Dr. Reichler’s Bio 311C MWF 1-2pm Print
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
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
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?
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.
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
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
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.