PCR
Polymerase Chain Reaction | Multimedia | Activities
Polymerase Chain Reaction - Activity 1 - PCR - Answers
Polymerase Chain Reaction - Activity 1 - PCR - Answers
Polymerase chain reaction is a technique scientists use to amplify (make copies of) DNA. A scientist locates the target sequence in the DNA, and then designs primers (short stretches of DNA) that bind to four or five nucleotides before the target sequence.
For example, say a scientist wants to make many copies of the sequence
Once the scientist has determined the primer and target sequence, many primers and pieces of DNA are put into a machine called a thermocycler, which raises and lowers the temperature of water. Also, an enzyme called Taq polymerase, as well as a number of single nucleotides are added into the machine. The scientist is now ready to begin Polymerase chain reaction.
There are three phases in each cycle of PCR, and at least three cycles must be completed before the target sequence is copied without any excess DNA.
The first phase occurs at about 95C. In this phase, the two strands of DNA are separated. In the second phase, around 50-65C, primers bind to the DNA. In the third phase, about 72C, Taq polymerase adds nucleotides to the primer, copying the original strand of DNA.
In this activity, the student will mimic the action of the second and third phases of the cycle.
You are given the follow strand of DNA. The sequence you wish to amplify is highlighted.
Questions
What 4 nucelotide primer would you use?
Once the primer binds, what sequence would add to the primer? (Remember, A pairs with T, C pairs with G)
The new strand is read right to left. What primer would you use to copy the sequence from the new strand of DNA?
What sequence do you get after the nucleotides add to the second primer? Is this a copy of your target sequence and primers only? Is there any extra DNA included?
Why do you need to do more than one cycle of PCR in order to obtain just the target sequence?
Why can’t you get a target sequence without primers on it?
Once the PCR is done, you will have many different length strands of DNA. The smallest will be your target sequence. How can you separate out the target sequence DNA from the rest of the DNA?
For example, say a scientist wants to make many copies of the sequence
ATCGGCATGCTA
that is part of the longer DNA strand
CGTTACGTGATCGAATCGGCATGCTATCGACGTTTAACCGGGCTAG
The primer the scientist would use is TCGA because that sequence is found immediately before the target sequence.
Once the scientist has determined the primer and target sequence, many primers and pieces of DNA are put into a machine called a thermocycler, which raises and lowers the temperature of water. Also, an enzyme called Taq polymerase, as well as a number of single nucleotides are added into the machine. The scientist is now ready to begin Polymerase chain reaction.
There are three phases in each cycle of PCR, and at least three cycles must be completed before the target sequence is copied without any excess DNA.
The first phase occurs at about 95C. In this phase, the two strands of DNA are separated. In the second phase, around 50-65C, primers bind to the DNA. In the third phase, about 72C, Taq polymerase adds nucleotides to the primer, copying the original strand of DNA.
In this activity, the student will mimic the action of the second and third phases of the cycle.
You are given the follow strand of DNA. The sequence you wish to amplify is highlighted.
GTCCAGTGCGTTGCGATCGTAAGTCGAATGCATGCGGTCA
Questions
What 4 nucelotide primer would you use?
Once the primer binds, what sequence would add to the primer? (Remember, A pairs with T, C pairs with G)
The new strand is read right to left. What primer would you use to copy the sequence from the new strand of DNA?
What sequence do you get after the nucleotides add to the second primer? Is this a copy of your target sequence and primers only? Is there any extra DNA included?
Why do you need to do more than one cycle of PCR in order to obtain just the target sequence?
Why can’t you get a target sequence without primers on it?
Once the PCR is done, you will have many different length strands of DNA. The smallest will be your target sequence. How can you separate out the target sequence DNA from the rest of the DNA?