Basic elements: C,H,O,N,S

N content in protein: The nitrogen content of various proteins is close and constant, with an average of 16%

Calculation formula for protein content: Protein content per gram of sample = Nitrogen content per gram of sample * 6.25

Kjeldahl method

Structural characteristics of amino acids

Classification of amino acids

Peptide bond: formed by the dehydration condensation of the α-carboxyl group of one amino acid and the α-amino group of another amino acid

Peptide: A compound composed of amino acids linked to each other by peptide bonds

Bioactive peptides: Many small molecule peptides with various important biological activities are synthesized in organisms.

Definition: refers to the sequence of amino acids from the N-terminus to the C-terminus in the protein polypeptide chain.

The primary structure of a protein is the basis for its biological activity and specific spatial structure

α-helix

β-sheet

β—turn angle

random curls

Most are spherical

Proteins with tertiary structure are mostly hydrophilic

After the polypeptide bonds are twisted, they form specific regions that exert biological functions on the surface or certain parts of the molecule. Proteins that are biologically active in organisms must have at least a tertiary structure

Definition: The spatial conformation of a protein consisting of two or more polypeptide chains with tertiary structure associated with each other.

Subunit: In the quaternary structure, each polypeptide chain with tertiary structure is called

When pH<pl, the protein carries cations; when pH>pl, the protein carries anions; When PH=pl, the total charge of the protein is 0 and it is a zwitterionic ion.

Isoelectric point: When pH = pl, the pH at this time is called the isoelectric point pl of the protein.

Electrophoresis: The phenomenon in which charged particles move in opposite directions in an electric field.

Not easily permeable through semi-permeable membrane

hydrocolloid

Definition: Under the action of certain physical and chemical factors, the spatial conformation of a protein is destroyed, resulting in changes in its physical and chemical properties and loss of biological activity.

Denaturation does not cause changes in primary structure

Renaturation: Removing denaturing factors can still restore or partially restore its original conformation and function.

Salting out method

organic solvent precipitation

Precipitation of certain acids

heavy metal salt precipitation