Enzymes Flashcards
1
Q
It may be defined as biocatalysts synthesized by living cells.
A
Enzymes
2
Q
Enzymes are protein in nature (exception - RNA acting as ribozyme, colloidal and thermolabile in character, and specific in their action.
A
True
3
Q
Enzymes are specialized proteins that function as biochemical catalysts.
A
Sometimes
4
Q
It is defined as a substance that increases the velocity or rate of a chemical reaction without itself undergoing any change in the overall process.
A
Catalyst
5
Q
What is the Greek meaning of Berzelius’ term of CATALYSIS that was coined in 1836?
A
to dissolve
6
Q
In 1878, he used the word enzyme (from Greek word en which means “in,” and zyme which means “yeast”) to indicate the catalysis taking place in the biological systems.
A
Kuhne
7
Q
In 1883, he achieved isolation of the enzyme system from cell-free extract of yeast. He named the active principle as zymase (later found to contain a mixture of enzymes), which could convert sugar to alcohol.
A
Buchner
8
Q
In 1926, he first achieved the isolation and crystallization of the enzymes urease from jack bean and identified it as a protein.
A
James Sumner
9
Q
An enzyme is an organic compound that acts as a catalyst for a biochemical reaction.
A
True
10
Q
Enzymes are globular proteins.
A
Sometimes
11
Q
Enzymes are simple proteins, consisting entirely of amino acid chains.
A
Sometimes
12
Q
Enzymes are conjugated proteins, containing additional chemical components.
A
Sometimes
13
Q
Enzymes undergo the reactions of proteins, including denaturation.
A
Always
14
Q
Slight alterations in pH, temperature, or other protein denaturants affect enzyme activity dramatically.
A
True
15
Q
Enzymes differ from nonbiochemical (laboratory) catalysts not only in size, being much larger, but also in that their activity is regulated by other substances present in the cell in which they are found.
A
Sometimes, usually regulated
16
Q
It is an enzyme composed only of protein (amino acid chains).
A
Simple enzyme
17
Q
It is an enzyme that has a nonprotein part in addition to a protein part.
A
Conjugated enzyme
18
Q
Apoenzyme + cofactor =
A
holoenzyme
19
Q
It is the protein part of a conjugated enzyme.
A
Apoenzyme
20
Q
It is the nonprotein of a conjugated enzyme.
A
Cofactor
21
Q
It is the functional unit of the enzyme. It is the biochemically active conjugated enzyme produced from an apoenzyme and a cofactor.
A
Holoenzyme
22
Q
Two broad categories of cofactors exist:
A
Simple metal ions and small organic molecules (coenzymes)
23
Q
The metal ion cofactors include Zn2+, Mg2+, Fe (Fe2+, Fe3+), and Cu (Cu+, Cu2+). It must be supplied to the human body through dietary intake.
A
Simple metal ions
24
Q
It is a small organic molecule that serves as a cofactor in a conjugated enzyme.
A
Small organic molecules (coenzymes)
25
Coenzymes are synthesized within the human body using building blocks obtained from other nutrients.
True
26
Enzymes are named by using a system that attempts to provide information about the function (rather than the structure) of the enzyme.
Sometimes
27
Type of reaction catalyzed and substrate identity are
focal points for the nomenclature
28
It is the reactant in an enzyme-catalyzed reaction. It is the substance upon which the enzyme acts.
Substrate
29
Substrate - Fats
Enzyme - Lipase
Product -
Fatty acids and glycerol
30
Substrate - Protein
Enzyme - Protease
Product -
Amino acids
31
Substrate - Starch
Enzyme - Amylase
Product -
Maltose
32
The suffix -ase identifies a substance as an enzyme. Thus urease, sucrase, and lipase are all called
Enzyme designations
33
The trypsin, chymotrypsin, and pepsin, its suffix -in is still found in the names of some of the first enzymes studied. What are these?
Digestive enzymes
34
The type of reaction catalyzed by an enzyme is often noted with a prefix. An example of this is an oxidase enzyme catalyzes an oxidation reaction, and a hydrolase enzyme catalyzes a hydrolysis reaction.
Sometimes
35
The identity of the substrate is noted in addition to the type of reaction.
Sometimes
36
Enzymes are considered under two broad categories, the intracellular and extracellular enzymes.
Sometimes
37
They are functional within cells where they are synthesized.
Intracellular enzymes
38
These enzymes are active outside the cell and all the digestive enzymes belong to this group.
Extracellular enzymes
39
What was the International Union of Biochemistry appointed in 1961? This committee made a thorough study of the existing enzymes and devised some basic principles for the classification and nomenclature of enzymes.
Enzyme Commission
40
It is an enzyme that catalyzes an oxidation-reduction reaction.
Oxidoreductase
41
Oxidation and reduction are independent processes but linked processes that must occur together, an oxidoreductase requires a coenzyme that is oxidized or reduced as the substrate is reduced or oxidized.
False
42
What is the formula of Oxidoreductase
AH2 + B --> A + BH2
43
Lactate dehydrogenase is an oxidoreductase that adds hydrogen atoms from a molecule.
False, removes
44
It is an enzyme that catalyzes the transfer of a functional group from one molecule to another.
Transferase
45
What is the formula of Transferase?
A - X + B --> A + B - X
46
What are the two major subtypes of transferase?
Transaminase and Kinases
47
It catalyzes the transfer of an amino group from one molecule to another.
Transaminase
48
It plays a major role in metabolic energy-production reaction, catalyzing the transfer of a phosphate group from ATP to give ADP and phosphorylated product (a product containing an additional phosphate group)
Kinase
49
It is an enzyme that catalyzes a hydrolysis reaction in which adding a water molecule to a bond causes the bond to break. Hydrolysis reactions are central to the process of digestion.
Hydrolase
50
What is the formula of Hydrolase?
A - B + H2O --> AH + BOH
51
Carbohydrases effect the breaking of glycosidic bonds in oligo- and polysaccharides, proteases effect the breaking of peptide linkages in proteins, and lipases effect the breaking of ester linkages in triacylglycerols.
True
52
It is an enzyme that catalyzes the addition of a group to a double bond or the removal of a group to form a double bond in a manner that does not involve hydrolysis or oxidation.
Lyase
53
Give some examples of lyase
Aldolase, fumarase, and histidase
54
What is the formula of lyase?
A - B + X - Y --> AX - BY
55
A dehydratase effects the removal of the removal of the components of water from a double bond and a hydratase effects the removal of the components of water to a double bond.
False, hydratase affects the addition of the components
56
It is an enzyme that catalyzes the isomerization (rearrangement of atoms) of a substrate in a reaction, converting it into a molecule isomeric with itself.
Isomerase
57
There is only one reactant and one product in reactions where isomerases are operative
True
58
What is the reaction of Isomerase?
A --> A'
59
It is an enzyme that catalyzes the bonding together of two molecules into one with the participation of ATP.
Ligase
60
ATP involvement in the ligase is required because such reactions are generally energetically unfavorable and they require the simultaneous input of energy obtained by a hydrolysis reaction in which ATP is converted to ADP.
True
61
Explanations of how enzymes function as catalysts in biochemical systems are based on the concepts of an enzyme active site and enzyme-substrate complex formation.
True
62
It is the small portion of an enzyme molecule that participates in the interaction with a substrate or substrates during a reaction.
Enzyme active site
63
Enzyme active site is relatively small part of an enzyme's structure that is actually involved in catalysis.
True
64
It is a 3D entity formed by groups that come from different parts of the protein chain: these groups are brought together by the folding and bending (secondary and tertiary structure) of the protein.
Enzyme Active Site
65
The active site is a crevicelike location in the enzyme
Sometimes
66
The existence of active site is due to the tertiary structure of protein resulting in 3d native conformation
True
67
The active site is made up of amino acids (known as catalytic residues) which are far from each other in the linear sequence of amino acids (primary structure of protein).
True
68
Active sites are regarded as clefts or crevices or pockets occupying a small region in a big enzyme molecule.
True
69
The active site is rigid in structure and shape. It is flexible to promote the specific substrate binding.
Never
70
The coenzymes or cofactors on which all enzymes depend are present as a part of the catalytic site.
Sometimes, some enzymes
71
What bond does the substrates binds at the active site.
Weak noncovalent bond
72
Enzymes are specific in their function due to the existence of active sites.
True
73
The commonly found amino acids at the active sites are Ser, Asp, His, Cys, Lys, Arg, Glu, Tyr.
True
74
The amino acid Ser is found at the active site.
Sometimes
75
The substrate (S) binds the enzyme (E) at the active site to form enzyme substrate complex (ES). The product (P) is released after the catalysis and the enzyme is available for reuse.
True
76
It is the intermediate reaction species that is formed when a substrate binds to the active site of an enzyme.
Enzyme-Substrate Complex
77
Within the enzyme-substrate complex, the substrate encounters more favorable reaction conditions than if it were free. The result is faster formation of product.
True
78
It is the simplest model. This theory was proposed by a German biochemist, Emil Fischer. This is in fact the very first model proposed to explain an enzyme catalyzed reaction.
Lock-and-Key Model
79
What is the other name of Lock-and-Key Model?
Fischer's Template Theory
80
In the lock-and-key model, the active site in the enzyme has a fixed, rigid geometrical conformation. Only substrates with a complementary geometry can be accommodated at such a site, much as a lock accepts only certain keys.
True
81
This is also known as Koshland's Model. Koshland, in 1958, proposed a more acceptable and realistic model for enzyme substrate complex formation.
Induced-Fit Model
82
Induced-Fit model allows for small changes in the shape or geometry of the active site of an enzyme to accommodate a substrate. It is a result of enzyme's flexibility and it adapts to accept the incoming substrate.
True
83
It is the extent to which an enzyme's activity is restricted to a specific substrate, a specific group of substrates, a specific type of chemical bond, or a specific type of chemical reaction.
Enzyme Specificity
84
The degree of enzyme specificity is determined by the active site.
True
85
Active sites accommodate only one particular compound, whereas others can accommodate a family of closely related compounds.
Sometimes, some active sites
86
This specificity means an enzyme will catalyze a particular reaction for only one substrate. This is most restrictive of all specificites.
Absolute Specificity
87
Give an enzyme with absolute specificity
Urease and catalase
88
This specificity means an enzyme can distinguish between stereoisomers (will act on particular isomer).
Stereochemical Specificity
89
Chirality is inherent in an active site, because amino acids are chiral compounds. L-Amino-acid oxidase will catalyze reactions of L-amino acids but not of D-amino acids.
True
90
This specificity involves structurally similar compounds that have the same functional groups, such as hydroxyl, amino, or phosphate groups.
Group specificity
91
Give an example of group specificity which cleaves amino acids, one at a time, from the carboxyl end of the peptide chain.
Carboxypeptidase
92
This specificity involves a particular type of bond, irrespective of the structural features in the vicinity of the bond. It is the most general of the specificities considered.
Linkage Specificity
93
It is a measure of the rate at which an enzyme converts substrate to products in a biochemical reaction.
Enzyme Activity
94
It is a factor affecting enzyme activity in which it is a measure of the kinetic energy (energy of motion) of molecules.
Temperature
95
The higher the temperature means molecules are moving faster and colliding more frequently.
True
96
As the temperature of an enzymatically catalyzed reaction increases, so does the rate (velocity) of the reaction up to a maximum and then declines.
True
97
When the temperature increases beyond a certain point, the increased energy begins to cause disruptions in the tertiary structure of the enzyme then denaturation is occurring.
True
98
Change in tertiary structure at the active site impedes catalytic action, and the enzyme activity quickly decreases as the temperature climbs past this point.
True
99
It is the temperature at which an enzyme exhibits maximum activity.
Optimum Temperature
100
This is a factor affecting enzyme activity in which hydrogen ions influence the enzyme activity by altering the ionic charges on the amino acids (particularly at the active site), substrate, ES complex etc.
pH
101
Small changes in pH (less than one unit) can result in enzyme denaturation and subsequent loss of catalytic activity.
True
102
It is the pH at which an enzyme exhibits maximum activity.
Optimum pH
103
This is an activity pattern in which the concentration of an enzyme is kept constant and the concentration of substrate is increased.
Saturation curve
104
Enzyme activity decreases, up to a certain substrate concentration and thereafter remains constant.
False, enzyme activity increases
104
As substrate concentration increases, the point is eventually reached where enzyme capabilities are used to their maximum extent. The rate remains constant from this point on.
True
105
It is the number of substrate molecules transformed per minute by one molecule enzyme under optimum conditions of temperature, pH, and saturation
Enzyme's turnover number
106
The concentration of substrate in a reaction is much higher than of the enzyme. If the amount of substrate present is kept constant and the enzyme concentration is increased, the reaction rate increases because more substrate molecules can be accommodated in a given amount of time.
True, Enzyme Concentration
107
The greater the enzyme concentration, the greater the reaction rate.
True
108
It is a substance that slows or stops the normal catalytic function of an enzyme by binding to it. It is substance which binds with the enzyme and brings about a decrease in catalytic activity of that enzyme.
Enzyme Inhibitor
109
The inhibitor is organic in nature
Sometimes, it can be inorganic
110
It is the inhibitor that binds noncovalently with enzyme and the enzyme inhibition can be reversed if the inhibitor is removed.
Reversible Inhibition
111
It is a molecule that sufficiently resembles an enzyme substrate in shape and charge distribution that it can compete with the substrate for occupancy of the enzyme's active site
Competitive Enzyme Inhibitor
112
When a competitive inhibitor binds to an enzyme active site, the inhibitor remains unchanged (no reaction occurs), but its physical presence at the site prevents normal substrate molecule from occupying the site. The result is a decrease in enzyme activity.
Reversible Competitive Inhibition
113
Why does the formation of an enzyme-competitive inhibitor complex is a reversible process?
Because it is maintained by weak interactions (hydrogen bonds, etc.)
114
If inhibitor concentration is greater than substrate concentration, the inhibitor dominates the occupancy process.
True
115
Competitive inhibition can be reduced by simply increasing the concentration of the substrate.
True
116
Give an example of competitive inhibitors of histidine decarboxylation, the enzymatic reaction that converts histidine to histamine.
Antihistamines
117
It is a molecule that decrease enzyme activity by binding to a site on an enzyme other than the active site.
Noncompetitive enzyme inhibitor
118
In this, the substrate can still occupy the active site, but the presence of the inhibitor causes a change in the structure of the enzyme sufficient to prevent the catalytic groups at the active site from properly effecting their catalyzing action.
Noncompetitive inhibition
119
In noncompetitive inhibition, increasing the concentration of substrate does not completely overcome the inhibitory effect. However, lowering the concentration of a noncompetitive inhibitor sufficiently does free up many enzymes, which then return to normal activity.
True
120
Give some examples of noncompetitive inhibitors
Heavy metal ions Pb2+, Ag+, and Hg2+
121
It is a molecule that inactivates enzymes by forming a strong covalent bond to an amino acid side-chain group at the enzyme's active site.
Irreversible Enzyme Inhibitor
122
In general, such inhibitors do not have structures similar to that of the enzyme's normal substrate. The inhibitor active site bond is sufficiently strong that addition of excess substrate does not reverse the inhibition process. Thus enzyme is permanently deactivated.
Irreversible Inhibition
123
Give some examples of irreversible inhibition
Actions of chemical warfare (nerve gases) and organophosphate insecticides
124
Give some examples of irreversible inhibition
Actions of chemical warfare (nerve gases) and organophosphate insecticides
124
A cell that continually produces large amounts of an enzyme for which substrate concentration is always very low is wasting energy. The production of the enzyme needs to be turned off.
True
125
A product of an enzyme-catalyzed reaction that is present in plentiful (more than needed) amounts in a cell, is a waste of energy if the enzyme continues to catalyze the reaction that produces the product. The enzyme needs to be turned off.
True
126
What are the three mechanisms existing by which enzymes within a cell can be turned on and turned off?
1. Feedback control associated with allosteric enzymes
2. Proteolytic enzymes and zymogens
3. Covalent modification
127
It is an enzyme with two or more protein chains (quaternary structure) and two kinds of binding sites (substrate and regulator).
Allosteric Enzymes
128
Enzymes are responsible for regulating cellular processes.
Always
129
Allosteric enzymes have quaternary structures; that is, they are composed of two or more protein chains.
Always
130
Allosteric enzymes have two kinds of binding sites; those for substrate and those for regulators.
Always
131
Active and regulatory binding sites are distinct from each other in both location and shape. Often the regulatory site is on one protein chain and the active site is on another.
True
132
Binding of a molecule at the regulatory site causes changes in the overall 3d structure of the enzyme, including structural changes at the active site.
True
133
These are substances that bind at regulatory sites of allosteric enzymes
Regulators
134
When binded, there is an increase of enzyme activity; the shape of the active site is changed such that it can more readily accept substrate.
Positive regulator
135
When binded, there is a decrease of enzyme activity; changes to the active site are such that substrate is less readily accepted.
Negative regulator
136
It is a process in which activation or inhibition of the first reaction in a reaction sequence is controlled by a product of the reaction sequence.
Feedback Control
137
The product of each step is the substrate for the next enzyme.
True
138
Feedback control is the only mechanism by which an allosteric
enzyme can be regulated.
Never
139
It is an enzyme that catalyzes the breaking of peptide bonds that maintain the primary structure of a protein. They are generated in an inactive form and then later, when they are needed, are converted to their active form.
Proteolytic Enzymes
140
Give some examples of proteolytic enzymes
Most digestive and blood-clotting enzymes
141
It is the inactive precursor of proteolytic enzyme.
Zymogen (proenzyme)
142
Activation of a zymogen requires an enzyme-controlled reaction that removes some part of the zymogen structure. Such modification changes the 3d structure (secondary and tertiary structure) of the zymogen, which affects active site conformation.
True
143
It is process in which enzyme activity is altered by covalently modifying the structure of the enzyme through attachment of a chemical group to or removal of a chemical group from a particular amino acid within the enzyme's structure. This also involves adding or removing a group from an enzyme through the forming or breaking of a covalent bond.
Covalent Modifications of Enzymes
