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Enzymes Flashcards

1
Q

It may be defined as biocatalysts synthesized by living cells.

A

Enzymes

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2
Q

Enzymes are protein in nature (exception - RNA acting as ribozyme, colloidal and thermolabile in character, and specific in their action.

A

True

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3
Q

Enzymes are specialized proteins that function as biochemical catalysts.

A

Sometimes

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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

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5
Q

What is the Greek meaning of Berzelius’ term of CATALYSIS that was coined in 1836?

A

to dissolve

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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

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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

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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

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9
Q

An enzyme is an organic compound that acts as a catalyst for a biochemical reaction.

A

True

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10
Q

Enzymes are globular proteins.

A

Sometimes

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11
Q

Enzymes are simple proteins, consisting entirely of amino acid chains.

A

Sometimes

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12
Q

Enzymes are conjugated proteins, containing additional chemical components.

A

Sometimes

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13
Q

Enzymes undergo the reactions of proteins, including denaturation.

A

Always

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14
Q

Slight alterations in pH, temperature, or other protein denaturants affect enzyme activity dramatically.

A

True

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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

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16
Q

It is an enzyme composed only of protein (amino acid chains).

A

Simple enzyme

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17
Q

It is an enzyme that has a nonprotein part in addition to a protein part.

A

Conjugated enzyme

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18
Q

Apoenzyme + cofactor =

A

holoenzyme

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19
Q

It is the protein part of a conjugated enzyme.

A

Apoenzyme

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20
Q

It is the nonprotein of a conjugated enzyme.

A

Cofactor

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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

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22
Q

Two broad categories of cofactors exist:

A

Simple metal ions and small organic molecules (coenzymes)

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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

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24
Q

It is a small organic molecule that serves as a cofactor in a conjugated enzyme.

A

Small organic molecules (coenzymes)

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25
Q

Coenzymes are synthesized within the human body using building blocks obtained from other nutrients.

A

True

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26
Q

Enzymes are named by using a system that attempts to provide information about the function (rather than the structure) of the enzyme.

A

Sometimes

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27
Q

Type of reaction catalyzed and substrate identity are

A

focal points for the nomenclature

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28
Q

It is the reactant in an enzyme-catalyzed reaction. It is the substance upon which the enzyme acts.

A

Substrate

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29
Q

Substrate - Fats
Enzyme - Lipase
Product -

A

Fatty acids and glycerol

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30
Q

Substrate - Protein
Enzyme - Protease
Product -

A

Amino acids

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31
Q

Substrate - Starch
Enzyme - Amylase
Product -

A

Maltose

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32
Q

The suffix -ase identifies a substance as an enzyme. Thus urease, sucrase, and lipase are all called

A

Enzyme designations

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33
Q

The trypsin, chymotrypsin, and pepsin, its suffix -in is still found in the names of some of the first enzymes studied. What are these?

A

Digestive enzymes

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34
Q

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.

A

Sometimes

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35
Q

The identity of the substrate is noted in addition to the type of reaction.

A

Sometimes

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36
Q

Enzymes are considered under two broad categories, the intracellular and extracellular enzymes.

A

Sometimes

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37
Q

They are functional within cells where they are synthesized.

A

Intracellular enzymes

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38
Q

These enzymes are active outside the cell and all the digestive enzymes belong to this group.

A

Extracellular enzymes

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39
Q

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.

A

Enzyme Commission

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40
Q

It is an enzyme that catalyzes an oxidation-reduction reaction.

A

Oxidoreductase

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41
Q

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.

A

False

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42
Q

What is the formula of Oxidoreductase

A

AH2 + B –> A + BH2

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43
Q

Lactate dehydrogenase is an oxidoreductase that adds hydrogen atoms from a molecule.

A

False, removes

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44
Q

It is an enzyme that catalyzes the transfer of a functional group from one molecule to another.

A

Transferase

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45
Q

What is the formula of Transferase?

A

A - X + B –> A + B - X

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46
Q

What are the two major subtypes of transferase?

A

Transaminase and Kinases

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47
Q

It catalyzes the transfer of an amino group from one molecule to another.

A

Transaminase

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48
Q

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)

A

Kinase

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49
Q

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.

A

Hydrolase

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50
Q

What is the formula of Hydrolase?

A

A - B + H2O –> AH + BOH

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51
Q

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.

A

True

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52
Q

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.

A

Lyase

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53
Q

Give some examples of lyase

A

Aldolase, fumarase, and histidase

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54
Q

What is the formula of lyase?

A

A - B + X - Y –> AX - BY

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55
Q

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.

A

False, hydratase affects the addition of the components

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56
Q

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.

A

Isomerase

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57
Q

There is only one reactant and one product in reactions where isomerases are operative

A

True

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58
Q

What is the reaction of Isomerase?

A

A –> A’

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59
Q

It is an enzyme that catalyzes the bonding together of two molecules into one with the participation of ATP.

A

Ligase

60
Q

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.

A

True

61
Q

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.

A

True

62
Q

It is the small portion of an enzyme molecule that participates in the interaction with a substrate or substrates during a reaction.

A

Enzyme active site

63
Q

Enzyme active site is relatively small part of an enzyme’s structure that is actually involved in catalysis.

A

True

64
Q

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.

A

Enzyme Active Site

65
Q

The active site is a crevicelike location in the enzyme

A

Sometimes

66
Q

The existence of active site is due to the tertiary structure of protein resulting in 3d native conformation

A

True

67
Q

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).

A

True

68
Q

Active sites are regarded as clefts or crevices or pockets occupying a small region in a big enzyme molecule.

A

True

69
Q

The active site is rigid in structure and shape. It is flexible to promote the specific substrate binding.

A

Never

70
Q

The coenzymes or cofactors on which all enzymes depend are present as a part of the catalytic site.

A

Sometimes, some enzymes

71
Q

What bond does the substrates binds at the active site.

A

Weak noncovalent bond

72
Q

Enzymes are specific in their function due to the existence of active sites.

A

True

73
Q

The commonly found amino acids at the active sites are Ser, Asp, His, Cys, Lys, Arg, Glu, Tyr.

A

True

74
Q

The amino acid Ser is found at the active site.

A

Sometimes

75
Q

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.

A

True

76
Q

It is the intermediate reaction species that is formed when a substrate binds to the active site of an enzyme.

A

Enzyme-Substrate Complex

77
Q

Within the enzyme-substrate complex, the substrate encounters more favorable reaction conditions than if it were free. The result is faster formation of product.

A

True

78
Q

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.

A

Lock-and-Key Model

79
Q

What is the other name of Lock-and-Key Model?

A

Fischer’s Template Theory

80
Q

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.

A

True

81
Q

This is also known as Koshland’s Model. Koshland, in 1958, proposed a more acceptable and realistic model for enzyme substrate complex formation.

A

Induced-Fit Model

82
Q

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.

A

True

83
Q

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.

A

Enzyme Specificity

84
Q

The degree of enzyme specificity is determined by the active site.

A

True

85
Q

Active sites accommodate only one particular compound, whereas others can accommodate a family of closely related compounds.

A

Sometimes, some active sites

86
Q

This specificity means an enzyme will catalyze a particular reaction for only one substrate. This is most restrictive of all specificites.

A

Absolute Specificity

87
Q

Give an enzyme with absolute specificity

A

Urease and catalase

88
Q

This specificity means an enzyme can distinguish between stereoisomers (will act on particular isomer).

A

Stereochemical Specificity

89
Q

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.

A

True

90
Q

This specificity involves structurally similar compounds that have the same functional groups, such as hydroxyl, amino, or phosphate groups.

A

Group specificity

91
Q

Give an example of group specificity which cleaves amino acids, one at a time, from the carboxyl end of the peptide chain.

A

Carboxypeptidase

92
Q

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.

A

Linkage Specificity

93
Q

It is a measure of the rate at which an enzyme converts substrate to products in a biochemical reaction.

A

Enzyme Activity

94
Q

It is a factor affecting enzyme activity in which it is a measure of the kinetic energy (energy of motion) of molecules.

A

Temperature

95
Q

The higher the temperature means molecules are moving faster and colliding more frequently.

A

True

96
Q

As the temperature of an enzymatically catalyzed reaction increases, so does the rate (velocity) of the reaction up to a maximum and then declines.

A

True

97
Q

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.

A

True

98
Q

Change in tertiary structure at the active site impedes catalytic action, and the enzyme activity quickly decreases as the temperature climbs past this point.

A

True

99
Q

It is the temperature at which an enzyme exhibits maximum activity.

A

Optimum Temperature

100
Q

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.

A

pH

101
Q

Small changes in pH (less than one unit) can result in enzyme denaturation and subsequent loss of catalytic activity.

A

True

102
Q

It is the pH at which an enzyme exhibits maximum activity.

A

Optimum pH

103
Q

This is an activity pattern in which the concentration of an enzyme is kept constant and the concentration of substrate is increased.

A

Saturation curve

104
Q

Enzyme activity decreases, up to a certain substrate concentration and thereafter remains constant.

A

False, enzyme activity increases

104
Q

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.

A

True

105
Q

It is the number of substrate molecules transformed per minute by one molecule enzyme under optimum conditions of temperature, pH, and saturation

A

Enzyme’s turnover number

106
Q

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.

A

True, Enzyme Concentration

107
Q

The greater the enzyme concentration, the greater the reaction rate.

A

True

108
Q

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.

A

Enzyme Inhibitor

109
Q

The inhibitor is organic in nature

A

Sometimes, it can be inorganic

110
Q

It is the inhibitor that binds noncovalently with enzyme and the enzyme inhibition can be reversed if the inhibitor is removed.

A

Reversible Inhibition

111
Q

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

A

Competitive Enzyme Inhibitor

112
Q

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.

A

Reversible Competitive Inhibition

113
Q

Why does the formation of an enzyme-competitive inhibitor complex is a reversible process?

A

Because it is maintained by weak interactions (hydrogen bonds, etc.)

114
Q

If inhibitor concentration is greater than substrate concentration, the inhibitor dominates the occupancy process.

A

True

115
Q

Competitive inhibition can be reduced by simply increasing the concentration of the substrate.

A

True

116
Q

Give an example of competitive inhibitors of histidine decarboxylation, the enzymatic reaction that converts histidine to histamine.

A

Antihistamines

117
Q

It is a molecule that decrease enzyme activity by binding to a site on an enzyme other than the active site.

A

Noncompetitive enzyme inhibitor

118
Q

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.

A

Noncompetitive inhibition

119
Q

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.

A

True

120
Q

Give some examples of noncompetitive inhibitors

A

Heavy metal ions Pb2+, Ag+, and Hg2+

121
Q

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.

A

Irreversible Enzyme Inhibitor

122
Q

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.

A

Irreversible Inhibition

123
Q

Give some examples of irreversible inhibition

A

Actions of chemical warfare (nerve gases) and organophosphate insecticides

124
Q

Give some examples of irreversible inhibition

A

Actions of chemical warfare (nerve gases) and organophosphate insecticides

124
Q

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.

A

True

125
Q

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.

A

True

126
Q

What are the three mechanisms existing by which enzymes within a cell can be turned on and turned off?

A
  1. Feedback control associated with allosteric enzymes
  2. Proteolytic enzymes and zymogens
  3. Covalent modification
127
Q

It is an enzyme with two or more protein chains (quaternary structure) and two kinds of binding sites (substrate and regulator).

A

Allosteric Enzymes

128
Q

Enzymes are responsible for regulating cellular processes.

A

Always

129
Q

Allosteric enzymes have quaternary structures; that is, they are composed of two or more protein chains.

A

Always

130
Q

Allosteric enzymes have two kinds of binding sites; those for substrate and those for regulators.

A

Always

131
Q

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.

A

True

132
Q

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.

A

True

133
Q

These are substances that bind at regulatory sites of allosteric enzymes

A

Regulators

134
Q

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.

A

Positive regulator

135
Q

When binded, there is a decrease of enzyme activity; changes to the active site are such that substrate is less readily accepted.

A

Negative regulator

136
Q

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.

A

Feedback Control

137
Q

The product of each step is the substrate for the next enzyme.

A

True

138
Q

Feedback control is the only mechanism by which an allosteric
enzyme can be regulated.

A

Never

139
Q

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.

A

Proteolytic Enzymes

140
Q

Give some examples of proteolytic enzymes

A

Most digestive and blood-clotting enzymes

141
Q

It is the inactive precursor of proteolytic enzyme.

A

Zymogen (proenzyme)

142
Q

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.

A

True

143
Q

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.

A

Covalent Modifications of Enzymes

Enzymes (1 decks)

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