This set of Enzyme Technology Multiple Choice Questions & Answers (MCQs) focuses on “Enzymes – Isoenzyme”.
1. Which of the following is not true for isoenzymes?
a) Many enzymes occur in several molecular forms called isoenzymes
b) Different isoenzyme catalyze same chemical reaction, but differ in their primary structure and kinetic properties
c) Isoenzymes are coded by different gene
d) Enzymes having other site
Explanation: “Enzymes having other site.” Is not true for isoenzymes, but allosteric enzymes. The following statements are true for isoenzymes:
• Many enzymes occur in several molecular forms called isoenzymes.
• Different isoenzyme catalyze same chemical reaction, but differ in their primary structure and kinetic properties.
• Isoenzymes are coded by different gene.
2. Which of the following is not true for isoenzymes?
a) Regulation specific to distinct tissue and development stages
b) Distinctive properties and patterns of metabolism to particular organ
c) Regulatory metabolites are called effector or modulator or modifier
d) Fine tuning of metabolism
Explanation: The statements which are true for isoenzymes are as follows:
• It provides a means of regulation specific to distinct tissue and development stages.
• Its distribution in tissues gives out distinctive properties and patterns of metabolism to particular organ.
• Its existence provides fine tuning of metabolism in order to meet the need of given tissue or development stage.
“Regulatory metabolites are called effector or modulator or modifier.” This statement in true in case of allosteric enzymes, and not isoenzymes.
3. Multiple forms of the same enzyme is referred to as __________
a) allosteric enzyme
Explanation: Multiple forms of the same enzyme is referred to as isoenzyme. The enzymes having allosteric sites, other than catalytic site which is used for binding for regulatory metabolites is referred to as allosteric enzymes. Biosensor is an analytical device which converts a biological response into an electrical signal. Regulatory metabolites required for binding to allosteric sites are called effectors.
4. Which of the following property is not shown by isoenzyme?
a) Sigmoidal shaped curve
b) Electrophoretic mobility
c) Kinetic properties
d) Aminoacid composition
Explanation: Sigmoidal shaped curve is observed when a plot of rate of reaction versus substrate concentration. This is as a property of allosteric enzyme. Following are the properties which are shown by isoenzyme:
• Electrophoretic mobility, kinetic properties, aminoacid composition and aminoacid sequence.
5. Which of the following is false for lactate dehydrogenase (LDH)?
a) It is a tetrameric enzyme
b) It catalyzes reversible phosphorylation of creatinine to creatinine phosphate by ATP
c) It has five isoenzymes
d) It is made up of two polypeptides
Explanation: “It catalyzes reversible phosphorylation of creatinine to creatinine phosphate by ATP.” This statement is not true for LDH, as LDH catalyzes L-lactate to pyruvate. The following statements are true for LDH:
• It is a tetrameric enzyme.
• It has five isoenzymes: LDH1, LDH2, LDH3, LDH4, LDH5.
• It is made up of two polypeptides: M-type (muscle) and H-type (heart).
6. An increase in serum level of LDH1 relative to LDH2 is an indication of ___________
a) muscular dystrophy
c) myocardial infarction
d) hepatitis with jaundice
Explanation: An increase in serum level of LDH1 relative to LDH2 is an indication of myocardial infarction. During muscular dystrophy, LDH5 activity is said to increase moderately. Predominant elevation of LDH2 and LDH3 is seen in cases of leukemia. Majorly, LDH3 is elevated due to malignancy of many tissues. LDH5 activity increase is seen during liver diseases like toxic hepatitis with jaundice.
7. Which of the following is not associated with increase of LDH activity in urine?
a) Megaloblastic anemia
b) Chronic glomerulonephritis
c) Diabetic nephrosclerosis
d) Kidney malignancies
Explanation: Megaloblastic anemia cause the erythrocyte precursor cell to breakdown in the bone marrow resulting in large quantities of LDH1 and LDH2 isoenzyme. Hence it is not associated with increase of LDH activity in urine. Following are associated with increase of LDH activity in urine: Chronic glomerulonephritis, diabetic nephrosclerosis, bladder and kidney malignancies.
8. LDH4 and LDH5: Bacterial meningitis:: LDH1 and LDH3: ___________
a) Kidney malignancies
b) Myocardial infarction
c) Intracranial hemorrhage
d) Viral meningitis
Explanation: An elevation of LDH4 and LDH5 is CSF is seen cases of bacterial meningitis. In the same way, an elevation of LDH1 through LDH3 is seen in cases of viral meningitis. LDH activity in urine is seen in cases of kidney malignancies. Myocardial infarction is indicated when there is an increase in serum level of LDH1 relative to LDH2. In neonates, elevation LDH-CSF is observed in cases of intracranial hemorrhage.
9. Which of the following is not an isoenzyme of acid phosphatase?
Explanation: Salivary is not an isoenzyme of acid phosphatase, but amylase. Amylase has other isoenzyme named pancreatic amylases. The following are the isoenzyme of acid phosphatase: Prostate, erythrocytes, platelets, liver, spleen, kidney and bone marrow.
10. Which of the following is not isoenzyme form of alkaline phosphatase?
Explanation: Bone, placenta, intestine, liver and kidney are the isoenzymes of alkaline phosphatase. Muscle along with liver (glucokinase) are isoenzymes of hexokinase enzyme.
11. Which of the following is not true for creatine kinase?
a) Its activity is greatest in striated muscle, brain and heart tissue
b) It catalyzes L-lactate to pyruvate
c) It is a dimer
d) It has three isoenzymes
Explanation: Following statements are true for creatine kinase:
• Its activity is greatest in striated muscle, brain and heart tissue
• It is a dimer which is made up of 2 polypeptide chains: muscle (M) type or brain (B) type.
• It has three isoenzymes: CK1, CK2, CK3.
It does not catalyze L-lactate to pyruvate, but creatinine to creatinine phosphate by ATP which a reversible phosphorylation reaction.
12. CK1: brain:: CK3: _________________
c) Skeletal muscle
d) Cardiac tissue
Explanation: Isoenzyme of creatine kinase CK1 is made of BB polypeptide and is present in brain. Whereas as CK3 isoenzyme is made MM polypeptide and is seen in skeletal and cardiac muscle.
13. Which is the only tissue which has mixed MB (CK2) isoenzyme?
c) Cardiac tissue
Explanation: CK2 is an isoenzyme of creatine kinase which is made up of 2 peptides muscle (M) and brain (B) type. Cardiac tissue is the only tissue which has mixed MB (CK2) isoenzyme. Detection of CK2 in serum strongly suggest myocardial damage.
14. Which of the following is not a clinical application of creatine kinase isoenzyme?
b) Damage of heart tissue
Explanation: Predominant elevation of LDH2 and LDH3 is seen in cases of leukemia. Hence Leukemia is not a clinical application of creatine kinase, but lactate dehydrogenase enzyme. Following are the clinical application of creatine kinase isoenzyme:
• Hypothyroidism shows an elevation CK activity, majorly CK3.
• Damage of heart tissue from myocardial infraction may detected my increased level of CK2 in blood.
• Myopathy and dystrophy has elevated levels of CK3 in serum.
15. Head injures can be detected by _______
a) increase of CK2 in blood
b) increase of CK1 in CSF
c) elevated levels of CK3 in serum
d) LDH2 and LDH3 increase
Explanation: Head injures can be detected by increase of CK1 in CSF. Increase of CK2 in blood shows damage of heart tissue from myocardial infraction. Elevated levels of CK3 in serum lead myopathy and dystrophy. LDH2 and LDH3 increase is used in the detection of leukemia.
Sanfoundry Global Education & Learning Series – Enzyme Technology.
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