Dr. Reichlerπs Bio 325 TTh 12:30-2pm Print Name:______________KEY_____________

Exam #1 Feb. 19, 2004

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 donπt 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 exam.

1. When designing an experiment using the rules of Strong Inference, what is the goal of the experiment? (4 pts)

To disprove one or more hypotheses.

2. What risks are there for a cell with many transposons?

When transposons move there is a risk that they can insert into a gene disrupting the expression of the gene. Too many transposons would increase the risk of having essential genes disrupted.

3. Could an RNA strand with absolutely no areas that were complementary to each other be a candidate for the first biological molecule? Why or why not?

No, complementary sequences within an RNA strand are critical for forming a 3-D structure, and the 3-D structure is critical for RNA having enzymatic activity.

4. During the experiment to test RNA self-ligation, the self-ligation success rate was very low at first and much greater later. How were the researchers able to accomplish this?

They passed the random RNA through a column, and only those that had successfully ligated to a tag sequence bound to the column. These successful ligators were then used for further rounds of the experiment, thus increasing efficiency by selecting successful sequences.

5. RFLP analysis, using restriction enzymes, of Sam and Joπs DNA yield exactly the same patterns. The experiment was done properly, and Sam and Jo are not related. What are two explanations for this result?

Any two of: There are differences, but the sequences recognized by the restriction enzymes were not different. A gene was used, and there are fewer differences between genes than non-gene DNA.

6. What genetic evidence demonstrates the human propensity for migration?

The genetic similarities between different geographic groups would indicate that humans have been sharing genes between different genetic groups for a long time and at a relatively commonly.

7. What conclusion can be reached about homosexuality if identical twins raised apart had a higher correlation of homosexuality than fraternal twins raised apart? Explain how the evidence leads to this conclusion.

Identical twins share identical DNA and fraternal twins are related as siblings. If identical twins raised apart have a higher correlation of homosexuality, this would lend credence to a genetic component of homosexuality. When the individuals grew up in different environments their similar sexuality indicates that some genetic component prevailed over their environment. The fraternal twins shared a womb, but their different DNA gives a lower correlation of behavior.

8. Prairie voles and montane voles both have the same oxytocin and vasopressin receptors in their brains. What is different about the DNA of these voles so that the same protein is produced in different quantities?

Any one of: One of the voles has an enhancer that increases gene expression while the other does not. One of the voles has a promoter that attracts transcription factors that are more efficient at recruiting RNA polymerase while the other has a less active promoter.

9. How can a mutation cause a cell to lose the ability to perceive an environmental stimulus?

The mutation could cause the receptor to become inactive or non-existant.

10. In guard cells, one of the first experiments we looked at showed that simply increasing the number of calcium spikes caused increasing closing of the stomata. What conclusion can be reached from this experiment alone?

Only that added amounts OR spikes increase stomata closing. This experiment alone cannot discern whether the increased stomata closing comes from increased calcium concentration or from the number of spikes.

11. How might calcium signaling specify a specific response in the signature hypothsis differently from the switch hypothesis?

The signature hypo says that specificity comes from the particular nature of the calcium response. The switch hypo says that specificity comes from the presence of calcium activating specific downstream effectors as in the micro-domain idea or that certain effectors are only present at certain times.

12. A cell responds to a signal by changing a membrane bound protein to a secreted protein. How does the cell do this?

As the protein is being translated on the rough ER, the signal peptide is clipped off thereby releasing the protein into the lumen of the ER, where it will travel through the Golgi to the exterior of the cell.

13. How could you test which part of a protein was the signal peptide that directed that protein to the nucleus?

Remove various parts of the protein and see whether it is still transported to nucleus. OR Add various parts of the protein to some other protein, and see whether the hybrid protein is transported to nucleus.

14. What are three parts of the DNA that do not code directly for amino acids?

Any three of: promoter, introns, terminator, non-gene DNA, genes coding for rRNA/tRNA/snRNA.

15. DNA is double stranded, but only one strand is used to make RNA. Why can each RNA polymerase read only one strand of DNA at a time?

RNA synthesis only occurs in a 3π direction. Since DNA is anti-parallel, only one of the two strands can be read.

16. Would two different proteins produced by alternate splicing be produced in different quantities? Why or why not?

Either answer is ok, it depends on the reasons: Similar quantities because transcription is controlled by one promoter, thus producing a set amount of mRNA, equal for both splicing versions. BUT Different quantities if the alternate splicing is uneven, then different quantities would be produced.

17. Apply rules 1 and 2 of Strong Inference (the parts prior to actually doing any experiments) to answer the following question: What causes diabetes?

Must use Strong Inference and make multiple hypotheses and experiments to eliminate hypotheses. Ex: hypoπs- Diabetes is caused by eating too much sugar. Diabetes is caused by eating too little sugar. Diabetes is caused by mutations in the gene for insulin. Expt- Feed two groups of people high and low sugar diets, and then test them for diabetes.

Bonus: Give an example of a gene that is dependent on the environment for its expression. For full credit you need to be specific about the gene and the environmental effect. (3pts)

Many possible answers. More info given = more credit. Ex.