Enzymes Introduction

Which protein catalysts increase the velocity of a chemical reaction without being consumed by decreasing the energy of activation (Ea)?
Enzymes
Isoenzymes
Cofactors
Zymogens

Since the majority of enzymes are proteins, by which specific agents can they be denatured?
Acids, strong bases, and detergents
Distilled water and physiological saline
Organic vitamins and trace minerals
Inorganic activators and competitive inhibitors

What term describes the specific physical site where a substrate interacts with an enzyme?
Active site
Allosteric site
Isoform region
Apoenzyme core

What term describes a cavity or site on an enzyme other than the active site where regulatory molecules can bind?
Allosteric site
Active site
Isoenzyme pocket
Proenzyme cleft

What term is defined as multiple forms of an enzyme with different genetic origins?
Isoenzyme
Isoform
Holoenzyme
Apoenzyme

What term describes the structural variations that result when an enzyme is subject to post-translational modifications?
Isoform
Isoenzyme
Coenzyme
Holoenzyme

What inorganic cofactor, such as magnesium, zinc, or calcium ions, is required for an enzyme reaction to occur?
Activators
Coenzymes
Prosthetic groups
Zymogens

Which specific metallic ion acts as the required inorganic activator for creatine kinase (CK)?
Mg2+
Zn2+
Ca2+
Fe2+

Which specific metallic ion acts as the required inorganic activator for lactate dehydrogenase (LD)?
Zn2+
Mg2+
Ca2+
Cl-

Which inorganic ion pair serves as the required activator configuration for amylase?
Ca2+ and Cl-
Mg2+ and Zn2+
Fe2+ and K+
Na+ and PO43-

What term describes an organic cofactor, such as pyridoxal phosphate or other vitamins, required for enzymatic activity?
Coenzymes
Activators
Apoenzymes
Proenzymes

Which organic vitamin derivative serves as the mandatory coenzyme for AST and ALT?
Pyridoxal Phosphate
Thiamine Pyrophosphate
Flavin Adenine Dinucleotide
Cyanocobalamin

What term describes the complete, active enzyme system consisting of the apoenzyme plus its prosthetic group or coenzyme?
Holoenzyme
Apoenzyme
Proenzyme
Zymogen

What term describes the inactive form of an enzyme that requires biochemical cleavage to become catalytically functional?
Proenzyme or zymogen
Holoenzyme
Isoenzyme
Isoform

Which class of enzymes catalyzes oxidation-reduction reactions between two substrates?
Oxidoreductases
Transferases
Hydrolases
Lyases

Which three enzymes are explicitly classified under the group of oxidoreductases?
Lactate dehydrogenase, glucose-6-phosphate dehydrogenase, and glutamate dehydrogenase
Aspartate aminotransferase, alanine aminotransferase, and creatine kinase
Alkaline phosphatase, acid phosphatase, and amylase
Aldolase, triosephosphate isomerase, and glutathione synthetase

Which class of enzymes catalyzes the transfer of a molecular group other than hydrogen from one substrate to another?
Transferases
Oxidoreductases
Hydrolases
Isomerases

Which structural group of enzymes belongs to the transferases class?
AST, ALT, CK, GGT, glutathione-S-transferase, glycogen phosphorylase, and pyruvate kinase
Lactate dehydrogenase, glucose-6-phosphate dehydrogenase, and glutamate dehydrogenase
Alkaline phosphatase, acid phosphatase, amylase, cholinesterase, and trypsin
Aldolase, triosephosphate isomerase, and glutathione synthetase

Which class of enzymes catalyzes the hydrolysis of various bonds through the addition of water?
Hydrolases
Lyases
Isomerases
Ligases

Which group of chemical catalysts represents the hydrolases class?
ALP, ACP, amylase, cholinesterase, chymotrypsin, elastase-1, 5-nucleotidase, lipase, and trypsin
Aspartate aminotransferase, alanine aminotransferase, and creatine kinase
Lactate dehydrogenase, glucose-6-phosphate dehydrogenase, and glutamate dehydrogenase
Aldolase, triosephosphate isomerase, and glutathione synthetase

Which class of enzymes catalyzes the removal of groups from substrates without hydrolysis, leaving behind double bonds in the product?
Lyases
Hydrolases
Isomerases
Ligases

Which specific enzyme found in skeletal muscle is classified under the lyases group?
Aldolase
Triosephosphate isomerase
Glutathione synthetase
Pyruvate kinase

Which class of enzymes catalyzes the structural interconversion of geometric, optical, or positional isomers?
Isomerases
Lyases
Ligases
Transferases

Which specific carbohydrate metabolic enzyme is classified under the isomerases group?
Triosephosphate isomerase
Aldolase
Glutathione synthetase
Glycogen phosphorylase

Which class of enzymes catalyzes the joining of two substrate molecules coupled with the breaking of the pyrophosphate bond in ATP?
Ligases
Isomerases
Lyases
Hydrolases

Which specific compound synthesizer belongs to the ligases class?
Glutathione synthetase
Triosephosphate isomerase
Skeletal muscle aldolase
Glucose-6-phosphate dehydrogenase

Which enzymatic reaction state occurs when the rate of reaction is almost directly proportional to substrate concentration at low levels?
First-order kinetics
Zero-order kinetics
Michaelis-Menten plateau
Activation velocity saturation

Which enzymatic reaction state occurs at high substrate concentrations where the substrate saturates all available enzymes, making the reaction rate independent of substrate concentration?
Zero-order kinetics
First-order kinetics
Michaelis-Menten linear velocity
Substrate-limited kinetics

When an enzymatic reaction reaches its maximum velocity (Vmax) under zero-order kinetics, what is the expected rate of increase in velocity?
Zero
Doubled
Tripled
Logarithmic

How is the Michaelis-Menten constant (Km) defined on a velocity-versus-substrate curve?
Substrate concentration at which the reaction velocity is half of the maximum level
Maximum substrate concentration that triggers enzyme denaturation
The total enzyme concentration required to reach zero-order kinetics
The rate constant at which the reaction velocity doubles

How is the Km of an enzyme reaction related to the physical affinity of a substrate to its enzyme?
Inversely proportional (lower Km means higher affinity)
Directly proportional (higher Km means higher affinity)
Completely independent of affinity changes
Logarithmically proportional to the active site volume

At what optimal pH range do most human metabolic enzymes react?
pH 7.0 - 8.0
pH 4.0 - 5.0
pH 9.0 - 10.0
pH 1.0 - 2.0

Which enzyme is a classic exception to the routine physiological pH range, requiring an optimal pH of 5 to function?
ACP
ALP
AMS
Lipase

Which enzyme is a classic exception to the routine physiological pH range, requiring an optimal pH of 10 to function?
ALP
ACP
CK
LDH

For each increase of how many degrees Celsius does the rate of an enzymatic reaction typically double?
10°C
5°C
20°C
1°C

Which substances are defined as structural or chemical agents whose presence can affect the reaction velocity by slowing down or preventing enzymatic catalysis?
Inhibitors
Coenzymes
Activators
Holoenzymes

Which type of enzyme inhibitors compete for the substrate at the active site of the enzyme to form an enzyme-inhibitor complex?
Competitive inhibitors
Non-competitive inhibitors
Uncompetitive inhibitors
Allosteric inhibitors

By what mechanism can competitive inhibition be successfully reversed inside a chemical reaction system?
By increasing substrate concentration
By adding an inorganic activator
By decreasing the operational temperature
By lowering the total enzyme concentration

Which type of enzyme inhibitors bind to the enzyme or enzyme-substrate at a site distinct from the active site, causing a change in its shape?
Non-competitive inhibitors
Competitive inhibitors
Uncompetitive inhibitors
Prosthetic inhibitors

Why cannot non-competitive inhibition be overcome by simply increasing the substrate concentration within an assay?
The inhibitor binds to a distinct regulatory site rather than competing for the active site
The inhibitor irreversibly cleaves the peptide bonds of the active site cavity
The inhibitor binds exclusively to the free substrate molecules in solution
The inhibitor accelerates the backwards breakdown of the active holoenzyme

Which type of enzyme inhibitors bind specifically to the enzyme-substrate complex, thereby preventing the formation of a final product?
Uncompetitive inhibitors
Competitive inhibitors
Non-competitive inhibitors
Zymogen inhibitors

What is the unique pharmacological consequence of increasing substrate concentration in a system undergoing uncompetitive inhibition?
Further increases inhibition
Completely reverses inhibition
Stabilizes maximum velocity (Vmax)
Accelerates the rate of product formation

Which method of measuring enzyme activity stops the reaction after a specific duration before a one-time measurement is performed?
Fixed time
Continuous monitoring
Kinetic measurement
Continuous flow tracking

Which method of measuring enzyme activity performs multiple measurements at different intervals to monitor the rate of the reaction dynamically?
Continuous monitoring or kinetic
Fixed time
End-point assay
Single-point calculation

What specific enzyme unit is defined as the amount of enzyme that will catalyze the reaction of 1 µmol of substrate in 1 minute?
1 International Unit (IU)
1 Katal
1 nkat
1 Somogyi unit

What specific enzyme unit is defined as the amount of enzyme that will catalyze the reaction of 1 mole of substrate in 1 second?
1 Katal
1 International Unit (IU)
1 Somogyi unit
1 Bodansky unit

What is the exact mathematical conversion factor established between 1 International Unit (IU) and nanokatals (nkat)?
1 IU = 17 nkat
1 IU = 1.7 nkat
1 IU = 100 nkat
1 IU = 58 nkat