Name: ______Period: ____
Introduction:
In 1968, scientists Werner Arber and Hamilton Smith discovered a group of enzymes (proteins that aid chemical reactions) in bacteria, which when added to any DNA result in the hydrolysis (breakage) of the sugar-phosphate backbone between recognition sites (specific nucleotide bases). This causes the double strand of DNA to break along the recognition site and the DNA molecule becomes fragmented.
These “molecular scissors” are called restriction enzymes (RE)
How Restriction Enzymes work:
REs cut the DNA backbone at a very specific sequence, which is unique to each different enzyme. Follow the example below to simulate the cutting action of the restriction enzyme, HaeIII.
Þ HaeIII recognizes the following sequence:
“GGCC”
Þ The enzyme will cut between the middle G and C every time it “sees” it.
“GG” “CC”
Þ Use the DNA sequence below to answer the following questions.
ATGGCCATTTCGGGCAATA
TACCGGTAAAGCCCGTTAT
Questions:
1. On the DNA sequence above, draw a line where HaeIII would cut.
2. How many fragments of DNA would result from cutting this sequence with HaeIII?
3. DNA fragment size can be expressed as the number of base pairs (bp) in the fragment. Indicate the size of the fragments.
Smaller fragment: ______bp
Larger fragment: ______bp
Modified from: Burke, M. 2009. Laboratory Handbook: From Phenotypes to Genotypes. School of Biological Sciences. University of California, Irvine.
Name: ______Period: ____
Review:
The term electrophoresis means “to carry with electricity.” Gel electrophoresis separates DNA fragments by size. The DNA is placed in wells created on a gel, electricity is turned on, and the DNA fragments will move through the gel towards the positive electrode. The smaller the fragment of DNA, the further it will move. We can use this technique to separate DNA fragments created by restriction enzymes.
Questions:
1. Read the length (in base pairs) of the following fragments:
GGTAATT (7 bp)
TTAG (4 bp)
AAAGGCTAT (9 bp)
2. Which fragment do you think would travel the furthest? ______
3. Which fragment would travel the least distance? ______
4. Where do you think you would find the other fragment? ______
5. Draw what you think a gel would look like after the above DNA had run through.
2 / Minority Science Programs – School of Biological Sciences – University of California, Irvine