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mixture until yellow color appears. The tube is cooled under a stream of cold

water, and add dropwise a solution of ammonia until orange appears. Write

the reaction equation (see the textbook). What amino acids will give a similar

reaction?

LESSON 24.

CHEMISTRY OF PEPTIDES AND PROTEINS

Required basic level of knowledge.

Structure and properties of amino acids. Mechanisms for the formation

of covalent, ionic, hydrogen, van der Waals bonds. Amphotericity. Acidic

properties, basic properties.

Questions for the preparation for the lesson.

1. Peptides. Definition. Scheme of the formation of a peptide bond by the

example of a tripeptide.

2. Proteins. Definition. Classification of proteins.

3. Structures of protein molecules. Definition, stabilizing bonds, scheme.

4. Sequencing. Determination of the primary structure of peptides and

proteins by the Edman method.

5. Properties of proteins.

• amphotericity: the definition, the cause of amphoteric proteins.

• isoelectric point and isoelectric state: the definition, examples, the reason

for the difference in the isoelectric points of different proteins. The charge of

proteins in different solution media, the recharging of the protein molecule.

• Reversible precipitation. Salting out. Definition, salts that cause reversible

precipitation. The medical and biological significance of salting out proteins.

• Irreversible precipitation. Denaturation. Definition, factors causing

denaturation. Protein structures damaged by denaturation. Medico-biological

significance of denaturation.

• forms of protein molecules, examples of globular and fibrillar proteins.

6. Qualitative reactions to proteins: ninhydrin, biuret, xanthoprotein (for the

presence of aromatic amino acids), the Fole reaction (for the presence of sulfur-

containing amino acids).

Test-control on the topic “Chemistry of amino acids, peptides and proteins”

Homework exercises.

1. Write formulas of six tripeptides containing alanine, threonine and

tryptophan.