Unit 7: Intracellular Transport and Protein Sorting Flashcards
A signal sequence that will direct a protein to a particular location within a eukaryotic cell
a) is attached to the protein as a post-translational modification
b) is translated from a sequence of bases in the transcript for that protein
c) refers to a sequence of bases added to the mRNA transcript for that protein after the transcription is exported from the nucleus
d) is encoded in the gene for that protein
e) both B and D are true
e) both b and d
Why are lysosomes considered part of the endomembrane system?
a) they deposit end-products of digestion in the endoplasmic reticulum
b) they facilitate movement between stacks of the Golgi
c) they are formed from membrane derived from the ER and Golgi, and contain proteins synthesized into the ER and processed by the Golgi
d) they are formed from the plasma membrane as a result of endocytosis
e) lysosomes are not part of the endomembrane system
c)
The nucleotide monomers of DNA and RNA enter the nucleus by:
a) diffusion through nuclear pores
b) expressing a nuclear localization signal recognized by a nuclear import receptor, that escorts them through a nuclear pore
c) diffusion through ion channels on the bilayers of the nuclear envelope
d) expression of an import sequence recognized by import receptors that escort them to translocator channels spanning the nuclear envelope
a) they are very small molecules
Most proteins that enter the ER:
a) cross the ER membrane in a folded state
b) are transported across the membrane while their synthesis is complete
c) begin to cross the ER membrane while still being synthesized
d) are fully synthesized on free ribosomes in the cytosol
e) never leave the ER
c) ribosomes bind to ER membrane while still translating proteins
Proteins found in the ER of an animal cell are about 20 amino acids longer when they are expressed in the lab in the cytosol of a bacterial cell. What is an explanation for the greater length of these polypeptides?
a) the sequence aids the bacterial ER to package these proteins for shipping to the Golgi
b) sequence normally serves as a signal sequence that directs the protein to the ER in the animal cell, where the signal would be cleaved off during translation. No such processing occurs in the bacterial cell
c) bacterial cell uses different genetic code and results in longer primary sequence
d) protein has a different function in the bacterial cell than in the ER of the animal cell
b) bacterial cells do not have internal membranes so no ER signal sequences are required
Which of the following best reflects the journey of a protein to be expressed on the plasma membrane?
a) lysosome –> endosome –> plasma membrane
b) ER –> transport vesicle –> Golgi –> lysosome –> plasma membrane
c) Er –> transport vesicle –> Golgi –> transport vesicle –> plasma membrane
d) Golgi –> endosome –> plasma membrane
c)
Although mitochondria have their own genome, most mitochondrial proteins are encoded by the nuclear genome. How do these proteins find their way into the mitochondria?
a) attachment of ribosomes to outer mitochondrial pores and direct deposition into the inner mitochondrial compartment
b) mRNAs that are manufactured in the nucleus, but translated by mitochondrial ribosomes
c) signal sequences
d) transport vesicles
c) signal sequences
Proton has already been translated and transcribed so no more need for ribosomes
After isolated the rough ER from the rest of the cytoplasm, you purify the mRNAs attached to it. Which of the following types of proteins do you expect these mRNAs to encode?
a) soluble secreted proteins
b) plasma membrane proteins
c) ER membrane proteins
d) a and c
e) a, b and c
e)
The process by which enzymes are released by epithelial cells of the salivary gland in response to an acetylcholine signal could be referred to as
a) exocytosis
b) pinocytosis
c) regulated secretion
d) halitosis
e) both a and c
e)
Oligosaccharides displayed on the extracellular surfaces of blood cells would have been attached to membrane proteins by enzymes:
a) in the extracellular matrix
b) acting at the cytosolic surface of the ER and Golgi
c) in the cytosol
d) in the lumen of the ER and Golgi
d)
Clathrin, a cytolisc protein involved in formation of spherical vesicles for intracullar trafficking, is:
a) important in the formation of coated pits on the plasma membrane
b) synthesized in the cytosol on free ribosomes
c) involved in the transport of materials from the trans face of the Golgi
d) a and c
e) a, b and c
e)
Tetanus toxin is known to cleave SNARE proteins. These toxins would be expected to interfere with:
a) ion transport
b) protein folding
c) gene transcription
d) nuclear transport
e) exocytosis
e)
A cell in which the rate of constitutive secretion significantly exceeded that of pinocytosis would be expected to:
a) divide by cytokinesis
b) enlarge
c) have large amounts of rough ER
d) shrink
e) rupture
b)
The Unfolded Protein Response:
a) results in the synthesis of more molecular chaperone proteins
b) involves detection of misfolded proteins in the cytosol
c) will lead to expansion of ER in cells synthesizing large quantities of secretory protein
d) a and c
e) a, b and c
d) UPR only responsible for proteins inside the ER not in the cytosol
The most extensive component of the endomembrane system, in terms of membrane surface area, is/are the:
a) plasma membrane
b) mitochondrial membranes
c) endoplasmic reticulum
d) nuclear envelope
e) Golgi apparatus
c)
