Welcome to Part 46 of our ASCP MLS Exam Practice Series, focused on Biochemistry – Fundamentals & Enzymes. This section covers the core principles every medical laboratory scientist must master, including biomolecules, chemical bonds, pH and buffer systems, enzyme kinetics, cofactors, isoenzymes, and their clinical importance. Understanding these fundamentals forms the backbone for interpreting biochemical test results and improving analytical accuracy in the clinical lab.
📘 Key Topics Covered
- Basic principles of biochemistry
- Structure and function of biomolecules (carbohydrates, lipids, proteins, nucleic acids)
- Water, buffers, and pH regulation
- Enzyme classification, kinetics, and mechanisms of action
- Factors influencing enzyme activity (temperature, pH, substrate concentration)
- Cofactors and coenzymes
- Isoenzymes and their diagnostic significance (LDH, CK, ALP, etc.)
- Clinical applications of enzymology in laboratory medicine
🧠 Learning Objectives
By the end of this section, you should be able to:
- Apply biochemistry fundamentals in laboratory interpretation and problem-solving.
- Define key biochemical terms and concepts.
- Explain how enzymes catalyze biochemical reactions.
- Identify clinically significant enzymes used in disease diagnosis.
60 MCQs (3701-3760):
- What is the primary function of serum albumin in the blood?
a) To act as an antibody for immune defense
b) To maintain colloidal osmotic pressure
c) To serve as a cofactor for enzymatic reactions
d) To transport lipids - The protein portion of an enzyme, which is inactive without its cofactor, is called the:
a) Coenzyme
b) Holoenzyme
c) Apoenzyme
d) Proenzyme - In the Lineweaver-Burk plot of an enzyme reaction, the intercept on the x-axis is used to calculate:
a) The Vmax
b) The enzyme concentration
c) The Michaelis-Menten constant (Km)
d) The turnover number - Which of the following enzymes catalyzes the conversion of starch to glucose and maltose?
a) Lipase
b) Lactate Dehydrogenase (LD)
c) Amylase
d) Trypsin - In a competitive inhibition model of enzyme kinetics, what is the effect on the apparent Km and Vmax?
a) Km increases; Vmax remains the same
b) Km decreases; Vmax remains the same
c) Km remains the same; Vmax decreases
d) Both Km and Vmax decrease - The international unit (IU) of enzyme activity is defined as the amount of enzyme that converts how much substrate per minute under standard conditions?
a) 1 mol
b) 1 mmol
c) 1 μmol
d) 1 nmol - Which of the following sets of enzymes are all classified as oxidoreductases?
a) Amylase, Lipase, Trypsin
b) Lactate dehydrogenase, Malate dehydrogenase, Glucose-6-phosphate dehydrogenase
c) Aspartate aminotransferase, Alanine aminotransferase, Creatine kinase
d) Alkaline phosphatase, Acid phosphatase, Gamma-glutamyl transferase - The biuret reaction for total protein quantification depends on the presence of:
a) Free amino groups
b) Tyrosine residues
c) Peptide bonds
d) Tryptophan residues - A patient’s serum shows a markedly elevated level of Creatine Kinase-MB (CK-MB). This is most indicative of damage to which tissue?
a) Liver
b) Skeletal Muscle
c) Myocardium (Heart Muscle)
d) Brain - In the assay of Lactate Dehydrogenase (LD), the product that is directly measured spectrophotometrically is:
a) Pyruvic Acid
b) Lactic Acid
c) NADH
d) ATP - Isoenzyme assays are performed primarily to improve diagnostic:
a) Precision
b) Accuracy
c) Sensitivity
d) Specificity - Which of the following is the Henderson-Hasselbalch equation?
a) pKa = pH + log([acid]/[salt])
b) pKa = pH + log([salt]/[acid])
c) pH = pKa + log([acid]/[salt])
d) pH = pKa + log([salt]/[acid]) - In serum protein electrophoresis at pH 8.6, which protein fraction migrates the fastest toward the anode?
a) Alpha-1 Globulin
b) Albumin
c) Gamma Globulin
d) Beta Globulin - A characteristic “flipped” pattern, where LD1 is greater than LD2, is most consistent with:
a) Viral Hepatitis
b) Myocardial Infarction
c) Pancreatitis
d) Renal Failure - Macroamylasemia is characterized by which of the following laboratory findings?
a) Increased serum amylase and increased urine amylase
b) Normal serum amylase and elevated urine amylase
c) Increased serum amylase and normal urine amylase
d) Decreased serum amylase and decreased urine amylase - What is the most sensitive enzymatic indicator of liver damage due to chronic ethanol intake?
a) Alanine Aminotransferase (ALT)
b) Aspartate Aminotransferase (AST)
c) Alkaline Phosphatase (ALP)
d) Gamma-Glutamyl Transferase (GGT) - The Regan isoenzyme is a variant of alkaline phosphatase that has properties most similar to the isoenzyme from the:
a) Liver
b) Bone
c) Intestine
d) Placenta - In a coupled enzyme assay for Aspartate Aminotransferase (AST), Malate Dehydrogenase is added to catalyze the conversion of:
a) Alpha-ketoglutarate to aspartate
b) Alpha-ketoglutarate to malate
c) Oxaloacetate to malate
d) Aspartate to oxaloacetate - The most heat-labile fraction of alkaline phosphatase is derived from which tissue?
a) Liver
b) Bone
c) Intestine
d) Placenta - Which substrate is considered the most specific for quantifying prostatic acid phosphatase?
a) p-Nitrophenylphosphate
b) Thymolphthalein Monophosphate
c) Beta-Naphthol-Phosphate
d) Beta-Glycerophosphate - A falsely increased LD1 fraction on electrophoresis is most commonly caused by:
a) Liver Disease
b) Specimen Hemolysis
c) An Older Specimen
d) Congestive Heart Failure - The presence of Bence Jones protein in urine is best identified by:
a) Sulfosalicylic Acid Test
b) Urine Reagent Strip
c) Immunofixation Electrophoresis
d) Biuret Reaction - In an enzyme reaction progress curve, a deviation from linearity shortly after initiation is most likely due to:
a) The reaction reaching equilibrium
b) Substrate depletion
c) Enzyme denaturation
d) The presence of an inhibitor - Which of the following amino acids contains a sulfhydryl (-SH) group?
a) Serine
b) Glycine
c) Cysteine
d) Tyrosine - The first step in analyzing a 24-hour urine specimen for quantitative total protein is to:
a) Add an appropriate preservative
b) Screen for albumin using a dipstick
c) Measure the total volume
d) Subculture for bacteria - The calculated creatinine clearance is used to estimate the:
a) Tubular Secretion Rate
b) Renal Blood Flow
c) Glomerular Filtration Rate
d) Urine Concentration Ability - In the Jaffe reaction, creatinine reacts with which reagent to form an orange-red complex?
a) Diazotized Sulfanilic Acid
b) Alkaline Picrate
c) Paradimethylaminobenzaldehyde
d) Cupric Sulfate - The main metabolic end product of purine metabolism in humans is:
a) Urea
b) Uric Acid
c) Allantoin
d) Ammonia - C-reactive protein (CRP) is a classic example of:
a) A transport protein
b) A coagulation factor
c) An acute-phase reactant protein
d) An enzyme inhibitor - The troponin complex, a key marker for myocardial injury, consists of which three subunits?
a) Troponin C, Troponin I, and Troponin T
b) Troponin A, Actin, and Myosin
c) Troponin I, Tropomyosin, and Calcium
d) Troponin T, Myoglobin, and Actin - Which of the following is the basic structural unit of proteins?
a) Monosaccharide
b) Fatty acid
c) Amino acid
d) Nucleotide - Which type of bond connects amino acids in a protein chain?
a) Hydrogen bond
b) Peptide bond
c) Ionic bond
d) Disulfide bond - The three-dimensional structure of a protein is primarily stabilized by:
a) Peptide bonds only
b) Hydrogen bonds, ionic interactions, and hydrophobic forces
c) Covalent bonding with water
d) Only disulfide bridges - Enzymes act as catalysts because they:
a) Increase the activation energy
b) Decrease the activation energy
c) Alter the equilibrium constant
d) Increase substrate concentration - Which of the following best describes a coenzyme?
a) A nonprotein part of an enzyme that is permanently bound
b) A small organic molecule required for enzyme activity
c) An enzyme inhibitor
d) A metallic activator - The enzyme that catalyzes oxidation-reduction reactions belongs to which class?
a) Transferases
b) Oxidoreductases
c) Hydrolases
d) Isomerases - Which enzyme class transfers phosphate groups between molecules?
a) Ligases
b) Transferases
c) Hydrolases
d) Lyases - The substrate concentration at which an enzyme works at half its maximum velocity is called:
a) Vmax
b) Km
c) Kcat
d) Ka - An enzyme that catalyzes the same reaction but differs in amino acid sequence from another enzyme is called:
a) Apoenzyme
b) Isoenzyme
c) Coenzyme
d) Allosteric enzyme - Which factor does not affect enzyme activity?
a) Temperature
b) pH
c) Light intensity
d) Substrate concentration - The optimal pH for most human enzymes is around:
a) 2
b) 5
c) 7
d) 10 - Which of the following acts as a competitive inhibitor?
a) A molecule resembling the substrate
b) A molecule binding to an allosteric site
c) A molecule that denatures the enzyme
d) A product of a distant reaction - In an enzyme-catalyzed reaction, the enzyme binds the substrate at the:
a) Regulatory site
b) Active site
c) Secondary structure
d) Allosteric center - The enzyme activity unit (U) is defined as:
a) Amount converting 1 mmol substrate per hour
b) Amount converting 1 µmol substrate per minute
c) 1 mg enzyme per reaction
d) 1 mol product per second - The enzyme catalase decomposes:
a) Urea
b) Hydrogen peroxide
c) Glucose
d) Ammonia - Which metal ion is essential for carbonic anhydrase activity?
a) Iron
b) Zinc
c) Copper
d) Magnesium - A holoenzyme consists of:
a) Apoenzyme only
b) Coenzyme only
c) Apoenzyme plus cofactor
d) Substrate and product - The enzyme that converts starch to maltose is:
a) Amylase
b) Lipase
c) Protease
d) Lactase - Which statement best describes an isoenzyme?
a) It has identical amino acid sequences but different cofactors
b) It catalyzes different reactions
c) It catalyzes the same reaction but differs structurally
d) It is inactive at all temperatures - The “lock and key” model of enzyme activity illustrates:
a) Enzyme denaturation
b) Specificity between enzyme and substrate
c) Noncompetitive inhibition
d) Enzyme activation by cofactors - The induced-fit model differs from the lock-and-key model because:
a) The enzyme changes shape upon substrate binding
b) The enzyme and substrate are rigid structures
c) No product is formed
d) The substrate changes the enzyme permanently - Which of the following is an example of an allosteric enzyme?
a) Creatine kinase
b) Aspartate transcarbamoylase
c) Amylase
d) Lipase - Denaturation of an enzyme results in:
a) Increased catalytic efficiency
b) Loss of its three-dimensional structure and activity
c) Permanent activation
d) No change in active site conformation - Which vitamin functions as a coenzyme in oxidation-reduction reactions?
a) Vitamin C
b) Vitamin D
c) Vitamin A
d) Vitamin K - Enzyme activity is commonly measured by monitoring:
a) Product disappearance
b) Enzyme color
c) Substrate consumption or product formation
d) Change in enzyme mass - The enzyme lactate dehydrogenase (LDH) requires which coenzyme?
a) NAD⁺
b) ATP
c) FADH₂
d) CoA - The reaction velocity of an enzyme becomes independent of substrate concentration when:
a) Substrate is very low
b) Enzyme is in excess
c) Enzyme is saturated
d) Reaction temperature is low - The primary buffer system of human blood is:
a) Phosphate buffer
b) Protein buffer
c) Bicarbonate–carbonic acid buffer
d) Ammonium buffer - Which statement about enzymes is true?
a) Enzymes are consumed during reactions
b) Enzymes alter reaction equilibrium
c) Enzymes accelerate reactions without being used up
d) Enzymes increase activation energy - An enzyme that joins two molecules using ATP energy is classified as:
a) Hydrolase
b) Ligase
c) Transferase
d) Lyase
📌 How to Use This Practice Set
- Answer each question before checking the key.
- Focus on why the correct answer is right and the others are wrong.
- Use this set as timed practice to simulate the real exam environment.
Answer Key
Answer Key:
- b) To maintain colloidal osmotic pressure
- c) Apoenzyme
- c) The Michaelis-Menten constant (Km)
- c) Amylase
- a) Km increases; Vmax remains the same
- c) 1 μmol
- b) Lactate dehydrogenase, Malate dehydrogenase, Glucose-6-phosphate dehydrogenase
- c) Peptide bonds
- c) Myocardium (Heart Muscle)
- c) NADH
- d) Specificity
- d) pH = pKa + log([salt]/[acid])
- b) Albumin
- b) Myocardial Infarction
- c) Increased serum amylase and normal urine amylase
- d) Gamma-Glutamyl Transferase (GGT)
- d) Placenta
- c) Oxaloacetate to malate
- b) Bone
- b) Thymolphthalein Monophosphate
- b) Specimen Hemolysis
- c) Immunofixation Electrophoresis
- b) Substrate depletion
- c) Cysteine
- c) Measure the total volume
- c) Glomerular Filtration Rate
- b) Alkaline Picrate
- b) Uric Acid
- c) An acute-phase reactant protein
- a) Troponin C, Troponin I, and Troponin T
- c) Amino acid
- b) Peptide bond
- b) Hydrogen bonds, ionic interactions, and hydrophobic forces
- b) Decrease the activation energy
- b) A small organic molecule required for enzyme activity
- b) Oxidoreductases
- b) Transferases
- b) Km
- b) Isoenzyme
- c) Light intensity
- c) 7
- c) A molecule that denatures the enzyme
- b) Active site
- b) Amount converting 1 µmol substrate per minute
- b) Hydrogen peroxide
- b) Zinc
- c) Apoenzyme plus cofactor
- a) Amylase
- c) It catalyzes the same reaction but differs structurally
- b) Specificity between enzyme and substrate
- a) The enzyme changes shape upon substrate binding
- b) Aspartate transcarbamoylase
- b) Loss of its three-dimensional structure and activity
- a) Vitamin C
- c) Substrate consumption or product formation
- a) NAD⁺
- c) Enzyme is saturated
- c) Bicarbonate–carbonic acid buffer
- c) Enzymes accelerate reactions without being used up
- b) Ligase
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
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