ENZYMOLOGY Flashcards
What is a coenzyme?
Organic molecules
A coenzyme or metal ion that is very tightly or even covalently bound to the enzyme is called?
Prosthetic group
complete catalytically active enzyme together with its bound coenzyme is called
Holoenzyme
The protein part of holoenzyme is called?
Apoenzyme
Which suffix is added to the name of the substrate or to a word or to a phrase describing the activity of enzyme, to name an enzyme?
-Ase
Which enzyme transfers phosphate groups?
Hexokinase
The site where enzyme catalyzed reaction takes place is called?
Active Site
The molecule that is bound and acted upon by the enzyme is called?
Substrate
Who proposed the existence of proteolytic enzymes as proteins?
Northrop
What will happen to the enzyme-catalyzed reaction if temperature is increased?
Rate of reaction increases
What will happen to reaction if more enzymes are added?
Rate of reaction increase
How metal ions participate in catalysis?
By causing reduction and oxidation reactions between enzyme and substrate
By causing ionic interactions between enzyme and substrate
What is Vmax
Maximum rate of reaction
What is Km in Michaelis-Menten Equation?
Michaelis-Menten constant
Which enzymes are said to follow Michaelis-Menten kinetics?
a. Enzymes which show parabolic dependence of rate of reaction and substrate
b. Enzymes which show circular dependence of rate of reaction and substrate
c. Enzymes which show hyperbolic dependence of rate of reaction and substrate
d. None of the above
Enzymes which show hyperbolic dependence of rate of reaction and substrate
Double-reciprocal plot is also called?
Line plot
Which scientist proposed lock and key model in 1894?
Emil Fisher
What is induced fit?
a. when enzyme change shape due to absence of substrate
b. when enzyme do not change shape due to absence of substrate
c. when enzyme change shape due to presence of substrate
d. when enzyme do not change shape due to presence of substrate
when enzyme change shape due to presence of substrate
Who postulated induced fit in year1958?
Daniel Koshland
A purely competitive enzyme inhibitor has which of the following kinetic effects?
increases Km without affecting Vmax
Enzymes as classic catalysts accomplish which of the following energy effects?
lower the energy of activation
Synthesis of an enzyme promoted by the substrate on which it acts, is characterized by the term
Induction
Which statement about the active site is incorrect?
A. It is composed of linearly arranged amino acid chain.
B. It is relatively small compared to the total bulk of the enzyme.
C. It does not generally form covalent interaction with substrates.
D. It is three-dimensional in quality.
E. none of these
It is composed of linearly arranged amino acid chain.
Which statement about most enzymes is incorrect?
A. They increase the rapidity of the reactions they catalyze.
B. They are specific for the substrate as well as the reaction catalyzed.
C. They are large polypeptides with high molecular weight.
D. They are most active near neutral pH.
E. They are not affected by changes in temperature.
They are not affected by changes in temperature.
Michaelis & Menten did not make which of the following assumptions concerning analyses of enzyme action?
A. The initial reaction of velocity should be measured since most of the substrate has not been converted to product.
B. Maximal velocity is reached when the concentration of ES complex is equal to the total number of enzymes.
C. The formation of the ES complex does not appreciably decrease the [S].
D. For analysis of enzyme kinetics, the total [E] studied at each [S] is fixed.
E. Plotting the reciprocal of [V] and [S] will produce an ideal linear curve.
E. Plotting the reciprocal of [V] and [S] will produce an ideal linear curve.
Which enzymes are used to diagnose liver diseases?
AST AND ALT
Which enzyme cannot be used to detect acute myocardial infarction (AMI)?
A. ACP
B. CK
C. AST
D. LDH
ACP
Which of the following enzyme pairs cannot be used in the diagnosis of liver disorders?
A. ALP & LAP
B. GGT & 5’-NT
C. LDH & AST
D. ACP & ALS
ACP AND ALS
which pair has clinical utility for AMI detection?
A. ALP & LAP
B. GGT & 5’-NT
C. LDH & AST
D. ACP & ALS
LDH AND AST
Which fraction is expected to be elevated in alcoholic cirrhosis of the liver?
GGT
Aspartate aminotransferase (AST) and alanine aminotransferase the following disease?
Viral hepatitis
Which two physiologic conditions can greatly elevate blood alkaline phosphatase?
growth, third trimester of pregnancy
A physician suspects his patient has pancreatitis. Which test(s) would be most indicative of this disease?
Amylase
Which of the following chemical determinations may be of help in establishing the presence of seminal fluid?
Acid phosphatase
The most sensitive enzymatic indicator for liver damage from ethanol intake is
Gamma-glutamyl transferase (GGT
. A serum sample drawn in the emergency room from a 42-year-old man yielded the following laboratory results:
CK 385 Units (Normal = 15-160)
AST 73 Units (Normal = 0-48)
CK-MB 106 Units (Normal = 2-12)
Myocardial Infarction
In competitive inhibition of an enzyme reaction the
A. Inhibitor binds to the enzyme at the same site as the substrate
B. Inhibitor often has a chemical structure different from that of the substrate
C. Activity of the reaction can be decreased by increasing the concentration of the substrate
D. Activity of the reaction can be increased by decreasing the temperature
Inhibitor binds to the enzyme at the same site as the substrate
The presence increased CK-MB activity on a CK electrophoresis pattern is most likely found in a patient suffering from
Myocardial Infarction
Which of the following enzymes catalyzes the conversion of starch to glucose and maltose?
Amylase
Which of the following enzymes are used in the diagnosis of acute pancreatitis?
Amylase and trypsin
The specific activity of an enzyme would be reported in which of the following units of measure:
Units of activity per milligram of protein
The Km value & Vmax in competitive inhibition are
A. increased and decreased respectively.
B. decreased and increased respectively.
C. increased and unchanged respectively.
D. unchanged and decreased respectively.
E. both decreased
increased and unchanged respectively.
The Km value & Vmax in noncompetitive inhibition are
unchanged and decreased respectively.
The Km value & Vmax in uncompetitive inhibition are
both decreased.
The functions of many enzymes, membrane transporters, and other proteins can be quickly activated or deactivated by phosphorylation of specific amino acid residues catalyzes by enzymes called:
Kinases
The chemotherapy drug fluorouracil undergoes a series of chemical changes in vivo that results in a covalent complex such that it is bound to both thymidylate synthase and methylene-tetrahydrofolate. The inhibition of deoxythymidilate formation and subsequent blockage of cell division is due to which of the following:
Irreversible inhibition
The Lineweaver-Burk plot is used to graphically determine Km and Vmax for an enzyme that obeys classic Michaelis-Menten Kinetics. When V is the reaction velocity at substrate concentration S, the Y axis experimental data in the Lineweaver- Burk plot are expressed as:
1/V
In the Lineweaver-Burk plot, the Vmax of an enzyme is:
a. Reciprocal of the absolute value of the intercept of the curve with the x axis
b. Reciprocal of the absolute value of the intercept of the curve with the y axis
c. Absolute value of the intercept of the curve with the x axis
d. Slope of the curve
e. Point of inflection of the curve
Reciprocal of the absolute value of the intercept of the curve with the y axis
noncompetitive inhibitor of an enzyme does which of the following:
Decreases Vmax
Digestive enzymes such a pepsin, trypsin, and chymotrypsin are synthesized as inactive precursors. The preproteins of the active enzymes are termed :
Zymogens
Competitive inhibitors typically resemble the:
Substrate(s)
enzymes used to detect hepatobiliary diseases:
a. GGT
b.ALT
c.ALP
d.ALS
e.LAP
GGT
ALP
LAP
choose enzymes used to detect hepatic parenchymal disorders.
a. SDH
b.LDH
c.CPK
d.AMS
e.ALT
SDH
LDH
ALT
corresponds to the diagnostic enzymes for acute myocardial infarction:
a. CK-MB
b. ALT
c. Troponin T
d. AST
e. HBD
CK-MD
AST
HBD
corresponds to the diagnostic enzymes for prostatic cancer:
PSA
ACP
Which enzyme is used to detect insecticide poisoning?
Acetylcholinesterase
The graph that plots substrate concentration versus reaction rate is called
Michaelis-Menten plot
Which of the following is not the property of enzyme:
a.to be converted in the course of reaction
b. specificity towards a substrate or a group of substrates
c. alters the rate of reaction a thousand or a million-fold
d. protein with which a substrate can attach reversibly
to be converted in the course of reaction
On which organism or sample was the term enzyme literally associated?
Yeast
In early 19the century, which scientist studied fermentation of sugar to alcohol using a cell-free extract?
Edward Buchner
What was the name given to enzymes by Louis Pasteur that he based from a process he himself discovered?
Ferment
In which year Edward Buchner discovered that yeast extract can cause the fermentation of sugar to alcohol?
1907
Who gave the word “enzymes” to catalytic molecules?
Kuhne
In which year James Sumner isolated and crystallized urease?
1926
All enzymes are made up of which biomolecules (or, biomolecules)?
Proteins
RNA
What is an inorganic cofactor?
Metal ions
What is a coenzyme?
Organic molecules containing metals
Organic molecules
Enzymes that differ in structure and origin but same reaction catalyzed are called:
Isoenzyme
A complete catalytically active enzyme together with its bound enzyme or metal ions is called?
Complex enzyme
The nonprotein part of holoenzyme is called?
Apoenzyme
Which suffix is added to the name of the substrate or to a word or to a phrase describing inactivity?
-ogen
In how many classes enzyme is divided by the IUBMB Enzyme Commission?
6
The site where enzyme catalyzed reaction takes place is called?
Active site
The molecule that is bound and acted upon by the enzyme but suppresses its function is termed:
Inactivator
The action of a biocatalyst affects:
Rate of reaction
What will happen to reaction if temperature is increased
Rate of reaction increase
What will happen to reaction if enzyme is added
Rate of reaction increase
The enzyme that does not require a carbohydrate substrate is:
Catalase
The step which decides the rate of reaction is called?
Rate limiting step
The step which decides the rate of reaction is called?
Rate of limiting step
How metal ions participate in catalysis?
a. By causing reduction and oxidation reactions between enzyme and substrate
b. By causing ionic interactions between enzyme and substrate
What are the most common point group for protease enzymes?
Serine
The enzyme chymotrypsin has this number of point groups in its active site:
3
What is enzyme kinetics?
a. Studying the mechanism of rate of reaction of enzyme
b. Looking into the factors affecting enzyme activity
c. Both a and b
What is Vmax?
Maximum rate of reaction
Who gave the general theory of enzyme action and saturable plot between [S] and V in 1913?
Leonor Michaelis and Maud Menten
In an enzyme catalyzed reaction, enzyme exists in which form?
Free form
Combined form
ES form
What does Km stand for in Michaelis-Menten equation?
Michaelis-Menten constant
Which enzymes are said to follow Michaelis-Menten kinetics?
Enzymes which show hyperbolic dependence of rate of reaction and substrate
Double-reciprocal plot is also called?
Lineweaver-Burk plot
What is k1?
The rate constant of the enzyme-substrate complex formation
What is the relationship between Km and enzyme affinity for substrate?
Inversely proportional
A purely competitive enzyme inhibitor has which of the following kinetic effects?
increases Km without affecting Vmax
Which statement about the active site is incorrect?
A. It is composed of linearly arranged amino acid chain.
B. It is relatively small compared to the total bulk of the enzyme.
C. It does not generally form covalent interaction with substrates.
D. It is three-dimensional in quality.
E. none of these
It is composed of linearly arranged amino acid chain.
Which statement about most enzymes is incorrect?
A. They increase the rapidity of the reactions they catalyze.
B. They are specific for the substrate as well as the reaction catalyzed.
C. They are large polypeptides with high molecular weight.
D. They are most active near neutral pH.
E. They are not affected by changes in temperature.
They are not affected by changes in temperature.
The official name of an enzyme is accompanied by an EC followed by 4 numbers separated by dots. What does EC stand for?
Enzyme commision
Which anticoagulant cannot be used for plasma collection for enzyme assays because it is regarded as an enzyme poison?
Flouride
In enzyme analysis of serum substances, buffers actually
act as a carrier for ions
A physician suspects his patient has acute hepatitis. Which test would be least indicative?
Amylase
In competitive inhibition of an enzyme reaction the
Inhibitor binds to the enzyme at the same site as the substrate
Which of the following enzymes catalyzes the conversion of starch to glucose and maltose?
Amylase (AMS)
The specific activity of an enzyme would be reported in which of the following units of measure:
Units of activity per milligram of protein
The inactive form of an enzyme is called the
Proenzyme
Aminotransferase enzymes (AST and ALT) catalyze the
Exchange of amino and keto groups between alpha-amino and alpha-keto acids
T he apoenzyme-coenzyme complex is also regarded as
holoenzyme
Enzyme activity can be measured via the following EXCEPT A. decrease in substrate concentration
B. extent of utilization of coenzyme
C. appearance of products due to catalysis
D. increase in temperature due to catalysis
D. increase in temperature due to catalysis
Biologic catalysts are characterized by all of the following EXCEPT
A. can either be organic or inorganic
B. decrease the energy of activation
C. not consumed or altered in the reaction
D. relatively high stereospecificity
A
Which of the following are surely derived from vitamin?
Coenzymes
The site where catalysis and conformational changes occur in an enzyme is the
Active site
The amount of enzyme that will convert 1 mole of substrate converted per second per liter of sample:
Katal unit
The amount of enzyme that will convert 1 micromole of substrate converted per minute per liter of sample:
IU/L
The prostatic ACP is characterized by the following, except:
A. It is tartrate-stable
B. It is not affected by Cu++ ions
C. It is formol-stable
D. It is associated with prostatic cancer
C
Select the polypeptide chain combination designated LD 5.
M4
A physician suspects his patient has pancreatitis. Which test(s) would be most indicative of this disease?
Amylase
One international unit of enzyme activity is the amount of enzyme that, under specified reaction conditions of substrate concentration, pH, and temperature, causes utilization of substrate at the rate of:
1 micromole/min
Which of the following chemical determinations may be of help in establishing the presence of seminal fluid?
Acid phosphatase
Increased total lactic dehydrogenase (LD) activity, confirmed to fraction 4 and 5 , is most likely to be associated with:
Acute viral hepatitis
Regan isoenzyme has the same properties as alkaline phosphatase that originates in the :
Placenta
Given the following results:
Alkaline phosphatase (markedly increase)
Alanine aminotransferase (slight increase)
Aspartate aminotransferase (slight increase)
Gamma-glutamyl transferase (marked increase)
This is most consistent with:
Chronic hepatits
Given the following results:
Alkaline phosphatase (slight increase)
Alanine aminotransferase (marked increase)
Aspartate aminotransferase (marked increase)
Gamma-glutamyl transferase (slight increase)
This is most consistent with:
Acute parenchymal liver disease
The presence increased CK-MB activity on a CK electrophoresis pattern is most likely found in a patient suffering from:
Myocardial infarction
- A serum sample drawn in the emergency room from a 42-year-old man yielded the following laboratory results:
CK 185 Units (Normal = 15-160)
AST 123 Units (Normal = 0-48)
CK-MB 6 Units (Normal = 2-12)
Which of the following conditions might account for these values?
Crush injury to the thigh
When myocardial infarction occurs, the first enzyme to become elevated is:
Ck
In the determination of lactate dehydrogenase at 340nm, using pyruvate as the substrate, one actually measures the:
Decrease in NADH
Which of the following enzymes catalyzes the conversion of starch to glucose and maltose?
Amylase
A scanning of a CK isoenzyme fractionation revealed two peaks: a slow cathodic peak (CK-MM) and an intermediate peak (CK-MB). A possible interpretation for this pattern is:
Myocardial infarction
Which of the following enzymes are used in the diagnosis of acute pancreatitis?
Amylase and lipase
Which of the following is a glycolytic enzyme that catalyzes the cleavage of fructose-1, 6-diphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate?
Aldolasw
The greatest activities of serum AST and ALT are seen in:
Metastatic hepatic carcinoma
An electrophoretic separation of lactate dehydrogenase isoenzymes that demonstrates an elevation in LD- 1 and LD-2 in a “flipped” pattern is consistent with:
Myocardial infarction
Which of the following is a characteristic shared by lactate dehydrogenase, malate dehydrogenase, isocitrate dehydrogenase and hydroxybutyrate dehydrogenase?
They are class III enzymes.
The most heat labile fraction of alkaline phosphatase is obtained from:
Bone
The aldehyde transport coenzyme is derived from:
Thiamine
