Enzymes Flashcards
(87 cards)
1
Q
Enzymes Properties
A
- Almost all enzymes are proteins.
- They are heat labile.
- They are water-soluble.
- They can be precipitated
- They contain 16% weight as nitrogen
2
Q
Almost all enzymes are proteins exception
A
ribozymes
3
Q
few RNA molecules with enzymatic activity
A
ribozymes
4
Q
enzymes are classified as
A
specialized proteins
5
Q
They contain 16% weight as nitrogen because enzymes are made up of many
A
amino acids
6
Q
Two general structural classes
A
Simple enzymes
Conjugated enzymes:
7
Q
only of protein (amino acid chains)
A
Simple enzymes
8
Q
nonprotein part + protein part
A
Conjugated enzymes
9
Q
Parts of an enzyme molecule
A
Non-protein part
Protein part
Holoenzyme
10
Q
Non-protein part
A
prosthetic group, cofactor or coenzyme
11
Q
Protein part
A
apoenzyme
12
Q
complete structure of apoenzyme and prosthetic group.
A
Holoenzyme:
13
Q
enzymes that contain tightly bound metal ions are termed
A
metalloenzymes.
14
Q
Prosthetic group examples
A
pyridoxal phosphate,
flavin mononucleotide (FMN),
flavin adenine dinucleotide (FAD),
thiamin pyrophosphate,
biotin,
15
Q
tight, stable incorporation into a protein’s structure
A
Prosthetic group
16
Q
bind in a transient, dissociable manner either to the enzyme or to a substrate such as ATP.
must be present/available in the medium surrounding the enzyme for catalysis to occur.
A
Cofactors
17
Q
Enzymes that require a metal ion cofactor are termed
A
metal-activated enzymes
18
Q
The most common cofactors also are
A
metal ions.
19
Q
serve as substrate shuttles
A
Coenzymes
20
Q
Coenzymes example
A
Dehydrogenases -Nicotinamide adenine dinucleotide
21
Q
Specificity
A
- Absolute Specificity.
- Stereochemical Specificity.
- Group Specificity.
- Linkage Specificity
22
Q
enzyme will catalyze (or speed up) a particular reaction for only one substrate.
A
- Absolute Specificity.
23
Q
enzyme can distinguish between stereoisomers.
A
Stereochemical Specificity.
24
Q
involves structurally similar compounds that have the same functional groups.
A
Group Specificity.
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Group Specificity example
Carboxypeptidase
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Stereochemical Specificity example
L-Amino-acid oxidase
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Absolute Specificity example
Urease
glucose oxidase
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Most general specificity Involves a particular type of bond, irrespective of the structural features in the vicinity of the bond.
Linkage Specificity
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Linkage Specificity example
Phosphatases
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takes the form of a cleft or pocket on the enzyme’s surface or, for some multimeric enzymes, at the interface between subunits.
The active site
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The active site function
1. provides a three-dimensional environment that both shields or protects substrates from solvent
2. where a substrate binds with
3. binds any cofactors and prosthetic groups that may be required for catalysis
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substrate bind with the substrate-binding site
1st Substrate recognition site.
2nd Appropriate angle.
3rd Proximity.
4th Functional group.
5th Transition state complex.
6th Products.
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Models for substrate binding
Lock-and-key model
Induced-fit model
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Lock-and-key model proposed by
Fischer
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active site already exists in proper conformation even in absence of substrate.
Lock-and-key model
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Induced-fit model proposed by
Koshland in 1963
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The substrate during its binding induces conformational changes in the active site to attain the final catalytic shape and form.
Induced-fit model
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Six classifications of enzymes
1. Oxidoreductase.
2. Transferases
3. Hydrolases:
4. Lyases
5. Isomerases
6. Ligases
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oxidoreductase requires a ________ that is ________ as the substrate is ________
coenzyme (a carrier) ; oxidized or reduced ; reduced or oxidized
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Oxidoreductase Examples:
alcohol dehydrogenase,
lactate dehydrogenase,
xanthine oxidase,
glutathione reductase,
glucose-6-phosphate dehydrogenase
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Alcohol + (NAD+) → Aldehyde + NADH + (H+)
Oxidoreductase; Alcohol dehydrogenase
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(IUB)
International Union of Biochemistry
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transfer of a functional group (except hydrogen) from one substrate to another
Transferases:
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Alcohol dehydrogenase; IUB name
Alcohol-NAD-oxidoreductase;
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transfer of an amino group from one molecule to another
transaminases
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transfer of a phosphate group from adenosine triphosphate (ATP) to give adenosine diphosphate (ADP) and a phosphorylated molecule
kinases
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Transferases Examples:
aspartate and alanine transaminase (AST/ALT),
hexokinase,
phosphoglucomutase,
hexose-1-phosphate uridyltransferase,
ornithine carbamoyl transferase,
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Hexose + ATP → Hexose-6-phosphate + ADP
Transferases; Hexokinase
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Hexokinase systematic name is
ATP-Hexose--6-phosphatetransferase
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bring about hydrolysis
Hydrolases
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hydrolyze ester, ether, peptide or glycosidic bonds by adding water and then breaking the bond
Hydrolases:
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breaking of glycosidic bonds in oligo- and polysaccharides
carbohydrases:
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breaking of peptide linkages in proteins,.
proteases:
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effect the breaking of ester linkages in triacylglycerols
lipases
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Hydrolases Examples:
glucose-6-phosphatase,
pepsin,
trypsin,
esterases,
glycoside hydrolases
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Acetyl choline + H2O → Choline + acetate
Hydrolases; or Acetyl choline hydrolase
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All ________ enzymes are hydrolases.
digestive
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removal of small molecule from a large substrate
Lyases
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remove groups from substrates or break bonds by mechanisms other than hydrolysis
Lyases
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effects the removal of the components of water from a double bond
dehydratase:
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effects the addition of the components of water to a double bond.
dehydratase:
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effects the addition of the components of water to a double bond.
hydratase:
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One of the product of dehydratase
Water
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Lyases Examples:
fumarase,
arginosuccinase,
histidine decarboxylase.
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Lyases reverse reaction
Synthase
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Fructose-1,6-bisphosphate → Glyceraldehyde-3-phosphate + dihydroxy acetone phosphate
Lyases; Aldolase
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isomerization of substrate
Isomerases
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produce optical, geometric or positional isomers of substrates. Catalyzes the isomerization of a substrate in a reaction, converting it into a molecule isomeric with itself.
Isomerases
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Isomerases Examples:
UDP-glucose,
epimerase,
retinal isomerase,
racemases,
triosephosphate isomerase.
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Glyceraldehyde-3-phosphate → Di-hydroxy-acetone-phosphate
Isomerases; Triose phosphate isomerase
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joining together two substrates
Ligases
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link two substrates together, usually with the simultaneous hydrolysis of ATP
Ligases
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Ligases examples
alanyl-t. RNA synthetase, glutamine synthetase, DNA ligases
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Acetyl CoA + CO2 + ATP → Malonyl CoA + ADP + Pi
Ligases; Acetyl CoA carboxylase
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Factors affecting enzymatic activity
Temperature
pH
Substrate concentration
Enzyme concentration
Concentration of the end-products
Inhibition
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temperature at which an enzyme exhibits maximum activity
Optimum temperature
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higher than the optimum temperature → more the atoms vibrate →
breaking of hydrogen bonds and
other forces
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The enzymatic activity is maximum at a particular pH which is called its
optimum pH.
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Each human enzyme has a characteristic optimum pH, which usually falls within the physiological pH
range of _______ (EXCEPT digestive enzymes).
7.0–7.5
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the rate equation for one substrate-enzyme catalyzed reaction.
Michaelis-Menten equation
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Non-substrate molecules → decrease in enzymatic activity
Inhibition
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active site or catalytic site of an enzyme is occupied by a substance other than the substrate → activity is inhibited
Competitive inhibition (Reversible)
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the inhibitor can be removed from its site of binding without affecting the activity of the enzyme. Attaches but not to the active site
Reversible-Non-competitive Inhibition
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the inhibitor can be removed only at the loss of enzymatic activity.
Irreversible Non-competitive Inhibition:
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enzyme is used for estimation of “true glucose” in blood and body fluids.
“Glucose oxidase”
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used for estimation of serum uric acid.
“uricase”
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used for estimation of urea in blood and body fluids.
“urease”
