Deck 2: The Cytoplasm

Question 1

In transmission EM preparations of cells the cell membrane often appears as a trilaminar structure having two parallel dark-staining components on either side of an unstained middle layer. This central poorly stained region of the membrane is primarily responsible for which of the following functions?

A) Creation of a barrier to water-soluble molecules
B) Binding by cellular receptions to specific ligands
C) Catalyzing membrane-associated activities
D) Transport of ions
E) Connections to the cytoskeleton

Answer 1

Creation of a barrier to water-soluble molecules

Question 2

Chaperonins are cytoplasmic proteins most likely to be found in which of the following organelles?

A) Lysosomes
B) Golgi complexes
C) Rough endoplasmic reticulum
D) Smooth endoplasmic reticulum
E) Mitochondria

Answer 2

Rough endoplasmic reticulum

Question 3

Which of the following best defines the term "exocytosis"?

A) The discharge of ions or small molecules from a cell by protein pumps in the cell membrane
B) The uptake of material at one domain of a cell's surface and its discharge from the opposite side of the cell
C) The process by which proteins move from one cytoplasmic compartment to another
D) The discharge of proteins in cytoplasmic vesicles from a cell following fusion of the vesicles with the plasmalemma
E) Diffusion of lipid-soluble molecules from a cell across the cell membrane

Answer 3

The discharge of proteins in cytoplasmic vesicles from a cell following fusion of the vesicles with the plasmalemma

Question 4

Cytoplasm often stains poorly because its lipid content is removed by the organic solvents used in the clearing step in routine histological preparations. This problem is most likely to occur with cytoplasmic regions rich in which of the following organelles?

A) Free polysomes
B) Mitochondria
C) Lysosomes
D) Smooth endoplasmic reticulum
E) Rough endoplasmic reticulum

Question 5

Polarity in microtubules is important in determining which of the following?

A) The strength of vinblastine binding to microtubules
B) The velocity of transport along microtubules with myosin motors
C) The overall dynamic instability of the microtubules
D) The linkage of microtubules to intermediate filaments
E) The direction of vesicular transport along microtubules

Question 6

Which of the following proteins is/are most likely to have initially contained a "signal peptide" that bound a "signal recognition particle" during its translation?

A) An enzyme of the respiratory chain
B) Lamins
C) Proteins in secretory granules
D) F-actin
E) Proteins in the large ribosomal subunit

Question 7

Vesicles of a Golgi apparatus that are destined to become part of other organelles most likely have which of the following on their membranes?

A) Channel proteins
B) Clathrin
C) COP II
D) Actin
E) GTP

Question 8

About 3 years ago, a 39-year-old construction worker became increasingly uncoordinated. His wife describes bouts of depression and apathy beginning about a decade ago. Laboratory tests are normal. MRI and CT reveal striatal and caudate atrophy with "boxcar ventricles." His mini-mental status examination score is $24 / 30$ . The cranial nerve examination shows dysarthria, saccadic extraocular eye movements, and a hyperactive gag reflex. There is increased tone in all extremities. Polymerase chain reaction reveals one normal band with $20 \mathrm{CAG}$ (trinucleotide) repeats and the other with 49 CAG repeats. Modulation of respiration and mitochondrial membrane potential, and bioenergetic failure are associated with the abnormal gene in this disease. Which of the following mechanisms used to establish the mitochondrial electrochemical gradient may be altered in this disease?

A) The action of ATP synthase
B) Transfer of electrons from NADH to $\mathrm{O}_{2}$ in the intermembrane space
C) Pumping of protons into the mitochondrial matrix by respiratory chain activity
D) Proton-translocating activity in the inner membrane
E) Transport of ATP out of the matrix compartment by a specific transporter

Question 9

A 56-year-old man has been taking atorvastatin because of a poor lipid profile and a family history of cardiovascular disease. The statin family of drugs enhances endocytosis of low-density lipoprotein (LDL) from the blood. Endocytosis of LDL differs from phagocytosis of bacterial cells in which of the following ways?

A) Use of membrane-enclosed vesicles in the uptake process
B) Coupling with the lysosomal system
C) Dependence on acidification
D) Use of clathrin-coated pits
E) Use of hydrolases

Question 10

A 14-year-old boy is diagnosed with epidermolysis bullosa simplex (EBS). His skin blisters easily with rubbing or scratching. Blisters occur primarily on his hands and feet and heal without leaving scars. Genetic analysis shows mutations in the KRT5 and KRT14 genes, which code keratin 5 and keratin 14 . What is the primary function of those proteins?

A) Generate movement
B) Provide mechanical stability
C) Carry out nucleation of microtubules
D) Stabilize microtubules against disassembly
E) Transport organelles within the cell