BIOL2200 Membrane Module Revision Quiz

The glucose uniporter GLUT1 has a Km of 1.5 mM for d-glucose and 30 mM for d-galactose. At a concentration of 5 mM for each, what is the rate of glucose transport relative to galactose transport? The Vmax may be assumed to be the same for both. a. 20-fold faster b. 5.5-fold faster c. equal d. 3.7-fold slower

b

Which of the four classes of ATP-powered pumps share overall similarity: several subunits, the same general organization, and a similar function as H+ transporters? a. ABC superfamily and F-class pumps b. F-class pumps and V-class pumps c. ABC superfamily and V-class pumps d. F-class pumps and P-class pumps e. ABC superfamily and P-class pumps

b

A mutant channel protein is expressed in an oocyte. Compared to patch clamping experiments in oocytes expressing the normal channel, the length of downward deviations is diminished by half. This indicates: a. the mutant channel behaves the same as the wild-type channel. b. the mutant channel doesn't make a functional channel. c. the mutant channel doesn't stay open as long. d. the mutant channel opens more frequently.

c

A transmembrane protein has the following properties: it has two binding sites, one for solute A and one for solute B. The protein can undergo a conformational change to switch between two states: either both binding sites are exposed exclusively on one side of the membrane, or both are exposed exclusively on the other side of the membrane. The protein can switch between the two conformational states only if both binding sites are occupied or if both binding sites are empty, but cannot switch if only one binding site is occupied. What kind of binding site do these properties define? a. antiporter b. uniporter c. symporter d. ion channel

c

Movement of phospholipids from one leaflet to the other a. occurs routinely. b. is restricted to mitochondrial membrane. c. requires flippases d. requires cholesterol. e. is impossible.

c

Normally Na+ ions cannot cross the plasma membrane except through the use of a transport protein. This is because: a. the Na+ ions form a bond to the negatively charged external surface of the membrane b. hydrophilic ions are attracted to the hydrophobic part of the lipid bilayer, and tightly bind to it c. hydrophilic ions and molecules are not soluble in the hydrophobic center of the lipid bilayer d. the external surface of the membrane is positively charged and the Na+ ions are repelled e. the external surface of the plasma membrane contains glycoproteins, which bind Na+ ions and prevent them from crossing the membrane

c

Phospholipid bilayers are NOT stabilised by: a. hydrophobic interactions b. ionic bonds c. covalent bonds d. van der Walls forces e. hydrogen bonds

c

Porins a. have many hydrophobic α-helical regions b. are peripheral membrane proteins c. allow small hydrophilic molecules to pass through a membrane. d. contain no hydrophobic amino acid residues e. are a class of lipid molecules

c

Predict which of the following organisms will have the highest percentage of unsaturated fatty acid chains in their membranes. a. thermophilic bacterium b. polar bear c. antarctic fish d. desert iguana e. human being

c

The difference between direct, or primary, active transport and indirect, or secondary, active transport is: a. in primary transport, the ion is transported from a low concentration to a high concentration, while in secondary transport, transport occurs in the opposite direction b. in primary transport, the ion is transported from a low concentration to a high concentration and ATP is expended; in secondary transport, the ion is transported from a high concentration to a low concentration and ATP is synthesized c. in primary transport, transport is directly coupled to the hydrolysis of ATP, while in secondary transport the source of energy for transport is an ion gradient d. primary active transport moves ions (e.g. Na+, H+) across the membrane, while secondary active transport moves molecules (e.g. glucose, amino acids) across the membrane e. primary active transport transports only one ion, while secondary active transport transports two ions

c

________________________________________________ are transmembrane proteins? a. Extracellular matrix proteins b. Peripheral membrane proteins c. Integral membrane proteins d. Lipid-anchored membrane proteins

c

Aquaporins are: a. ABC proteins. b. type of sterol lipid. c. beta-barrel proteins in the outer membrane of bacteria. d. water channels. e. symporters.

d

In a laboratory activity, red-labeled glucose, blue-labeled water, and green-labeled ethanol are added to a solution placed over an artificial, pure phospholipid membrane. Which colors will be observed on the other side of the membrane after 10 minutes? a. red b. blue c. green d. b and c

d

In which of the following cases is energy NOT needed for transmembrane transport? a. Lysine moves into the cell against its concentration gradient via the Na+/lysine symporter. b. Potassium ions (K+) move out of the cell down the K+ concentration gradient via potassium channels. c. Glucose moves into the cell down its concentration gradient via a glucose uniporter. d. The second and third answers are correct. e. all of the above

d

Which of these substances are unable to pass through membranes passively through simple diffusion? a. CO2 b. Urea c. Water d. Glycerophospholipids e. Triacylglycerides

d

All the following statements describe biomembranes except a. Some biomembranes have free edges. b. Some phospholipids and cholesterol may cluster to form lipid rafts. c. Different biomembranes may contain different proportions of the same phospholipids d. The two leaflets of a biomembrane may contain different phospholipids

d,c? nope try a next then b

What type of single-pass membrane protein would contain a hydrophobic membrane-spanning alpha-helix? a. integral membrane protein and peripheral membrane protein b. integral membrane protein c. transmembrane protein d. peripheral protein e. transmembrane protein and integral membrane protein

e

Which of the following classes of lipids is (are) present in biomembranes? a. phosphoglycerides b. sphingolipids c. sterols d. saccharolipids e. all of the above

e

A symporter would function as an antiporter if its orientation in the membrane was reversed (meaning the portion of the protein normally exposed to the cytosol faced the outside of the cell instead). True False

False

The co-transport of Na+ and a solute into the cell, which harnesses the energy of the Na+ gradient, is an example of primary active transport. True False

False

The plasma membrane is highly impermeable to all charged molecules? True False

False

Order the molecules on the following list according to their ability to diffuse through a lipid bilayer, beginning with the one that crosses the bilayer most readily. RNA Ca2+ CO2 Ethanol H20 Glucose

RNA = 6 Ca2+ = 5 CO2 = 1 Ethanol = 2 H20 = 3 Glucose = 4 the capacity of molecules to diffuse through a lipid bilayer depends on size and polarity

Although lipid molecules are free to diffuse in the plane of the bilayer, they cannot flip-flop across the bilayer unless enzyme catalysts called phospholipid translocators are present in the membrane True False

True

Although lipid molecules are free to diffuse in the plane of the bilayer, they cannot flip-flop across the bilayer unless enzyme catalysts called phospholipid translocators are present in the membrane True or False?

True

Monomeric single-pass transmembrane proteins span a membrane with a single alpha-helix that has characteristic chemical properties in the region of the bilayer. Which of the four 20-amino-acid sequences listed below is the most likely candidate for such a transmembrane helix? a. ITLIYFGVMAGVIGTILLIS b. ITPIYFGPMAGVIGTPLLIS c. ITEIYFGRMAGVIGTDLLIS d. ITEIYFGRMAGPPGTDLLIS

a

Phosphoglyceride is a. The main type of phospholipid in animal cell membranes, with two fatty acids and a polar head group attached to a three-carbon glycerol backbone. b. A lipid molecule with a characteristic four-ring structure that is an important component of plasma membranes of animal cells, c. Artificial phospholipid bilayer vesicle formed from an aqueous suspension of phospholipid molecules. d. A small region of the plasma membrane enriched in sphingolipids and cholesterol. e. An integral membrane protein.

a

Which statement about cholesterol is INCORRECT? a. Cholesterol is an integral membrane protein b. Cholesterol has a four-ring molecular structure c. The nuclear membrane contains cholesterol d. Cholesterol is a major component of the plasma membrane in animal cells e. Ergosterol is structurally similar to cholesterol

a