Enzymes and clinical enzymology

71 Kerala PSC Lab Technician Gr II practice questions on Enzymes and clinical enzymology, part of Biochemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   Serum acid phosphatase was traditionally used as a marker of cancer of the:

   1. AStomach
   2. BBreast
   3. CProstate
   4. DThyroid

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   Answer: C · Prostate

   The prostate is the richest source of acid phosphatase, and the serum level rises when prostatic cancer spreads beyond the gland, especially to bone. Prostate-specific antigen, which is more sensitive, has now largely replaced it. Acid phosphatase is unstable, so serum must be separated quickly and acidified or frozen, and samples are taken before any rectal examination.

   • A: Stomach cancer has no acid phosphatase marker.
   • B: Breast cancer is monitored with CA 15-3, not acid phosphatase.
   • D: Thyroid cancer is followed with thyroglobulin or calcitonin.

2. Question 2 · Hard

   A 60-year-old man had severe chest pain 6 days ago but did not seek care. Which result is most likely still abnormal now?

   1. ALDH with flipped LD1:LD2
   2. BCK-MB activity
   3. CTotal CK activity
   4. DSerum myoglobin

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   Answer: A · LDH with flipped LD1:LD2

   After myocardial infarction, myoglobin rises within 1-3 hours and returns to normal within about a day. CK and CK-MB rise in 4-6 hours, peak at about 24 hours and are normal again within 2-4 days. LDH rises after 12-24 hours and stays raised for 8-14 days, with LD1 above LD2 (the flipped pattern) because heart muscle is rich in LD1. Today cardiac troponin, which stays raised for about 1-2 weeks, is the preferred marker.

   • B: CK-MB returns to normal within 2-3 days of infarction.
   • C: Total CK returns to normal within about 3-4 days.
   • D: Myoglobin returns to normal within about a day.

3. Question 3 · Medium

   A raised serum ALP may come from bone or liver. Which enzyme, when also raised, points to a liver origin?

   1. A5'-Nucleotidase
   2. BAldolase
   3. CAcid phosphatase
   4. DCreatine kinase

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   Answer: A · 5'-Nucleotidase

   5'-Nucleotidase, like GGT, is found in hepatobiliary membranes and rises in cholestasis, but it is not raised in bone disease. A raised ALP with a raised 5'-nucleotidase therefore indicates a hepatobiliary source, while a raised ALP with a normal 5'-nucleotidase suggests bone, as in growing children, Paget disease or bone metastases. Heat inactivation and electrophoresis of ALP isoenzymes are other ways to find the source.

   • B: Aldolase is raised in muscle disease.
   • C: Tartrate-resistant acid phosphatase comes from osteoclasts, pointing to bone, not liver.
   • D: Creatine kinase is a muscle enzyme and does not show the source of ALP.

4. Question 4 · Easy

   A 4-year-old boy has difficulty climbing stairs and enlarged calves. Which serum enzyme is markedly raised in his likely condition?

   1. AAmylase
   2. BAcid phosphatase
   3. CCreatine kinase
   4. DAlkaline phosphatase

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   Answer: C · Creatine kinase

   The picture suggests Duchenne muscular dystrophy, in which creatine kinase leaks from damaged muscle fibers and is very high, often from birth, before weakness appears. Most of it is CK-MM, the skeletal muscle isoenzyme. CK is also used in family studies, as many female carriers have a raised value.

   • A: Amylase rises in pancreatitis and salivary gland disease.
   • B: Acid phosphatase rises in prostatic cancer and some bone diseases.
   • D: Alkaline phosphatase rises in bone and cholestatic liver disease, not muscle disease.

5. Question 5 · Easy

   The coenzyme required by AST and ALT is:

   1. AFlavin adenine dinucleotide
   2. BThiamine pyrophosphate
   3. CPyridoxal phosphate
   4. DNAD+

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   Answer: C · Pyridoxal phosphate

   Aminotransferases move an amino group from an amino acid to a keto acid, and pyridoxal phosphate (from vitamin B6) carries it as pyridoxamine phosphate. AST transfers it from aspartate and ALT from alanine to 2-oxoglutarate. Reference methods add pyridoxal phosphate to the reagent so that patients low in vitamin B6, such as those with alcoholism or on dialysis, are not under-measured.

   • A: FAD serves oxidases and some dehydrogenases.
   • B: Thiamine pyrophosphate serves decarboxylases and transketolase.
   • D: NAD+ serves dehydrogenases; the assay's indicator step uses NADH, not the aminotransferase itself.

6. Question 6 · Medium

   In a kinetic (rate) enzyme assay, enzyme activity is calculated from:

   1. AA single reading at time zero
   2. BThe change in absorbance per minute
   3. CThe absorbance of the reagent blank
   4. DThe absorbance after the reaction stops

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7. Question 7 · Medium

   An enzyme with a low Km for its substrate:

   1. AHas a low maximum velocity
   2. BHas a high affinity for the substrate
   3. CHas a low affinity for the substrate
   4. DHas a high maximum velocity

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8. Question 8 · Medium

   Prolonged apnea after suxamethonium during surgery suggests an inherited deficiency of:

   1. ARed cell acetylcholinesterase
   2. BPlasma cholinesterase
   3. CGlucose-6-phosphate dehydrogenase
   4. DMonoamine oxidase

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9. Question 9 · Medium

   In acute pancreatitis, serum lipase is preferred to amylase because lipase:

   1. AIs cleared rapidly by the kidneys
   2. BIs more specific and stays raised longer
   3. CRises within an hour and falls in a day
   4. DIs also raised in mumps and parotitis

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10. Question 10 · Easy

    Glucose-6-phosphate dehydrogenase is the first enzyme of the:

    1. ACitric acid cycle
    2. BGlycolytic pathway
    3. CHexose monophosphate shunt
    4. DUrea cycle

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11. Question 11 · Easy

    All of the following enzymes are hydrolases EXCEPT:

    1. ALipase
    2. BAlkaline phosphatase
    3. CLactate dehydrogenase
    4. DAmylase

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12. Question 12 · Medium

    ALT, AST and LDH assays are commonly followed at 340 nm. The reason is that at this wavelength:

    1. ABoth coenzyme forms absorb equally
    2. BPyruvate absorbs light strongly
    3. CNAD+ absorbs light but NADH does not
    4. DNADH absorbs light but NAD+ does not

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13. Question 13 · Easy

    Which enzyme is a sensitive marker of alcohol intake and is induced by drugs such as phenytoin?

    1. APancreatic lipase
    2. BCreatine kinase
    3. CAlanine aminotransferase
    4. DGamma-glutamyltransferase

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14. Question 14 · Hard

    A 48-year-old man has AST 190 IU/L, ALT 75 IU/L, GGT 450 IU/L and ALP 140 IU/L (reference: AST and ALT up to 40, GGT up to 50, ALP 40-130). What is the most likely diagnosis?

    1. AMyocardial infarction
    2. BAcute viral hepatitis
    3. CObstructive jaundice
    4. DAlcoholic liver disease

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15. Question 15 · Hard

    In an ALT kinetic assay at 340 nm, readings at 1-minute intervals are 1.200, 1.170, 1.140 and 1.110. The kit factor is 1,746. What is the ALT activity?

    1. A157 U/L
    2. B105 U/L
    3. C39 U/L
    4. D52 U/L

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16. Question 16 · Hard

    In an enzyme assay, 0.05 mL of serum converts 0.30 µmol of substrate in 5 minutes. What is the enzyme activity in U/L?

    1. A1,200 U/L
    2. B6,000 U/L
    3. C60 U/L
    4. D1.2 U/L

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17. Question 17 · Medium

    Creatine kinase reagent kits (CK-NAC) contain N-acetylcysteine. Why?

    1. AIt replaces the magnesium CK needs
    2. BIt is a sulphur donor used as substrate
    3. CIt removes adenylate kinase interference
    4. DIt restores CK's oxidized thiol groups

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18. Question 18 · Hard

    A 22-year-old man has aching muscles the day after a very heavy first gym session. AST 380 U/L, ALT 140 U/L (reference up to 40), CK 28,000 U/L (reference up to 200), GGT and bilirubin normal. The raised transaminases most likely come from:

    1. AMyocardial infarction
    2. BAcute viral hepatitis
    3. CInjured skeletal muscle
    4. DAlcoholic liver injury

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19. Question 19 · Easy

    How do enzymes speed up a reaction?

    1. ARaising its activation energy
    2. BSupplying energy to the reactants
    3. CLowering its activation energy
    4. DShifting its equilibrium point

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20. Question 20 · Medium

    A healthy woman in her 34th week of pregnancy has serum ALP twice the upper reference limit, with normal GGT, bilirubin and transaminases. The extra ALP most likely comes from the:

    1. ABone
    2. BIntestine
    3. CPlacenta
    4. DLiver

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21. Question 21 · Medium

    The prostatic fraction of serum acid phosphatase is the part that is inhibited by:

    1. ACupric ions
    2. BL-tartrate
    3. CLevamisole
    4. DFormaldehyde

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22. Question 22 · Medium

    When velocity is plotted against substrate concentration, an allosteric enzyme with cooperative binding gives a curve that is:

    1. ABell-shaped
    2. BSigmoid
    3. CHyperbolic
    4. DA straight line

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23. Question 23 · Easy

    FAD and FMN, the coenzymes of many dehydrogenases, are formed from which vitamin?

    1. AThiamine
    2. BNiacin
    3. CRiboflavin
    4. DPantothenic acid

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24. Question 24 · Easy

    Which creatine kinase isoenzyme is most specific for heart muscle?

    1. ACK-BB
    2. BMitochondrial CK
    3. CCK-MB
    4. DCK-MM

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25. Question 25 · Easy

    In the IUBMB classification, class 1 enzymes (EC 1) are the:

    1. AHydrolases
    2. BOxidoreductases
    3. CTransferases
    4. DLigases

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