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

Introduction to Proteins

• Proteins are polymers made up of many amino acids.

• Amino acids are the monomers that form proteins.

• A chain of amino acids can also be termed a polypeptide.

• The bonds connecting amino acids are called peptide bonds.

Structure of Amino Acids

• Each amino acid contains:

  • A chiral carbon (central carbon atom).

  • An amine group (-NH2).

  • A carboxyl group (-COOH).

  • An R group (side chain) that varies among amino acids.

• The N-terminal refers to the end with the amine group, and the C-terminal refers to the end with the carboxyl group.

Formation of Peptide Bonds

• Amino acids link together via a condensation reaction, where water is lost.

• This reaction also called a dehydration reaction, results in the formation of a peptide bond (amide bond).

• The resulting molecule from linking two amino acids is called a dipeptide.

• Peptide bonds are covalent bonds, making them strong and difficult to break.

Levels of Protein Structure

1. Primary Structure

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

• The specific sequence influences the protein's shape and function.

2. Secondary Structure

• Refers to localized folding patterns within the protein.

• Two common types:

  • Alpha Helix:

    • Stabilized by hydrogen bonds between the NH group of one amino acid and the carbonyl group of another.

    • Each turn has approximately 3.6 amino acid residues.

  • Beta Pleated Sheet:

    • Also stabilized by hydrogen bonds between carbonyl groups and NH groups, but forms a different structure than the alpha helix.

3. Tertiary Structure

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

• Combines various secondary structures (e.g., alpha helices and beta sheets) into a single subunit.

4. Quaternary Structure

• Formed by the combination of multiple subunits (tertiary structures).

• Example: Hemoglobin, which has four subunits (two alpha and two beta).

Conclusion

• The video provides an overview of protein structure and highlights the significance of amino acid sequence in determining protein shape and function.