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Enzymes 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
Se is a cofactor for which enzyme?
Glutathionate peroxidase
26
zn2+ is a cofactor for which enzyme?
Carbonic anhydrase, alcohol dehydrogenase carboxypeptidase a and B
27
What is a holoenzyme?
The enzyme plus it's cofactor. Entire complex
28
What is an apoenzyme?
Enzyme protein without its cofactor. Protein part
29
What is a prosthetic group?
A coenzyme that's very tightly ( covalently bonded ) attached to the protein . A non protein part.
30
Describe simple proteins?
Composed solely of protein, single or multiple subunits .
31
Describe enzyme regulation ?
The enzymes can be activated or inhibited so that the rate of product formation responds to the needs of the cell.
32
Describe allosteric binding sites?
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.
33
What effect does allosteric enzymes have on the enzymes?
Alters the affinity of the enzyme for its substrate or modify the maximum catalytic activity of the enzyme or both.
34
There are two types of effectors in allosteric binding. What are they?
Negative effectors and positive effectors
35
Describe negative effectors?
Effectors that inhibit enzyme activity
36
Positive effectors
Increase enzyme activity
37
Homotropic effectors
When the substate itself serves as an effector.
38
Heterotrophic effectors
Different from the substate .see figure 4.18 in lippincott
39
Three ways in which enzymes can be regulated
Allosteric binding site Regulation of enzymes by covalent modification Induction and repression of enzyme synthesis
40
Allosteric can be divided into two segments.
Homotropic and heterotrophic
41
Regulation of enzymes by covalent modification
Most enzymes can be regulated by the frequent removal or addition of phosphate groups from specifically serine, threonine residues of the enzyme .
42
Phosphorylation and devphosphorylation
Phosphorylation is catalalysed by enzymes protein kinase, which uses ATP as a proton donor.
43
Phosphate groups are cleaves from phosphorylates enzymes by the action of
Phosphoprotein
44
Response of enzyme to phosphorylation
Depending on the specific enzyme, the phosphorylated form may be less or more active than the unphosphorylated enzyme.
45
Induction
Up regulation or increase in gene expression, synthesis of more enzyme molecules.
46
Repression
Down regulation , decrease gene expression, decrease in synthesis of enzyme molecules
47
Sequestration.
Enzyme forms inactive polymers.
48
Susbstrate availability typically effects?
Substrate and there is a change in velocity and the time change is immediate.
49
Product inhibition
Typical effector is the product. Results in Vm and of Km.
50
Allosteric
End product and change in Vm and or Km
51
Covalent modification
Another enzyme, change in Vm and Km
52
Synthesis or degeneration of enzyme
Hormone or metabolite , change in the amount of enzyme , hours to days
53
Alteration of plasma enzyme levels in diseases states.
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
What does an increase in tissue damage indicates?
Reflects damage to the corresponding tissues.
55
What are the enzymes involved in identifying myocardi al infarction?
Creatine kinase, lactate dehydrogenase, (ldh), glutamate oxaloactate transaminase (GOT)
56
Quaternary structure of isoenzymes.
Many isoenzymes contain different subunits in various combinations.
57
Example of the quaternary structure of creative kinase
Occurs are 3 isoenzymes. | Each isoenzyme is a dimer composed of two polypeptides (b and m) associated in one of the three combinations.
58
CK1
BB
59
CK2
MB
60
Ck3
Mm
61
Diagnosis of MI
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
In addition to CK2 hat other enzyme is found elevated after an MI?
lactate dehydrogenase, peaks after 3-6 days after MI
63
What is an inhibitor?
Any substance that can diminish the velocity of an enzyme catalyst reaction.
64
Describe reversible inhibitor
Binds non covalently to the receptor site.
65
Irreversible inhibitors.
Occurs when inhibited enzyme does not regain activity upon dilution of the enzyme inhibitor complex. And form covalent bonds.
66
Competive inhibition
Inhibitors binds reversibility to the same site that the substate binding.
67
Effect on Vmax
The effect of inhibitors is reversed by increased (s).
68
Effect on KM in competitive inhibition
a competitive inhibitor increases the apparent Km for a given substrate.
69
Enzymatic reactions in the cytosol
Glycolysis HMP pathway Fatty acid synthesis
70
Enzymatic pathways occurring in the mitochondria
TCA cycle, fatty acid oxidation , oxidation of pyruvate.
71
How enzymes work have no perspectives
A) energy changes occurring during the reaction | The chemistry of active site
72
Free energy of activation
Is the energy difference between that of the reactants and high energy difference intermediate that occurs during the formation of product.
73
Free energy of activation
This peak of energy represents the transition state in which a high energy intermediate is formed during the conversion of reactant to product.
74
Rate of reaction
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
True or false, the higher the activation rate the faster the reaction.
False
76
Alternate reaction pathway
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
Steps in enzymatic activity
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
What are the two types active sites.
Catalytic site Binding site
79
Catalytic site
Is where the reaction actually takes place
80
Active site
• 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
Two types of enzyme mechanisms
Lock and key | Induced fit model
82
What is key and lock.
1.Lock and key model - 1890 | •assumes only a substrate of the proper shape could fit with the enzyme
83
What is the purpose of induced fit?
* assumes continuous changes in active site structure as a substrate binds * more widely-accepted
84
List factors that affect enzymes?
Environmental factors • temperature, pH Cofactors • metal ions Effectors • species that alter enzyme activity
85
What is the optimum ph of pepsin ?
Environmental factors • temperature, pH Cofactors • metal ions Effectors • species that alter enzyme activity
86
What is the optimum ph of catalase
7
87
What is the optimum temperature of enzymes?
• optimum temperature is usually 25 - 40 ºC (but | not always)
88
What is kinetics?
• Kinetics is the study of the rate of change of reactants to products
89
What is velocity?
Velocity (v) refers to the change in conc. of substrate or product per unit time
90
What is velocity?
• Rate (k) refers to the change in total quantity (of reactant or product) per unit time
91
Initial velocity
• Initial velocity (v0) is the change in reactant or product conc. during the linear phase of a reaction
92
Michaelis-Menten Kinetics 3 basic assumptions
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
Examples of compounds that inhibit compounds?
substrate analogs toxins drugs metal complexes

Cell Biology (13 decks)

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