Dr. Reichler’s Bio 311C   MWF 1-2pm    Print Name:____________Key___________
Exam #2   October 30, 2006

    Read each question carefully and don’t hesitate to ask if a question seems unclear.  If possible, answer each question in the space provided, but if needed, continue on the back.  If you use a drawing as part of your answer, be sure to also include a written explanation. 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.  This exam is worth 100 points with the points for each question noted in parentheses.

1. Some blood cells were suspended in a salt solution and almost immediately the solution turned pink, indicating that the cells had lysed (burst).  Why did the cells lyse? (6 pts)
The solution was hypotonic, and water moved into the cells.

2. Glucose and Mg+2 are brought into a cell by different mechanisms.  How do the mechanisms for each differ, and how are they similar?  Include in your answer a description of any membrane structures or enzymes required.  Describe any sources of energy that are required.  If none of these are required, state this. (8 pts)
For Mg2+ answer requires them to mention integral membrane protein ion channels; no energy required
For glucose answer requires them to mention integral membrane protein channel through which both Na+ and glucose move together, Na+ moving down its gradient because it was pumped out of the cell by the Na+-K+ pump and thus providing energy for glucose to enter the cell against its gradient.

3. In the origin of life, do researchers believe that complex molecules of DNA or RNA existed first?  Explain. (6 pts)
RNA.  RNA can have both enzymatic activity and complementary so that it could be self-replicating.

4. Describe how you would use a microscope to identify two different membrane bound cellular organelles.  Include the type of microscope you would use and how you would know you were looking at that particular organelle. (8 pts)
Any two of:  Nucleus- could use a dye that binds to DNA and a light microscope or EM would show DNA in nucleus.  ER- with either a light microscope or EM could see rough ER and connections between ER and nuclear membrane.  Golgi- either light microscope or EM would show stacks absent ribosomes.  Chloroplast- light microscope would allow visualization of pigments or EM would show specific inner membrane structure.  Mitochondria- EM could show inner membrane structure.  Vacuole- light microscope or EM could show large membrane bound organelle.

5. Would you expect to find saturated or unsaturated phospholipids in the membranes of a thermoacidophile archae?  Why? (6 pts)
Saturated.  High temperatures cause membrane instability, therefore the more ordered tails of saturated lipids would keep the membrane from becoming too fluid.

6. Could you use a microscope to tell the difference between a heterotrophic or autotrophic bacterial cell?  Why or why not? (6 pts)
No, no internal structures to identify different way they get nutrients.
Yes, autotrophic bacteria may have pigments that could be seen in a light microscope.

7. What are three pieces of information encoded by a gene’s promoter? (6 pts)
Any three of:  Where transcription begins.  When a gene should be transcribed (where transcription factors bind).  What direction the RNA polymerase should go.  Which strand will be transcribed.

8. Not including the poly-A tail, what are the fewest number of nucleotides that could code for a 200 amino acid protein?  Would you expect the coding region of the gene coding for this protein to be smaller or larger than this number of nucleotides?  Why? (8 pts)
604.  1=5’cap, 600= codons, 3= stop codon.  The coding region would be larger because of introns.

9. The DNA of a gene can be divided into the coding strand, which is transcribed, or the non-coding strand, which is not transcribed.  Which strand has the same sequence as the tRNA?  What are two potential differences between the DNA and tRNA sequence?  Explain. (6 pts)
Coding strand.  Redundancy in codons means that the tRNA may not always have exact sequence as gene.  DNA has T, RNA U.

10. Is the promoter on the 5’ or 3’ end of the coding strand?  Explain. (6 pts)
3’ end.  RNA is made 5’-3’, and the coding strand is read 3’-5’, and the promoter is at the beginning of the gene.

11. Would the human gene for collagen (a component of the animal cell extracellular matrix) be properly expressed in a bacterial cell?  Why or why not? (8 pts)
Any of:  No, collagen needs to be translated on the ER to correctly have the signal peptide removed.  No, eukaryotic promoters are different from prokaryotic promoters.

12. How would the production of collagen (a component of the extracellular matrix) differ from the production of proteins that comprise a gap junction? (8 pts)
Collagen is secreted and has its signal peptide removed.  Gap junctions are integral membrane proteins, and their signal peptides are retained.

13. A mutation in what gene would prevent exocytosis?  Explain. (6 pts)
Any of:  cytoskeleton protein (actin, tubulin, intermediate filaments (keratin, laminins)) or motor proteins would prevent vesicle movement. 

14. Why do plant cells need both chloroplasts and mitochondria? (6 pts)
Chloroplasts produce sugars that can be used to make ATP in mitochondria.

15. What would you know about the amino acids in the part of an integral membrane protein that spans the membrane? (6 pts)
They are hydrophobic.