1. Which of the following statements about passive and primary active transport proteins is FALSE?

Transcription

1 Biological Membranes 1. Which of the following statements about passive and primary active transport proteins is FALSE? A. They are both integral membrane proteins. B. They both show a high degree of selectivity. C. Both require a concentration gradient to function. D. They both change conformation during transport. 2. Which one of the following statements is TRUE for passive transport across a biological membrane? A. Passive transport is driven by a solute concentration gradient. B. Passive transport is driven by ATP. C. Passive transport is endergonic. D. Passive transport is irreversible. E. Passive transport is not specific with respect to the substrate. 3. Which of the following determines the force that "drives" an ion through an ion channel in a membrane? A. The size of the concentration gradient across the membrane. B. The size and shape of the channel. C. The size of the ion. D. The properties of the selectivity filter. 4. Which of the following statements about biological membranes is TRUE? A. Integral membrane proteins penetrate or span the lipid bilayer, interacting with the hydrophobic lipid acyl chains. B. The composition of membrane lipid bilayers may be varied slightly, to maintain it in the gel crystalline state. C. The bilayer is stabilized by hydrophobic interactions between the polar lipid head groups and the aqueous environment. D. Peripheral membrane proteins are covalently bound with the polar lipid head groups of the bilayer.

2 5. Which of the following is never found in biological membranes? A. Glycerophospholipids B. Cholesterol C. Sphingolipids D. Triacylglycerols E. Sphingolipids and Triacylglycerols 6. A transporter protein moves substances X and Y as shown in the following diagram. It moves X down its concentration gradient and Y up its concentration gradient. What type of transport is this? A. Primary active antiport. B. Primary active symport. C. Secondary active antiport. D. Secondary active symport. 7. The following are steps which incompletely describe the mechanism by which Na + and K + ions are transported by the Na + K + ATPase. What is the correct sequence for the events listed, assuming that Na+ ions have just dissociated? 1. The phosphate group on the protein is hydrolyzed. 2. ATP binds to the protein. 3. The protein's conformation changes, exposing K + binding sites to the cell interior. 4. Na + ions bind. A. 1, 3, 2, 4 B. 1, 3, 4, 2 C. 4, 2, 3, 1 D. 4, 2, 1, 3

3 8. Why are glycerophospholipids capable of spontaneously assembling into the bilayer structure found in biological membranes? A. Glycerophospholipids are amphipathic. B. Glycerophospholipids have two acyl chains that align easily side by side to form a bilayer. C. Fatty acids are weakly amphipathic. D. Glycerophospholipids are amphipathic. Secondly, glycerophospholipids have two acyl chains that align easily side by side to form a bilayer. E. All of the statements are true. 9. Which of the following statements most accurately defines the term symport.? A. A protein which transports two substances in the same direction. B. A protein which transports two substances in opposite directions. C. A protein which transports two substances in the same direction up their concentration gradients. D. A protein which transports two substances in opposite directions up their concentration gradients. 10.Transport of digested glucose across intestinal cells from the intestinal space to the blood requires multiple transporters. Which one of the following is NOT required? A. The Na-glucose symporter. B.The Na + K + -ATPase antiporter. C. The K + channel uniporter. D.The glucose uniporter. 11. You have discovered a protein that transports Ca2+ ions up a concentration gradient, from the cytoplasm into the endoplasmic reticulum. No other ions move during this transport. Which type of transport protein does this appear to be? A. Ca 2+ ion channel. B. Ca 2+ ion porin. C. Primary active uniport. D. Secondary active uniport

4 12. Which one of the following statements about passive transport across a membrane is TRUE? A. A specific membrane protein lowers the activation energy for movement of the solute across the membrane. B. It can increase the size of a transmembrane concentration gradient of the diffusing solute. C. It is impeded by the solubility of the transported solute in the nonpolar interior of the lipid bilayer. D. It is responsible for the transport of gases such as O 2, N 2, and CH 4 across biological membranes. 13. Ion channels are selective whereas porins are not. Which of the following statements explains this difference? A. In porins the channel is located within a single subunit, whereas in ion channels it is located between subunits. B. Ion channels transport charged substances, whereas porins transport polar substances. C. The quarternary structure of ion channels includes amino acids that are positioned to form non covalent interactions with the ion. D. Porins typically cross the lipid bilayer as barrels, whereas the subunits in ion channels cross the lipid bilayer as helices.

5 14. This graph shown represents the rates of two distinct enzyme catalyzed reactions. Which of the following statements is TRUE? A. The dotted curve for enzyme 2 represents positive allostery. B. Enzyme 1 has a lower affinity for its substrate compared to enzyme 2. C. The substrate for enzyme 2 is a homoallosteric inhibitor of enzyme 2. D. An inhibitor of enzyme 1 would cause the solid curve to assume the shape of the dotted curve. 15. In the figure shown which of the labelled carbons is the beta carbon? A. V B. X C. Y D. Z

6 16. Which of the following conclusions can be drawn regarding the protein shown, given ONLY the information in the diagram? A. This protein is a transporter protein. B. This protein is an ion channel. C. This protein is not a porin. D. This protein is not an active transporter.

7 17.Which of the following does NOT correctly describe the picture below? A. Polyunsaturated B. 18:2delta9,12 C. Fatty acid. D. Forms a bilayer in aqueous solution.

8 18. The attached diagram shows the structure of an integral membrane protein. The solid lines indicate the approximate location of the polar headgroups of the lipid bilayer. Which arrow most correctly identifies a region in the protein where you would expect to find amino acid residues such as Leu, Ile, Val and Ala? A. 1 B. 2 C. 3 D Which of the following is TRUE for BOTH primary and secondary active transporters? A. Transport occurs via proteins that form a channel through the membrane. B. They catalyze ATP hydrolysis to pump a substance against its concentration gradient. C. They couple the transport of one substance against its gradient with cotransport of a second substance down its concentration gradient. D. They require free energy input to move a substance against its concentration gradient.