MODELING GENETIC ENGINEERING
INTRODUCTION
An understanding of the basis of inheritance has led to a new form of applied genetics called genetic
engineering. Genetic engineering is the use of genetics for practical purposes. For example, it can
be used to identify genes for specific traits or transfer genes for a specific trait from one organism
to another organism.
Gene transfer was first implemented in the field of medicine in the production of insulin. From
1912 to the early 1990s, diabetic patients needed to obtain insulin from pigs or cows in an effort to
control their blood sugar. Although pig or cow insulin worked effectively on most patients, some
suffered allergic reactions. Gene transfer allowed the mass production of human insulin without
potential side effects.
HOW DOES IT WORK?
STEP 1
Use handout 3 to create a model plasmid.
The plasmid is a ring of DNA found in bacteria in addition to their main chromosome.
1.
2.
3.
4.
STEP 2
Cut the plasmid strips along the dotted lines.
Shuffle the strips and tape them together to form a single long strip.
The letters should all be in the same direction when the strips are taped.
Tape the two ends together to form a circular plasmid from a bacterium.
Use handout 4 to create a human DNA sequence.
1. Cut out the base sequence strips along the dotted lines.
2. Tape the strips together in numeric order to form a single long strip.
3. Note that the shaded area is the insulin gene.
STEP 3
Select a restriction enzyme able to cut open the plasmid in one specific location.
Restriction enzymes are like chemical scissors that can recognize very specific sections of
DNA. Look for example, at the DNA sequence below. The restriction enzyme recognizes
the nucleotide sequence CAATT on both chains of DNA. In one chain, the sequence runs
from left to right; on the complementary chain, the sequence runs from right to left.
Use handout 5 to select the restriction enzyme:
1.
2.
3.
4.
Cut out the restriction enzyme cards.
The enzyme cards illustrate a short DNA sequence that each enzyme can cut.
Compare the base sequence on each enzyme card with the base sequence of the plasmid.
Some restriction enzymes may be able to cut open the plasmid in multiple locations while
others may not be able to cut open the plasmid at all. You are in search of an enzyme
able to cut the plasmid sequence once and only once!
5. List the enzymes able to cut open the plasmid in only one location: ________________.
6. Mark the cutting location of the restriction enzymes on the plasmid.
STEP 4
Select a restriction enzyme able to cut open the human DNA in two specific locations.
1. Compare the restriction enzymes able to cut open the plasmid against the human DNA.
2. Find an enzyme that will also make two cuts in the DNA sequence:
one just above and one just below the shaded insulin gene.
3. Mark the two cutting locations of the restriction enzyme on the human DNA sequence.
Which restriction enzyme is uniquely able to cut open the DNA in all three locations:
below the insulin gene, above the insulin gene, and also the plasmid? ______
STEP 5
Create “sticky ends.”
Sticky ends are the “tails” created when restriction enzymes cut open DNA.
1. Select the one unique enzyme able to cut both the plasmid and human DNA sequences.
2. Cut open the circular plasmid at the location you marked in pencil.
3. Cut out the insulin gene at the 2 locations you marked.
plasmid DNA
human DNA
containing the
insulin gene
STEP 6
Modify the plasmid.
1.
2.
3.
4.
At this point both your plasmid DNA and human DNA have “sticky ends.”
Insert the human DNA sequence containing the insulin gene into the plasmid DNA.
Tape the sticky ends of the insulin gene onto the sticky ends of the plasmid.
Neatly fold and staple your modified plasmid to this handout.
NOW WHAT HAPPENS?
1. The modified plasmid is inserted in a bacterium. Note that the plasmid
now carries the human insulin gene capable of producing insulin.
2. The bacteria reproduce. Bacteria are able to reproduce at a prodigious rate.
Each of the bacteria offspring can now produce insulin. The remarkable
result is the ability to produce insulin en masse for diabetic patients.
REVIEW
1. What is a plasmid?
______________________________________________________________________________
2. What is a restriction enzyme?
______________________________________________________________________________
3. Why is it important to find a restriction enzyme that will cut the plasmid only once?
______________________________________________________________________________
4. Why is it important to cut the DNA strand as close to the insulin gene as possible?
______________________________________________________________________________
5. Use the Internet to find an application of genetic engineering other than the production of insulin.
Print your Internet source and staple it to this activity.
______________________________________________________________________________
______________________________________________________________________________