Summary of Protein Structure and Functions

Introduction to Proteins

• Proteins serve various biological functions:
  • Transport nutrients
  • Catalyze chemical reactions
  • Provide structural support
• All proteins are composed of 21 building blocks known as amino acids.

Composition of Amino Acids

• Atoms making up amino acids: Carbon, Oxygen, Nitrogen, Hydrogen (some contain Sulfur).
• Unique amino acid: Selenocysteine (contains Selenium).
• Structure of amino acids:
  • Amino group
  • Carboxyl group
  • Side chain (R group) - varies among amino acids and determines their properties.

Classification of Amino Acids

• Hydrophobic: Carbon-rich side chains; poorly interact with water.
• Hydrophilic: Polar side chains; interact well with water.
• Charged: Interact with oppositely charged particles.

Protein Structure

Primary Structure

• Defined as the linear sequence of amino acids determined by DNA.
• Peptide bonds: Connect amino acids by linking the amino group of one to the carboxyl group of another.
  • Water is released during bond formation.

Secondary Structure

• Two main types:
  • Alpha Helices: Right-handed coils stabilized by hydrogen bonds.
  • Beta Sheets: Formed when hydrogen bonds stabilize adjacent strands.

Tertiary Structure

• The three-dimensional shape of a protein.
• Characteristics:
  • Determined by the nature of the side chains.
  • Proteins often fold into globular shapes with hydrophobic residues hidden.

Quaternary Structure

• Formation of functional molecules from multiple polypeptide chains.
• Example: Hemoglobin consists of four subunits that increase oxygen transport efficiency.

Importance of Protein Structure

• The three-dimensional shape of proteins is critical for their function.
• Examples:
  • Hemoglobin: Binds oxygen effectively due to its structure.
  • Antibodies: Flexible arms bind to pathogens for immune response.
  • Insulin: Regulates blood glucose levels; stable shape during circulation.
  • Alpha Amylase: Enzyme initiating starch digestion in saliva.
  • Calcium Pump: Utilizes ATP for calcium ion transport in muscle cells.
  • Ferritin: Stores iron, features a hollow interior for iron management.
  • Collagen: Provides structural support through a strong triple helix formation; important for skin and tendons.

Visualization of Protein Structure

• Different representations of proteins include:
  • Space-filling diagrams: Shows all atoms present.
  • Ribbon diagrams: Highlights backbone organization and secondary structures.
  • Surface representations: Illustrates areas accessible to water.
• Size example: Hemoglobin is approximately 6.5 nanometers.

Conclusion

• Understanding protein functions and structures is enhanced by resources like the RCSB Protein Data Bank for further exploration of molecular machines.