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Enzymology Flashcards

1
Q

What are the general reactions of amino acids?

A

Reactions due to the carboxyl side:
i) Decarboxylation
ii) Amine group formation

Due to the amino side:
i) Transamination
ii) Oxidative deamination
iii) Formation of carbamino compound

Due to the side chains
i) Transmethylation
ii) Ester formation by OH group
iii) Reaction of the amide group
iv) Reaction of SH group

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2
Q

Which of these proteins serve as a source of nitrogen for nucleic acid synthesis and why?

a) Arginine
b) Leucine
c) Glutamine
d) Proline

A

c) Glutamine

Amide group present in it serves as a source of Nitrogen for nucleic acid synthesis.

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3
Q

One of the most important functions of protein is?

A

Catalysis

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4
Q

Enzymes can increase the rate of reaction by a factor of ?

A

Up to 10^20

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5
Q

All catalysts are enzymes?

A

False.

Ribozyme is an RNA catalyst.

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6
Q

Non enzyme catalysts increase the rate of reaction by a factor of ?

A

10^2 or 10^4

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7
Q

The first enzyme to be recognized was?

urease

maltose

diastase

aminotransferase

A

diastase or amylase

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8
Q

Who discovered the first enzyme and what year?

A

French scientists Anselme Payen & Jean Persoz in 1833

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9
Q

First enzyme discovered in its pure state is? And what year?

A

Urease, crystallized from Jack beans in 1926 by James Sumner.

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10
Q

What are the residues in the active site of an enzyme called?

A

Catalytic group

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11
Q

What is the active site of enzymes?

A

This is the region that binds with the substrate and contributes residues that participate directly in the making and breaking of bonds

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12
Q

Residues that are close to eachother in the linear amino acid sequence interact more strongly than residues that are far apart

T/F

A

F

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13
Q

The 3D entity made up groups from different part of the amino acid sequence is the _____ of the enzyme?

A

Active site

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14
Q

All enzymes have active sites that are devoid of water

T/F

A

F.
Hydrolases use water as their reactant

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15
Q

How many amino acids are present in lysozyme?

A

129

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16
Q

What are the important groups in the active site of lysozyme?

A

Residue: 35, 52, 62, 63 & 101

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17
Q

What it is the importance of non polar characteristics of binding site crevices?

A

To enhance binding of substrates

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18
Q

Importance of residues in the active site of enzymes?

A

For recognition of substrates

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19
Q

Lock and key model off enzyme action was proposed by? When?

A

Fischer in 1894

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20
Q

Who proposed the lock and key model? When?

A

Fischer
1894

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21
Q

The active site has a shape that fits that if the substrate when binding is going on
T/F

A

F

Active site has the shape that complements that of the substrate only after substrate is bound.

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22
Q

What is the lock and key model postulation?

A

It proposes that the active site of the enzyme is the perfect fit for a specific substrate and that after the substrate is bound to the enzyme no other changes occurs.

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23
Q

Which of the active site theory predicts that the the residues in the active site enhance recognition of the substrate by the enzyme?

A

Induced fit hypothesis

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24
Q

Induced fit hypothesis

A

It assumes that the active site is flexible and continues to change shape until the substrate is completely bound.

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25
Cofactor?
Nonprotein molecules required by some enzymes for enzymatic activities. They participate directly in substrate binding or in catalysis
26
Groups under cofactor
Coenzyme Prosthetic group Metal ion activator.
27
What is a coenzyme
A coenzyme is a non protein organic molecule that is loosely attached to the protein part
28
Functions of coenzymes?
- To serve as recyclable shuttles that carry many substrates from one point within the cell to another. - They facilitate the recognition and binding of small chemical groups e.g folate, acetate, etc., to by their target enzymes. - They stabilise species that are too reactive to stay for a significant period in water or organic molecules that permeate the cell interior.
29
Prosthetic group?
Nonprotein organic molecules tightly and stably incorporated into the protein's structure by covalent or noncovalent bonds.
30
Examples of prosthetic group cofactors
Thiamine pyrophosphate, FAD, flavin monocleuotide, pyridoxal phosphate, Biotin Vit B 1,2,6,7
31
Enzymes that require metal ion activators for activity are called?
Metal-activated enzymes
32
What class of enzyme is reffered to as synthases?
Lyases
33
Reaction mediated by Coenzyme A?
Acyl transfer (vit B5)
34
Reaction mediated by NAD+ NADP?
Oxidation-reduction (Vit B3, Niacin)
35
When was the IUB nomenclature adopted?
1972
36
Full meaning of IUBMB
International Union of Biochemistry and Molecular Biology
37
What group of enzymes is referred to as synthetases?
Ligases
38
_____ is the only macromolecule with no monomeric unit?
Lipids
39
What are lipids?
Heterogeneous compounds that are not readily soluble in water or polar solvents but are readily soluble in organic solvents such as chloroform, hydrocarbons, etc.
40
Types of enzyme specificity
Group Linkage Absolute Stereochemical specificity
41
Describe absolute specificity
Enzyme catalyzes only one reaction
42
Describe group specificity
Enzyme catalyzes only the reactions of molecules with specific functional groups
43
Describe linkage specificity
Enzyme acts on specific type of chemical bond regardless of the rest of the molecular structure
44
Examples of linkage specificity
Trypsin cleaves the peptide bond on the carboxyl side of Arginine and lysine residues only. Chymotrypsin cleaves the peptide bond where the carboxyl side is a large hydrophobic amino acid (Trp, Phe, Tyr)
45
Stereochemical specificity
Enzyme acts on a specific optical or steric isomer. E.g beta-glycosidase which reacts only with beta-glycosidic bonds which are present in cellulose.
46
Human enzymes show stability at what temperature?
45-55⁰C
47
Optimal pH of: Trypsin Pepsin Chymotrypsin
10 2 8
48
General properties of enzymes
1) Enzymes possess enormous catalytic power 2) They are highly specific both in the reaction catalyzed and their choice of reactants 3) They do not alter reaction equilibria 4) They are stable over a limited range of temperature 5) They are stable over a limited range of pH 6) They are influenced by the concentration of substrates
49
Cytochrome P450 falls under what class of enzymes?
Oxidoreductase under subclass oxygenases (monooxygenases)
50
How do peroxidases work?
Peroxidases utilize H2O2 rather than O2 as the oxidant é.g catalase
51
Transferases
These are enzymes that catalyze the transfer of one chemical group from one molecule to another, thus they have 2 substrates and 2 products e.g aminotransferase, hexokinase, glucosyl & phosphoryl transferases.
52
What is enzyme activity?
Amount of enzymes required to turn 1microM of substrate to product per minute under specified assay conditions
53
Turnover number of an enzyme
Unit of activity of enzyme per mole of enzyme
54
Vmax
Velocity obtained under conditions of substrate saturation of the enzyme and specified conditions of temperature, pH & ionic strength
55
How do enzyme inhibitors work?
They decrease the activity of enzymes by binding to the active site or other sites on the enzyme.
56
The binding of inhibitor enzymes isn't irreversible T/F
False. The binding of inhibitor enzymes is both reversible and irreversible.
57
What bonds are present in inhibitor enzymes
Covalent and Non covalent bonds Irreversible inhibitors react with the enzymes and modify it permanently through covalent bond formation. Reversible inhibitors bind non-convalently forming different kinds of inhibition depending on if the inhibitor binds with the free enzyme, enzyme-substrate (ES) complex or both.
58
Subclasses of hydrolases
Peptidases Esterases Phosphatases
59
Subclasses of lyases
Decarboxylases Dehydratases
60
Subclasses of transferases
Kinases, aminotransferases, glucosyl and phosphoryl transferases and phosphomutases
61
According to MM eq When km > [s]
V = Vmax [S] / Km i.e at low [S], rate of rxn is directly proportional to [S]
62
According to MM eq When Km = [S]
V = ½Vmax therefore, at ½Vmax, Km = [S]
63
According to MM eq When Km < [S]
V = Vmax At high [S] velocity obtained is maximal.
64
How does penicillin act as an inhibitor?
It inhibits the enzyme glycopeptide transpeptidase which is responsible for the completion of cross links between 2 adjacent peptidoglycan chains in bacteria cell wall.
65
What drug is used to treat alcoholism and how?
Disulfiram It irreversibly modifies aldehyde dehydrogenase the enzyme that converts acetaldehyde to acetic acid.
66
How do NSAIDs work?
Non-steriodal antiinflammatory drugs like aspirin inhibit the enzyme cyclooxygenase by irreversibly blocking the channel for arachidonate in the enzyme.
67
How do sulfa drugs work?
Sulfa drugs inhibit folic acid synthesis in microorganisms (Dihydropteroate synthase)
68
Competitive inhibition? (Thorough description)
In this type of inhibition, inhibitors bind with the free enzyme thereby competing with the normal substrate for binding at the active site. It acts reversibly with the enzyme to form EI (enzyme-inhibitor) complex which is analogous to the ES complex. Competitive inhibitors at often structurally similar to the real substrate.
69
Uncompetitive inhibition (thorough description)?
In this inhibition, the inhibitor binds with the ES complex to give an inactive ESI complex that can not undergo further reaction. It is common in 2 substrate reactions. The uncompetitive inhibitor doesn't resemble the substrate
70
M. M equation
V = Vmax [S] / Km + [S]
71
Idoacetamide acts how?
By irreversibly inhibiting the catalytic activity of some enzymes by modifying essential cysteine residues
72
What enzyme catalyses the first step in the pyrimidine biosynthesis pathway?
ATcase (Aspartate Transcarbomylase)
73
What is the shape of the curve for allosteric enzyme?
Sigmoidal (S-curve)
74
How is ATcase inhibited?
ATcase is feedback-inhibited by the end product of the metabolic pathway (Cystidine Triphosphate (CTP)) which acts as an allosteric inhibitor.

OAU BCH (7 decks)

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