ECA
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Study Notes

Unit 3: Proteins

Amino Acids & Peptide Bonds

Proteins are polymers of amino acids. Every amino acid has a central carbon bonded to an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen, and a variable side chain (R group). The side chain gives each amino acid its unique properties; some are polar, some non-polar, some contain sulfur or a hydroxyl.

  • Amino acids are joined by peptide bonds (formed by dehydration synthesis)
  • A chain of amino acids is a polypeptide
  • Proteins contain C, H, O, N, and sometimes S
  • Some proteins have both hydrophobic and hydrophilic regions

Four Levels of Protein Structure

Protein shape determines function, and shape is built in four levels.

  • Primary: the sequence of amino acids. Bonds are peptide bonds. DNA directly codes for this level
  • Secondary: local folding into an alpha helix or beta pleated sheet
  • Tertiary: the overall 3D folding of one polypeptide. Held by hydrophobic interactions, disulfide bridges, and intermolecular forces (R-group interactions)
  • Quaternary: several polypeptide chains linked together (e.g., hemoglobin has four chains)

Enzymes

Enzymes are proteins that speed up chemical reactions. Like all proteins, they contain C, H, O, and N, and many contain S. Their function depends on their 3D shape.

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