Lehninger’s Biochemistry Chapter 11 – Flashcards

Which one of the following statements about membranes is true? A) Most plasma membranes contain more than 70% proteins. B) Sterol lipids are common in bacterial plasma membranes. C) Sterol lipids are common in human cell plasma membranes. D) Sterol lipids are common in plant cell plasma membranes. E) The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.

The inner (plasma) membrane of E. coli is about 75% lipid and 25% protein by weight. How many molecules of membrane lipid are there for each molecule of protein? (Assume that the average protein is Mr 50,000 and the average lipid is 750.) A) 1 B) 50 C) 200 D) 10,000 E) 50,000

Which of these statements about the composition of biological membranes is false? A) In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially the same complement of lipids and proteins. B) The carbohydrate found in membranes is virtually all part of either glycolipids or glycoproteins. C) The plasma membranes of the cells of vertebrate animals contain more cholesterol than the mitochondrial membranes. D) The ratio of lipid to protein varies widely among cell types in a single organism. E) Triacylglycerols are not commonly found in membranes

Which of these statements about the composition of membranes is true? A) All biological membranes contain cholesterol. B) Free fatty acids are major components of all membranes. C) The inner and outer membranes of mitochondria have different protein compositions. D) The lipid composition of all membranes of eukaryotic cells is essentially the same. E) The lipid:protein ratio varies from about 1:4 to 4:1

Membrane proteins: A) are sometimes covalently attached to lipid moieties. B) are sometimes covalently attached to carbohydrate moieties. C) are composed of the same 20 amino acids found in soluble proteins. D) diffuse laterally in the membrane unless they are anchored E) have all of the properties listed above.

Peripheral membrane proteins: A) are generally noncovalently bound to membrane lipids. B) are usually denatured when released from membranes. C) can be released from membranes only by treatment with detergent(s). D) may have functional units on both sides of the membrane. E) penetrate deeply into the lipid bilayer.

An integral membrane protein can be extracted with: A) a buffer of alkaline or acid pH. B) a chelating agent that removes divalent cations. C) a solution containing detergent. D) a solution of high ionic strength. E) hot water.

The shortest helix segment in a protein that will span a membrane bilayer has about _____ amino acid residues. A) 5 B) 20 C) 50 D) 100 E) 200

A hydropathy plot is used to: A) determine the water-solubility of a protein. B) deduce the quaternary structure of a membrane protein. C) determine the water content of a native protein. D) extrapolate for the true molecular weight of a membrane protein. E) predict whether a given protein sequence contains membrane-spanning segments.

Which of these statements is generally true of integral membrane proteins? A) A hydropathy plot reveals one or more regions with a high hydropathy index. B) The domains that protrude on the cytoplasmic face of the plasma membrane nearly always have covalently attached oligosaccharides. C) They are unusually susceptible to degradation by trypsin. D) They can be removed from the membrane with high salt or mild denaturing agents. E) They undergo constant rotational motion that moves a given domain from the outer face of a membrane to the inner face and then back to the outer.

Which of these is a general feature of the lipid bilayer in all biological membranes? A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer. B) Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the other monolayer. C) Polar, but uncharged, compounds readily diffuse across the bilayer. D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules. E) The polar head groups face inward toward the inside of the bilayer.

The type of motion least common in biological membranes is: A) flip-flop diffusion of phospholipid from one monolayer to the other. B) lateral diffusion of individual lipid molecules within the plane of each monolayer. C) lateral diffusion of membrane proteins in the bilayer. D) lateral diffusion of protein molecules in the lipid bilayer E) random motion of the fatty acyl side chains in the interior of the phospholipid bilayer.

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by: A) a decrease in temperature. B) an increase in fatty acyl chain length. C) an increase in the number of double bonds in fatty acids. D) an increase in the percentage of phosphatidyl ethanolamine E) the binding of water to the fatty acyl side chains.

The fluidity of a lipid bilayer will be increased by: F) decreasing the number of unsaturated fatty acids. C) decreasing the temperature. G) increasing the length of the alkyl chains. D) increasing the temperature. E) substituting 18:0 (stearic acid) in place of 18:2 (linoleic acid).

When a bacterium such as E. coli is shifted from a warmer growth temperature to a cooler growth temperature, it compensates by: A) increasing its metabolic rate to generate more heat. B) putting longer-chain fatty acids into its membranes. C) putting more unsaturated fatty acids into its membranes. D) shifting from aerobic to anaerobic metabolism. E) synthesizing thicker membranes to insulate the cell.

Membrane fusion leading to neurotransmitter release requires the action of: A) cadherins. B) selectins. C) flipases. D) tSNARE and vSNARE. E) none of the above.

Integrins are: A) membrane proteins that are involved in ion transport. B) membrane proteins that are involved in sugar transport. C) membrane proteins that mediate cell adhesion. D) proteins of the extracellular matrix that bind to cell surface proteins. E) proteins that are found at the membrane-cytoplasm interface.

A process not involving the fusion of two membranes or two regions of the same membrane is: A) endocytosis. B) entry of enveloped viruses into cells. C) entry of glucose into cells. D) exocytosis. E) reproductive budding in yeast

According to the current model for HIV infection, which of the following is not involved in the process of membrane fusion? A) A cell surface co-receptor protein B) A cell surface receptor protein C) A viral glycoprotein complex D) The viral chromosome E) The viral envelope

Which of these statements about facilitated diffusion across a membrane is true? A) A specific membrane protein lowers the activation energy for movement of the solute through 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 O2, N2, and CH4 across biological membranes. E) The rate is not saturable by the transported substrate

Facilitated diffusion through a biological membrane is: A) driven by a difference of solute concentration. B) driven by ATP. C) endergonic. D) generally irreversible. E) not specific with respect to the substrate

Glucose transport into erythrocytes is an example of: A) active transport. B) antiport. C) electrogenic uniport D) facilitated diffusion. E) symport.

For the process of solute transport, the constant Kt is: A) analogous to Ka for ionization of a weak acid. B) analogous to Km for an enzyme-catalyzed reaction. C) analogous to Vmax for an enzyme reaction D) proportional to the number of molecules of glucose transporter per cell. E) the maximum rate of glucose transport.

The type of membrane transport that uses ion gradients as the energy source is: A) facilitated diffusion B) passive transport. C) primary active transport. D) secondary active transport. E) simple diffusion.

Consider the transport of glucose into an erythrocyte by facilitated diffusion. When the glucose concentrations are 5 mM on the outside and 0.1 mM on the inside, the free-energy change for glucose uptake into the cell is: (These values may be of use to you: R = 8.315 J/mol•K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.) A) less than 2 kJ/mol. B) about 10 kJ/mol. C) about 30 kJ/mol. D) about -30 kJoule/mol. E) impossible to calculate without knowledge of the membrane potential.

Consider the transport of K+ from the blood (where its concentration is about 4 mM) into an erythrocyte that contains 150 mM K+. The transmembrane potential is about 60 mV, inside negative relative to outside. The free-energy change for this transport process is: (These values may be of use to you: R = 8.315 J/mol.K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.) A) about 5 J/mol. B) about 15 J/mol. C) about 5 kJ/mol. D) about 15 kJ/mol. E) impossible to calculate with the information given.

An electrogenic Na+ transporter: A) catalyzes facilitated diffusion of Na+ from a region of high Na+ concentration to one of lower Na+ concentration. B) must catalyze an electron transfer (oxidation-reduction) reaction simultaneously with Na+ transport. C) must transport both Na+ and a counterion (Cl-, for example). D) transports Na+ against its concentration gradient. E) transports Na+ without concurrent transport of any other charged species.

In one catalytic cycle, the Na+/K+ ATPase transporter transports: A) 2 Na+ out, 3 K+ in, and converts 1 ATP to ADP + Pi. B) 3 Na+ out, 2 K+ in, and converts 1 ATP to ADP + Pi. C) 3 Na+ in, 2 K+ out, and converts 1 ATP to ADP + Pi. D) 1 Na+ out, 1 K+ in, and converts 1 ATP to ADP + Pi. E) 2 Na+ out, 3 K+ in, and converts 1 ADP + Pi to ATP.

Movement of water across membranes is facilitated by proteins called: A) annexins. B) aquaporins. C) hydropermeases. D) selectins. E) transportins.

The specificity of the potassium channel for K+ over Na+ is mainly the result of the: A) differential interaction with the selectivity filter protein. B) hydrophobicity of the channel. C) phospholipid composition of the channel. D) presence of carbohydrates in the channel. E) presence of cholesterol in the channel.

A ligand-gated ion channel (such as the nicotinic acetylcholine receptor) is: A) a charged lipid in the membrane bilayer that allows ions to pass through. B) a membrane protein that permits a ligand to pass through the membrane only when opened by the appropriate ion. C) a membrane protein that permits an ion to pass through the membrane only when opened by the appropriate ligand. D) a molecule that binds to the membrane thereby allowing ions to pass through. E) always requires a second ligand to close the channel once it is opened.