Department of Biochemistry. The theme of the lesson № 8: Carbohydrates. Biological importance. Digestion of carbohydrates in gastrointestinal tract.. Experiment: Quantitative determination of a blood serum glucose.

Medical Academy named after S. I. Georgievsky of Vernadsky CFU

Department of Biochemistry

Semester 3. The general ways of metabolism. Metabolism of carbohydrates, lipids and its regulation

The theme of the lesson № 8: Carbohydrates. Biological importance. Digestion of carbohydrates in gastrointestinal tract.

Experiment: Quantitative determination of a blood serum glucose.

The purposes of the lesson are:

1) to learn properties of carbohydrates and their biological importance;

2) to understand the process of digestion of carbohydrates in gastrointestinal tract;

3) to know how to perform a biochemical test for quantitative determination of blood serum glucose.

Recommendations for preparation of the lesson:

It's necessary to know:

1) the structure of monosaccharides (glyceraldehyde, dihydroxyacetone, ribose, glucose, fructose, galactose, mannose);

2) the structure of disaccharides (sucrose, lactose, maltose);

3) the structure and biological importance of polysaccharides (glycogen, starch,

cellulose, hyaluronic acid, chondroitin sulfate, heparin);

4) the enzymes and the main stages of digestion of carbohydrates in gastrointestinal tract;

5) the quantity of glucose in blood serum at normal state. What is hyperglycemia, glucosuria and hypoglycemia?

6) how to perform a biochemical test for quantitative determination of blood serum glucose;

7) the diagnostic importance of determination of blood serum glucose.

Review questions:

1. Monosaccharides: structure and biological importance.

2. Disaccharides: structure and biological importance.

3. Homopolysaccharides: structure and biological importance.

4. Heteropolysaccharides: structure and biological importance.

5. Digestion and absorption of carbohydrates in gastrointestinal tract.

References:

1. Robert K. Murray, Daryl K. Granner, Peter A. Mayes, Victor W. Roduell. Harper's Biochemistry (23-th edition), 1996. − P. 131−141.

2. Robert K. Murray, Daryl K. Granner, Peter A. Mayes, Victor W. Roduell. Harper's Biochemistry (24-th edition), 1998. − P. 135−144.

3. Robert K. Murray, Daryl K. Granner, Peter A. Mayes, Victor W. Roduell. Harper's Biochemistry (25-th edition), 2000. − P. 149−158.

4. Michael Lieberman, Allan D. Marks. Basic Medical Biochemistry A clinical approach (4-th edition), 2013. – P. 493 – 512

5.http://103.4.234.46/books/Lippincotts%20Illustrated%20Reviews%20Biochemistry%205th%20edition.pdf

6. Summary.

Lesson 8

Experiment. Quantitative determination of a blood serum glucose.

Glucose becomes blue-green colour if it'll be heated with ortho-toluidin reagent in acetic acid solution. Intensity of this colour proportionate to the glucose concentration and it'll be determined on a photoelectrocolorimeter.

Procedure. Pour 0.9 ml 3% trichloracetic acid solution into two centrifuge test tubes, then add 0.1 ml of blood serum to one of them and 0.1 ml of glucose standard solution to another. Contents of tubes stir up and centrifuge about 3000 rotations per minute for 10 minutes. Then it's necessary to take 0.5 ml upper part of precipitate and put it into standard dry test tubes, add 4.5 ml ortho-toluidin reagent into both test tubes. Put them in boiling water-bath for 8 minutes. It's necessary to watch whether water is sufficiently boiled. Then test tubes must be cool off by running tap water till a room temperature. After all their absorption must be measured on photoelectrocolorimeter (620 nm).

Calculation. Calculation make on formula:

C_st ´ E_exp

C_exp = , where

E_st

C_exp − is concentration of glucose in blood serum;

C_st− is concentration of glucose in standard solution;

E_exp − absorption of sample blood serum;

E_st − absorption of glucose standard solution.

Clinical and diagnostic meanings. Normal content of glucose in the human blood serum is 3.33‑5.55 mmol/l.

A high level of glucose lead to hyperglycemia and glucosuria.

An excess of insulin may cause severe hypoglycemia.