CC2 LEC: L2 (P) AST ALT

starting over agen

A

What is the primary function of enzymes in biochemical reactions?

a. They act as biological catalysts that speed up reactions without being used up.

b. They permanently bond to substrates to create structural tissue.

c. They serve as secondary energy sources for the Krebs cycle.

d. They inhibit cellular metabolism during periods of rest.

A

Which specific region of an enzyme is responsible for interacting with substrate amino acid residues?

a. Active site

b. Allosteric site

c. Prosthetic group

d. Coenzyme cleft

A

Where do regulator molecules bind on an enzyme to cause allosteric effects?

a. Allosteric site

b. Active site

c. Peptide backbone

d. Terminal amino group

A

What is the definition of a substrate in an enzymatic reaction?

a. The molecule(s) that the enzyme works on

b. The final product released after catalysis

c. The inorganic cofactor required for stability

d. The protein inhibitor that blocks the active site

A

What occurs during allosteric inhibition?

a. An inhibitor binds to the allosteric site and changes the active site so the substrate cannot bind.

b. A substrate binds directly to the active site and halts all metabolic pathways.

c. An activator increases the turnover rate of the enzyme-substrate complex.

d. The enzyme completely breaks down into individual amino acids.

A

What is the role of an activator in allosteric regulation?

a. It binds to allow the substrate to bind to the active site.

b. It blocks the active site to prevent substrate binding.

c. It destroys the secondary structure of the enzyme.

d. It replaces the cofactor entirely.

A

Which enzyme class catalyzes oxidation-reduction reactions between two substrates?

a. Oxidoreductases

b. Transferases

c. Hydrolases

d. Isomerases

A

Which class of enzymes catalyzes the transfer of groups other than hydrogen from one substrate to another?

a. Transferases

b. Oxidoreductases

c. Lyases

d. Ligases

A

Hydrolases are enzymes that catalyze what type of reaction?

a. Hydrolysis of various bonds

b. Joining of two substrate molecules with ATP cleavage

c. Removal of groups without hydrolysis, leaving double bonds

d. Interconversion of geometric isomers

A

Which enzyme class removes groups from substrates without hydrolysis, resulting in products containing double bonds?

a. Lyases

b. Ligases

c. Hydrolases

d. Transferases

A

What type of reactions do isomerases catalyze?

a. Interconversion of geometric, optical, or positional isomers

b. Oxidation and reduction of carbon-nitrogen bonds

c. Hydrolysis of peptide bonds

d. Transfer of amino groups to alpha-keto acids

A

Which enzyme class joins two substrate molecules, coupled with the breaking of a pyrophosphate bond in ATP?

a. Ligases

b. Transferases

c. Oxidoreductases

d. Lyases

A

In the breakdown of starch by salivary amylase, what is the resulting product?

a. Maltose

b. Glucose exclusively

c. Sucrose

d. Lactose

A

During the first-order kinetics phase of an enzymatic reaction involving substrate concentration, what happens as substrate concentration increases?

a. The reaction rate increases.

b. The reaction rate drops to zero immediately.

c. The reaction rate remains completely constant.

d. The enzyme is permanently denatured.

A

What type of kinetics occurs when enzymes are completely saturated with excess substrate?

a. Zero-order kinetics

b. First-order kinetics

c. Second-order kinetics

d. Pseudo-first-order kinetics

A

What is the typical optimal pH range for most enzymes?

a. 7.0-8.0

b. 1.0-3.0

c. 9.0-11.0

d. 4.0-5.0

A

Acid phosphatase (ACP) functions best in which type of environment?

a. Acidic pH only

b. Strongly alkaline pH

c. Neutral pH only

d. Fluctuating pH environments

A

At what common temperature are enzyme assays frequently set in U.S. laboratories?

a. 37°C

b. 20°C

c. 56°C

d. 4°C

A

What are inorganic cofactors that assist enzyme activity?

a. Ions such as calcium, magnesium, and zinc

b. Vitamins and NAD molecules

c. Large polypeptide chains

d. Lipid bilayers

A

Which of the following describes organic coenzymes?

a. Vitamins or NAD that may act as secondary substrates or prosthetic groups

b. Inorganic metal ions that precipitate proteins

c. Amino acid residues in the active site

d. Carbohydrate side chains on glycoproteins

A

Which group of enzymes is particularly clinically significant for differentiating functional versus mechanical liver disease?

a. Aminotransferases

b. Lipases exclusively

c. Amylases only

d. Cholinesterases

A

Which tissues contain Alanine Aminotransferase (ALT)?

a. Liver, skeletal muscle, and kidney

b. Heart and lungs exclusively

c. Brain tissue only

d. Pancreas and spleen

A

Which aminotransferase is considered more liver-specific?

a. ALT

b. AST

c. CK-MB

d. Amylase

A

What type of liver damage is predominantly indicated by elevated ALT levels?

a. Hepatocellular (functional) liver damage

b. Post-hepatic mechanical obstruction only

c. Biliary tree atresia exclusively

d. Primary splenic infarction

A

How long can AST and ALT remain elevated following acute hepatocellular injury?

a. Up to 2-6 weeks

b. Only 2-3 hours

c. Exactly 24 hours

d. Exactly 6 months

B

What was the former name for Aspartate Aminotransferase (AST)?

a. Serum glutamic pyruvic transaminase

b. Serum glutamic oxaloacetic transaminase

c. Serum lactic dehydrogenase

d. Serum alkaline phosphatase

B

What coenzyme is strictly required by AST for its transamination reaction?

a. Nicotinamide adenine dinucleotide

b. Pyridoxal phosphate

c. Flavin adenine dinucleotide

d. Thiamine pyrophosphate

B

Which AST isoenzyme fraction is the predominant form found in normal serum?

a. Mitochondrial AST

b. Cytoplasmic AST

c. Microsomal AST

d. Membrane-bound AST

B

What are the primary products formed by the transamination action of AST?

a. Pyruvate and alanine

b. Oxaloacetate and glutamate

c. Lactate and malate

d. Aspartate and alpha-ketoglutarate

B

What is the reference interval range for AST given in the text?

a. 7-45 U/L

b. 5-35 U/L

c. 50-100 U/L

d. 0-15 U/L

B

During an Acute Myocardial Infarction (AMI), when does AST typically begin to rise?

a. 1-2 hours

b. 6-8 hours

c. 24-36 hours

d. 3-4 days

B

At what time point does AST typically peak following an Acute Myocardial Infarction?

a. 6 hours

b. 24 hours

c. 72 hours

d. 7 days

B

Within how many days does AST typically normalize after an Acute Myocardial Infarction?

a. 1 day

b. Within 5 days

c. 10 days

d. 14 days

B

Which condition is associated with a pronounced elevation (greater than 5 times normal) of AST?

a. Mild pulmonary infarction

b. Acute hepatocellular damage

c. Uncomplicated pericarditis

d. Early-stage cirrhosis

B

Which of the following causes a slight elevation (up to 3 times normal) of AST?

a. Alcoholic Hepatitis

b. Cirrhosis

c. Massive circulatory collapse (shock)

d. Acute pancreatitis

B

Why should hemolysis strictly be avoided when collecting blood specimens for AST testing?

a. Red blood cells contain large amounts of AST, which falsely decreases serum levels.

b. Hemolysis dramatically increases serum AST concentration.

c. Hemoglobin precipitates the dinitrophenylhydrazone reagent.

d. It completely stops the malate dehydrogenase reaction.

B

For how many days is AST activity stable in serum kept at refrigerated temperatures?

a. 1 to 2 days

b. 3 to 4 days

c. 7 to 10 days

d. 30 days

B

What is the name of the coupled enzymatic reaction method used for measuring AST?

a. Reitman-Frankel method

b. Karmen method

c. Caraway method

d. Jaffe method

B

In the Karmen method for AST, what substance is measured by the loss of absorbance at 340 nm?

a. Formed oxaloacetate

b. Formed NAD+ (loss of NADH)

c. Remaining alpha-ketoglutarate

d. Unreacted aspartate

B

What is the optimal pH range for the Karmen method assay of AST?

a. 5.0-6.0

b. 7.3-7.8

c. 8.5-9.0

d. 2.0-4.0

B

What chemical colorimetric method for AST uses dinitrophenylhydrazone and measures a color complex at 505 nm?

a. Karmen method

b. Reitman-Frankel method

c. Jaffe reaction

d. Urease-GLDH method

B

What is a major drawback of the Reitman-Frankel colorimetric method for aminotransferases?

a. It requires expensive ultraviolet spectrophotometers.

b. It lacks specificity and reacts with any keto-compound.

c. It only works on hemolyzed samples.

d. It has an extremely narrow linear range.

B

What was the former name for Alanine Aminotransferase (ALT)?

a. Serum glutamic oxaloacetic transaminase

b. Serum glutamic pyruvic transaminase

c. Serum creatine phosphokinase

d. Serum acid phosphatase

B

What substrates are utilized in the enzymatic reaction catalyzed by ALT?

a. Aspartate and alpha-ketoglutarate

b. Alanine and alpha-ketoglutarate

c. Pyruvate and glutamate

d. Oxaloacetate and NADH

B

What is the reference interval range for ALT given in the text?

a. 5-35 U/L

b. 7-45 U/L

c. 50-90 U/L

d. 100-150 U/L

B

Why is ALT measurement preferred over AST as a screening test for post-transfusion hepatitis or toxic exposure?

a. It is cheaper to perform in manual batches.

b. It is more sensitive and specific for liver tissue.

c. It is completely unaffected by temperature fluctuations.

d. It has a shorter half-life in whole blood.

B

What is another name for the AST/ALT ratio?

a. Reticulocyte index

b. De Ritis ratio

c. Partition coefficient

d. Enzymatic quotient

B

An AST/ALT ratio between 1 and 2 is typically characteristic of which origin?

a. Viral hepatitis origin

b. Non-viral origin (such as Cirrhosis)

c. Acute toxic mushroom poisoning

d. Alcoholic hepatitis

B

An AST/ALT ratio greater than 2 is strongly suggestive of which condition?

a. Acute viral hepatitis A

b. Alcoholic hepatitis or hepatocellular carcinoma

c. Obstructive biliary stones

d. Normal healthy adult liver

B

An AST/ALT ratio less than 1 is typically associated with which origin?

a. Alcoholic liver disease

b. Viral origin (such as Viral hepatitis A, B, C, D, E, G)

c. Biliary tract carcinoma

d. Acetaminophen overdose

C

How long is ALT stable in serum kept at 4°C?

a. 24 hours

b. 2 days

c. 3 to 4 days

d. 14 days

C

In the enzymatic methodology for ALT, which auxiliary enzyme is added to convert pyruvate and NADH to lactate and NAD+?

a. Malate dehydrogenase

b. Glutamate dehydrogenase

c. Lactate dehydrogenase

d. Creatine kinase

C

Which of the following describes the effect of hemolysis on ALT testing according to the text guidelines?

a. Hemolysis dramatically invalidates ALT and should never be accepted.

b. Hemolysis increases ALT by exactly 50%.

c. ALT is relatively unaffected by hemolysis, but hemolyzed samples should still not be accepted.

d. Hemolysis activates ALT enzyme kinetics.

C

Which enzyme requires pyridoxal phosphate as a coenzyme and transfers an amino group between aspartate and alpha-keto acids?

a. Alanine aminotransferase

b. Alkaline phosphatase

c. Aspartate aminotransferase

d. Gamma-glutamyl transferase

C

Which of the following enzymes features both a cytoplasmic and a mitochondrial isoenzyme fraction?

a. ALT

b. Amylase

c. AST

d. Lipase

C

What color developer is utilized in the Reitman-Frankel colorimetric method for transaminases?

a. Sodium hydroxide alone

b. Picric acid and sodium carbonate

c. 2,4-Dinitrophenylhydrazone (2,4-DNPH)

d. Bromphenol blue

C

What color intensifier is used in the Reitman-Frankel method after adding the color developer?

a. 1.0 N Hydrochloric acid

b. Glacial acetic acid

c. 0.4 N Sodium hydroxide

d. Concentrated sulfuric acid

C

What wavelength is typically utilized to measure the colored complex formed in the Reitman-Frankel method?

a. 340 nm

b. 405 nm

c. 505 nm

d. 620 nm

C

What is the reference method recommended for the measurement of aminotransferases?

a. Colorimetric Reitman-Frankel

b. Diazonium salt coupling

c. Enzymatic rate (kinetic) method

d. Manual microdiffusion

C

Which organ contains the absolute highest concentration of Alanine Aminotransferase (ALT)?

a. Heart

b. Skeletal muscle

c. Liver

d. Kidney cortex

C

What is the primary tissue distribution pattern of Aspartate Aminotransferase (AST)?

a. Exclusively cardiac tissue

b. Exclusively hepatic tissue

c. Widely distributed, highest in cardiac tissue, liver, and skeletal muscle

d. Restricted to smooth muscle and red blood cells

C

Which of the following conditions produces a moderate (3 to 5 times normal) elevation of AST?

a. Acute hepatocellular damage

b. Massive shock and circulatory collapse

c. Biliary tract obstruction

d. Severe acute pancreatitis

C

Which of the following is categorized as a liver enzyme used to evaluate liver injury and differentiate functional versus mechanical disease?

a. Blood urea nitrogen

b. Serum creatinine

c. Aminotransferases

d. Uric acid oxidase

C

What is the definition of an enzyme-substrate complex as shown in catalytic pathway models?

a. The permanent covalent bond formed between enzyme and product

b. The denatured state of a protein at high temperatures

c. The temporary union formed when substrate molecules bind to the enzyme's active site

d. The allosteric inhibitor locked onto a regulatory subunit

C

Which of the following best describes the structural outcome after an enzyme catalyzes a reaction?

a. The enzyme is permanently consumed and destroyed.

b. The enzyme splits into two smaller polypeptide chains.

c. The enzyme is released unchanged to catalyze another reaction.

d. The enzyme converts entirely into substrate molecules.

C

What type of factor is a nonprotein helper or ion required for optimal enzyme activity?

a. A substrate analog

b. A coenzyme inhibitor

c. A cofactor

d. A denaturing agent

C

What is the effect of extremely high temperatures (above 40°C-50°C) on most enzymes?

a. They react at maximum perpetual velocity without stopping.

b. They freeze into inactive crystalline structures.

c. They undergo heat denaturation, losing their active site structure.

d. They spontaneously mutate into different enzyme classes.

C

Which of the following describes how low temperatures affect enzyme activity?

a. They permanently destroy the enzyme peptide bonds.

b. They instantly convert enzymes into cofactors.

c. They slow activity down but can preserve enzymes if denaturation is avoided.

d. They accelerate reaction rates beyond zero-order kinetics.

C

Which of the following statements regarding the stability and storage of enzyme samples is correct?

a. Samples should be repeatedly frozen and thawed daily to maintain activation.

b. Samples must be stored at room temperature indefinitely without refrigeration.

c. Samples are stored cold but should not be repeatedly frozen and thawed.

d. Samples should be stored in strong acid solutions to prevent bacterial growth.

C

What reaction step follows the formation of oxaloacetate and glutamate in the Karmen method for AST?

a. Addition of urease to split urea into ammonia

b. Addition of uricase to form allantoin

c. Addition of malate dehydrogenase and NADH to convert oxaloacetate to malate

d. Addition of alkaline picrate to form a red-orange tautomer

C

Which liver enzyme group includes Alkaline Phosphatase among others?

a. Aminotransferases

b. Phosphatases

c. Carboxylesterases

d. Dehydrogenases

C

What is the role of alanine aminotransferase in clinical management besides diagnosing hepatic disorders?

a. It monitors the progression of bone fractures.

b. It tracks the severity of acute myocardial infarctions.

c. It monitors the course of liver treatment and the effects of drug therapy.

d. It evaluates glomerular filtration rate adequacy.

C

Which of the following conditions is classified under moderate elevations of AST?

a. Viral hepatitis with massive necrosis

b. Severe skeletal muscle crush injury

c. Congestive heart failure

d. Normal physiological pregnancy

C

What happens to the reaction rate when enzyme concentration is in excess and substrate concentration is continuously increased?.

a. The rate drops to zero immediately.

b. The rate remains constant at zero-order kinetics regardless of further substrate additions.

c. The rate accelerates exponentially forever.

d. The enzyme precipitates out of solution.

C

Which description characterizes transferases among enzyme classifications?

a. They split water molecules across peptide bonds.

b. They catalyze oxidation-reduction between two cofactors.

c. They catalyze the transfer of a group other than hydrogen from one substrate to another.

d. They form cyclic compounds by eliminating phosphoric acid.

D

Which of the following best defines an enzyme?

a. An inorganic mineral salt that precipitates proteins in serum.

b. A non-nitrogenous lipid molecule that stores cellular energy.

c. A synthetic chemical compound used to lower laboratory reaction temperatures.

d. A specific protein that catalyzes biochemical reactions essential to physiologic functions.

D

What is the relationship between enzyme concentration and reaction rate when substrate is present in excess?

a. The reaction rate is inversely proportional to enzyme concentration.

b. The reaction rate is completely independent of enzyme concentration.

c. The reaction rate fluctuates randomly regardless of enzyme presence.

d. The reaction rate is directly proportional to the amount of enzyme present.

D

How do extreme deviations in pH affect enzymatic reactions?

a. They enhance the binding affinity of allosteric activators.

b. They convert enzymes into stable inorganic cofactors.

c. They cause zero-order kinetics to persist indefinitely.

d. They can alter ionization, denature proteins, or change active site structure.

D

Which of the following enzymes is explicitly listed under liver enzymes in the text?

a. Creatine kinase MB

b. Amylase and lipase

c. Glucose-6-phosphate dehydrogenase

d. Gamma glutamyl transferase

D

Which clinical condition is associated with a slight elevation of AST (up to 3 times normal)?

a. Acute myocardial infarction

b. Severe circulatory collapse

c. Acute viral hepatitis peak

d. Cerebrovascular acciden

D

Which of the following parameters is evaluated using AST determination?

a. Glomerular filtration rate exclusively

b. Nutritional nitrogen balance

c. Exocrine pancreatic function

d. Evaluation of myocardial infarction, hepatocellular disorders, and skeletal muscle involvement

D

What specific change occurs in the Karmen method spectrophotometric reading as the reaction proceeds?

a. Increase of absorbance at 505 nm due to blue color formation

b. Constant absorbance with zero fluctuation

c. Rapid turbidity development measured at 620 nm

d. Measurement of the loss of absorbance at 340 nm due to NADH oxidation

D

What are the end products resulting from the transamination reaction of ALT?

a. Oxaloacetate and glutamate

b. Malate and NAD+

c. Aspartate and alpha-ketoglutarate

d. Glutamate and pyruvate

D

Which statement is true regarding ALT levels in blood banking and screening?.

a. ALT is useless for screening blood products.

b. ALT levels are exclusively elevated in cardiac muscle disease.

c. ALT screening is replaced entirely by urea nitrogen testing.

d. ALT measurement is used to screen blood levels and detect post-transfusion hepatitis.

D

Which of the following enzyme classes is characterized by catalyzing the removal of groups without hydrolysis, leaving double bonds?

a. Hydrolases

b. Transferases

c. Ligases

d. Lyases

D

What is the functional role of the active site on an enzyme molecule?

a. It binds allosteric inhibitors to shut down transcription.

b. It stores excess vitamins and organic coenzymes.

c. It serves as the structural anchor for cell membrane attachment.

d. It is the specific region where the substrate interacts with amino acid residues.

D

Which of the following describes the mechanism of allosteric inhibition?

a. Substrate binds tightly to the active site and prevents enzyme turnover.

b. An activator molecule permanently destroys the enzyme's primary structure.

c. Temperature increases cause the enzyme to refold into an active conformation.

d. A regulator molecule binds to the allosteric site, altering the active site so the substrate

D

Which of the following is true regarding cofactors in enzymatic assays?

a. They are omitted from assays to keep reaction rates slow.

b. They are consumed permanently during the first reaction step.

c. They are added in limiting amounts to control reaction velocity.

d. They are provided in excess so the reaction rate is not limited by their availability.

D

Which condition is listed as causing a pronounced elevation of AST (5 times normal)?

a. Mild muscular dystrophy

b. Uncomplicated pulmonary infarction

c. Stable chronic cirrhosis

d. Infectious mononucleosis

D

Which of the following is a potential cause of slight AST elevation?

a. Acute hepatocellular necrosis

b. Severe acute pancreatitis

c. Major myocardial infarction

d. Pulmonary infarction

D

What is the primary reason why hemolysis must be avoided in AST collections?

a. Red cells consume all the available substrate.

b. Red cells release color-quenching lipids.

c. Hemoglobin precipitates the dinitrophenylhydrazone dye.

d. Red blood cells contain high levels of AST, causing falsely elevated serum results.

D

What is a key characteristic of the Reitman-Frankel method for AST and ALT?

a. It measures ultraviolet absorbance at 340 nm continuously.

b. It is an electrochemical method using ion-selective electrodes.

c. It relies on isotope dilution mass spectrometry.

d. It is a colorimetric method measuring a colored complex at 505 nm using a dinitrophenylhydrazone reage

D

Which enzyme test is noted for being a more sensitive and specific screening marker for occupational toxic exposure?

a. Aspartate aminotransferase

b. Alkaline phosphatase

c. Lactate dehydrogenase

d. Alanine aminotransferase

D

What does an AST/ALT ratio greater than 2 typically indicate in clinical evaluation?

a. Acute viral hepatitis infection

b. Normal liver function

c. Obstructive biliary duct stones

d. Alcoholic hepatitis or hepatocellular carcinoma

D

Which of the following enzymes belongs to the aminotransferase group?

a. Amylase

b. Acid phosphatase

c. Creatine kinase

d. Alanine aminotransferase

D

Which term describes the biological catalyst that speeds up a chemical reaction without being consumed?

a. Substrate

b. Cofactor

c. Coenzyme

d. Enzyme

D

What happens during the first-order kinetics phase when substrate concentration is low?

a. Reaction rate is independent of substrate concentration.

b. Reaction rate drops immediately to zero.

c. Enzyme molecules become completely saturated.

d. Reaction rate increases as substrate concentration increases.

D

Which of the following accurately describes the effect of organic coenzymes like NAD?

a. They serve as rigid structural supports for cell walls.

b. They act as irreversible allosteric inhibitors.

c. They precipitate proteins out of solution during deproteinization.

d. They may act as secondary substrates or prosthetic groups.

D

Which pathological condition is associated with moderate elevations of AST?

a. Massive acute liver necrosis

b. Severe circulatory shock

c. Acute pancreatitis

d. Cardiac arrhythmias

D

Which of the following is a characteristic feature of the enzyme ALT?

a. It is primarily localized in cardiac muscle tissue.

b. It requires malate dehydrogenase as a primary coenzyme.

c. It catalyzes the transfer of amino groups from aspartate.

d. It catalyzes the transfer of an amino acid group from alanine to alpha-ketoglutarate.