Welcome to Part 50 of the ASCP MLS Exam Practice Series, focusing on Nucleic Acids and Molecular Diagnostics. This section explores the molecular foundation of life — DNA and RNA — and their essential role in genetic inheritance, protein synthesis, and disease diagnosis. Modern molecular diagnostic techniques have revolutionized clinical testing, allowing precise detection of infectious diseases, genetic disorders, and cancers at the DNA level.
📘 Key Topics Covered
- Structure and function of nucleic acids (DNA & RNA)
- Nucleotide composition and base pairing rules
- DNA replication, transcription, and translation
- Genetic code and mutations
- Molecular diagnostic principles and workflow
- PCR (Polymerase Chain Reaction) and its variants (RT-PCR, qPCR)
- Hybridization techniques (Southern, Northern, Western blot)
- DNA sequencing and electrophoresis
- Clinical applications in infectious disease, oncology, and genetics
🧠 Learning Objectives
By the end of this part, you should be able to:
- Describe the structure and function of DNA and RNA.
- Explain the key molecular processes of replication, transcription, and translation.
- Identify major molecular diagnostic techniques and their applications.
- Recognize the importance of nucleic acid testing in clinical laboratories.
60 MCQs (3941-4000):
- A condition in which erythrocyte protoporphyrin is increased is:
a) Acute intermittent porphyria
b) Iron deficiency anemia
c) Porphyria cutanea tarda
d) Acute porphyric attack - The definitive diagnosis for hereditary coproporphyria (HCP) is a marked increase in:
a) Urine δ-aminolevulinic acid (ALA)
b) Urine porphobilinogen (PBG)
c) Fecal coproporphyrin III
d) Erythrocyte protoporphyrin - Which of the following enzymes in the heme biosynthesis pathway is inhibited by lead?
a) δ-Aminolevulinate dehydratase
b) Porphobilinogen synthase
c) Uroporphyrinogen synthase
d) Bilirubin synthetase - A 9-month-old boy of Ashkenazi Jewish descent presents with a loss of motor skills and seizures. Laboratory analysis reveals an accumulation of GM2-ganglioside in neurons and a deficiency of hexosaminidase A. These findings are most consistent with:
a) Niemann-Pick disease
b) Tay-Sachs disease
c) Phenylketonuria
d) Hurler syndrome - The initial analysis for a urine sample received for “porphyrins” without further specification should include:
a) Porphyrin screen and quantitative total porphyrin
b) Quantitative total porphyrin and porphobilinogen screen
c) Porphyrin and porphobilinogen screen
d) Porphobilinogen screen and ion-exchange analysis - The presence of basophilic stippling in RBCs on a peripheral smear and an elevated erythrocyte protoporphyrin level would lead to suspicion of poisoning by which heavy metal?
a) Arsenic
b) Iron
c) Mercury
d) Lead - In the context of heme synthesis, ALA (aminolevulinic acid) is produced by the enzyme:
a) ALA dehydratase
b) ALA synthase
c) Porphobilinogen deaminase
d) Ferrochelatase - The screening test for congenital hypothyroidism in newborns is primarily based on the level of:
a) Free T4
b) Thyroid-binding globulin
c) Thyroid-releasing hormone
d) Total thyroxine (T4) or TSH - The laboratory test most useful for monitoring the course of a patient with testicular cancer is:
a) Carcinoembryonic antigen (CEA)
b) Alpha-fetoprotein (AFP)
c) Prolactin
d) Testosterone - Which of the following statements correctly describes the utility of clinical laboratory assays for tumor markers?
a) Tumor markers are highly specific for screening asymptomatic patients.
b) Tumor markers are useful for tracking the efficacy of cancer treatment.
c) Tumor markers confirm the absence of disease.
d) Tumor markers identify patients at risk for developing cancer. - The method of choice for confirming a positive immunoassay screen for barbiturates in a urine drugs of abuse panel is:
a) Nephelometry
b) Thin-layer chromatography
c) Gas chromatography/mass spectrometry
d) Ultraviolet absorption spectroscopy - The recommended specimen for forensic toxicology to detect drugs of abuse over a longer time period is:
a) Random urine
b) Serum
c) Whole blood
d) Hair follicle - In molecular separation techniques, High-Performance Liquid Chromatography (HPLC) involves:
a) Separation in a gel medium under an electric field.
b) Separation in a column with a liquid mobile phase under high pressure.
c) Vaporization of the sample with a carrier gas.
d) Ionization and separation based on mass-to-charge ratio. - The tumor marker CA 125 is most strongly associated with which type of carcinoma?
a) Breast
b) Colon
c) Lung
d) Ovarian and endometrial - A “Hook effect” in a tumor marker immunoassay, resulting in a falsely low value, can be suspected when:
a) The patient is an African American male.
b) A very high level of the antigen is present.
c) The specimen was drawn after a digital rectal exam.
d) The patient is a smoker. - The principle of the test for occult blood in feces depends on the:
a) Coagulase ability of blood
b) Oxidative power of atmospheric oxygen
c) Hydrogen peroxide in hemoglobin
d) Peroxidase-like activity of hemoglobin - The process by which a drug is metabolized can be studied using a technique where separation occurs in a column with a liquid pumped under high pressure. This describes:
a) High-pressure focused electrophoresis
b) High-performance liquid chromatography
c) Gas liquid chromatography
d) Mass spectrophotometry-mass spectrometry - The metabolite 11-nor-tetrahydrocannabinol-9-COOH is detected in the urine following the use of:
a) Methamphetamine
b) Cocaine
c) Benzodiazepine
d) Marijuana - A patient with Wilson’s disease would be expected to have which of the following laboratory findings?
a) Increased serum copper and decreased urine copper
b) Decreased serum copper and increased urine copper
c) Increased serum ceruloplasmin and increased urine copper
d) Decreased serum copper and decreased urine copper - The definitive diagnosis of an active myocardial infarction is best supported by an elevation of which of the following?
a) Total Creatine Kinase (CK)
b) CK-MB isoenzyme
c) Lactate Dehydrogenase (LD)
d) Troponin I or T - The primary urinary metabolite measured to assess epinephrine and norepinephrine production is:
a) Dopamine
b) Dihydroxyphenylalanine (DOPA)
c) Homovanillic acid (HVA)
d) Vanillylmandelic acid (VMA) - 24-hour homovanillic acid (HVA) is a useful test to aid in the diagnosis of:
a) Cushing disease
b) Malignant neuroblastoma
c) Conn disease
d) Graves disease - The most common form of congenital adrenal hyperplasia (21-hydroxylase deficiency) is detected by elevated plasma levels of:
a) Cortisol
b) Aldosterone
c) 17-OH-progesterone
d) 11-deoxycortisol - In the context of therapeutic drug monitoring, the “steady state” of a drug is best defined as when:
a) The drug is completely absorbed from the gut.
b) The rate of drug administration equals the rate of elimination.
c) The drug is fully protein-bound.
d) The maximum tissue concentration is achieved. - The screening test for fetal neural tube defects involves measuring which substance in maternal serum or amniotic fluid?
a) Estriol
b) Human Chorionic Gonadotropin (hCG)
c) Alpha-fetoprotein (AFP)
d) Progesterone - A patient’s serum is tested for a tumor marker using a chemiluminescent EIA. The reaction is quantified by measuring the:
a) Absorption of light by the product.
b) Amount of light produced by the reaction.
c) Change in electrical potential.
d) Scatter of light by microparticles. - In a patient with suspected hemolytic anemia, which of the following laboratory results would be expected?
a) Increased haptoglobin
b) Decreased haptoglobin
c) Increased serum iron
d) Decreased unconjugated bilirubin - The different forms of hemoglobin (e.g., HbA, HbS, HbC) can be separated and identified based on their charge using:
a) Immunoassay
b) Electrophoresis
c) Mass Spectrometry
d) Ion-Selective Electrode - A patient with a microcytic, hypochromic anemia has a low serum iron and low total iron-binding capacity (TIBC). This pattern is most consistent with:
a) Iron deficiency anemia
b) Anemia of chronic disease
c) Hemochromatosis
d) Sideroblastic anemia - The laboratory investigation of a comatose patient with suspected methanol poisoning would most likely reveal:
a) A low osmolal gap and a low anion gap.
b) A high osmolal gap and a high anion gap.
c) A low osmolal gap and a high anion gap.
d) A high osmolal gap and a low anion gap. - The basic structural unit of DNA is called a:
a) Nucleoside
b) Nucleotide
c) Amino acid
d) Ribosome - A nucleotide is composed of:
a) Sugar and phosphate only
b) Sugar, phosphate, and nitrogen base
c) Phosphate and base only
d) Base and amino group - The sugar present in DNA is:
a) Ribose
b) Deoxyribose
c) Fructose
d) Glucose - The complementary base of adenine in DNA is:
a) Thymine
b) Cytosine
c) Uracil
d) Guanine - The complementary base of adenine in RNA is:
a) Thymine
b) Cytosine
c) Uracil
d) Guanine - The backbone of DNA is formed by:
a) Base pair hydrogen bonds
b) Phosphate-sugar linkages
c) Peptide bonds
d) Sulfhydryl groups - DNA replication is described as:
a) Conservative
b) Semiconservative
c) Dispersive
d) Random - The enzyme responsible for unwinding the DNA double helix is:
a) DNA polymerase
b) DNA ligase
c) DNA helicase
d) RNA polymerase - The enzyme that synthesizes RNA using a DNA template is:
a) DNA polymerase
b) RNA polymerase
c) Ligase
d) Primase - In eukaryotes, DNA is located in the:
a) Cytoplasm
b) Ribosome
c) Nucleus
d) Endoplasmic reticulum - The process of RNA synthesis from a DNA template is called:
a) Translation
b) Replication
c) Transcription
d) Transformation - The process of protein synthesis from mRNA is called:
a) Transcription
b) Translation
c) Replication
d) Recombination - The start codon in mRNA is:
a) UAA
b) UAG
c) AUG
d) UGA - The anticodon is located on:
a) mRNA
b) rRNA
c) tRNA
d) DNA - Which type of RNA carries amino acids to the ribosome?
a) mRNA
b) tRNA
c) rRNA
d) snRNA - The genetic code is said to be:
a) Ambiguous
b) Universal and degenerate
c) Random
d) Specific to humans - A mutation that replaces one nucleotide with another is called a:
a) Deletion
b) Insertion
c) Substitution
d) Frameshift - PCR (Polymerase Chain Reaction) is used to:
a) Sequence amino acids
b) Amplify DNA
c) Transcribe RNA
d) Measure enzyme activity - The enzyme responsible for DNA synthesis in PCR is:
a) RNA polymerase
b) Taq polymerase
c) DNA ligase
d) Helicase - In PCR, the process of separating DNA strands is called:
a) Annealing
b) Denaturation
c) Extension
d) Amplification - The temperature range for DNA denaturation in PCR is approximately:
a) 30–40°C
b) 50–60°C
c) 70–80°C
d) 90–95°C - Agarose gel electrophoresis separates nucleic acids based on:
a) Shape
b) Size and charge
c) Sequence
d) Color - The Southern blot technique is used to detect:
a) RNA
b) DNA
c) Proteins
d) Antibodies - The Northern blot technique is used for:
a) DNA detection
b) RNA detection
c) Protein detection
d) Enzyme activity - The Western blot technique identifies:
a) DNA
b) RNA
c) Proteins
d) Lipids - The method used to determine the sequence of nucleotides in DNA is:
a) PCR
b) ELISA
c) Sanger sequencing
d) Immunofluorescence - The main advantage of real-time PCR (qPCR) over conventional PCR is:
a) Faster gel electrophoresis
b) Quantitative measurement of DNA amplification
c) Reduced sample requirement
d) Color detection only - Which of the following is used to separate DNA fragments by size?
a) Spectrophotometer
b) Electrophoresis
c) Chromatography
d) Centrifuge - The term “amplicon” refers to:
a) A restriction enzyme
b) A piece of DNA amplified by PCR
c) A DNA polymerase inhibitor
d) A transcription factor - Which biosafety practice is most important when working with molecular samples?
a) Use of dry heat sterilization
b) Avoidance of UV exposure
c) Preventing contamination with gloves and filtered tips
d) Running PCR near open flames
📌 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) Iron deficiency anemia
- c) Fecal coproporphyrin III
- a) δ-Aminolevulinate dehydratase
- b) Tay-Sachs disease
- c) Porphyrin and porphobilinogen screen
- d) Lead
- b) ALA synthase
- d) Total thyroxine (T4) or TSH
- b) Alpha-fetoprotein (AFP)
- b) Tumor markers are useful for tracking the efficacy of cancer treatment.
- c) Gas chromatography/mass spectrometry
- d) Hair follicle
- b) Separation in a column with a liquid mobile phase under high pressure.
- d) Ovarian and endometrial
- b) A very high level of the antigen is present.
- d) Peroxidase-like activity of hemoglobin
- b) High-performance liquid chromatography
- d) Marijuana
- b) Decreased serum copper and increased urine copper
- d) Troponin I or T
- d) Vanillylmandelic acid (VMA)
- b) Malignant neuroblastoma
- c) 17-OH-progesterone
- b) The rate of drug administration equals the rate of elimination.
- c) Alpha-fetoprotein (AFP)
- b) Amount of light produced by the reaction.
- b) Decreased haptoglobin
- b) Electrophoresis
- b) Anemia of chronic disease
- b) A high osmolal gap and a high anion gap.
- b) Nucleotide
- b) Sugar, phosphate, and nitrogen base
- b) Deoxyribose
- a) Thymine
- c) Uracil
- b) Phosphate-sugar linkages
- b) Semiconservative
- c) DNA helicase
- b) RNA polymerase
- c) Nucleus
- c) Transcription
- b) Translation\
- c) AUG
- c) tRNA
- b) tRNA
- b) Universal and degenerate
- c) Substitution
- b) Amplify DNA
- b) Taq polymerase
- b) Denaturation
- d) 90–95°C
- b) Size and charge
- b) DNA
- b) RNA detection
- c) Proteins
- c) Sanger sequencing
- b) Quantitative measurement of DNA amplification
- b) Electrophoresis
- b) A piece of DNA amplified by PCR
- c) Preventing contamination with gloves and filtered tips
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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