Protein Structure and Function

General Overview of Amino Acids

• Amino acids have a central structure and a variable group known as the R group.
• There are 20 different R groups, leading to 20 different amino acids.
• Importance of R Groups:
  • They determine amino acid properties, e.g., hydrophilic or hydrophobic.
  • Influence amino acid interactions and protein function.

Levels of Protein Structure

Primary Structure

• Sequence of amino acids connected by peptide bonds.
• Peptide bonds form by condensation between carboxyl and amine groups (removal of water).
• The sequence dictates the protein's final conformation and function.

Secondary Structure

• Initial folding patterns due to hydrogen bonds among the backbone atoms.
• Alpha Helix: Coiled structure formed by hydrogen bonds.
• Beta Pleated Sheet: Sheet-like structure formed by hydrogen bonds.

Tertiary Structure

• Complex 3D shape formed by R group interactions and further folding.
• Types of Bonds and Interactions:
  • Hydrogen bonds between R groups (e.g., asparagine, serine).
  • Ionic bonds (e.g., lysine and aspartic acid).
  • Hydrophilic and hydrophobic interactions.
  • Disulfide bridges (e.g., between two cysteine amino acids).
• Impact of Polarity:
  • Globular Proteins: Spherical shapes due to polar/nonpolar interactions.
  • Integral Proteins: Embedded in cell membranes, interact with phospholipid tails.

Quaternary Structure

• Combination of two or more protein chains.
• Conjugated vs. Non-Conjugated:
  • Non-Conjugated: Only protein chains (e.g., insulin).
  • Conjugated: Includes non-protein structures (e.g., hemoglobin with heme groups).

Examples of Protein Structures & Functions

• Form Fits Function: The shape of proteins determines their role.
  • Insulin:
    • Non-conjugated, globular shape.
    • Stable and mobile, binds to insulin receptors.
  • Collagen:
    • Non-conjugated, fibrous structure.
    • Provides tensile strength, used for structural support.

Key Points to Remember

• The sequence of amino acids (primary structure) is crucial for the protein's final shape and function.
• Different levels of protein structure (secondary, tertiary, quaternary) create complex shapes and interactions.
• Protein shapes are adapted to their functions, demonstrating the principle "form fits function."