Ch 15 set 6

Investigators have engineered a gene that encodes a protein bearing an ER signal sequence followed by a nuclear localization signal. What would be the likely fate of that protein?

The protein will be recognized by an SRP and enter the ER

Which of these statements is true?

Membrane-bound ribosomes and free ribosomes are structurally and functionally identical; they differ only in the proteins they are making at a particular time

ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria?

The protein could slip back out of the mitochondria during transport

Which of the following correctly describe steps required for protein transport into the rough ER?

A. cleavage of the signal sequence from the protein by signal peptidase
B. recognition and binding of the protein signal sequence by SRP
C. passing of the protein to a protein translocation channel in the ER membrane

How does a polyribosome differ from the rough ER?

A polyribosome will synthesize a single type of protein.

How does the nuclear pore restrict the passage of large molecules that do not bear the correct nuclear localization signal?

Nuclear pore proteins contain disordered segments that form a gel-like meshwork inside the pore.

Botulism is a potentially fatal foodborne disease caused by the bacterium Clostridium botulinum. C. botulinum produces different toxins, several of which are proteases that cleave neuronal SNARE proteins. What normal process is blocked by cleavage and inhibition of SNARE proteins?

fusion of vesicles with taraget membranes

Researchers studying yeast discovered that, for some mutants, when the temperature at which the cells are grown is elevated from 25ºC to 37ºC, their secretory pathway no longer functions and the cells grow dense with unsecreted protein.When these cells are examined microscopically, they can be divided into groups that vary in terms of where the unsecreted proteins accumulate. In some of the mutants, proteins accumulate in the ER; in others, the Golgi; in others, they accumulate in vesicles near the plasma membrane.

Different temperature-sensitive mutations affect different stages of the transport process

Ricin is one of the most powerful toxins known. The protein consists of two subunits: the A chain is an enzyme that inhibits translation and the B chain is a lectin that binds to carbohydrates on the cell surface. What is the most likely mechanism by which ricin enters the cell?

the protein is internalized by endocytosis

A single-pass transmembrane protein destined for one of the organelles in the endomembrane system would be marked by what type of signal sequence?

a cleaved N-terminal ER signal sequence and an internal stop-transfer sequence