Biosynthesis of purine bases A, T

The formation of the purine ring immediately occurs on the ribose-5-phosphate. As a result of sequential reactions inosine-5'-phosphate (inosinic acid) is formed.

Glycine, aspartate, glutamine, carbon dioxideand derivatives of tetrahydrofolic acid are donors of carbon and nitrogen atoms for the purine ring.

Inosine-5'-phosphate is oxidized to xantozin-5'-phosphate. As a result of inosine-5'-phosphate amination adenosine-5'-phosphate is formed, and the xantosine-5'-phosphate amination gives guanosine-5'-phosphate.

Inosine-5'-phosphate Xantosine-5'-phosphate

+ Asp - fumarate + Gln - Glu

+ GTP - GDP, -P_i + ATP - AMP, -PP_i

Adenosine-5'-phosphate Guanosine-5'-phosphate

Purine nucleosides, as well as pyrimidine nucleosides, are converted to nucleoside triphosphates in the reaction with ATP. Purine nucleotide synthesis is controlled by a feedback mechanism.

The synthesis of deoxyribonucleotides

Deoxyribonucleotides are formed from ribonucleotides by a reduction of ribose residue which is catalyzed by the enzyme ribonucleotide reductase.

Tioredoxin reductase catalyzes the hydrogenation of oxidized thioredoxin.

Deoxyribonucleoside diphosphates are converted to deoxyribonucleoside triphosphates by the kinases action.

dGDF + ATP ®dGTP + ADP

Test questions

1. What are characteristic features of protein metabolism?

2. Define the concept of "nitrogen balance".

3. What are the main reasons for the breadown of tissue proteins?

4. Describe the process of protein digestion in the gastrointestinal tract.

5. What is the mechanism of activation of the gastrointestinal tract proteases?

6. What conversions amino acids undergo under the influence of intestinal microflora?

7. What proteins are the most adequate for a human?

8. Enumerate types of amino acid deamination.

9. What is the significance of transamination reactions?

10. Give examples of reactions involving carboxyl group of amino acids.

11. In what form ammonia and amine nitrogen come from peripheral tissues to liver for urea synthesis?

12. Why is the content of urea cycle enzymes increases either at abundant protein diet, or at starvation?

13. What substances are formed during the degradation of hemoglobin?

14. What enzymes are involved in the degradation of nucleic acids?

15. What are end products of degradation of purine and pyrimidine bases?

16. What compounds are donor of atoms of pyrimidine and purine bases rings?

Date: 2016-04-22; view: 915