475

53 heat to a boil. Add 5 drops of a 10% solution of Pb (CH 3 COO) 2 to the resulting alkaline solutionand again boil. What are you watching? Specify the color of the obtained precipitate. What α-amino acids can be discovered by this reaction? Write a reaction scheme. Experiment 4. Precipitation of proteins with tannin . Mix a few drops of the tannin solution with a few drops of the protein solutionin a test tub e.W hat are you observing? How can this phenomenon be explained? LESSON 25. CHEMISTRY OF NUCLEIC ACIDS Required basic level of knowledge. Structure and properties of ribose and deoxyribose. Definition, scheme of formation of glycosides and glycosidic bonds. The scheme for the formation of complex ester bonds in the phosphorus derivatives of ribose and deoxyribose. The mechanism of hydrogen bond formation. Complementarity of nitrogenous bases. Questions for the preparation for the lesson. 1. Nitrogen bases. Definition. The structure of purine and pyrimidine with atomic numbering, the structure and lactim-lactam transformations of purine (guanine) and pyrimidine (uracil, cytosine, thymine) nitrogen bases. 2. Nucleosides. Definition, the scheme for the formation of nucleosides and N‑glycosidic bonds. Nomenclature of purine and pyrimidine nucleosides. Numbering of atoms in a nitrogenous base and in pentose. 3. Nucleotides. Definition, scheme for the formation of 5’-nucleotides and 3’-nucleotides, complex ester bond. Nomenclature of nucleotides. Structure of ATP, biological role. Cyclic nucleotides: 3’, 5’-cAMP, 2’, 3’-cAMP, 3’, 5’- cGMP, 2’, 3’-cGMP. Biological role. 4. Nucleic acids. Definition, variety. Distinctions of DNA from RNA. Types of RNA, distinctive features. Scheme and conditions for the hydrolysis of nucleic acids. 5. Nucleic Acid Structures: • primary structure of nucleic acids – composition and sequence of nucleotides. Structure of the polynucleotide chain. Scheme of formation of 3’, 5’-phosphodiester bond on the example of a dinucleotide. • secondary structure of DNA and t‑RNA. The role of hydrogen bonds in complementary pairs of nitrogenous bases in the formation of the secondary structure of nucleic acids.