A nitrogen-containing macromolecule with a specific spatial structure composed of amino acids connected by peptide bonds.

C, H, O, N, S, nitrogen are characteristic elements, accounting for 16% Grams of nitrogen per g sample × 6.25 × 100 = protein content in 100g sample

L-alpha-amino acids (except glycine)

Non-polar aliphatic amino acids, polar neutral amino acids, aromatic amino acids Acidic amino acids (Asparagus, Gu), basic amino acids (Laijing group)

1. Nature of sexual dissociation 2. UV absorption properties (conjugated double bond tryptophan, tyrosine 280nm) 3. Color-forming reaction (coheating with ninhydrin in a weakly acidic environment)

Peptide bond: -CO-CN- Peptide: A compound formed by condensation of amino acids through peptide bonds Peptide bond plane: The C-N bond in the peptide bond cannot rotate freely due to resonance. Keep the peptide bond in a rigid plane Bioactive peptide: glutathione (reduced GSH)

Primary structure: N→C sequence of amino acids, maintaining chemical bonds: peptide bonds

Secondary structure: (the relative spatial position of the bead curtain skeleton atoms does not involve the conformation of the side chains of the amino acid residues) Maintaining chemical bonds: hydrogen bonds √Main forms: α-helix, β-turn, random coil, Ω ring Tertiary structure: (relative spatial position of all amino acid residues) Maintaining chemical bonds: secondary bonds Structural motif (super secondary structure): zinc finger structure √ Structural domain: independent functional area at the three-level structural level Quaternary structure: (spatial arrangement of each subunit); maintaining chemical bonds: ionic bonds, hydrogen bonds, etc. Subunit: Peptide chain with independent tertiary structure