Clinical Chemistry (Enzymes and Cardiac Assessment)
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What does an increase in the serum enzyme levels indicate? A. Decreased enzyme catabolism B. Accelerated enzyme production C. Tissue damage and necrosis D. Increased glomerular filtration rate
In the assay of an enzyme, zero-order kinetics are best described by which of the following statements? A. Enzyme is present in excess; rate of reaction is variable with time and dependent only on the concentration of the enzyme in the system. B. Substrate is present in excess; rate of reaction is constant with time and dependent only on the concentration of enzyme in the system. C. Substrate is present in excess; rate of reaction is constant with enzyme concentration and dependent only on the time in which the reaction is run. D. Enzyme is present in excess; rate of reaction is independent of both time and concentration of the enzyme in the system.
Based on the following graph of velocity of an enzyme reaction versus substrate concentration, you are designing a new method to measure the activity of an enzyme of clinical interest. To formulate the new methodology so that enzyme activity is assessed using zero-order kinetics, which concentration of substrate should you initially determine experimentally? Michaelis-Menten Curve | vmax| _____________________ | / 1/2 vmax|–/ |/_______________________ A. Substrate concentration a B. Substrate concentration b C. Substrate concentration c D. Substrate concentration d
When measuring enzyme activity, if the instrument is operating 5°C lower than the temperature prescribed for the method, how will the results be affected? A. Lower than expected B. Higher than expected C. Varied, showing no particular pattern D. All will be clinically abnormal.
Given the following information for a rate reaction, calculate the activity of a serum specimen for alanine aminotransferase in international units per liter (IU/L). Time Absorbance 1 min 1.104 2 min 1.025 3 min 0.950 4 min 0.873 Specimen volume = 20 uL Reagent volume = 3.0 mL Molar absorptivity for NADH at 340 nm = 6.22 x 10^3 L/mol*cm Light path = 1 cm A. 186 B. 198 C. 1857 D. 1869
The properties of enzymes are correctly described by which of the following statements? A. Enzymes are stable proteins. B. Enzymes are protein catalysts of biological origin. C. Enzymes affect the rate of a chemical reaction by raising the activation energy needed for the reaction to take place. D. Enzyme activity is not altered by heat denaturation.
Which of the following is a true statement concerning serum enzymes? A. The presence of hemolyzed red cells is of no significance for an accurate assay of most serum enzymes. B. Serum asparate transaminase (AST), but not serum lactate dehydrogenase (LD), is usually elevated in acute myocardial infarction. C. Increased serum alkaline phosphatase may be found in bone disease. D. Aspartate transaminase was formerly known as glutamate pyruvate transaminase
Enzymes that catalyze the transfer of groups between compounds are classified as belonging to which enzyme class? A. Hydrolases B. Eyases C. Oxidoreductases D. Transferases
Which of the following enzymes does not belong to the class of enzymes known as the hydrolases? A. Alkaline phosphatase B. Aldolase C. Amylase D. Lipase
To what class of enzymes does lactate dehydrogenase belong? A. Isomerases B. Ligases C. Oxidoreductases D. Transferases
Which of the following enzymes catalyzes the transfer of amino groups causing the interconversion of amino acids and a- oxoacids? A. Amylase B. Aspartate transaminase C. Alkaline phosphatase D. Lactate dehydrogenase
What abbreviation has been used in the past to designate alanine aminotransferase? A. AST B. AAT C. GOT D. GPT
When measuring CK-MB, which of the following would provide the most sensitive method? A. Electrophoretic B. Colorimetric C. Kinetic D. Mass immunoassay
Which of the following does not accurately describe properties associated with lactate dehydrogenase? A. Optimum pH for the catalysis of lactate to pyruvate is 7.4-7.8. B. LD is increased in a hemolyzed serum specimen. C. LD catalyzes the oxidation of lactate to pyruvate with mediation of nicotinamide-adenine dinucleotide. D. LD-4 and LD-5 are labile in the cold
Which test, if elevated, would provide information about risk for developing coronary artery disease? A. Troponin B. CK-MB C. hs-CRP D. Myoglobin
Lactate dehydrogenase (LD) catalyzes the following reaction: Lactate + NAD+ ⇌ (LD) ⇌ pyruvate + NADH As the reaction is written, which of the following techniques can be used to assess LD activity? A. Measure the colorimetric product pyruvate. B. Measure the colorimetric product NADH. C. Measure the increase in absorbance at 340 nm as NADH is produced. D. Measure the decrease in absorbance at 340 nm as NADH is produced.
Which of the following is false about myoglobin as it relates to acute myocardial infarction (AMI)? A. Measure serially B. Cardiac specific C. Initial increase occurs in 1-3 hours D. Doubling of initial value within 1-2 hours suggestive of AMI
Which of the following disorders is not associated with an elevation of serum creatine kinase? A. Cerebrovascular accidents B. Hypothyroidism C. Bone disease D. Intramuscular injection
Which of the following statements concerning creatine kinase is false? A. Rises within 4-6 hours after acute myocardial infarction B. Catalyzes the phosphorylation of creatine by ATP C. Requires Ca2+ for activity D. Found mainly in skeletal and cardiac muscles and in brain tissue
Which enzyme is measured by methodologies that use small oligosaccharides and 4-nitrophenyl-glycoside for substrates? A. Lipase B. Amylase C. Creatine kinase D. Cholinesterase
Which statement concerning gammaglutamyltransferase is false? A. Present in almost all cells of the body B. Elevated in liver and some pancreatic diseases C. Elevated in chronic alcoholism D. Elevated in bone disease
Which of the following statements correctly describes alkaline phosphatase? A. Decreased in Paget disease B. Decreased in third trimester of a normal pregnancy C. Increased in obstructive jaundice D. Primarily found in cardiac muscle
Which of the following enzymes would not be useful to quantify in the assessment of liver function? A. Alanine aminotransferase B. Creatine kinase C. Alkaline phosphatase D. Gamma-glutamyltransferase
In acute pancreatitis, a significant increase in which serum enzyme would be expected diagnostically? A. Creatine kinase B. Amylase C. Alkaline phosphatase D. Aspartate aminotransferase