Deck 9: Membranes and Membrane Transport

Question 1

Lipid bilayers differ from micelles in that micelles are:

A) self limiting structures.
B) formed spontaneously.
C) stable in aqueous solution.
D) often transformed into vesicles.
E) all are true.

Answer 1

A

Question 2

Which of the following IS NOT a property of integral membrane proteins (intrinsic proteins)?

A) they contain both hydrophobic surfaces and hydrophilic surfaces
B) they dissociate from the membrane by treatment with salt solutions
C) they are exposed to at least one aqueous surface surrounding the membrane
D) they are inserted into the membrane and sequestered largely by hydrophobic interactions
E) they have significant lateral mobility

Answer 2

B

Question 3

Generally, over 90% of all membrane phosphatidyl serine (PS) is found on the inner monolayer of the cell membrane. Which of the following explains this phenomenon?

A) when PS is found in the outer monolayer, a floppase enzyme is used to move it to the inner monolayer
B) the movement of phospholipids from one monolayer to another is a very slow reaction despite the fact that it works with the concentration gradient
C) under normal conditions within the cell, the activity of scramblase enzymes is relatively low and thus does not allow for movement between monolayers
D) All of the above are correct
E) B and C above are correct

Answer 3

E

Question 4

Flippases are enzymes that flip:

A) fatty acids from one position on glycerol to another position.
B) glucose from α- to β-glucose.
C) amino acids from one position to another in a protein.
D) cholesterol from one organelle to another.
E) phospholipids across to the other side of a membrane.

Question 5

In eukaryotic cells phospholipids, glycolipids and cholesterol are synthesized by enzymes located in the ____ and ____, and flow of these components to other membranes in the cell is mediated by ____.

A) plasma membrane; mitochondria; osmosis
B) endoplasmic reticulum; Golgi; osmosis
C) plasma membrane, Golgi; lipid transfer proteins
D) endoplasmic reticulum; Golgi; lipid transfer proteins
E) endoplasmic reticulum; plasma membrane; flippases

Question 6

G protein-α-subunits are anchored into membranes by:

A) amine-linked myristoyl anchors.
B) thioester-linked fatty acyl anchors.
C) amide-linked prenyl anchors.
D) thioester-linked prenyl anchors.
E) amide-linked glycosyl phosphatidylinositol anchors.

Question 7

The plasma membrane is responsible for all EXCEPT:

A) energy transduction.
B) exclusion of certain toxic ions and molecules.
C) signal transduction.
D) accumulation of cell nutrients.
E) all are true.

Question 8

Which of the following is true regarding membrane function?

A) a caveola contains a very high concentration of cholesterol and unsaturated phospholipids
B) scaffolding proteins, particularly those containing BAR domains, result in curvature of the cell membrane
C) lateral membrane diffusion within a biological membrane is a completely unrestricted process
D) membrane fusion with vesicles is often accomplished with the aid of a SNARE protein
E) both b and d are correct

Question 9

Liposomes are all EXCEPT:

A) used to introduce contrast agents into the body for diagnostic imaging procedures.
B) able to fuse with cells.
C) highly stable structures.
D) possible to prepare with different inside and outside solutions.
E) all are true.

Question 10

The Ras proteins are associated to the membrane via what mechanism?

A) thioester-linked fatty acyl anchor
B) thioether-linked prenyl anchor
C) carboxy terminal ester-linked prenyl anchor
D) insertion of a portion of an amphipathic helix into the membrane
E) both b and c

Question 11

Which of the following would be the most likely interaction between a peripheral membrane protein that contained a high lysine content and a membrane?

A) ionic interaction
B) hydrophobic interaction
C) hydrogen bonding
D) covalent bonding
E) both a and c

Question 12

Which of the following is a commonly used mechanism for anchoring a protein to a membrane?

A) attaching a fatty acid to a serine residue to form an ester
B) attaching a fatty acid to a methionine residue to form a thioester
C) attaching a farnesyl group to a cysteine residue to form a thioether
D) attaching a fatty acid to a glutamine residue to form an amide
E) none of the above

Question 13

All are true for phase transitions of lipid bilayers EXCEPT:

A) the transitions are exothermic.
B) particular phospholipids display characteristic transition temperatures.
C) pure phospholipid bilayers have narrow transition ranges.
D) volume changes usually are associated with phase transitions.
E) solutes interacting with membrane lipids affect transition temperatures.

Question 14

The porin proteins (e.g., maltoporin) utilize the ____ structural motif.

A) single transmembrane α-helix
B) multiple transmembrane α-helixes
C) single β-sheet
D) multiple β-sheet
E) none of the above

Question 15

Which of the following is an example of a unilamellar vesicle?

A) monolayer
B) bilayer
C) liposome
D) micelle
E) an inside out micelle

Question 16

In passive diffusion, the transported species moves across the membrane in the ____ favored direction ____.

A) kinetically; using a transport protein
B) kinetically; without a specific transport system/molecule
C) thermodynamically; using a transport protein
D) thermodynamically; without a specific transport system/molecule
E) none of the above.

Question 17

The two major phospholipids on the outer leaflet of erythrocytes are:

A) phosphatidylcholine and phosphatidylethanolamine.
B) phosphatidylcholine and sphingomyelin.
C) phosphatidylethanolamine and sphingomyelin.
D) phosphatidylserine and sphingomyelin.
E) phosphatidylcholine and phosphatidylserine.

Question 18

Glycophorin is a membrane protein with:

A) multiple transmembrane segments.
B) most of the mass oriented outside the surface of the cell.
C) about 10% carbohydrate and 90% protein.
D) transmembrane β-barrel segments.
E) All are true

Question 19

When we say that biological membranes are asymmetric structures we mean that:

A) The lipids are not evenly distributed transversely in the membrane.
B) The proteins are not evenly distributed over the surface of the membrane.
C) Patches of cholesterol and other lipids occur on the surface of the membrane.
D) Certain membrane proteins seem to prefer association with specific lipids.
E) All are true

Question 20

Lipids that spontaneously form micelles, monolayers and bilayers have what property?

A) waxy
B) polar
C) amphipathic
D) bipolar
E) polyisoprenoid

Question 21

Ouabain, an effective inhibitor of Na⁺, K⁺-ATPase, exhibits all of the following characteristics EXCEPT:

A) It has a basic steroid structure.
B) It contains an unsaturated lactone ring at C-17.
C) It binds on the extracellular surface of Na⁺, K⁺-ATPase.
D) It binds tightly to the enzyme/ATP complex in producing the inhibition.
E) It is a cardiac glycoside.

Question 22

The System A for alanine transport into liver is a(n) ____ system that can be activated by ____ and ____.

A) Na⁺-symport; substrate (alanine); hormones
B) K⁺-symport; substrate (alanine); hormones
C) H⁺-antiport; pH change; alanine
D) ATP-antiport; alanine; pH change
E) None are true

Question 23

Hydropathy plots for transport proteins are utilized to reveal:

A) amino acid residues which may be highly modified.
B) amino acid residues which may be directly involved in facilitated transport.
C) stretches of amino acid residues that make up hydrophobic regions, which may be directly associated with the lipid bilayer.
D) amino acid residues which are hyper-reactive due to their location.
E) whether there is interaction between N-terminal and C-terminal amino acids.

Question 24

Multiple Drug Resistant (MDR)-ATPase is a ____ repeat protein that uses ATP hydrolysis to actively transport a wide variety of drugs ____ the cell.

A) multiple; into
B) multiple; out of
C) tandem; into
D) tandem; out of
E) triple; into

Question 25

Secondary active transport across a membrane refers to

A) Movement of a molecule across a membrane and against its concentration gradient powered by an ion gradient that is created by a different transporter
B) Movement of a molecule across a membrane and against its concentration gradient through a transporter that is directly powered by ATP hydrolysis
C) Movement of a molecule across a membrane powered by its own concentration gradient
D) Movement of a molecule across a membrane through a transporter that has an alpha-helical secondary structure.
E) none of the above

Question 26

The transport of glutamine across a membrane was measured, and the results obtained are presented in the following table. What type of transport does Gln exhibit?

A) primary active transport
B) secondary active transport
C) passive diffusion
D) facilitated diffusion
E) cannot determine from the given data

Question 27

In a typical Na⁺,K⁺-ATPase, _____ sodium ions are moved from the _____ of the cell while _____ potassium ions are moved from the _____ of the cell

A) 2; inside to outside; 3; outside to inside
B) 3; inside to outside; 2; outside to inside
C) 2; outside to inside; 3; inside to outside
D) 3; outside to inside; 2; inside to outside
E) none of the above

Question 28

Active transport is uniquely characterized by:

A) transport of hydrophobic molecules.
B) transport of hydrophilic molecules.
C) transport of a molecule or ion across a membrane, with the species going from a greater concentration to a lesser concentration.
D) the tight coupling of an input of energy to drive a thermodynamically unfavorable reaction.
E) absolute requirement for ATP hydrolysis, and light energy or ion gradient energy will not work.

Question 29

Pore-forming toxins solve the problem of a need to provide hydrogen-bonding partners for the polypeptide background N−H and C=O groups in the bilayer that lacks hydrogen-bond donors and acceptors by utilizing extensive:

A) salt bridge formation.
B) disulfide bond formation.
C) β-turns.
D) α-helices and β-sheets.
E) none of the above.

Question 30

H⁺-transporting ATPases found in ____ break down bone during normal bone remodeling are of the ____ type of ATPases.

A) osteoclasts; vacuolar (V-)
B) osteoclast; H⁺, K⁺-ATPase
C) osteoblast; H⁺, K⁺-ATPase
D) osteoblast; vacuolar (V-)
E) osteoclast; Na⁺, K⁺-ATPase

Question 31

In the Na⁺, K⁺-ATPase mechanism, ATP is involved in all EXCEPT:

A) binding E₂ to change conformation to E₁ and release of K⁺.
B) binding E₁ to facilitate binding of Na⁺.
C) transferring a phosphate group to make sodium phosphate.
D) hydrolysis to ADP and E₁-P.
E) none of the above.

Question 32

Secondary active transport is:

A) establishment of a cation or anion gradient with an ATPase that subsequently drives transport of an amino acid or sugar against a concentration gradient.
B) the use of an ATPase to establish an anion or cation gradient.
C) the antiport process of transporting species in opposite directions.
D) establishment of an ATP gradient across a membrane that drives uptake of sugars.
E) symport of malate and glutamate so that metabolism can synthesize ATP.

Question 33

Bacteriorhodopsin affects a light driven ____ proton transport that results in a proton gradient sufficient to drive ____.

A) inward; Na⁺-import
B) outward; ATP synthesis
C) inward; K⁺-export
D) outward; light emission
E) none are true

Question 34

The Ca²⁺-ATPase structure is like many of the other active transport proteins in that it has all of the components EXCEPT:

A) transmembrane domain of ten α-helical segments.
B) a large cytoplasmic domain with nucleotide binding domain.
C) a phosphorylation domain.
D) an actuator domain.
E) all are true.

Question 35

People with high blood pressure have high blood levels of an endogenous Na⁺, K⁺-ATPase ____ that results in ____ of sodium and calcium in cells lining the blood vessel wall.

A) inhibitor; decrease
B) stimulator, decrease
C) inhibitor; accumulation
D) stimulator; accumulation
E) none of the above

Question 36

Nearly all of the calcium ions in muscle are sequestered inside vesicles called:

A) mitochondria.
B) sarcoplasmic reticulum.
C) endoplasmic reticulum.
D) Golgi.
E) secretory vesicles.

Question 37

Discuss the preferred locations of different amino acids in transmembrane proteins.​

Question 38

Glucose transport across cell membranes varies depending upon blood glucose levels. When glucose levels are high, glucose transport exhibits saturation kinetics. When glucose concentrations are low, the transport of glucose across the membrane is dependent upon the sodium ion concentration. What types of transport is observed for glucose?

A) facilitated diffusion at high [glucose], secondary active transport at low [glucose]
B) simple diffusion at high [glucose], secondary active transport at low [glucose]
C) facilitated diffusion at high [glucose], primary active transport at low [glucose]
D) simple diffusion at high [glucose], primary active transport at low [glucose]
E) none of the above are correct

Question 39

All are characteristic of the gastric proton pump EXCEPT:

A) Gastric proton pump requires high levels of dietary K⁺ to create a K⁺ gradient.
B) Gastric proton pump is a H⁺, K⁺-ATPase.
C) Gastric proton pump maintains a pH gradient of about 6.6 across the mucosal cell membrane.
D) Gastric proton pump is electroneutral.
E) Gastric proton pump produces a net influx of HCl into the stomach.

Question 40

Muscle Ca²⁺-ATPase resembles Na⁺, K⁺-ATPase in many ways EXCEPT:

A) Both have α-subunits of similar size.
B) Both form covalent E-P intermediates during ATP hydrolysis.
C) Both have similar mechanisms of ATP hydrolysis.
D) Both have similar ion transport mechanisms.
E) Both have residence on the sarcoplasmic reticulum.

Question 41

Explain the structure of caveolae.​

Question 42

Explain how gradients of Na⁺ and H⁺ drive secondary active transport systems.​

Question 43

Discuss ClC channels.​

Question 44

Explain the formation of thioether-linked prenyl anchor proteins.​