BIOL 541 Reading Quiz (unit 2: 11,12 &15)
A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)? a. short, unsaturated fatty acid tails b. long, saturated fatty acid tails c. long, unsaturated fatty acid tails d. short, saturated fatty acid tails
b.
A phospholipid is inserted into the cytosolic side of the ER membrane. Which of the following could randomly reposition this phospholipid to the other (lumen) side of the ER membrane? a. flippase b. scramblase c. glycolipids d. Golgi apparatus
b.
How are voltage-gated ion channels opened by voltage sensors? a. Voltage sensors on the channel change their amino acid side chains from positively to negatively charged. b. When membrane potential changes sufficiently, the electrical force causes voltage sensor domains to change conformation. c. Ion binding to voltage sensors causes the channel pore to widen and open. d. Changes in membrane potential lead to increased gene expression of voltage-gated ion channel proteins.
b.
A less permeable membrane is likely to have a. more cholesterol. b. less cholesterol. c. many unsaturated fatty acids. d. shorter fatty acid tails.
a.
Detergent molecules are ___________ in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane. a. amphipathic b. hydrophobic c. hydrophilic d. polar
a.
Fully folded proteins can be transported into which of the following organelles? a. nucleus b. mitochondrion c. chloroplasts d. endoplasmic reticulum
a.
How is an electrical signal converted to a chemical signal at a nerve terminal? a. Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters. b. Ligand-gated channels are bound by ions and open to allow the flow of neurotransmitters out of the cell. c. Mechanically gated channels change conformation due to the electrical signal and create a mechanical signal. d. The influx of ions leads to a pH change, chemical transformation, and signaling.
a.
If a phospholipid is located in the outer layer of the bilayer in a vesicle, where will it end up when the vesicle fuses with the plasma membrane? a. the cytosolic face of the bilayer b. the extracellular face the bilayer c. randomly on one side or another d. Vesicles cannot fuse with the plasma membrane.
a.
If the backbone of a polypeptide is hydrophilic, how can a transmembrane alpha helix span the hydrophobic portion of the lipid bilayer? a. because amino acid side chains in a transmembrane helix are hydrophobic and interact with the hydrophobic interior of the bilayer b. because the membrane bends in such a way that the polar heads of the lipids contact the transmembrane helix c. because the hydrophilic backbone makes a hole in the membrane d. because many transmembrane alpha helices must come together in a way that neutralizes the hydrophilic backbone
a.
Nuclear pores restrict larger molecules from traversing the membrane due to their a. interwoven meshwork of protein fibrils. b. very small pore size. c. hydrophobic interior. d. double membrane.
a.
Plasma membrane proteins that move ions in and out of cells using active transport are called a. transporters. b. channels. c. anchors. d. receptors.
a.
What is one of the main differences in the behavior of the proteins in a vesicle destined for constitutive secretion, and the proteins in the vesicle destined for regulated secretion? a. Proteins in the regulated secretion vesicle tend to aggregate and become highly concentrated in the ionic conditions in the vesicle. b. Proteins in the constitutive secretion vesicle unfold to keep the concentration in the vesicle low, and then refold at the cell surface. c. Proteins in the constitutive secretion vesicle are stored for release in response to a signal. d. The regulated secretion vesicle proteins are bound to lipids for supplying the plasma with new lipids.
a.
What is the conformation of the voltage-gated Na+ channel that keeps the action potential from traveling backward along the axonal membrane? a. inactivated b. open c. closed d. triggered
a.
What is the molecular target of the antidepressant Prozac? a. the symport that drives reuptake of serotonin b. the Na+ channels that activate the neuron c. the K+ channels that deactivate action potentials d. the serotonin receptor, a transmitter-gated ion channel
a.
Where are new phospholipids made? a. endoplasmic reticulum b. Golgi apparatus c. mitochondria d. nucleus
a.
Which of the endocytic pathways involves the ingestion of large particles or microorganisms and is performed mainly by specialized cells? a. phagocytosis b. pinocytosis c. exocytosis d. receptor-mediated endocytosis
a.
Which of the following ions has a low cytosolic concentration so that a flood of this ion into the cell can be used as a signal for cell processes like fertilization? a. Ca2+ b. H+ c. K+ d. phosphate
a.
Which of the following is a cell type in humans that uses voltage-gated ion channels? a. muscle cells b. skin cells c. liver cells d. gut epithelial cells
a.
Which of the following is a covalent modification that occurs mainly in the ER? a. formation of disulfide bonds b. addition of phosphate groups c. maturation of oligosaccharide chains d. methylation of side chains
a.
Which type of movement is the least common for lipids in a bilayer? a. flip-flop b. lateral diffusion c. flexion d. rotation
a.
________ are the most abundant molecules in the animal cell membrane, whereas ________ make up 50% of the membrane by mass. a. Lipids, proteins b. Proteins, lipids c. Lipids, carbohydrates d. Carbohydrates, lipids
a.
Which of the following organelles is the site of steroid hormone synthesis in endocrine cells? a. smooth endoplasmic reticulum b. cytosol c. mitochondrion d. nucleus
a
How does an action potential spread along the cell membrane? a. Potassium leak channels quickly reverse the action potential to move the membrane depolarization away from the original site. b. A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction. c. Voltage-gated Ca2+ channels are activated by the action potential and the calcium diffuses along the membrane. d. The ions entering the cell upon triggering an action potential travel laterally along the membrane to carry the charge.
b.
In a fluorescence recovery after photobleaching (FRAP) experiment, a fluorescently tagged membrane protein, A, shows very little recovery of fluorescence ten minutes after photobleaching, while membrane protein B shows a rapid increase in fluorescence after bleaching, recovering nearly 80% of its original fluorescent signal by ten minutes. Based on this information, which of the following statements can be made? a. Protein A has faster mobility in the membrane. b. Protein B is diffusing in a more fluid membrane. c. Proteins A and B interact with each other in a complex. d. Protein A is easily denatured.
b.
Ion channels contain a selectivity filter that a. binds with extreme sensitivity to their specific ion, akin to an enzyme forming a specific binding site for a substrate. b. selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel. c. selects for size of ions based on interactions with the ion transport protein. d. selects for positively charged ions by virtue of the negatively charged amino acids lining the pore, but allows similar ions through, like Na+ and K+.
b.
Phospholipids assemble into in a membrane using a. enzymes. b. hydrophobic forces. c. assembly proteins. d. covalent bonds.
b.
Proteins that are associated with the membrane by noncovalent interactions with other membrane proteins are called ___________ proteins. a. integral membrane b. peripheral membrane c. monolayer-associated d. lipid-linked
b.
What is responsible for moving glucose from the gut lumen into intestinal epithelial cells? a. uniport glucose transporter b. glucose-sodium symport c. glucose-sodium antiport d. passive diffusion
b.
What is the role of K+-gated ion channels in an action potential? a. They lead to the action potential reaching its highest state of cell depolarization. b. They help reverse the action potential by repolarizing the cell. c. They do not have a role in action potentials. d. They provide the energy for the sodium-potassium pump to reestablish resting potential.
b.
What would the final destination be for a protein bearing both an ER sorting signal and a nuclear localization signal? a. nucleus b. endoplasmic reticulum c. cytoplasm d. Golgi apparatus
b.
Which ion is generally maintained at a high concentration inside the cell and a low concentration outside the cell? a. Na+ b. K+ c. Cl- d. H+
b.
Why do cells regulate their membrane fluidity? a. so they don't freeze in cold temperatures b. to allow membrane proteins to diffuse to where they are needed for their function c. so that large, charged molecules can easily pass through the membrane d. to keep two neighboring cells from easily fusing
b.
A single-pass transmembrane protein destined for one of the organelles in the endomembrane system would be marked by what type of signal sequence? a. a cleaved N-terminal ER signal sequence b. an internal ER signal sequence c. a cleaved N-terminal ER signal sequence and an internal stop-transfer sequence e. an internal ER signal sequence and an internal stop-transfer sequence
c.
A sodium-potassium antiport maintains the extracellular concentration of sodium at levels that are about 20-30 times higher than inside the cells. What directly supplies the energy for maintaining this gradient? a. Potassium supplies the energy, as it is moving along its concentration gradient. b. Sodium supplies the energy, as it is moving along its concentration gradient. c. ATP hydrolysis drives the function of the pump. d. A proton gradient in the mitochondria drives the antiport.
c.
Approximately what percentage of the volume of a typical eukaryotic cell is comprised of cytosol? a. 10% b. 20% c. 50% d. 80%
c.
How do clathrin-coated vesicles select their cargo molecules? a. Specific cargo molecules have a high affinity for clathrin. b. Cargo is selected randomly and is sorted later in the endosomes. c. Cargo receptors bind specifically to cargo proteins and to clathrin. d. Cargo is actively transported into preformed clathrin-coated vesicles.
c.
Proteins encoded by nuclear genes and destined for the mitochondrial matrix are a. able to diffuse into the mitochondrial intermembrane space first. b. transported across the membrane as a folded protein. c. in possession of a signal sequence for targeting to the mitochondria. d. synthesized on ribosomes on the rough ER.
c.
Which factors determine the force driving the passive transport of charged solutes across the membrane? a. concentration gradient only b. membrane potential only c. electrochemical gradient d. ATP gradient
c.
Which of the following is a common transmembrane protein structure that can traverse the membrane to form a pore or channel by alternating hydrophobic and hydrophilic amino acids? a, single-pass alpha helix b. multipass alpha helix c. beta barrel d. beta sheet
c.
Which of the following is a difference between transporters and channels? a. Transporters move solutes against their concentration gradient, whereas channels can move solutes with or against their concentration gradient. b. Channels do not discriminate between ions, whereas transporters bind their solute with extreme specificity. c. Transporters can facilitate both active or passive transport of solutes; channels facilitate only passive transport. d. Channels are single-pass transmembrane proteins, whereas transporters are multipass transmembrane proteins.
c.
Which of these macromolecules is NOT commonly found in the plasma membrane? a. carbohydrates b. proteins c. nucleic acids d. fatty acids
c.
Cells, compared with the extracellular fluid are a. electrically neutral. b. slightly positively charged. c. extremely positively charged. d. slightly negatively charged.
d.
In a famous experiment, mouse cells and human cells were fused into hybrid cells and the membrane proteins of human origin and mouse origin were specifically tagged and examined. After cell fusion and incubation, what was observed by investigators? a. The mouse and human proteins remained separated from each other on opposite sides of the hybrid cell. b. The mouse proteins mixed throughout the membrane of the hybrid cell, whereas the human proteins remained in half of the membrane, in their original location. c. The human proteins mixed throughout the membrane of the hybrid cell, whereas the mouse proteins remained in half of the membrane, in their original location. d. The mouse and human proteins mixed evenly throughout the membrane of the hybrid cell.
d.
Which of the following compartments receives proteins directly from cytosol? a. Golgi apparatus b. lysosomes c. endosomes d. peroxisomes
d.
Which of the following is NOT a way that cells restrict the lateral movement of membrane proteins? a. anchoring to internal cell components like actin or other proteins b. tethering to external cell components like the extracellular matrix or adjacent cells c. establishing diffusion barriers in the membrane d. reducing the temperature of the membrane
d.
Which of the following is NOT used as a source of energy by a transmembrane pump to actively transport a solute? a. ATP b. Na+ c. H+ d. K+
d.
Which of the following is a difference between exocytic and endocytic pathways? a. Exocytic pathways utilize transport vesicles, whereas endocytic pathways use only endosomes. b. Endocytic pathways transfer proteins to the Golgi apparatus, whereas exocytic pathways transfer proteins from the Golgi. c. Endocytic pathways bring in soluble proteins only, whereas exocytic pathways move both soluble proteins and membrane-bound proteins. d. Exocytic pathways often start with synthesis of proteins, whereas endocytic pathways involve breaking down macromolecules like proteins.
d.
Which of the following organelles is surrounded by a single membrane? a. nucleus b. mitochondria c. chloroplasts d. Golgi apparatus
d.
Which of the following pathways helps selectively concentrate substances to be ingested by their binding to proteins on the cell surface? a. phagocytosis b. pinocytosis c. exocytosis d. receptor-mediated endocytosis
d.
Which of the following would be able to cross a protein-free lipid bilayer most rapidly? a. a chloride ion (charged, small) b. glucose (uncharged polar, large) c. ethanol (uncharged polar, small) d. a steroid hormone (nonpolar, large)
d.