77. Discribe the method, shown at the picture below:

Answer: Differential centrifugation is used to separate certain organelles from whole cells for further analysis of specific parts of cells. In the process, a tissue sample is first homogenised to break the cell membranes and mix up the cell contents. The homogenate is then subjected to repeated centrifugations, each time removing the pellet and increasing the centrifugal force. Finally, purification may be done through equilibrium sedimentation, and the desired layer is extracted for further analysis.

Separation is based on size and density, with larger and denser particles pelleting at lower centrifugal forces. As an example, unbroken whole cells will pellet at low speeds and short intervals such as 1,000g for 5 minutes. Smaller cell fragments and organelles remain in the supernatant and require more force and greater times to pellet. In general, one can enrich for the following cell components, in the separating order in actual application:

• Whole cells and nuclei;

• Mitochondria, lysosomes and peroxisomes;

• Microsomes (vesicles of disrupted endoplasmic reticulum); and

• Ribosomes and cytosol.

78. Discribe the method, shown at the picture below:

Answer: polyacrylamide gel electrophoresis (PAGE) - separation of molecules on the by applying an electric field. Successful separation can be accomplished by electrophoresis in various gels (semisolid suspensions in water) rather than in a liquid solution. Gels are cast between a pair of glass plates by polymerizing a solution of acrylamide monomers into polyacrylamide chains and simultaneously cross-linking the chains into a semisolid matrix. Gel pore size can be varied by adjusting the concentrations of polyacrylamide and the cross-linking reagent. Highly cross-linked polyacrylamide gel = pores are quite small. Such a gel could resolve small proteins and peptides, but large proteins would not be able to move through it smaller proteins migrate faster than larger proteins through the gel. Gel's pore size and strength of the electric field influence the rate of movement.

79. Discribe stages of DNA sample electrophoresis:

Answer:

Section іі Enzymes, structure and classification. Regulation of metabolism

1. Chose a correct statement about common feature of enzymes and inorganic catalysts:

1. Acceleration of thermodynamically permitted reactions

2. Dependence of activity on pH of medium

3. High selectivity to type of catalyzed reaction

4. Specific dependence on substrate concentration

5. Dependence on the presence of cofactors

2. Enzymes differ from inorganic catalysts by the next property:

1. Thermolability

2. Acceleration of reaction equilibrium achievement

3. Sensitivity to catalyst poisons

4. Thermostability

5. No selectivity to type of catalyzed reaction

3. Enzymes accelerate chemical reaction due the to next effect:

1. Enzymes lower the energetic barrier of chemical reaction

2. Enzymes shift the position of equilibrium of chemical reaction.

3. Enzymes make possible endergonic reaction without energy supply

4. Enzymes increase the free energy of activation

4. Enzymes accelerate the rate of reactions by:

1. Decreasing the energy of activation

2. Increasing the equilibrium constant of reactions

3. Increasing the energy of activation

4. Decreasing the free energy change of the reaction

5. Decreasing the equilibrium constant of reactions

5. The energy required to start an enzymatic reaction is called:

1. Activation energy

2. Chemical energy

3. Metabolic energy

4. Potential energy

5. Free energy

6. Chose from listed below enzymes ONE which exhibits selectivity to stereochemical epimers of substrate:

1. Urease

2. Trypsin

3. Aminopeptidase

4. Alcohol dehydrogenase

5. Lactate dehydrogenase

7. An enzyme is a:

1. Protein

2. Carbohydrate

3. Lipid

4. Nucleic acid

5. Amino acid

8. Which of the following is not true regarding enzymes?

1. They are destroyed after the completion of the reaction they catalyse

2. They catalyze only a particular type of reaction

3. They remain active even after separation from the source

4. They are irreversibly destroyed at high temperature

5. Their activity depends on the pH of the solution

9. Active center of enzyme can be defined as follows:

А. Site on the enzyme molecule, which binds substrate and provides its further transformation.

В. Part of the molecule, which easily splits from apoenzyme.

С. Nonprotein component of enzyme molecule

D. Site for binding of allosteric effector.