C2006/F2402 '02 -- Review Questions for Exam #1 = Exam #1 of '01
For each question circle all the correct answers, fill in the blank, etc. and explain. When there are choices, there may be more than one right answer. You should be able to explain ALL your answers.
Many of the questions on this exam are based (directly or indirectly) on a very short article from Science, which is included below. The article is from a section of the magazine that summarizes work that was published elsewhere. The editors include work that is "hot" and might interest the readers of Science. Please read the article before you answer the questions.
Cell Biology: Psychedelic Trafficking
Visualization of multiple proteins moving in live cells has become possible with the introduction of green fluorescent protein (GFP) variants. Keller et al. (Nature. Cell Biol. 3, 140 (2001)) used GFP fusion proteins and sophisticated image analysis to monitor the sorting of proteins upon exit from the Golgi apparatus. They found that cargo protein destined for the apical surface of polarized epithelial cells was segregated from basolateral cargoes in the Golgi and trans-Golgi network. Furthermore, these proteins were transported in separate carriers to their destinations without intersecting with incoming endocytic traffic, which had been suggested in earlier studies. Using total internal reflection microscopy, the authors could image the delivery and fusion of carrier vesicles with both apical and basolateral surfaces, and they observed that particular regions seemed to be particularly likely fusion sites.
Article in Science included a colored picture with red, yellow and green tracks on it. Legend of picture said : apical (green) and basolateral cargoes (red) move along separate routes with occasional mixing (yellow). Multiple images were processed to reveal movement.
1. Consider the proteins they are monitoring
"upon exit from the Golgi" in the Science article.
A. These proteins should be made on ribosomes that are (in the soluble part of the cytoplasm) (part of the rough ER) (part of the smooth ER) (part of the Golgi) (depends on which of the proteins we are talking about), AND
B. These proteins could be (transmembrane proteins) (extrinsic or peripheral proteins on the cytoplasmic side of the plasma membrane) (extracellular proteins) (soluble cytoplasmic proteins). Circle all reasonable possibilities.
2. Suppose a certain protein, call it protein P,
is found entirely within the lumen of one of the 'carrier vesicles' mentioned in
A. If the carrier vesicle fuses with the apical surface of the epithelial cells lining the intestinal lumen, where will protein P end up? (in the apical surface membrane) (in the lumen of the intestine) (in the interstitial fluid -- extracellular fluid surrounding body cells) (in the cytoplasm of the cell) (in an organelle inside the cell), AND
B. The gene for normal protein P should code for (no signal peptide) (a signal peptide on the amino end) (a signal peptide on the carboxyl end) (an internal signal peptide) (one signal peptide, but can't be sure where) (at least one additional stop/start transfer sequence), AND
C. The number of transmembrane sequences in mature (completely processed) protein P should be (0) (1) (1 or more) (can't tell). Explain how you arrived at your answers to A-C.
3. The scientists who did the experiments
described in Science started with ordinary genes and made recombinant
genes that coded for recombinant proteins. The recombinant proteins contain the
GFP fused to part of a regular protein (say protein P as described above).
Consider the following results: If the GFP is fused to one end of protein P, in
place of the usual 20 amino acids on that end, the fusion protein never gets to
the Golgi. If the GFP is fused to the other end of protein P, instead of the
usual 20 amino acids on that end, Protein P goes to the Golgi and continues on
to its normal destination just like normal protein P. Given these results, then
A. The GFP added to protein P in the experiments described in Science (must be on the amino end) (must be on the carboxyl end) (could be on either end) AND
B. The fusion protein that never makes it to the Golgi probably ends up (inside the lumen of the ER) (in the membrane of the ER) (in the cytoplasm) (in some other organelle) (outside the cell) (in the plasma membrane) (any of these are equally likely). AND
C. You would expect GFP to have (0) (1) (2) (>2) transmembrane segments and (no SP) (an SP on one end) (an internal SP). Explain how you arrived at your answers to A-C. (Part C was not on the exam, but is added for study purposes).
4. Suppose the epithelial cells described in Science line the lumen of the intestine.
D-1. Under normal conditions,
transport of glucose into these cells occurs mainly by (primary active
transport) (secondary active transport) (RME) (facilitated diffusion using a
carrier) (diffusion through a channel) (active transport -- can't say which
kind) (passive transport, but can't say which kind) AND glucose transport
out of the cell occurs mainly by (primary act. transp.) (secondary act.
transp.) (RME) (carrier mediated fac. dif.) (fac. dif. through a channel) (act.
transp -- either kind.) Pick only one choice for each part of D-1.
D-2. Suppose that the concentrations of Na+ inside and outside the cell are reversed from normal, because of the presence of some inhibitor. Assume that the relative glucose concentrations inside and outside remain the same as under normal conditions. Now suppose the inhibitor is removed. What should happen next? When the inhibitor is removed, Na+ should be transported into the cell across (the basolateral membrane) (the apical membrane) (both) (neither), AND glucose should be transported out of the cell across (the basolateral membrane) (the apical membrane) (both) (neither). Explain D-2.
5. The type of microscopy described in Science is probably (light microscopy) (SEM = scanning electron microscopy) (EM = regular (transmission) electron microscopy) (EM or SEM) (any of these).Explain very briefly.
6. The note in Science refers to
"incoming endocytic traffic."
A. This process is most likely to refer to uptake of (Na+) (K+) (glucose) (Na+ & glucose) (Na+ & K+) (all of these) (none of these), AND
B. The process of entry is best described as (RME) (facilitated diffusion using a carrier) (diffusion through a channel) (passive transport) (more than one of these since more than one process is involved), AND
C. The process of entry requires (transmembrane protein(s)) (peripheral membrane protein(s)) (both). Name ONE function or step carried out by each type of protein chosen.
7. Suppose that glucose passes directly from one epithelial cell into another. It is most likely to be transported through a (tight junction) (gap junction) (spot desmosome) (belt desmosome or adherens junctions) (junction of one kind or another -- any of these are equally likely) (none of these allow transport) AND the glucose is most likely moving (down its gradient) (up its gradient) (either way) (neither -- this sort of transport is impossible).Explain briefly.
8. Consider the movement of material from the
Golgi to the cell surface. This process involves kinesin or similar proteins.
9. Hormone H binds to a receptor on the plasma
membrane and enters cells by receptor mediated endocytosis. The hormone is
degraded and the receptors are recycled back to the plasma membrane. If you
follow tagged molecules of receptor and hormone into the cell, you would expect
F. Fill in the blanks below
with (lysosomes) (endosomes) (plasma membrane) (exocytotic vesicles) (coated
vesicles) to indicate the order that tagged material would follow. Fill in
as many blanks as you need for each case.
For Hormone: Plasma membrane --> ____________ --> _______________ --> ________________ -->______________ --> __________________