GRE Subject Test: Biology : Understanding Cloning and PCR
Study concepts, example questions & explanations for GRE Subject Test: Biology
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Example Questions
Example Question #11 : Understanding Cloning And Pcr
Which step of PCR thermocycling is meant to allow the DNA polymerase to add nucleotides to the complementary strand?
Extension
Annealing
Hot start
Final hold
Denaturation
Extension
The extension or elongation step of thermocycling is used to allow the DNA polymerase to create the new complementary strand to the template DNA strand. Temperature depends on the DNA polymerase being used but generally ranges from 75-80°C.
Denaturation is done at a high temperature generally around 94-98°C to break apart the hydrogen bonds of double stranded DNA into single strands.
Annealing is the second step of thermocycling completed at 50-65°C. This step must be done at a temperature low enough allowing primers to attach to the single strand, but high enough that hybridization is specific.
Prior to the stages of thermocycling there is a often a hot start step to activate the polymerase if necessary. Following the stages of thermocycling is a final extension stage and final hold stage.
Example Question #451 : Gre Subject Test: Biology
The goal of a PCR reaction is to __________.
determine a DNA profile
separate DNA based on fragment size
produce copies of a targeted DNA region(s)
sequence a DNA template region(s)
None of these answers
produce copies of a targeted DNA region(s)
The purpose of a PCR reaction is to amplify a targeted DNA region into millions of copies. PCR helps to yield several copies of DNA in a few hours allowing analysis. Each PCR cycles approximately doubles the amount of DNA present in the reaction.
Example Question #452 : Gre Subject Test: Biology
rtPCR quantification method is a technique that __________.
determines the melting point of the DNA fragments during each cycle of PCR
separates DNA fragments based on their size
determines if the primers used in the PCR reaction are annealing
measures the amount of non-specific amplification products
measures the amount of fluorescence produced which is proportional to DNA concentration with each cycle of PCR
measures the amount of fluorescence produced which is proportional to DNA concentration with each cycle of PCR
Real time PCR is a technique that measures the amount of fluorescence that occurs with each cycle of PCR. The amount of fluorescence is directly proportional to the DNA concentration. The assay can also provide info such as the possible presence of inhibitors.
It is important to know how much DNA is present in a sample to optimize downstream processing.
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