Cell Biology Exam 4 Ch 11-14

Which of the following phenomena will be observed if a cell's membrane is pierced?

the membrane reseals

The the presence of plasma membrane serves many functions, many of which depend on specialized membrane proteins. Which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins?

selective permeability

While many prokaryotic cells have a single membrane bilayer, all eukaryotic cells have a complex system of internal membrane-bound compartments. How might it be advantageous for the cell to have these additional compartments?

Compartmentalization using intracellular membranes allows eukaryotic cells to separate a variety of cell processes. Although this requires a higher degree of coordination, the cell also gains a more stringent degree of control over these processes (examples include: the separation of transcription and translation; the separation of enzymes involved in protein modifications for secreted versus cytosolic substrates; the separation of proteolytic events in the lysosomes versus the cytosol; the separation of anaerobic metabolism in the cytosol and aerobic metabolismin the mitochondria).

Which type of lipids are the most abundant in the plasma membrane?

phospholipids

Indicate whether the following statements are false.

Phosphatidylserine is the most abundant type of phospholipid found in cell membranes and The highly ordered structure of the lipid bilayer makes its generation andmaintenance energetically unfavorable.

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

cholesterol

Formation of a lipid bilayer is energetically favorable. How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable?

Water molecules form cagelike structures around hydrophobic molecules.

Which of the following statements is true?

Membrane lipids diffuse within the plane of the membrane

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 membrane fluidity?

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

The specialized functions of different membranes are largely determined by the

__________________ they contain. Membrane lipids are __________________

molecules, composed of a hydrophilic portion and a hydrophobic portion. All cell

membranes have the same __________________ structure, with the

__________________ of the phospholipids facing into the interior of the

membrane and the __________________ on the outside. The most common lipids in

most cell membranes are the __________________. The head group of a

glycolipid is composed of __________________.

proteins, amphipathic, lipid bilayer, fatty acid tails, hydrophilic head groups, phospholipids, and sugars

Some lipases are able to cleave the covalent bonds between the glycerol backbone and the attached fatty acid. What final products do you expect to accumulate through the action of the enzyme monoacylglycerol lipase?

glycerol and free fatty acid

Which of the following phospholipid precursors is the most hydrophobic?

triacylglycerol

Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in Figure Q11-14. For which of these phospholipids does a flippase probably exist?

X and Y

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

in the endoplasmic reticulum

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 a "cage" of water to form?

2-methylpropane

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

vesicles form

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

switching between lipid layers

There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?

15 carbons with 2 double bonds

Thermal motion promotes lateral position exchanges between lipid molecules within a monolayer. In an artificial bilayer, this movement has been estimated to be

~2 µm/second. This represents the entire length of a bacterial cell. Do you expect the lateral movement of a lipid molecule within a biological membrane to be equally fast? Explain your answer

No. Although the rate of movement may be similar, it will most likely be slower in a biological membrane. An artificial bilayer is primarily phospholipids. Biological membranes contain a large number of protein components and specialized membrane domains that could limit the rate of lateral diffusion.

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

membrane thickness

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

unsaturated hydrocarbons

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

cytosolic, endoplasmic reticulum

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

flippases

Membrane curvature is influenced by the differential lipid composition of the two

membrane monolayers. Which factor do you think has the largest impact on the curvature of biological membranes?

size of the lipid head group

Glycolipids are found on the surface of healthy cells, and contribute to the cell's defense against chemical damage and infectious agents.

A. In which organelle are sugar groups added to membrane lipids?

B. By what mechanism are glycolipids transported to the plasma membrane and

presented to the extracellular environment?

A. Golgi Apparatus

B. Membranes that contain newly synthesized glycolipids bud from the Golgi apparatus to form vesicles. These vesicles then fuse with the plasma membrane. The glycolipids that were facing the lumen of the Golgi will now face the extracellular environment

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

anchors

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.

Although membrane proteins contribute roughly 50% of the total mass of the membrane, there are are in cellular about 50 times more lipid molecules than there protein molecules membranes. Explain this apparent discrepancy.

Membrane proteins are much larger molecules than the membrane lipids. Thus, fewer are required to represent the same total mass contributed by the lipid components of the membrane. By this estimation, the molecular weight of the average membrane protein is 50 times that of the average membrane lipid.

which of these statements are false

Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer and A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix.

Porin proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels?

They are made primarily of α helices.

Even though proteins can form channels across biological membranes using either α helices or the physical βsheets, channels made of αhelices are more versatile. Explain constraints on β-barrel structures and why these constraints do not apply to channels made of α helices

β-Barrel structures are composed of individual β strands that form a β sheet that needs to be curved to make the structure of a pore in the membrane. The physical constraints are due to very specific positioning of each strand to maintain the necessary hydrogen-bonding network within the sheet. The relative positions of α helices can vary and still form strong interactions with other helices in the transmembrane region of a protein.

The amino acid sequences below represent the sequences of transmembrane helices. The characteristics of α helices that form a channel are different from those that form a single transmembrane domain. Select the helix that forms a single transmembrane domain.

IMIVLVMLLNIGLAILFVHF

Unlike soluble, cytosolic proteins, membrane proteins are more difficult to purify. Which of the following substances is most commonly used to help purify a membrane protein?

detergent

Sodium dodecyl sulfate (SDS) and Triton X-100 are both detergents that can be used to lyse cells.

A. If the goal is to study the activity of membrane proteins after cell lysis, explain

why SDS would not be a good choice.

B. How does Triton X-100 work in cell lysis, and why is it a better choice of

detergent to help you extract proteins?

A. SDS is a strong ionic detergent. When cells are exposed to SDS, membrane proteins are not only extracted from the membrane, they are completely unfolded. After denaturation, they cannot be studied as functional molecules.

B. Triton X-100 has a smaller nonpolar portion and a polar but uncharged end, allowing it to mimic more closely the type of solvation effect of the membrane lipids. Triton X-100 forms a shell around the hydrophobic portion of the protein without disrupting the existing structure. This makes it possible to then place the protein into a new, synthetic membrane bilayer for study.

Join our community and turn your knowledge into income!There are several ways that membrane proteins can associate with the cell membrane. Membrane proteins that extend through the lipid bilayer are called __________________ proteins and have __________________ 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 __________________. Other proteins are __________________ attached to lipid molecules that are inserted in the membrane.

__________________ membrane proteins are linked to the membrane through

noncovalent interactions with other membrane-bound proteins.

transmembrane, hydrophobic, amphipathic, covalently and peripheral

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

H

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 shift in the conformation of the protein's seven, membrane spanning α helices, allowing a proton to leave the cell.

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

cortex

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

Anemia, a condition that results in individuals with a low red blood cell count, can be caused by a number of factors. Why do individuals with defects in the spectrin protein often have this condition?

Spectrin is the primary protein in the cortex of red blood cells. A defect in the spectrin protein directly affects the strength and shape of the cortex. Red blood cells that contain mutated spectrin molecules have an irregular shape and are prone to lysis as a result of cortical fragility, leading to a smaller population of red blood cells

Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

When a mouse cell is fused with a human cell, the movement of the respective membrane proteins is restricted to their original locations at the time of fusion, The longest carbohydrates found on the surfaces cells are linked molecules, and The only role of the carbohydrate layer on the cell surface is to absorb water, which creates a slimy surface and prevents cells from sticking to each other.

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which a budding yeast cell designates the site of new bud formation during cell division?

proteins are tethered to the cell cortex

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which focal adhesions are formed to promote cell motility?

proteins are tethered to the extracellular matrix

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which neutrophils are recruited by endothelial cells?

proteins are tethered to the proteins on the surface of another cell

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which nutrients are taken up at the apical surface of the epithelial cells that line the gut and released from their basal and lateral surfaces?

protein movement is limited by the presence of a diffusion barrier

The lateral movement of transmembrane proteins can be restricted by several different mechanisms. Which mechanism best describes the process by which an antigen presenting cell triggers an adaptive immune response?

proteins are tethered to the proteins on the surface of another cell

Consider cells, illustrated the apical location of a particular protein expressed in epithelial in Figure Q11-49A. Which type of defect described below is the most likely to cause the redistribution of that protein around the entire cell, shown in Figure Q11-49B?

the deletion of a junctional protein

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in Figure Q11-50A. When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in Figure Q11-50B. Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A?

the complex calcium is required to maintain the structural integrity of junctional

Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways?

all of the above ( varying the types of sugar monomers used, varying the types of linkages between sugars, and varying the number of branches in the chain)

Which of the following statements about the carbohydrate coating of the cell surface is false?

The arrangement of the oligosaccharide side chains is highly ordered, much like the peptide bonds of a polypeptide chain.

Cell membranes are fluid, and thus proteins can diffuse laterally within the lipid bilayer. However, sometimes the cell needs to localize proteins to a particular membrane domain. Name three mechanisms that a cell can use to restrict a protein to a particular place in the cell membrane.

Any combination of the following four answers is acceptable.

1. The protein can be attached to the cell cortex inside the cell.

2. The protein can be attached to the extracellular matrix outside the cell.

3. The protein can be attached to other proteins on the surface of a different cell.

4. The protein can be restricted by a diffusion barrier, such as that set up by specialized junctional proteins at a tight junction.

Both glycoproteins and proteoglycans contribute to the carbohydrate layer on the surface of the cell. Which of the following is not true of glycoproteins?

They have long carbohydrate chains

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

You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round. One of the mutants has a defect in a protein you call A and the other has a defect in a protein you call B. First, you grind up each type of mutant cell and normal cells separately and separate the plasma membranes from the cytoplasm, forming the first cell extract. Then you set aside a portion of each fraction for later the with a low testing. Next, you wash the remaining portion of membrane fractions concentration of urea (which will unfold proteins and disrupt their ability to interact with other proteins) and centrifuge the mixture. The membranes and their constituent proteins form a pellet, and the proteins liberated from the membranes by the urea wash remain in the supernatant. When you check each of the fractions for the presence of A or B, you obtain the results given below.

Protein A is an integral membrane protein that interacts with B, a peripheral membrane protein that is part of the cell cortex and The mutation in A affects its ability to interact with B.

10-57 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

In order to study the activity of isolated transmembrane proteins, the membrane lipids must be completely stripped away and FRAP is a method used to study the movement of individual proteins.

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

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

12-1 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.

The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content and larger, folded Transporters are similar to channels, except that they are allowing proteins as well as smaller organic molecules to pass through them.

Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found?

an aquaporin

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-

Circle the molecule in each pair that is more likely to diffuse through the lipid bilayer.

benzene, ethanol, glycerol, oxygen, and adenosine

We can test the relative permeability of a phospholipid bilayer by using a synthetic

membrane that does not contain any protein components. Some uncharged, polar

molecules are found to diffuse freely across these membranes, to varying degrees. Which

of the following has the lowest rate of diffusion across an artificial membrane? Why?

glucose

Below is a list of molecules with different chemical characteristics. Knowing that all

molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of these molecules (fastest to slowest).

alanine estrogen propanol sodium

estrogen > propanol > alanine > sodium

A molecule moves down its concentration gradient by __________________ transport,

but requires __________________ transport to move up its concentration gradient.

Transporter proteins and ion channels function in membrane transport by providing a __________________ pathway through the membrane for specific polar solutes or

inorganic ions. __________________ are highly selective in the solutes they transport,

binding the solute at a specific site and changing conformation so as to transport the solute across the membrane. On the other hand, __________________ discriminate

between solutes mainly on the basis of size and electrical charge.

passive, active, hydrophilic, transporter proteins, and ion channels

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+

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+

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following negatively charged ions is not primarily used to buffer positive charges inside the cell?

Cl-

Negatively charged ions are required to balance the net positive charge from metal ions ++2+ such as K, Na, and Ca. Which of the following negatively charged ions is the most abundant in outside the cell and which ion does most often neutralize(written parentheses)?

Cl-+) (Na

Which of the following statements about resting membrane potential is not 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.

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 + 2P + H+ 2CO + 2CH3CH2OH + 2ATP + 2H2O

i2

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 could account for the yeast cell's demise?

inability to import sugar into the cell

Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Explain your answer.

H+

Some cells have aquaporins—channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what regulates the rate and direction of water diffusion across the membrane?

solute concentrations on either side of the membrane

Transporters, in contrast to channels, work by ________________.

specific binding to solutes.

Pumps are transporters that are able to 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.

Indicate whether the statements below are true or false. If a statement is false, explain why it is false

Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient and The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.

It is thought that the glucose transporter switches between two conformational states in a completely random fashion. How is it possible for such a system to move glucose across the membrane efficiently in a single direction?

Although the opening of the glucose transporter on one side of the membrane or the other is random, the binding of glucose into the binding site of the transporter is not a random event. The affinity between the glucose molecule and the transporter governs the binding event: transporter + glucose ↔ transporter-glucose

At high glucose concentrations, the complex formation is favored; at low glucose concentrations, dissociation of glucose from the transporter is favored. So, as long as there is a large concentration gradient, efficient transport can occur by the simple rules of binding

equilibrium

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

-K-K maintaining the high extracellular sodium ion concentration and the high

intracellular potassium ion concentration. What happens immediately after the

pump hydrolyzes ATP?

the pump is phosphorylated

If ATP production is blocked in an animal cell, the cell will swell up. Explain this

observation.

-K balance. The pump requires ATP hydrolysis to drive its pumping cycle. So, in the +absence of ATP production, the Na concentration inside the cell will increase. This is followed cell to swell. by passive diffusion of water across the membrane, causing the

12-26 Indicate whether the statements below are true or false. If a statement is false, explain why it is false

Cytosolic Ca2+ concentration is kept low by the use of chelators such as EDTA and The primary mechanism by which Ca2+ acts as a signaling molecule is by increasing the net charge in the cytosol

You have generated antibodies that recognize the extracellular domain of the Ca2+

-pump. Adding these antibodies to animal cells blocks the active transport of Ca2+

from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+

Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low.

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

-H

12-29 Which of the following statements is true?

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

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

_____________.

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

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its __________________ gradient. On the other hand, for a charged molecule, the __________________ 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 __________________ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called __________________ 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) __________________; if the ions move in opposite directions, the transporter is considered a(n) __________________.

concentration, membrane potential, electrochemical, coupled, symport, antiport

The movement of glucose into the cell, against its concentration gradient, can be powered by the co-transport of Na+ into the cell. Explain this movement with respect to the net entropy of the system (that is, thermodynamics).

The movement of Na+ ions from an area that has a high Na concentration to a new area of low Na+ concentration is energetically favorable because the net entropy in the system is increasing. As long as the difference in Na+ ion concentration across the membrane is large, the entropic factor will be sufficient to drive the import of glucose into the cell, which represents a decrease in entropy with respect to the population of glucose molecules inside

the cell.

You are testing the rate of glucose transport into vesicles using the Na+ -glucose pump. A. In experiment 1, you employ liposomes that have the pump in the same

orientation as that found in the plasma membrane in epithelial cells. These liposomes contain glucose but no Na+ ions. You then transfer the liposomes to a

series of tubes with solutions containing the same glucose concentration as that

inside the vesicle and 0, 1, 2, 3, or 10 mM Na+. You measure the initial rates of

glucose transport and plot your results (Figure Q12-33). Why do the initial rates of glucose transport into the liposome reach a plateau as the concentration of Na+ increases? In experiment 2, there is one new variable: you have included leaky Na+

channels in the liposomal membrane. Figure Q12-33 shows your results. Explain the reason for obtaining such different results in experiment 2 from those in experiment 1.

A. Because transporters require recognition and binding of the transport substrate before moving it across the membrane, the transporters can reach a maximum capacity (saturation) at which we observe the maximum rate at which transport can occur, regardless of any further increase in the concentration of transport substrate. In this case, it seems that 10 mM Na+ is close to saturating the

experimental system being used.

B. The leaky Na++ channels allow rapid equilibration of Na ions across the liposomal membranes, destroying the gradient required for glucose transport into the liposome. Thus, there is no net movement of glucose into the liposome at any of the Na+ ion concentrations tested.

Describe the process by which gut epithelial cells use transporters to take up ingested glucose (against the concentration gradient) and to distribute glucose to other tissues by moving it back out of the cell (down the concentration gradient).

Ca2+ is exported using ATP-powered pumps. There are no other solutes that are being moved by these pumps.

Which of the following occur without coupling transport of the solute to the movement of a second solute?

export of Ca2+ from the cytosol

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

It opens more frequently in response to a given stimulus.

The flow of ions through a gated channel can be studied using a method called "patch clamp recording

A. How is a detached patch-clamp experiment set up, and what exactly does it mean to "clamp" an ion channel?

B. How is it possible to collect the recordings shown in Figures Q12-37A and Q12-

37B from a single ion channel?

A. A detached patch-clamp experiment requires the removal of a portion of the cell membrane by sealing the microelectrode to the membrane surface. After lifting the patch of membrane stuck to the microelectrode, it is placed into a solution of controlled medium. The voltage applied to the membrane patch can be fixed (clamped) while other parameters are studied.

B. By manipulating ion concentrations in the two chambers or simply reversing the direction of the current in the system, the ion flow through the channel can be reversed, resulting in the recording of negative values for current when the channel opens.

12-38 Indicate whether the statements below are true or false. If a statement is false, explain why it is false.

Gap junctions are large pores that connect the cytosol to the extracellular space, Aquaporin channels are found in the plasma membrane, and allow the rapid passage of water molecules and small ions in and out of cells, and the ion selectivity of a channel depends solely on the charge of the amino acids lining the pore inside the channel.

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?

stress-gated

The acetylcholine receptor in skeletal muscle cells is a(n) _________ ion channel.

_________ ion channels are found in the hair cells of the mammalian cochlea. _________ ion channels in the mimosa plant propagate the leaf-closing response. _________ ion channels respond to changes in membrane potential. Many receptors for neurotransmitters are _________ ion channels.

ligand gated, stress gated, voltage gated, voltage gated, ligand gated

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?

Some channels remain closed and some open completely.

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

true?

The electrochemical potential across the membrane is zero.

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+ at zero.

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 =

-52.7 mV

When using the Nernst equation to calculate membrane potential, we are making

several assumptions about conditions in the cell. Which of the following is not a

good assumption?

The plasma membrane is primarily permeable to Na+

If Na+ channels are opened in a cell that was previously at rest, how will the resting

membrane potential be affected?

It becomes more positive.