polypeptides.

Example Proteins

• Insulin: Small protein with two polypeptides (21 and 30 amino acids respectively).
• Titin: Largest known human polypeptide with 34,350 amino acids.

Dietary Requirements for Amino Acids

• Essential Amino Acids: Must be obtained from food.
• Non-Essential Amino Acids: Synthesized from other amino acids.
• 9 essential amino acids come from diet, abundant in animal/dairy products.
• Vegans must find plant-based sources.

Peptide Chain Diversity

• Amino acid sequence in polypeptides is stored in genes.
• Synthesis:
  • Occurs at ribosomes, amino acids linked by peptide bonds.
  • Amino acids added in a specific sequence.
  • Sequence determines the three-dimensional structure.

Polypeptide Diversity

• Calculation:
  • Dipeptide: 20x20 possible sequences.
  • Polypeptide with 400 amino acids: 20^400 sequences.

Functional Proteins

• Haemoglobin: Composed of 4 polypeptides, transports oxygen in red blood cells.
• Immunoglobulin: Antibodies produced by B-cells, bind to antigens on pathogens.
• Rhodopsin:
  • Found in retina, pigment in rod cells.
  • Absorbs light, changes shape to send nerve impulse.
• Collagen:
  • Component of skin, bones, teeth.
  • Fibrous, rope-like with three polypeptides.
  • Provides structural integrity and resistance to tearing.
• Keratin:
  • Fibrous protein with high tensile strength.
  • Found in hair, nails, claws, and hooves.

Key Concepts

• Proteins are diverse due to various sequences of amino acids.
• Structural properties are dependent on the sequence and type of amino acids.
• Essential for various bodily functions, including structural support and immune response.