Protein Structure - Primary, Secondary, Tertiary, & Quarternary - Biology

Introduction to Proteins

• Proteins are polymers made up of many amino acids.

  • Each amino acid is a monomer.

  • A chain of amino acids is referred to as a polypeptide.

  • The bonds connecting amino acids are known as peptide bonds.

Structure of Amino Acids

• Amino acids contain:

  • A chiral carbon atom.

  • A hydrogen atom attached to the chiral carbon.

  • An amine group (-NH2).

  • A carboxyl group (-COOH).

  • An R group that varies for different amino acids.

• Terminology:

  • The left side (with nitrogen) is called the N-terminal.

  • The right side (with carboxyl group) is called the C-terminal.

• Amino acids can react through a:

  • Condensation reaction: where water is lost as two amino acids bond.

  • This process forms a peptide bond.

  • The result is a dipeptide if two amino acids are combined.

  • Peptide bonds are covalent and difficult to break.

Levels of Protein Structure

• Proteins have four distinct levels of structure:

  • Primary Structure:

    • Defined by the sequence of amino acids in the protein.

    • Even a single amino acid change can affect protein shape and function.

  • Secondary Structure:

    • Refers to localized shapes of proteins.

    • Two main types:

      • Alpha Helix:

        • Stabilized by hydrogen bonds.

        • Contains about 3.6 amino acid residues per turn.

      • Beta Pleated Sheet:

        • Also stabilized by hydrogen bonds between carbonyl and NH groups of amino acids.

  • Tertiary Structure:

    • Represents the overall three-dimensional folding of a protein.

    • Includes combinations of alpha helices and beta sheets.

  • Quaternary Structure:

    • Formed when multiple polypeptide subunits combine.

    • Example: Hemoglobin has four subunits—two alpha and two beta subunits.

Conclusion

• Understanding the basic structure of proteins and their levels of organization is crucial for comprehending their biological functions.