Chapter 12 Flashcards
What does the restrictions enzyme do to the DNA?
The restriction enzyme cuts up a specific DNA sequence.
Why are the DNA samples and restriction enzyme incubated for 5 minutes?
The DNA samples and restriction enzyme are incubated because the enzyme needs time to break up the DNA, which is really long.
What will happen to the DNA if the enzyme did not find a restriction site? How many fragments will you have if the enzyme cuts the DNA two times?
If the restriction enzyme didn’t find a restriction site, there would only be the one double-stranded DNA molecule. If the DNA was cut two time, there would be 4 DNA fragments.
What is the function of the agarose gel?
The gel slows down the DNA’s movement towards the positive electrode so that the DNA breaks up into fragments that are of different sizes.
Predict what would happen if you used 0.02 g of agarose instead of 0.2 g to make a gel. What effect would that have on the experiment? Would there be more or less separation of DNA fragments?
The smaller amount of gel would allow the DNA to move more freely and quickly which would mean that the experiment would not last as long. There would be more separation of DNA fragments because the more freely the DNA is able to move through the gel, the smaller the fragments become, meaning that there will be more fragments.
Why is the gel in electrophoresis buffer?
The gel is in the electrophoresis buffer so that the DNA does not continue to go past the box if it does travel out of the gel.
Describe what is occurring in the gel when the electric current is applied.
When the electric current is applied, the DNA is attracted to the positive end and becomes fragmented inside the gel. The DNA breaks up into different sized fragments that show up at different places in the gel.
Predict what would happen if you put the wells of the agarose gel at the positive electrode.
If I put the wells of the gel at the positive electrode, the DNA will go towards it and into the buffer, so we will never get to see the fragmented DNA. If this happens, we will not be able to use the data for DNA fingerprinting.
You use a restriction enzyme to cut up a long DNA molecule that has three copies of the enzyme’s recognition sequence clustered near one end. When you separate the restriction fragments by gel electrophoresis, how do you expect the bands to appear?
three bands near the positive pole at the bottom of the gel (the smaller fragments broken up by the restriction enzyme) and one band near the negative pole at the top of the gel (the large fragment not broken up by the restriction enzyme)
Why is only the slightest trace of DNA at a crime scene often sufficient for forensic analysis?
because PCR (polymerase chain reaction: a way to identify and multiply a specific sequence of DNA) can be used to produce enough molecules for analysis
What are STRs, and why are they useful for DNA profiling?
STRs (short tandem repeats) are nucleotide sequences repeated many times in a row within the human genome. STRs are valuable for DNA profiling because different people have different numbers of repeats at the various STR sites.
