L2 AST & ALT

b

In the bloodstream, free ammonia exists predominantly in equilibrium as which of the following ions?

a. Hydroxide ion

b. Ammonium ion (NH4)

c. Nitrite ion

d. Bicarbonate ion

a

Which condition is defined as a severe metabolic encephalopathy and fatty liver degeneration occurring primarily in children following a viral infection?

a. Reye's Syndrome

b. Lesch-Nyhan Syndrome

c. Hepatic Encephalopathy

d. Alcoholic Hepatitis

c

Which analytical method is considered the gold standard for measuring ammonia on automated clinical chemistry analyzers?

a. Conway Microdiffusion

b. Ion-Selective Electrode (ISE)

c. Enzymatic Method (GLDH)

d. Colorimetric / Spectrophotometric Method

a

To arrest in vitro bacterial metabolism and spontaneous deamination, how must venous blood collected for ammonia analysis be handled?

a. Placed immediately into an ice slush ($0-4^\circ\text{C}$)

b. Incubated in a 37 C water bath

c. Frozen instantly at -20 C

d. Left at room temperature for 20 minutes before processing

b

What exogenous factor can cause falsely increased plasma ammonia levels, requiring patients to abstain from it prior to venipuncture?

a. Excessive hydration

b. Tobacco smoke

c. Lactulose administration

d. Diphenhydramine administration

c

What term describes specialized protein catalysts that accelerate chemical reaction rates without undergoing permanent chemical alteration or being consumed?

a. Substrates

b. Coenzymes

c. Enzymes

d. Hydrolases

c

What is the specific region composed of amino acid residues where the substrate binds to undergo catalysis?

a. Allosteric Site

b. Apoenzyme cleft

c. Active Site

d. Ligase domain

a

Which clinical condition typically presents with a De Ritis Ratio (AST/ALT ratio) of less than 1.0 due to high hepatic cytosolic release?

a. Acute Viral Hepatitis

b. Cirrhosis

c. Alcoholic Hepatitis

d. Hepatocellular Carcinoma

c

Which major IUBMB enzyme class catalyzes the transfer of a functional group (such as an amino or phosphate group) other than hydrogen?

a. Oxidoreductases

b. Lyases

c. Transferases

d. Isomerase

d

Correct Answer: c. Transferases

Alkaline Phosphatase (ALP) operates strictly in an environment with what optimal pH range?

a. 5.0

b. 7.0-8.0

c. 7.3-7.8

d. 9.8-10.5

c

At what temperature do enzymes typically reach their optimum kinetic energy and collision efficiency before thermal damage occurs?

a. 0-4 C

b. 25 C

c. 37 C

d. 40-50 C

b

Which kinetic order describes a reaction where substrate excess saturates all enzyme active sites, causing the rate to depend strictly on enzyme concentration?

a. First-Order Kinetics

b. Zero-Order Kinetics

c. Second-Order Kinetics

d. Reversible Kinetics

c

What term refers to nonprotein organic molecules, such as Pyridoxal Phosphate, that act as secondary substrates and are required for full catalytic activity?

a. Inorganic Activators

b. Competitive Inhibitors

c. Coenzymes

d. Hydrolases

c

What is the former clinical name for the enzyme Aspartate Aminotransferase (AST)?

a. Serum Glutamic-Pyruvic Transaminase (SGPT)

b. Serum Glutamic-Oxaloacetic Transaminase (SGOT)

c. Lactate Dehydrogenase (LDH)

d. Creatine Kinase (CK)

b

AST catalyzes the reversible transfer of an amino group between L-aspartate and alpha-ketoglutarate, forming L-glutamate and which of the following products?

a. Pyruvate

b. Oxaloacetate

c. Malate

d. Lactate

b

Which isoenzymatic form of AST is predominantly released into circulation during severe tissue necrosis?

a. Cytoplasmic AST

b. Mitochondrial AST

c. Nuclear AST

d. Lysosomal AST

c

Following the onset of chest pain in an Acute Myocardial Infarction (AMI), when does serum AST activity typically peak?

a. 6 to 8 hours

b. 12 hours

c. 24 hours

d. Within 5 days

b

In the Karmen Method for measuring AST, which coupled enzyme oxidizes NADH to $NAD^+$ to allow continuous monitoring at 340 nm?

a. Lactate Dehydrogenase (LDH)

b. Malate Dehydrogenase (MDH)

c. Glutamate Dehydrogenase (GLDH)

d. Alkaline Phosphatase (ALP)

d

What chemical is utilized as the color developer in the Reitman-Frankel method to yield a blue-colored hydrazone measured at 505 nm?

a. Bromophenol Blue

b. 0.4 N NaOH

c. Pyridoxal Phosphate

d. 2,4-dinitrophenylhydrazone (DNPH)

b

Alanine Aminotransferase (ALT) transfers an amino group from L-alanine to alpha-ketoglutarate, forming L-glutamate and what other specific product?

a. Oxaloacetate

b. Pyruvate

c. Malate

d. Lactate

b

Which aminotransferase enzyme is considered significantly more liver-specific?

a. Aspartate Aminotransferase (AST)

b. Alanine Aminotransferase (ALT)

c. Gamma-Glutamyl Transferase (GGT)

d. Malate Dehydrogenase (MDH)

c

A De Ritis ratio (AST/ALT ratio) greater than 2.0 is clinically most indicative of which pathology?

a. Acute Viral Hepatitis

b. Non-viral Chronic Liver Disease

c. Alcoholic Hepatitis or Hepatocellular Carcinoma (HCC)

d. Pericarditis

c

n the Wroblewski & LaDue coupled enzymatic reaction for ALT, which indicator enzyme reduces pyruvate to lactate while oxidizing NADH to NAD+?

a. Malate Dehydrogenase (MDH)

b. Glutamate Dehydrogenase (GLDH)

c. Lactate Dehydrogenase (LDH)

d. Pyruvate Decarboxylase

a

In what cellular compartment is Alanine Aminotransferase (ALT) exclusively found?

a. Cytoplasm

b. Mitochondria

c. Lysosomes

d. Ribosomes

c

Which major IUBMB enzyme class catalyzes the structural rearrangement or interconversion of geometric, optical, or positional isomers?

a. Transferases

b. Lyases

c. Isomerases

d. Ligases

b

Which enzyme class catalyzes the joining of two substrate molecules coupled with ATP hydrolysis?

a. Hydrolases

b. Ligases

c. Lyases

d. Oxidoreductases

c

What happens to human enzymes when temperatures reach the $40-50^\circ\text{C}$ range?

a. They shift to zero-order kinetics

b. Their kinetic energy is optimized

c. The protein structure unfolds completely, causing permanent loss of catalytic activity

d. They catalyze reverse reactions exclusively

b

Why is a hemolyzed specimen strictly unacceptable for ammonia analysis?

a. Red blood cells absorb plasma ammonia rapidly in vitro

b. Red blood cells contain 2 to 3 times higher concentration of ammonia than plasma

c. Hemoglobin irreversibly binds to the GLDH reagent

d. Hemolysis destroys allosteric sites on parenchymal enzymes

a

What is the structural mechanism of action during allosteric inhibition?

a. The inhibitor binds to the allosteric site, altering the active site structure so the substrate cannot bind

b. The inhibitor covalently degrades the primary structure of the enzyme

c. The activator binds to the active site to competitively block the substrate

d. The inhibitor denatures the enzyme via temperature elevation

c

In the Conway Microdiffusion analytical method for ammonia, how is the diffused ammonia gas quantified?

a. By continuous monitoring of absorbance at 540 nm

b. By potentiometric pH measurement

c. Via titration

d. By observing a blue color complex