John Hay
John Hay Biomedical
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Genetics of Disease (Medical Interventions)
Unit 2: Unit 2.1 Testing Methods (PCR/Gel/Microarray)MI 2.1Biotechnology Research and Experiments

Diagram A PCR

Diagram a PCR cycle: order the three steps (denature, anneal, extend) and label what happens at each temperature.

Builds on (2 levels back)inferred · high confidence
  • Control logic: Molecular results need positive and negative controls.
  • Signal interpretation: Bands, colors, curves, and E-values must be compared to a rule.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Diagram a PCR by reading each labeled step and saying what it does: denature separates strands, anneal binds primers, extend copies DNA.

Step 1: Read the step labels
Use the diagram: each box names a step and its temperature. Denature is about 95 C, anneal is about 55 C, and extend is about 72 C.
PCR cycle with three labeled temperature steps
Step 2: Find the strand-separating step
The hottest step, denature (about 95 C), is the one that pulls the double-stranded DNA apart into two single strands.
Step 3: Name the limit
The diagram shows the steps and what each does, but it does not tell you how many cycles a real test needs or whether the target DNA was present.
Practice

Use the PCR diagram. Which step separates the two DNA strands?

Reviewed
PCR cycle with three labeled temperature steps
  1. A.Denature
  2. B.Anneal
  3. C.Extend
  4. D.None of them separate strands
Show the worked solution ▾

Answer: A. Denature

  1. Step 1: Read the box labels: The denature box (about 95 C) says the two strands come apart.
  2. Step 2: Match the job: Anneal binds primers and extend copies DNA; only denature splits the strands.

Why it's right: Denature, the hottest step (about 95 C), separates the double-stranded DNA into two single strands.

Why the others miss:
  • B: Anneal (about 55 C) is where primers bind, not where strands separate.
  • C: Extend (about 72 C) is where the polymerase copies DNA, not where strands separate.
  • D: Denature separates the strands, so one step does.

Aligned to Biotechnology Research and Experiments · reading level ~grade 9

Where you'd see this
  • A lab traces the PCR diagram and points to the 95 C denature step as the moment the strands split.
Careers that use this
Molecular Technologist: Reads PCR step labels to know which temperature splits the strands versus copies them.
Video library
Watch: Diagram A PCR
PCR (Polymerase Chain Reaction)
Amoeba Sisters · ~7 min
Guided notes

Fill these in as you work through the lesson.

Big idea: A PCR cycle has three steps in order: denature (about 95 C, split the strands), anneal (about 55 C, primers bind), and extend (about 72 C, polymerase copies DNA).
Key terms: write the meaning
  • Denature (about 95 C, separates strands):  
  • Anneal (about 55 C, primers bind):  
  • Extend (about 72 C, polymerase copies):  
  • Primer (short DNA piece that binds first):  
The rule

In one PCR cycle the order is denature, then  , then  ; the   step is the one that separates the two DNA strands.

Check yourself
  1. Which step separates the strands? 
  2. What is the correct order of the three steps? 
  3. What does the polymerase do, and at which step? 
Work one example

Using the diagram, put the three steps in order and write what each one does to the DNA.