Dr. Reichler’s Bio 301L  1-2pm        Print Name:_______KEY___________
In-class Exam #2  October 18, 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 100 points possible for this exam.

1. a.  Cancer is partly caused by the absence of certain proteins.  How can a mutation cause a protein to not be produced?
A mutation in a promoter causes RNA poly/transcription factors to not bind and therefore not make the mRNA and protein.
5 of 6 pts for the following:  mutation in coding region causes incorrect amino acids.  Mutation in coding region causes incorrect splicing/editing of mRNA leading to wrong protein.

b. Does an mRNA that exists in the cytoplasm for a long period of time always lead to a high quantity of that protein being produced?  Why or why not?
No, the translation of mRNA may be blocked.

2. a.  Why can a cell that has just finished dividing not immediately divide a second time?
It first needs to replicate its DNA.

b. How is DNA packaged during cell division?  Why?
In chromosomes or very tightly.  The DNA must be compact so that it can be moved around the cell.

3. a.  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.

b. Why is surgery not an appropriate treatment for a malignant cancer?
Malignant cancers are cancer cells that are spreading to other parts of the body.  Surgery will only remove the tumor, leaving other cancer cells in the body to form new tumors.

c. If you were designing a new drug to kill cancer cells, how would you be certain that it killed the cancer cells without killing healthy cells?
Any of:  Direct drug to slow down/inhibit MDR transport, Kill cells with high levels of MDR,  Kill cells with many mutations, kill cells with mutations in positive or negative regulators, drugs go into cells via MDR
3 of 6 pts for:  Kill cells expressing telomerase, Kill rapidly dividing cells

d. How can a mutation cause a cell to produce elevated levels of Multi-Drug Resistance protein (MDR)?
Any of:  The mutation is in the promoter, causing RNA poly to bind when it should not.  The mutation changes the mRNA or protein so that it is degraded slowly/lasts a long time.

4. a.  Detergents cause holes in membranes.  How would exposing a mitochondria to a detergent stop ATP production?
ATP is produced when H+ ions diffuse across a channel in the mitochondrial membrane.  If the membrane has holes, the gradient can not form, the H+ ions will move freely across the membrane and not through the channel.

b. Why is sunlight necessary for life on earth?
Plants use the energy in sunlight to produce sugar/glucose.  Other organisms use the plant-produced sugar to make cellular energy/ATP.

5. Where would you expect to find C4 plants?  How are these plants specifically adapted to this environment?
In hot and dry environments.  They can fix CO2 at low concentrations, thereby producing glucose while maintaining their stomata closed to conserve water.  They fix CO2 in the mesophyll, and have RUBISCO in bundle sheath cells where the CO2 is released and used to make glucose.

6. a.  What are one similarity and one difference between selective breeding and genetic engineering?
Any one of:
Similar- DNA manipulated, choosing traits desirable for humans, can change characteristics
Selective breed: done in fields, indirect manipulate of DNA, choose individuals based on traits
Gen eng: done in lab, direct manipulate of DNA, choose individuals based on selection of herbicide resistance etc

b. Why are “sticky ends” used during genetic engineering of bacteria?
The two pieces of DNA are held together by base pairing/hydrogen bonds so that ligase can make covalent bonds.

c. How are bacteria involved in the genetic engineering of plants?
Agrobacteria naturally insert some of their DNA into plant cell DNA.  Scientists can put DNA into the Agro, and then let the Agro insert it into the plant.

7. Answer only one of the following questions:  You do not need to name the gene, just describe what its product does.(8 pts)
What genes might you change to genetically engineer plants to be drought resistant?
Any one of:  an improved rubisco that only binds CO2, genes to maintain stomata closed, genes to make bundle sheath cells like a C4 plant, genes to open stomata only at night.  Genes for longer roots or roots that can absorb water better

What genes might you change to genetically engineer plants to grow faster?
Genes to encourage cell division or DNA replication, genes for more photosynthesis

What genes might you change to genetically engineer plants to make more ATP?
More ATP synthase gene, more or more efficient H+ pumps, genes to make more mitochondria

8. Using rules 1 and 2 of Strong Inference (the parts prior to actually doing any experiments), answer the following question…Are genetically modified foods safe? (8 pts)
Devise multiple hypotheses, design experiments to eliminate one or more hypotheses.
Example: hypos-  They are safe for humans to eat.  They are not safe for humans to eat.  Expt-  Feed genetically modified foods and non-genetically modified food to a group of people.  Watch for good or bad effects.