practice problems: Flashcards
Explain how the experiments conducted by Dr. Gunter Blobel allow him to conclude that a secretory
protein is co-translatinoal translocated into the lumen of the ER and that an ER signal sequence is cleaved off from the protein.
- his experiment indicated that, without the N-terminal signal peptide, there was no incorporation
The signal sequence is necessary for ER import
- import only occurred when microsomes were present while synthesis took place = co-translational
- imported proteins had their N-terminus signal peptide removed = ER signal sequence is cleaved off
Many protein hormones are produced in the lumen of the ER, sent to the Golgi apparatus in COPII vesicles, and then sent secreted in secretory vesicles. Supposed you wanted to re-route a particular hormone to be ended up in the lysosome instead (reminder: the lysosome is an organelle where proteins are degraded). What would you need to change/mutate in order to accomplish this rerouting
mutate the hormone itself by remove any possible sorting signal to secretory vesicles and adding a sorting signal (M6P patch) to the protein
so it can be packaged into clathrin vesicles at TGN
The defect is an accumulation of secretory vesicles. Name 4 types of proteins that could be defective in this yeast
secretory vesicles are leaving the Golgi apparatus but not fusing with the plasma membrane.
could have defective (1) v-SNAREs, (2) t- SNAREs, (3) Rab proteins, (4)
Rab effectors e.g. tethering factors, and perhaps motor protein
ARF1 is a GTPases involved in COPI vesicle formation in the Golgi apparatus. Imagine you have a drug that, when administered, immediately stops the GTPase activity of ARFs. In other words, the ARF1 becomes trapped in the GTP state. Predict the effects of this drug on the following variable:
a) Percentage of naked COPI vesicles
b) Rate of COPI vesicle formation
c) Size and shape of COPI vesicles
d) Rate of COPI vesicles reaching their final target.
explain whether the variable goes up, goes down, or doesn’t change. Note that some variables
may change as a function of time
a) Percentage of naked vesicles goes down as the coat will not shed off
b) Rate of vesicle formation increases (note: they may be non-specifically formed) but decreases over time as no vesicle will fuse.
c) Size and shape of vesicles does not change, but do not become uncoated
d) Rate of vesicles reaching their final target decreases because vesicles no longer lose their coats and thus are unable to fuse
Below, you will see a drawing of the plasma membrane (gray line) showing endocytosis in 4 steps. Time is passing from left to right, from initial invagination of the membrane (step 1) to completion of endocytosis (step 4).
sequence of endocytosis events for a dynamin knock-out condition & a dynamin mutant that cannot hydrolyze GTP.
In the dynamin knock-out condition, there is no dynamin-GTP, thus, there is no ‘neck’ formed and the emerging vesicle is not detached from the plasma membrane. Eventually, the clathrin coat will dissociate and endocytosis fails
In the dynamin GTPase mutant, dynamin can still oligomerize around the “neck” of the emerging vesicle so ‘long neck’ formed but cannot successfully separate it from the membrane
