Answers to Student Questions: Lesson 1 - CTE Online



Answers to Student Questions: Lesson 1

1. What does PCR allow you to do with DNA?

PCR allows you to make enough copies of DNA to perform analysis.

2. What components do you need to perform PCR?

A template, DNA polymerase enzyme, nucleotides (dNTPs), primers, and buffer (containing Tris, salt, etc.).

3. What is in the master mix and why do you need each component?

• Taq polymerase – a polymerase that is not sensitive to heat. It "sews" together the deoxynucleotide triphosphates to make a new DNA strand that is complementary to the template.

• Deoxynucleotide triphosphates ATCG – used to make the complementary strand.

• Primers – short sequences of DNA that are complementary to DNA one wishes to amplify. There are 2 types: forward and reverse. They are separated by the base pairs in the sequence of DNA being amplified. The size of the PCR product is equal to the size of the amplified region of DNA plus the number of base pairs in the primers.

• Buffers and cofactors needed to make the reaction take place at an optimal rate.

4. Why do you need to perform PCR on DNA evidence from a crime scene?

PCR is needed because there is usually not enough DNA obtained from a crime scene to analyze or visualize.

5. What steps make up a PCR cycle, and what happens at each step?

Each PCR cycle is made up of 3 steps.

• Denaturation – the DNA strands are melted apart.

• Annealing – primers bind to complementary sequences on the DNA.

• Extension – DNA polymerase adds nucleotides to primers.

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