🧬 Molecular Diagnostics Review for the MedTech Board Exam

What the Molecular Diagnostics course covers

1. Unit 1: Molecular Biology Basics

   The cell, DNA structure and replication, RNA, and how genes become proteins.

   Cells & DNA structure · Replication · RNA & protein

2. Unit 2: Specimens & Nucleic Acid Extraction

   Collecting molecular specimens, isolating DNA and RNA, and checking their quality.

   Molecular specimens · Isolating DNA & RNA · Measuring nucleic acid

3. Unit 3: Amplification

   PCR and its ingredients, real-time and reverse-transcription PCR, and other amplification methods.

   PCR · Real-time & RT-PCR · Other amplification methods

4. Unit 4: Detection & Analysis

   Restriction enzymes, electrophoresis, blotting and hybridization, sequencing and microarrays.

   Restriction enzymes & electrophoresis · Blotting & hybridization · Sequencing & arrays

5. Unit 5: Genetic Disease & Molecular Oncology

   Mutation types, inherited disorders, cancer markers and pharmacogenetics.

   Mutations & inheritance · Inherited disorders · Molecular oncology

6. Unit 6: Infectious Disease & Identity Testing

   Molecular microbiology, viral load, DNA-based identification, parentage and engraftment.

   Molecular infectious disease · DNA identity testing

Sample Molecular Diagnostics board exam questions

A few practice questions from the course, with explanations. Thousands more are in the app.

1. 1. A DNA strand reads 5′-ATGCCG-3′. Its complementary strand, written 5′ to 3′, is:

   1. 5′-TACGGC-3′
   2. 5′-CGGCAT-3′
   3. 5′-GCCGTA-3′
   4. 5′-ATGCCG-3′
   Show answer

   Answer: B. 5′-CGGCAT-3′

   Each base pairs with its partner (A–T, G–C) and the strands run antiparallel. The complement of 5′-ATGCCG-3′ is 3′-TACGGC-5′. Written in the standard 5′→3′ direction, that reads 5′-CGGCAT-3′.

2. 2. A PCR on a patient’s blood fails, but the same test works on a repeat EDTA sample. The first tube was most likely:

   1. Plain red top
   2. Heparin
   3. ACD
   4. EDTA
   Show answer

   Answer: B. Heparin

   Heparin is a highly charged polysaccharide that binds Taq polymerase and inhibits PCR, and it is hard to remove during extraction. EDTA and ACD are the preferred tubes for molecular testing.

3. 3. In real-time PCR, sample A has Ct 22 and sample B has Ct 25 (100% efficiency). Sample A has about how much more starting target?

   1. 3 times more
   2. 25 times more
   3. The same amount
   4. 8 times more
   Show answer

   Answer: D. 8 times more

   With 100% efficiency, the product doubles each cycle. Sample A reaches the threshold 3 cycles earlier, so it started with 2³ = 8 times more target than sample B.

4. 4. A 250-bp PCR product and a 1,200-bp product are run on an agarose gel. Which is true?

   1. Neither moves toward the anode
   2. Both run the same distance
   3. The 1,200-bp band runs farther
   4. The 250-bp band runs farther from the well
   Show answer

   Answer: D. The 250-bp band runs farther from the well

   DNA is negatively charged and moves toward the anode. Smaller fragments slip through the agarose pores more easily, so the 250-bp product travels farther than the 1,200-bp product.

5. 5. A boy has intellectual disability, long face and large ears. Testing shows over 200 CGG repeats in FMR1. The diagnosis is:

   1. Fragile X syndrome (full mutation)
   2. Duchenne muscular dystrophy
   3. Myotonic dystrophy
   4. Huntington disease
   Show answer

   Answer: A. Fragile X syndrome (full mutation)

   Fragile X is caused by expansion of CGG repeats in FMR1 to over 200. The gene becomes methylated and silenced, so the FMRP protein isn’t made, causing intellectual disability, a long face and large ears.

6. 6. An HIV viral load falls from 100,000 copies/mL to 1,000 copies/mL. This is a change of:

   1. 99 log₁₀
   2. 2 log₁₀
   3. 0.5 log₁₀
   4. 1 log₁₀
   Show answer

   Answer: B. 2 log₁₀

   log₁₀(100,000) = 5 and log₁₀(1,000) = 3, so the fall is 2 log₁₀, a 100-fold drop. Viral load changes are reported in logs because they span many orders of magnitude.

7. 7. Two 100-bp DNA fragments: one is 70% GC, the other 30% GC. Which statement is true?

   1. Both melt at the same temperature
   2. GC content does not affect Tm
   3. The 70% GC fragment has a higher melting temperature
   4. The 30% GC fragment has more hydrogen bonds
   Show answer

   Answer: C. The 70% GC fragment has a higher melting temperature

   G–C pairs are held by three hydrogen bonds and stack more strongly than A–T pairs, which have two. A GC-rich fragment needs more heat to separate its strands, so its melting temperature (Tm) is higher.

8. 8. A DNA sample reads A260 = 0.25 and A280 = 0.18 after a 1:20 dilution. The concentration and purity are:

   1. 250 µg/mL; ratio 1.39 — protein contamination
   2. 250 µg/mL; pure
   3. 25 µg/mL; RNA contamination
   4. 12.5 µg/mL; pure
   Show answer

   Answer: A. 250 µg/mL; ratio 1.39 — protein contamination

   Concentration = A260 × 50 µg/mL (for dsDNA) × dilution = 0.25 × 50 × 20 = 250 µg/mL. Purity = A260/A280 = 0.25/0.18 ≈ 1.39. Pure DNA is about 1.8, so a lower ratio means protein contamination.

Practice more Molecular Diagnostics questions

How you review in MedTech Reviewer

• Learning path: short lessons, each followed by questions, with a checkpoint at the end of every unit.
• Spaced repetition: questions you miss come back sooner, so key facts stick for exam day.
• Flashcards and timed quizzes in exam style, with an explanation for every answer.
• Board-readiness score per subject, so you know where to focus.
• Arcade games, PvP battles and Guilds to keep reviewing fun with classmates.

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