The PCR technique requires a DNA polymerase from an organism that can endure high heat, such as Thermus aquaticus. What step of the protocol makes the heat-stability most necessary?

Question

A.  Synthesis
B.  Primer annealing
C.  Denaturation
D.  Antibody binding

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?
 
Gather Content
· What do you already know about the PCR technique?

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
 
Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  Denaturation

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the PCR technique.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.
· What key words does the question contain and what do they mean?
        o The PCR technique is a method for amplifying DNA.
        o DNA polymerase is the enzyme that synthesizes DNA.
        o Heat-stability means that the protein can withstand high temperatures.
 
Gather Content
· What do you already know about the PCR technique?
        o PCR is a method for amplifying DNA from a starting template.
        o It has three steps that are repeated in multiple rounds: Denaturation, Annealing of primer, and Synthesis.
        o Each of these steps takes place at a different optimum temperature.

  Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o Does antibody binding require the enzyme to be heat-stabile? No – there is no antibody binding in the PCR technique.
        o Does the Synthesis step require the enzyme to be heat-stabile? No. Synthesis uses the enzyme, but it takes place at 72°C.
        o Does the Primer Annealing step require the enzyme to be heat-stabile? No. Annealing takes place at around 50-60°C.
 
Choose Answer · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Does the Denaturation step require the enzyme to be heat-stabile? Yes! Denaturation takes place at 95°C, which is hot enough to quickly destroy normal enzymes.

  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked why PCR requires a heat-stable polymerase.
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that the denaturation step has the highest temperature?