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Enzymes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are enzymes?

A

Protein catalyst that increase the rate of reactions without themselves being changed in the overall process

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2
Q

What are the six classes of enzymes?

A

Oxidoreductases, transferase, hydrolases, isomerase, lyases, ligases

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3
Q

Oxidoreductases enzymes are responsible for?

A

Oxidation reduction reactions such as lactate to pyruvate

Lactate dehydrogenase

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4
Q

Transferase

A

Catalyses the reaction of C, N, P containing groups

Serine to glycine

Serine hydroxy methyl transferase

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5
Q

Hydrolases

A

Catalyses the cleavage of bonds by addition water.

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6
Q

Example of hydrolases reaction

A

The catalytic reaction of urease to urea and water

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7
Q

Lyases

A

Catalyses cleavage of C-C, C-S, and certain C-N bonds

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8
Q

Example of lyases

A

Pyruvate to acetaldehyde in the presence of pyruvate decarboxylase.

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9
Q

Isomerase

A

Catalyses racemization of optical or geometric isomers

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10
Q

Examples of isomerase

A

Methylmalony CoA to succinyl CoA in the presence of methylmalo ny Co A mutase

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11
Q

Ligases

A

Catalyses formation of bonds between carbon and O,S,N coupled to hydrolysis of high energy phosphates

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12
Q

Example of ligases

A

Pyruvate and co2 in the presence of pyruvate carboxylate to oxaloactate.

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13
Q

What is an active site ?

A

It a cleft or special pocket in the enzyme that the substrate binds to.

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14
Q

What does the active site contain?

A

Amino acids side chains that create a 3D surface complementary to the substrate.

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15
Q

Describe catalytic efficiency? What is turnover?

A

The number of substrate molecules converted to product per enzyme molecule per second . Enzyme catalytic reactions are fast er than uncatalysed reactions.

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16
Q

Describe enzyme specificity?

A

Enzymes are specific for a single molecule or a structurally related group of substrates . Usually only 1 enzyme per reaction type.

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17
Q

What is a cofactor?

A

Inorganic component need for enzyme function

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18
Q

Cu2+ is a cofactor for which enzyme?

A

Cytochrome oxidase

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19
Q

Fe2+ or fe3+ is a cofactor for which enzyme?

A

Cytochrome oxidase , peroxidase and catalase

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20
Q

K+ is a cofactor for which enzyme?

A

Pyruvate kinase

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21
Q

Mg2+ is a cofactor for which enzyme?

A

Hexokinase, glucose 6 phosphatase, pyruvate kinase

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22
Q

Mn2+ is a cofactor for which enzyme?

A

Arginase, ribonucleotide reductase

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23
Q

Mo is a cofactor for which enzyme?

A

Dinitrogenase

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24
Q

Ni 2+

A

Urease

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25
Q

Se is a cofactor for which enzyme?

A

Glutathionate peroxidase

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26
Q

zn2+ is a cofactor for which enzyme?

A

Carbonic anhydrase, alcohol dehydrogenase carboxypeptidase a and B

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27
Q

What is a holoenzyme?

A

The enzyme plus it’s cofactor. Entire complex

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28
Q

What is an apoenzyme?

A

Enzyme protein without its cofactor. Protein part

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29
Q

What is a prosthetic group?

A

A coenzyme that’s very tightly ( covalently bonded ) attached to the protein . A non protein part.

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30
Q

Describe simple proteins?

A

Composed solely of protein, single or multiple subunits .

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31
Q

Describe enzyme regulation ?

A

The enzymes can be activated or inhibited so that the rate of product formation responds to the needs of the cell.

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32
Q

Describe allosteric binding sites?

A

Binding to a receptor site on the enzyme and not the active site. Allosteric effectors are bounded non covalently at a site other than the active site.

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33
Q

What effect does allosteric enzymes have on the enzymes?

A

Alters the affinity of the enzyme for its substrate or modify the maximum catalytic activity of the enzyme or both.

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34
Q

There are two types of effectors in allosteric binding. What are they?

A

Negative effectors and positive effectors

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35
Q

Describe negative effectors?

A

Effectors that inhibit enzyme activity

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36
Q

Positive effectors

A

Increase enzyme activity

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37
Q

Homotropic effectors

A

When the substate itself serves as an effector.

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38
Q

Heterotrophic effectors

A

Different from the substate .see figure 4.18 in lippincott

39
Q

Three ways in which enzymes can be regulated

A

Allosteric binding site
Regulation of enzymes by covalent modification
Induction and repression of enzyme synthesis

40
Q

Allosteric can be divided into two segments.

A

Homotropic and heterotrophic

41
Q

Regulation of enzymes by covalent modification

A

Most enzymes can be regulated by the frequent removal or addition of phosphate groups from specifically serine, threonine residues of the enzyme .

42
Q

Phosphorylation and devphosphorylation

A

Phosphorylation is catalalysed by enzymes protein kinase, which uses ATP as a proton donor.

43
Q

Phosphate groups are cleaves from phosphorylates enzymes by the action of

A

Phosphoprotein

44
Q

Response of enzyme to phosphorylation

A

Depending on the specific enzyme, the phosphorylated form may be less or more active than the unphosphorylated enzyme.

45
Q

Induction

A

Up regulation or increase in gene expression, synthesis of more enzyme molecules.

46
Q

Repression

A

Down regulation , decrease gene expression, decrease in synthesis of enzyme molecules

47
Q

Sequestration.

A

Enzyme forms inactive polymers.

48
Q

Susbstrate availability typically effects?

A

Substrate and there is a change in velocity and the time change is immediate.

49
Q

Product inhibition

A

Typical effector is the product. Results in Vm and of Km.

50
Q

Allosteric

A

End product and change in Vm and or Km

51
Q

Covalent modification

A

Another enzyme, change in Vm and Km

52
Q

Synthesis or degeneration of enzyme

A

Hormone or metabolite , change in the amount of enzyme , hours to days

53
Q

Alteration of plasma enzyme levels in diseases states.

A

The levels of specific enzyme activity in the plasma frequently correlates with the extent of tissue damage. The degree of elevation is often useful in the evaluating the prognosis for the patient .

54
Q

What does an increase in tissue damage indicates?

A

Reflects damage to the corresponding tissues.

55
Q

What are the enzymes involved in identifying myocardi al infarction?

A

Creatine kinase, lactate dehydrogenase, (ldh), glutamate oxaloactate transaminase (GOT)

56
Q

Quaternary structure of isoenzymes.

A

Many isoenzymes contain different subunits in various combinations.

57
Q

Example of the quaternary structure of creative kinase

A

Occurs are 3 isoenzymes.

Each isoenzyme is a dimer composed of two polypeptides (b and m) associated in one of the three combinations.

58
Q

CK1

A

BB

59
Q

CK2

A

MB

60
Q

Ck3

A

Mm

61
Q

Diagnosis of MI

A

The appearance of CK2 marks an MI, after an MI, this isoenzyme occurs 4-8hours after onset of chest chain and reaches a peak in activity at approximately 24 hours.

62
Q

In addition to CK2 hat other enzyme is found elevated after an MI?

A

lactate dehydrogenase, peaks after 3-6 days after MI

63
Q

What is an inhibitor?

A

Any substance that can diminish the velocity of an enzyme catalyst reaction.

64
Q

Describe reversible inhibitor

A

Binds non covalently to the receptor site.

65
Q

Irreversible inhibitors.

A

Occurs when inhibited enzyme does not regain activity upon dilution of the enzyme inhibitor complex. And form covalent bonds.

66
Q

Competive inhibition

A

Inhibitors binds reversibility to the same site that the substate binding.

67
Q

Effect on Vmax

A

The effect of inhibitors is reversed by increased (s).

68
Q

Effect on KM in competitive inhibition

A

a competitive inhibitor increases the apparent Km for a given substrate.

69
Q

Enzymatic reactions in the cytosol

A

Glycolysis
HMP pathway
Fatty acid synthesis

70
Q

Enzymatic pathways occurring in the mitochondria

A

TCA cycle, fatty acid oxidation , oxidation of pyruvate.

71
Q

How enzymes work have no perspectives

A

A) energy changes occurring during the reaction

The chemistry of active site

72
Q

Free energy of activation

A

Is the energy difference between that of the reactants and high energy difference intermediate that occurs during the formation of product.

73
Q

Free energy of activation

A

This peak of energy represents the transition state in which a high energy intermediate is formed during the conversion of reactant to product.

74
Q

Rate of reaction

A

For molecules to react they must have sufficient energy . In the absence of an enzyme , only a small proportion of the population of molecules may possess enough energy to achieve the transition state between reactants and products.

75
Q

True or false, the higher the activation rate the faster the reaction.

A

False

76
Q

Alternate reaction pathway

A

An enzyme provides an alternative pathway that lowers the rate of reactions. The enzyme does not change the free energies of the reactants or products and therefore does not change equilibrium of the reaction .

77
Q

Steps in enzymatic activity

A
  1. Enzyme and substrate combine to form a complex.
  2. Complex goes through a transition state – not quite substrate or product
  3. A complex of the enzyme and the product is produced.
  4. Finally, the enzyme and product separate.
78
Q

What are the two types active sites.

A

Catalytic site

        Binding site
79
Q

Catalytic site

A

Is where the reaction actually takes place

80
Q

Active site

A

• area that holds the substrate in proper place

• enzymes use weak, non-covalent interactions to
hold the substrate in place based on R groups of
amino acids

• shape is complementary to the substrate and
determines the specificity of the enzyme

• sites are pockets or clefts on the enzyme surface

81
Q

Two types of enzyme mechanisms

A

Lock and key

Induced fit model

82
Q

What is key and lock.

A

1.Lock and key model - 1890

•assumes only a substrate of the proper shape could fit with the enzyme

83
Q

What is the purpose of induced fit?

A
  • assumes continuous changes in active site structure as a substrate binds
  • more widely-accepted
84
Q

List factors that affect enzymes?

A

Environmental factors
• temperature, pH

Cofactors
• metal ions

Effectors
• species that alter enzyme activity

85
Q

What is the optimum ph of pepsin ?

A

Environmental factors
• temperature, pH

Cofactors
• metal ions

Effectors
• species that alter enzyme activity

86
Q

What is the optimum ph of catalase

A

7

87
Q

What is the optimum temperature of enzymes?

A

• optimum temperature is usually 25 - 40 ºC (but

not always)

88
Q

What is kinetics?

A

• Kinetics is the study of the rate of change of reactants to products

89
Q

What is velocity?

A

Velocity (v) refers to the change in conc. of substrate or product per unit time

90
Q

What is velocity?

A

• Rate (k) refers to the change in total quantity (of reactant or product) per unit time

91
Q

Initial velocity

A

• Initial velocity (v0) is the change in reactant or product conc. during the linear phase of a reaction

92
Q

Michaelis-Menten Kinetics 3 basic assumptions

A

1: ES complex is in a steady state, i.e.
remains constant during the initial phase of a
reaction

2: when enzyme is saturated all enzyme is in the
form of ES complex

3: if all enzyme in ES then rate of product
formation is maximal:

93
Q

Examples of compounds that inhibit compounds?

A

substrate analogs
toxins
drugs
metal complexes

Cell Biology (13 decks)

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