35. You are working in a research lab that studies cystic fibrosis. Your job is
ID: 260696 • Letter: 3
Question
35. You are working in a research lab that studies cystic fibrosis. Your job is to image the CFTR protein lung cells obtained from cystic fibrosis patients. In one of the screened patients you find out that CFTR protein is stuck in the ER. Which of the reasons below cannot be an explanation for your observation? a. CFTR has a mutation in the "go to Golgi" signal b.CFTR is misfolded c.CFTR has a mutation introducing a stop codon just before the "go to Golgi" signal d. CFTR mRNA is not spliced properly 36. You are performing an experiment isolating transport vesicles from the cell and trying to identify a reliable approach to select vesicles transporting cargo to the cellular membrane. All vesicles travelling to the cellular membrane have the same: a. amount of cholesterol b. amount of unsaturated fatty acid tails c. amount of transmembrane proteins d.coat 37. Microtubules grow from their plus end because: a. their plus end cannot bind ATP b. their minus end is attached to capping proteins c. their minus end is attached to the centrosome d. all of the above 38. The same motor protein can transport many different types of cargo due to: a. its ability to use different tail subunits b. its ability to move in multiple directions c. its ability to use different head subunits d. all of the above 39. Transcytosis is the process of a. combining a vesicle with a lysosome and degrading or releasing the contents b. recycling the contents of the endosome back to the surface of the cell c.transporting a vesicle from one side of a cell to the other and releasing the contents by exocytosis d. storing the contents of the lysosome 40. If the membrane transporter "X" is involved in antiport transport, then it: a. transports substances from places with lower concentration to places with higher concentration of the transported substance. b. transports simultaneously two substances in the same direction. c. transports vesicles to the peroxisomes. d.none of the above.Explanation / Answer
35. D. CFTR mRNA is not pliced properly. cannot be the reason.
In order to make it out of the endoplasmic reticulum, the CFTR must engage a protein complex known as coat complex II (COPII). COPII is responsible for recognizing when the synthesis of CFTR is finished and then grabbing it, packaging it in transport vesicle, and sending it on its way—eventually leading to CFTR's transport to the outside of the cell.
Normally, once the CFTR protein is expressed and folded in the membrane of the ER, it presents its "exit code" or “ go to golgi” code to the COPII protein, which then packs it and ships it. But the mutant protein loses its the ability of the exit code to be seen by COPII. It fails to engage the COPII exit machinery and exit the endoplasmic reticulum. Mutation in the amino acid chain is likely to cause a change in the structure that disrupts this interaction. Thus, CFTR becomes stuck in the endoplasmic recticulum and will eventually be degraded as the cell conducts its routine housecleaning. THerefore, A and B options can be valid. Also, since endoplasmic-reticulum-associated protein degradation (ERAD) designates a cellular pathway which targets misfolded proteins of the endoplasmic reticulum for ubiquitination and subsequent degradation by the proteasome, thus, option B is also a valid option.
36. D. coat. All vesicles targeted to plasma membrane have the same protein coat of clathrin . Different amount of proteins and other others may be getting transported to plasma membrane, therefore, option A ,B and C are incorrect.
37. C is correct. The rates of change at either end are not balanced — one end grows more rapidly and is called the plus end, whereas the other end is known as the minus end. In cells, the minus ends of microtubules are anchored in structures called centrosome. Whether a microtubule grows or shrinks is determined by the rate of tubulin addition relative to the rate of GTP hydrolysis. As new GTP-bound tubulin molecules are added more rapidly than GTP is hydrolyzed, the microtubule retains a GTP cap at its plus end and microtubule growth continues. However, if the rate of polymerization slows, the GTP bound to tubulin at the plus end of the microtubule will be hydrolyzed to GDP. If this occurs, the GDP-bound tubulin will dissociate, resulting in rapid depolymerization and shrinkage of the microtubule.
38. A option is correct. The identity of the track and the direction of movement are determined by the motor domain (head), while the identity of the cargo ( the biological function of the individual motor protein) is determined by the tail of the motor protein.
39. C option is correct. The process of receptor-mediated uptake of a ligand on one side of the cell, its vesicular transport across the cell, followed by exocytosis of the vesicle contents on the opposite side is known as transcytosis.
40. D is correct, i.e, none of the above answers are true. An antiport is an integral membrane transporter protein that simutaneously transports two different molecules, in opposite directions, across the membrane.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.