Dr. Reichler’s Bio 212 1-2pm Print
In-class Exam #3 November 11, 2002
Answer each question as succinctly as possible in the
space provided. If needed, continue on the back. If you use a
drawing as part of your answer, be sure to also include a written explanation.
Read each question carefully and don’t hesitate to ask if a question seems
unclear. These questions have specific answers, although for some,
more than one answer is possible. To receive full credit you must clearly
and fully answer the question being asked. Each question is worth 6
pts, unless otherwise noted, for a total of 103 points possible for this
1. a. Why are plasmids used to genetically modify bacteria?
They do not contain critical information for the bacteria, so the plasmid
DNA can be manipulated without negatively affecting the cell. OR
Plasmids can be removed/inserted into the bacteria.
b. Describe the basic steps involved in genetically modifying bacteria to
produce the protein in spider webs? What you would do and why is each
step necessary? (12 pts)
- Cut plasmid with restriction enzyme – to open plasmid.
- Use PCR to amplify gene from spider DNA – so that it can be cut.
- Cut spider DNA with same restriction enzyme – so it has matching
- Place spider and plasmid DNA together with DNA ligase – now they
are joined as one plasmid.
- Place plasmid plus spider DNA into bacteria – now the DNA is in
the bacteria, and can be expressed.
- Grow bacteria on antibiotic media – to check for bacteria containing
plasmid with antibiotic resistance gene and spider gene.
c. What additional steps would be involved in putting this protein into plants?
- Must use Agrobacteria.
- Remove tumor/gall genes (this is optional).
- As above, but put spider DNA into Agro Ti-plasmid.
- Mix Agro (with plasmid) and plant together.
- Agro will insert DNA into plant.
- Check for success by selection using herbicide resistance.
2. a. Why can a cell that has just finished dividing not immediately
divide a second time?
It first must replicate the DNA.
Partial credit (3 of 6 pts) it must grow/gain nutrients/gain energy.
b. Why does DNA need to be packaged into chromosomes for a cell to divide?
The DNA must be moved without damaging it.
c. Why is it a critical checkpoint that cells wait until all of the chromosomes
are in the middle of the cell before mitosis continues? (This is called
the metaphase checkpoint.)
The DNA will move equally to the 2 sides of the cell. If the split
is not equal, the resulting cells may not have all needed genetic info.
d. Describe how the metaphase checkpoint might be regulated. In other
words, what might activate the movement of the chromosomes to the sides of
Any of: phosphorylate or de-phosphorylate motor proteins (kinetechore)
to activate movement.
e. If CDK (cyclin dependent kinase) levels are constant, why is the cell
not constantly dividing?
Cyclin and CDK are needed to form Mitosis Promoting Factor (MPF).
Without cyclin, CDK is inactive.
3. a. How is cancer harmful to the body?
Cancer cells are not doing their normal function. OR Tumors
take up space, blocking or disturbing normal functions.
b. Why do the risks of cancer increase as people get older?
Any of: DNA repair is less efficient as people get older.
Older people have had more exposure to mutagens.
c. What is meant when we say that cancer is spreading?
Tumor cells are being dislodged from original location and are moving
to another location.
d. How could genetic engineering be used to treat cancer?
Could add a gene for a negative signal to cancer cells.
4. a. What cells undergo meiosis in your body, and why?
Gametes (sperm and/or egs), to produce haploid cells for sexual reproduction.
b. If an organism has 3 pairs of chromosomes, how many possible combinations
of chromosomes exist? (3 pts)
c. How would the resulting cells be different if crossing-over (recombination)
between two chromosomes did not occur equally?
Some cells would have extra DNA/genetic info, some would have incomplete
d. In the drawing to the right there are three genes (X, Y, Z), each with
two alleles. Why might genes X and Y be more likely to be inherited
together than X and Z?
X and Y are closer together, and therefore crossing-over/recombination
is less likely to occur between them than between X and Z.
Bonus: Why is surgery not an appropriate treatment for a malignant
cancer? (3 pts)
Malignant cancers can fomr in several parts of the body, so surgery may
not remove all of the cancer cells.