Basics about the Membrane
What are the two major components of membranes? Hint: they are macromolecules
lipids and proteins
Where does membrane synthesis begin?
ER
Which of the following correctly describes a transporter versus a channel?
a. transporters form continuous pores that remain open at all times
b. channels undergo conformational changes to bind and release specific solutes
c. transporters bind solutes and undergo conformational changes to move them across the membrane
d. channels require ATP for every molecule they move
c. transporters bind solutes and undergo conformational changes to move them across the membrane
Which of the following statements about membrane lipids is TRUE?
a. phospholipids are entirely hydrophobic
b. phosphatidylcholine has a polar head and two polar tails
c. membrane phospholipids are amphipathic molecules
d. lipids are only found on the cytosolic side of the plasma membrane
c. membrane phospholipids are amphipathic molecules
Which of these statements about passive vs active transport is TRUE?
a. passive transport always require ATP
b. active transport moves molecules down their concentration gradient
c. passive transport of charged molecules through channels is driven by the electrochemical gradient
d. active transport never involves conformational changes in the transporter
c. passive transport of charged molecules through channels is driven by the electrochemical gradient
What drives the spontaneous formation of the lipid bilayer in water?
hydrophobic interactions that make the tail edges seal off to minimize exposure
Which enzyme transfers new phospholipids from one leaflet to another in the Golgi?
flippase
The Na+/K+ pump moves ions in which directions across the plasma membrane?
3 Na+ out, 2 K+ in
Which of these statements about membrane fluidity is FALSE?
a. cholesterol decreases membrane permeability
b. longer hydrocarbon tails increase membrane rigidity
c. unsaturated fatty acids pack tightly together, increasing viscosity
d. bacteria can adjust the degree of tail saturation in response to temperature
c. unsaturated fatty acids pack tightly together, increasing viscosity
Which of the following about ion gradients is FALSE?
a. the Na+/K+ pump maintains a higher Na+ concentration inside the cell
b. electrochemical gradients depend on both charge and concentration
c. Ca+2 pumps help maintain low cytosolic calcium levels
d. the proton pump in lysosomes acidifies the organelle interior
a. the Na+/K+ pump maintains a higher Na+ concentration inside the cell
Shorter fatty acid tails make the membrane more or less fluid?
more fluid
The hydrophobic core of the lipid bilayer primarily interacts with what region of a transmembrane protein?
non-polar side chains of the transmembrane a-helices
Which ion's gradient provides the energy that drives the secondary active transport in many animal cells?
Na+
Which of the following statements about membrane proteins is TRUE?
a. peripheral proteins span the bilayer and contain hydrophobic regions
b. intergral proteins can be removed easily without disrupting the membrane
c. B-barrel proteins are made of a-helices arranged in a cylinder
d. multipass transmembrane proteins contain several a-helices that form channels
d. multipass transmembrane proteins contain several a-helices that form channels
Which of these statements about glucose transporters is TRUE?
a. the Na+/glucose symporter uses Na+ downhill movement to drive glucose uptake
b. the glucose uniporter directly hydrolyzes ATP for energy
c. the Na+/glucose symporter releases glucose down its concentration gradient
d. the glucose transporter is an ion channel that opens and closes rapidly
a. the Na+/glucose symporter uses Na+ downhill movement to drive glucose uptake
How do bacteria in cold environments adjust to their membranes?
by increasing unsaturated and shorter fatty acid tails -- increasing fluidity
Why do detergents disrupt membranes?
they are ionic and amphipathic, form micelles and extract lipids/proteins from membrane
Why does Na+ bind first to the Na+/glucose symporter and what is its effect?
Na+ has steep electrochemical gradient that makes it bind first and it's binding increases the pump's affinity for glucose
Which statement correctly distinguishes integral and peripheral membrane proteins?
a. integral proteins are attached by non-covalent forces, which peripheral ones are embedded in bilayer
b. integral proteins can be removed without detergents
c. peripheral proteins can be released by high salt or pH changes (extractions), while integral proteins require detergents for removal
d. peripheral proteins contain hydrophobic transmembrane a-helices
c. peripheral proteins can be released by high salt or pH changes (extractions), while integral proteins require detergents for removal
Which of the following pairs is correctly matched?
a. Na+/K+ pump - secondary active transport
b. glucose uniporter- passive transport
c. proton pump - passive diffusion
d. Na+/glucose symporter - primary active transporter
b. glucose uniporter - passive transport
How does cholesterol affect the permeability of the bilayer?
fills the gaps between unsaturated tails; stiffening the membrane which prevents small molecules passing (decreases permeability and fluidity)
they are added to the Golgi lumen, which becomes the extracellular side after vesicle fusion
How does the Na+/K+ pump and Ca+2 pump get the energy needed to drive their processes?
the pump hydrolyzes ATP itself, phosphorylating itself
Which of the following statements about membrane asymmetry is most accurate?
a. both leaflets have identical lipid composition due to flip flop
b. asymmetry is generated in the ER and maintained by scramblases
c. asymmetry is established in the Golgi by flippases and preserved during vesicle trafficking
d. asymmetry only applies to proteins, not lipids
c. asymmetry is established in the Golgi by flippases and preserved during vesicle trafficking
A defect in the Ca+2 pump (SERCA) would directly lead to:
a. excess Ca+2 in the ER lumen
b. elevated cytosolic Ca+2 and impaired muscle relaxation
c. increased ATP synthesis
d. reduced Na+/K+ exchange
b. elevated cytosolic Ca+2 and impaired muscle relaxation