(1) According to the structure of the R group: aliphatic amino acids, aromatic amino acids, heterocyclic amino acids, heterocyclic imino acids

(2) According to the structural polarity of the R group: polar and non-polar amino acids

(3) According to the acidity and alkalinity of amino acids: neutral, acidic and basic amino acids

(4) According to nutritional status: essential amino acids and non-essential amino acids

Physical properties: colorless crystals, existing in the state of zwitterionic ions in crystals or solutions; very high melting point, different optical rotations (except glycine), and different absorption spectra...

Absorption spectrum: Trp, Tyr and Phe can absorb light near 280nm, other amino acids do not absorb visible light

Amphoteric properties: Amino acids have acid-base properties and are a type of amphoteric electrolytes

(1) Ninhydrin reaction

(2) Nitrous acid reaction

(3) Dinitrofluorobenzene reaction (Sanger reaction)

(4) Phenyl isothiocyanate reaction (Edman reaction)

(5) Dansyl-cl reaction

Force: secondary bonds, including hydrogen bonds, hydrophobic forces, ionic bonds, van der Waals forces, coordination bonds, ester bonds, etc.

Amide Plane and Peptide Unit

Definition: The spatial arrangement of the polypeptide chain main chain due to the action of hydrogen bonds (i.e. the way the main chain itself folds and coils)

Type: α-helix, β-sheet, β-turn, γ-turn, random coil

Definition: Refers to the combination of adjacent secondary structural units (α-helix, β-sheet, etc.) and approaching each other to form a spatially identifiable and regular secondary structure assembly.

Type: αα, βxβ, β-Zigzag, β-pleated barrel, etc.

Motif: refers to two or three peptide segments with secondary structures that are close to each other in space to form a special spatial structure.

Structural domain domain: refers to the three-dimensional structure of larger globular protein molecules or subunits that can often form two or more spatially distinct regions. This relatively independent three-dimensional entity is called a structural domain.

It refers to that based on the secondary structure, the polypeptide chain is further folded and coiled into a more complex three-dimensional structure, which is mainly maintained by non-covalent bonds (hydrogen bonds, ionic bonds, hydrophobic bonds, disulfide bonds). It can be understood as: a collection of secondary structure units forms a tertiary structure

Refers to the three-dimensional arrangement of subunits in oligomeric proteins and the interactions between subunits. It can be understood as the way in which protein subunits polymerize into macromolecules (a subunit refers to each polypeptide chain with a three-dimensional structure in an oligomeric protein and is the smallest covalent unit of a protein molecule). Note: Single-chain proteins do not have quaternary structure.