Protein Structure in A-Level Biology

Introduction

• Proteins are essential biological molecules made up of amino acids.
• Amino acids are the monomers that form proteins.
• The lecture aims to connect GCSE knowledge to A-Level concepts about proteins.

Amino Acid Structure

• Central Carbon with four groups:
  • Amino Group (Amine): Nitrogen (N) and two Hydrogens (H).
  • Carboxyl Group: Carbon (C), double bond oxygen (O), and hydroxyl (OH).
  • R Group: Variable group, 20 different possible "R" groups.
  • Hydrogen Atom.

Formation of Proteins

• Condensation Reaction: Joins two amino acids, forms a peptide bond, and releases water.
  • Water formation involves hydroxyl from carboxyl and hydrogen from the amine group.
• Peptide Bond: Formed when water is removed.

Levels of Protein Structure

1. Primary Structure

• The sequence of amino acids in a polypeptide chain.
• Defined by peptide bonds.
• Importance of the sequence: Different sequences result in different proteins.

2. Secondary Structure

• Alpha Helix or Beta Pleated Sheets:
  • Held by hydrogen bonds.
  • Hydrogen bonds between oxygen (of C double bond O) and hydrogen (of amino group).

3. Tertiary Structure

• 3D Folding:
  • Further folding of the secondary structure.
  • Held by ionic, hydrogen, and disulfide bonds.
  • Bonds form between R groups.
  • Disulfide bonds require sulfur-containing R groups.

4. Quaternary Structure

• More than one polypeptide chain forms a unique 3D shape.
• Example: Hemoglobin (four polypeptide chains).

Importance of Protein Structure

• Functionality: The shape determines function (e.g., enzymes, carrier proteins).
• Denaturation:
  • High temperature or pH changes can break bonds, altering shape and function.
  • Disruption of ionic and hydrogen bonds.

Causes of Changes in Protein Structure

• Mutations: Changes in DNA that can affect the amino acid sequence, altering protein structure and function.

Summary

• Proteins are polymers of amino acids.
• Understanding of primary, secondary, tertiary, and quaternary structures is essential.
• Importance of bond locations and types in defining protein shape and function.

• For further study, refer to biochemical tests for proteins or other biological molecules.