BIO final exam homework + quiz

Which of the following statements best explains how the noncytosolic monolayer of animal cell plasma membranes becomes enriched in phosphatidylcholine?

Flippase enzymes move other types of phospholipids from the noncytosolic to the cytosolic monolayer, leaving the former enriched in phosphatidylcholine.

The length of time that a G protein will signal is determined by the

GTPase activity of Gα.

We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin. This protein uses sunlight as the source of energy to pump __________ out of the cell.

H+

Which of the following statements is true regarding the termination of the adrenaline signaling pathway, which in turn promotes glycogen breakdown?

The phosphate group is removed from glycogen phosphorylase kinase by a phosphatase, which inactivates the enzyme.

Consider a transport vesicle containing a membrane glycoprotein. The glycoprotein and the vesicle's phospholipids are delivered to the plasma membrane, as shown in the figure below. Which of the following is an accurate description of the outcome of this process?

The phospholipids that are delivered to the noncytosolic face of the plasma membrane used to be in the interior (luminal) face of the vesicle.

Porin proteins form large, barrel-like channels in the membrane. Which of the following statements about these channels is FALSE?

They are made primarily of α helices.

Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. In comparison to proteoglycans, which of the following statements about glycoproteins is FALSE?

They have long carbohydrate chains.

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell?

They keep the electrochemical gradient for K+ near zero.

Which of the following statements about GABA receptors is FALSE?

They promote neuronal uptake of Na+.

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?

a mutation that prevents RGFR from binding to RGF

You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in the figure below. Normal cells grown under standard conditions (without ligand) are 14 μm in diameter, while normal cells exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells?

addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to __

create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.

New membrane phospholipids are synthesized by enzymes bound to the __________ side of the __________ membrane.

cytosolic; endoplasmic reticulum

Which of the following gated ion channels are involved in inhibitory synaptic signaling?

glycine-gated Cl- channels

Which of the following phospholipid precursors is the most hydrophobic?

triacylglycerol

Which of the following is required for the secretion of neurotransmitters in response to an action potential?

voltage-gated Ca2+ channels

The following descriptions refer to the structures of various hydrophobic fatty acid tails in membrane phospholipids. Which one would yield the most highly mobile phospholipid?

15 carbons with two double bonds

Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?

Cl-

What role does GAP play in the RTK pathway?

GAP stimulates the hydrolysis of GTP to GDP in the Ras protein, and thus helps to inactivate the RTK pathway.

Ion channels are classified as membrane transport proteins. They discriminate between ions based on size and charge. In addition to Na+, which of the following ions would you expect to be able to freely diffuse through an Na+ channel?

H+

Which of the following best describes the behavior of a gated channel?

It opens more frequently in response to a given stimulus.

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows cells to form specialized attachment structures called focal adhesions to promote cell motility. Which of the following mechanisms describes how motile cells form focal adhesions on the plasma membrane?

Proteins are tethered to the extracellular matrix.

Which of the following mechanisms describes the process by which neutrophils are recruited by endothelial cells lining blood vessels at the site of an infection?

Proteins interact with the proteins on the surface of another cell.

Which of the following statements is true?

The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.

Which of the following channels would NOT be expected to generate a change in voltage by movement of its substrate across the membrane?

an aquaporin

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components. Which type of membrane protein is expected to be the least mobile, based on its function?

anchors

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a __.

hormone

A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ → 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following is the most likely cause of the yeast cell's demise?

inability to import sugar into the cell

Foreign substances like nicotine, morphine, and menthol exert their initial effects by __

interacting with cell-surface receptors, causing the receptors to transduce signals inappropriately in the absence of the normal stimulus.

Consider the apical location of a particular protein expressed in epithelial cells, as illustrated in part A of the Figure below. Part B shows the redistribution of this protein around the entire cell. Which of the following defects is most likely to have caused this redistribution?

the deletion of a junctional protein

Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. The figure below shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty?

the expression of a constitutively active phospholipase C

What is the primary purpose of the K+ leak channels in the gut epithelial cells?

to keep the Na+ pump fully functional

Most animal fats form solids at room temperature, while plant fats remain liquid at room temperature. Which of the following is a feature of plant lipids that best explains this difference?

unsaturated hydrocarbons

Membranes undergo spontaneous rearrangement if torn. Which of the following would happen if a cell membrane underwent a large tear?

vesicles reform

The Nernst equation can be used to calculate the membrane potential based on the ratio of the outer and inner ion concentration. In a resting cell, membrane potential is calculated taking only K+ ions into account. What is V when Co = 15 mM and Ci = 106 mM?

-52.7 mV

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its _____1_____ gradient. On the other hand, for a charged molecule, the _____2_____ must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the _____3_____ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called _____4_____ transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) _____5_____; if the ions move in opposite directions, the transporter is considered a(n) _____6_____. a. antiport b. coupled c. concentration d. electrochemical e. membrane potential f. symport

1. C 2. E 3. D 4. B 5. F 6. A

Water molecules readily form hydrogen bonds with other polar molecules, and when they encounter nonpolar molecules, they must form hydrogen-bonding networks with neighboring water molecules. Which of the following molecules will cause one of these so-called water cages to form?

2-methylpropane

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold?

A few channels remain closed and most open completely.

If a chemical blocks the voltage-gated K+ channels in an action potential, which region of the action potential will be the most affected?

C

Which of the following statements is true?

Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell?

K+

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is NOT one of the common ways to perform active transport?

K+-coupled

Which of the following statements is true regarding the behavior of lipids in cell membranes?

Membrane lipids diffuse laterally within the plane of the membrane.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell?

Na+

The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP?

Na+ remains bound to the sodium binding sites until the protein is dephosphorylated.

Cells make use of H+ electrochemical gradients in many ways. Which of the following proton transporters is used to regulate cytosolic pH in animal cells?

Na+-H+ exchanger

When the cytosolic tail of the __________ receptor is cleaved, it migrates to the nucleus and affects gene regulation.

Notch

Which of the following statements is true?

The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.

In the photosynthetic archaean Halobacterium halobium, a membrane transport protein called bacteriorhodopsin captures energy from sunlight and uses it to pump protons out of the cell. The resulting proton gradient serves as an energy store that can later be tapped to generate ATP. Which statement best describes how bacteriorhodopsin operates?

The absorption of sunlight triggers a contraction of the β barrel that acts as the protein's central channel, squeezing a proton out of the cell.

A group of membrane proteins can be extracted from membranes only by using detergents. All the proteins in this group have a similar amino acid sequence at their C terminus: -KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C stands for cysteine). This sequence is essential for their attachment to the membrane. What is the most likely way in which the C-terminal sequence attaches these proteins to the membrane?

The cysteine residue is covalently attached to a membrane lipid.

When the net charge on either side of the plasma membrane is zero, what else is true?

The electrochemical potential for potassium ions to leave the cell is increased.

Which of the following is most likely to occur after the lipid bilayer is pierced?

The membrane reseals.

Which of the following statements about resting membrane potential is true?

The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.

What happens when a G-protein-coupled receptor (GPCR) activates a G protein?

The α subunit exchanges its bound GDP for GTP.

Although cholesterol is a hydrophobic molecule, it has a hydrophilic functional group that resembles the hydrophilic head group of other membrane lipids.

True

The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions?

acetylcholine

Pumps are transporters that can harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called __

active transport

With which of the following solvents would you expect phospholipids to be compatible?

both hydrophilic and hydrophobic solvents

Both excitatory and inhibitory neurons form junctions with neurons. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?

by opening Cl- channels

Which of the following membrane lipids does not contain a fatty acid tail?

cholesterol

Where does most new membrane synthesis take place in a eukaryotic cell?

in the endoplasmic reticulum

Membrane lipids are capable of many different types of movement. Which of these does NOT occur spontaneously in biological membranes?

moving between lipid layers

Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for __

preventing Ca2+ from altering the activity of Ca2+-dependent molecules in the cytosol.

Transporters, in contrast to channels, work by __

specific recognition of transport substrates.

Given the generic signaling pathway in figure below, match the letter with its corresponding descriptor below.

1. B 2. D 3. C 4. A

Match the numbered lines in the diagram with the following structures. a. nerve terminal b. cell body c. axon d. dendrite

1. B 2. D 3. C 4. A

The specialized functions of different membranes are largely determined by the _____1_____ they contain. Membrane lipids are _____2_____ molecules, composed of a hydrophilic portion and a hydrophobic portion. All cell membranes have the same _____3_____ structure, with the _____4_____ of the phospholipids facing into the interior of the membrane and the _____5_____ on the outside. The most common lipids in most cell membranes are the _____6_____. The head group of a glycolipid is composed of _____7_____. a. lipid bilayer b. fatty acid tails c. sugars d. phospholipids e. proteins f. hydrophilic head groups g. amphipathic

1. e 2. g 3. a 4. b 5. f 6. d 7. c

We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called (what does the abbreviation stand for)?

FRAP

Phosphatidylserine is the most abundant type of phospholipid found in cell membranes.

False

The Na+-K+ pump has been inhibited in the gut epithelial cells with a chemical like ouabain. What will happen to glucose transport on the apical membrane, and why?

Inward glucose transport will slowly decrease into the epithelial cells because of the slow accumulation in intracellular Na+.

Which of the following mechanisms inactivates the fight or flight response, including the breakdown of glycogen to glucose in muscle?

Phosphodiesterase breaks down cAMP to AMP and protein kinase A becomes inactivated.

Which of the following mechanisms best describes the process by which nutrients are taken up selectively at the apical surface and then released from the basal and lateral surfaces of the epithelial cells that line the gut?

Protein movement is limited by the presence of a diffusion barrier.

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows budding yeast cells to designate a specific location on the plasma membrane for bud formation during cell division. Which of the following mechanisms describes how budding yeast cells accomplish this outcome?

Proteins are tethered to the cell cortex.

It is possible to follow the movement of a single molecule or a small group of molecules. This requires the use of antibodies linked to small particles of gold, which appear as dark spots when tracked through video microscopy. What is this method called (what does the abbreviation stand for)?

SPT

In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes. Which of the following statements about the patch-clamp method is FALSE?

Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

Which of the following statements best reflects the nature of synaptic plasticity?

Synaptic response changes in magnitude depending on frequency of stimulation.

In the absence of a ligand binding to its receptor tyrosine kinase, which of the following scenarios would still result in a proliferation signal via the kinase cascade?

a constitutively active MAP kinase and a defective GAP

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of fluidity in its cell (plasma) membrane?

add lipids with hydrocarbon tails that are shorter and have more double bonds

Acetylcholine binds to a GPCR on heart muscle, making the heart beat slower. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in in the figure below. Which of the following would enhance this effect of the acetylcholine?

addition of a high concentration of a nonhydrolyzable analog of GTP

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling.

contact dependent

Plasma membranes are extremely thin and fragile, requiring an extensive support network of fibrous proteins. This network is called the ___.

cortex

If the K+ concentration increases in extracellular space, the membrane potential of a cell will become

depolarized

Which of the following substances is most commonly used to help purify a membrane protein?

detergent

The local mediator nitric oxide (NO) stimulates the intracellular enzyme guanylyl cyclase by

diffusing into cells and stimulating the cyclase directly.

What category of membrane transport are channels a part of?

facilitated diffusion

Three phospholipids, X, Y, and Z, are distributed in the plasma membrane as indicated in the figure below. The composition of the extracellular (noncytosolic) layer is different from that of the cytosolic layer. Which of the following factors is responsible for establishing this compositional asymmetry?

flippase

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both tasks?

flippases

Which of the following was demonstrated by the cell fusion experiment depicted in the figure below?

lateral diffusion of membrane proteins

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use?

mechanically gated

Cholesterol serves several essential functions in mammalian cells. Which of the following is NOT influenced by cholesterol?

membrane thickness

The endothelial cells found closest to the site of an infection express proteins called lectins. Each lectin binds to a particular __________ that is presented on the surface of a target cell.

oligosaccharide

Which of the following functions of the plasma membrane is possible without membrane proteins?

selective permeability

Membrane curvature is influenced by the differential lipid composition of the two membrane monolayers. Which of the following factors has the largest impact on the curvature of biological membranes?

size of the lipid head group

Red blood cells have been very useful in the study of membranes and the protein components that provide structural support. Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell?

spectrin

Some cells express aquaporin proteins—they are channel proteins that facilitate the flow of water molecules through the plasma membrane. What regulates the rate and direction of water diffusion across the membrane?

the concentration of water on either side of the membrane

The Nernst equation determines what value?

the membrane potential necessary to maintain the ion concentrations across the cell membrane, if the membrane is permeable to those ions

Approximately how many distinct synapses are established on the dendrites and cell body of a motor neuron in the spinal cord?

thousands

A molecule moves down its concentration gradient by _____1_____ transport but requires _____2_____ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a(n) _____3_____ pathway through the membrane for specific polar solutes or inorganic ions. _____4_____ are highly selective in the solutes they transport, binding the solute at a specific site and changing conformation to transport the solute across the membrane. On the other hand, _____5_____ discriminate between solutes mainly based on size and electrical charge. a. active b. ion channels c. passive d. hydrophilic e. transporter proteins

1. C 2. A 3. D 4. E 5. B

The action potential is a wave of _____1_____ that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is _____2_____ negative than the resting membrane potential. The action potential is propagated by the opening of _____3_____-gated channels. During an action potential, the membrane potential changes from _____4_____ to _____5_____. The action potential travels along the neuron's _____6_____ to the nerve terminals. Neurons chiefly receive signals at their highly branched _____7_____. a. less b. axon c. depolarization d. dendrites e. positive f. voltage g. negative

1. C 2. A 3. F 4. G 5. E 6. B 7. D

There are several ways that membrane proteins can associate with the cell membrane. Membrane proteins that extend through the lipid bilayer are called _____1_____ proteins and have _____2_____ regions that are exposed to the interior of the bilayer. On the other hand, membrane-associated proteins do not span the bilayer and instead associate with the membrane through an α helix that is _____3_____. Other proteins are _____4_____ attached to lipid molecules that are inserted in the membrane. _____5_____ membrane proteins are linked to the membrane through noncovalent interactions with other membrane-bound proteins. a. amphipathic b. transmembrane c. covalently d. peripheral e. hydrophobic

1. b 2. e 3. a 4. c 5. d