1. Substrate concentration at which reaction rate is half maximal

2. Optimal pH for activity of enzyme

3. Enzyme concentration, which provides half maximal velocity of reaction

4. Concentration of substrate, at which rate of reaction reach maximal value

5. Ionic strength of medium favoring maximal activity of enzyme

57. When [s] is equal to Km, which of the following conditions exist?

1. Half the enzyme molecules are bound to substrate

2. The velocity of the reaction is equal to Vmax

3. The velocity of the reaction is independent of substrate concentration

4. Enzyme is completely saturated with substrate

5. The velocity of the reaction is independent of enzyme concentration

58. Michaelis-Menten constants of two enzymes are 1,3x10^-5 M/l and 2,3x10^-3 M/l subsequently. Indicate true statement about the affinity of these enzymes to substrate.

1. The second enzyme has higher affinity to substrate

2. Enzymes possess equal affinity to substrate

3. The first enzyme has higher affinity to substrate

4. For decision an information on concentration of enzyme is needed

5. Data are incomplete and it is impossible to draw a conclusion

59. In an enzyme assay the substrate concentration was taken much higher than K_m. In this conditions the rate of the reaction will be as follows:

1. Shows zero-order kinetics

2. Approaches 50 % value of V_max

3. Is proportional to substrate concentration

4. Is independent of enzyme concentration

5. Is independent of temperature

60. The Michaehis-Menten hypothesis:

1. Postulates the formation of an enzyme substrate complex

2. Enables us to calculate the isoelectric point of an enzyme

3. States that the rate of a chemical reaction may be independent of substrate concentration

4. States that the reaction rate is proportional to substrate concentration

61. ‘Lock’ and ‘Key’ model of enzyme action proposed by Fisher implies that:

1. The active site is complementary in shape to that of the substrate

2. The active site is flexible and adjusts to substrate

3. The active site requires removal of PO₄ group

4. The active site is not changed

5. Substrates change conformation prior to active site interaction

62. According to international convention (EC) as a unit of enzymatic activity is accepted 1 catal, which can be defined as:

1. Quantity of enzyme which transform 1 mole of substrate in 1 second

2. Quantity of enzyme which transform 1 umole of substrate in 1 minute

3. Quantity of enzyme which transform 1 umole of substrate in 1 second

4. Activity of 1 mg of pure enzyme

5. Number of substrate molecules transformed in 1 minute

63. The specific activity of an enzyme is:

1. The number of enzyme units per miсrogram of enzyme protein

2. The amount of enzyme that produces 1 mole of product per second under standard conditions

3. The activity of an enzyme in relation to a standard preparation of the enzyme

4. The amount of enzyme causing transformation of one micromole of substrate per minute under standard conditions

5. The activity of an enzyme in the presence of its preferred substrate molmin-1 of protein -1 or U/mg

64. Acetylcholin esterase cleaves acetylcholin hydrolytically. Insecticides, pesticides and nerve gases of fluorophosphates structure irreversibly inhibit acetylcholin esterase. How do they act?

1. Inhibitors bind with serine residue in active center

2. Inhibitors are structural analogs of true substrate

3. Inhibitors bind with histidine residue in allosteric center

4. Inhibitors form complex with acetylcholine

5. Inhibitors induce denaturation of enzyme

65. Trypsin and related to it proteolytic enzymes (chymotrypsin, thrombin et al.) contain in active center a specific amino acid residue, which is covalently modified by fluorophosphate compounds with irreversible lost of enzymatic activity. What is this amino acid residue?

1. Serine

2. Tyrosine

3. Threonine

4. Aspartate

5. Methionine

66. Pancreatic juice has a great number of enzymes. Some of them are secreted in inactive form. What these enzymes are?

1. Trypsinogen, chymotrypsinogen

2. Amylase, sucrase

3. Ribonuclease, pepsin

4. Lipase, phosphatase

5. DNA-ase, aminopeptidase

67. Zymogens of proteolytic enzymes are activated by the next process:

1. Limited proteolysis

2. Phosphorylation of serine residues in protein molecule

3. Carboxylation of glutamic acid

4. Decarboxylacion of aspartic acid side chain

5. Hydroxylation of lysine

68. Note substance, which induce transformation of pepsinogen to pepsin:

1. Hydrochloric acid

2. Enterokinase

3. Adenosine triphosphate

4. Bile acids

5. Trypsin

69. Trypsinogen is produced in exocrine /endocrine (chose the correct position) part of pancreatic gland and excreted to duodenum, where it is activated by the next factor:

1. Enteropeptidase

2. Secretin

3. Gastrin

4. Cholecystopancreozymine

5. Chymotrypsinogen

70. In course of chymotrypsinogen activation the next effect is achieved:

1. Formation of active center

2. Formation of allosteric center

3. Elimination of allosteric inhibitory sites

4. Attachment of specific cofactor (coenzyme) determining enzymatic activity

5. Modification of amino acid residues involved into allosteric center

71. The activation of chymotrypsinogen is achieved by the next process:

1. Limited proteolysis

2. Phosphorylation of serine residues with the use ofATP

3. Acetylation of free amino groups

4. ADP-ribosylation

5. Carboxylation of aspartic acid residues

72. Enzymes requiring NAD as co-substrate can be assayed by measuring change in absorbance at:

1. 340 nm

2. 210 nm

3. 290 nm

4. 365 nm

5. 690 nm

73. Chose from listed below organs one producing and secreting amylase:

1. Salivary gland parotis

2. Liver

3. Kidneys

4. Intestinal mucosa

5. Spleen

74. What diagnostic significance has enhanced activity of amylase in urine?

A. Indicates on damage of exocrine pancreas tissue

B. Indicates on disorder in liver tissue

C. Indicates on some disease of bones

D. Indicates on riquets

E. Indicates on vitamin C deficiency

75. What is the mechanism of inhibition of folic acid synthesis by sulfanylamides?