Cell Bio Exam 3

Mutation in the hemoglobin gene can cause sickle-cell anemia. The defective protein found in sickle-cell anemia causes red blood cells to "sickle"—become a misshapen C shape. These misshapen cells abnormally stick to each other and can become trapped by leukocytes (white blood cells) that are rolling or paused on the endothelial cells lining the vessel. This causes blockages of small blood vessels, causing severe pain and strokes called vaso-occlusive crisis. A new drug that binds and blocks selectin proteins is in phase III clinical trials to test for improvement in patients' symptoms. Why might this be an effective treatment for vaso-occlusive crisis?

Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells.

Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter with receptors (5-HT receptors) located in cells throughout the body. There are more than a dozen different types of serotonin receptors that fall into several different classes. One class consists of serotonin-activated ion channels and the other receptor classes are G-protein-coupled receptors that associate with different G proteins. The 5-HT7A receptor couples to Gs and activates adenylyl cyclase, while the 5-HT2B receptor couples to Gq and activates phospholipase C. The diversity of receptor types has led pharmacologists to search for drugs that will bind to and modulate just a single receptor class in order to limit systemic side effects (see 5-Hydroxytryptamine Receptor Subtypes and their Modulators with Therapeutic Potentials). Place into bins the downstream effects predicted for a drug that exclusively activates the 5-HT7A receptor versus a drug that exclusively activates the 5-HT2B receptor.

5-HT7A: PKPA activation, cAMP production, 5-HT2B: IP3 production, cytosolic calcium increase, PKC activation

Which of the following describes negative feedback regulation?

A component late in the pathway inhibits an enzyme early in the pathway.

Which of the following steps are required in the activation of the G-protein signaling pathway?

A. Activated Gα influences target proteins. B. Ligand binds to the G-protein-coupled receptor. C. Gα exchanges GDP for GTP.

Why would a cell express the aquaporin protein if water can cross the membrane in the absence of aquaporin?

Aquaporin facilitates the faster movement of water molecules across the membrane.

Identify chemicals that will diffuse through the lipid bilayer based on the comparison pattern that is established by the figure. Drag the labels to their targets.

B(oxygen small nonpolar),D(water small polar),A(glucose large polar),C(sodium ions)

Which of the following signaling pathways would be likely to trigger the most rapid cell response?

Acetylcholine binds to anion-channel-coupled receptor that allows Na+ to flow down its electrochemical gradient, triggering contraction of a skeletal muscle cell.

The drug scopolamine is used to treat dizziness, motion sickness, and smooth muscle spasms. When isolated muscle cells are incubated with scopolamine, addition of acetylcholine no longer depolarizes the muscle cell membrane or stimulates muscle cell contraction. Which would best explain how scopolamine exerts its muscle-relaxing effects?

It inhibits the opening of acetylcholine-gated Na+ channels in the muscle cell membrane.

To pass through the pore of an ion channel, what must be true of an ion?

It must interact with polar groups in the narrowest part of the channel.

How does IP3 function in the inositol phospholipid pathway?

It opens Ca2+ channels that are embedded in the ER membrane, allowing Ca2+ to enter the cytosol.

A toxin present in scorpion venom prolongs the duration of action potentials in nerve cells. Which of these actions would best explain how this toxin exerts its effect?

It slows the inactivation of voltage-gated Na+ channels.

How does the inclusion of cholesterol affect animal cell membranes?

It tends to make the lipid bilayer less fluid.

Which ion is generally maintained at a high concentration inside the cell and a low concentration outside the cell?

K+

Which is true of the GTP-binding proteins that participate in intracellular signaling?

Only trimeric GTP-binding proteins relay messages from G-protein-coupled receptors.

Optogenetics is a powerful tool that uses light to control the activity of specific neurons. These neurons contain artificially introduced light-gated ion channels. A number of different light-gated channels with different ion specificities have been either found in nature (such as the sodium-specific channelrhodopsin, originally found in green algae) or produced via genetic engineering (the production of a chloride ion-specific form of channelrhodopsin). There are also light-gated ion channels specific for potassium or calcium. Sort each light-activated channel type based on whether activation of this channel will tend to depolarize cells or not.

PROMOTE: sodium channel, calcium channel, INHIBIT: chloride channel, potassium channel

A subset of breast cancers overexpress the receptor tyrosine kinase (RTK), known as human epidermal growth factor receptor 2 (HER2). Patients with HER2-positive breast cancers often benefit from treatment with a HER2-binding antibody known as Pertuzumab. Given that antibodies are large proteins that cannot cross the cell membrane, what might be directly impacted by Pertuzumab to limit cell proliferation?

Pertuzumab prevents receptor dimerization.

Which statements are true about the differences between phospholipids and detergents?

Phospholipids form bilayers in water, whereas detergents tend to form micelles. Detergents are shaped like cones, whereas phospholipids are more cylindrical. Phospholipids have two hydrocarbon tails, whereas detergents have just one.

Which statement about positive feedback regulation is accurate?

Positive feedback regulation can generate an abrupt, all-or-none response in which the cell moves from ignoring a signal to responding to it very strongly.

Which of these represents a mechanism used to terminate a signal transmitted by activated RTKs?

The RTKs are internalized and digested in lysosomes.

Ethylene is a hormone that promotes the ripening of fruit. What happens in the absence of ethylene?

The activated ethylene receptor promotes the degradation of a transcription regulator and the ethylene-responsive genes remain turned off.

In the technique called optogenetics, light-gated Na+ channels are introduced into the brains of living animals. Activation of these channels by light can depolarize the membranes of neurons that contain them, selectively activating these target cells.Since its inception, optogenetics has been expanded to include other types of light-gated channels, such as a channel that is selective for Cl- instead of Na+. If this light-gated Cl- channel were introduced into neurons in a region of the brain that stimulates feeding, what might you expect to see?

The animals would avoid eating, even when they are hungry—but only when the channels are activated by light.

The epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body?

The cells have glucose uniports in their plasma membrane.

The activity of a kinase called Src is regulated by phosphorylation. The kinase is inactivated by phosphorylation at a C-terminal tyrosine residue (Tyr527) and is activated by interaction with an activated RTK, which stimulates Src to autophosphorylate a different tyrosine residue (Tyr416). Full activation of Src requires removal of the inhibitory phosphate group and binding to an activated RTK.Based on this information, which statement about the activity of Src kinase is correct?

The kinase is active only when Tyr527 is dephosphorylated and Tyr416 is phosphorylated.

When the transport vesicle shown below fuses with the plasma membrane, which monolayer will face the cell cytosol?

The orange monolayer will face the cytosol.

Signaling via a GPCR ceases when which condition occurs?

The α subunit hydrolyzes its bound GTP.

GPCRs are sometimes referred to as "seven-pass transmembrane receptors" for which reason?

Their polypeptide chain crosses the lipid bilayer seven times.

In a patch of animal cell membrane about 10 μm in area, which will be true?

There will be more lipids than proteins.

What is true of the GTP-binding proteins that act as molecular switches inside cells?

They are active when GTP is bound.

What is typically true of ion channels?

They are gated.

The P-type ATPase Ca2+ pump transports Ca2+ ions into the sarcoplasmic reticulum in muscle cells in a series of steps. Put the following steps into the correct order.

Two Ca+2 ions from the cytosol side bind to a pocket in the Ca+2 pump, ATP is hydrolyzed and a conserved aspartate group is phosphorylated, ADP is exchanged for a new ATP, the pump opens to the lumen side of the sarcoplasmic reticulum, two protons bind to the pump and are exported from the sarcoplasmic

Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes?

Two asparagines in the center of the pore prevent protons from passing through the channel, The channel has a narrow pore that is only wide enough for a single water molecule to pass through.

What do the phosphorylated tyrosines on activated RTKs do?

They serve as binding sites for a variety of intracellular signaling proteins.

How is an electrical signal converted to a chemical signal at a nerve terminal?

Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters.

Which membrane would show a more rapid recovery of fluorescence in a FRAP study?

a membrane containing a larger proportion of unsaturated fatty acids

In general, which of the following will diffuse across a lipid bilayer most rapidly?

a small hydrophobic molecule

Which of the following describes the resting membrane potential of a neuron?

a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced

Which of the following would be able to cross a protein-free lipid bilayer most rapidly?

a steroid hormone (nonpolar, large)

One of the grand challenges in biology is understanding how the first cells formed on Earth. Since all cells are bound by a cell membrane, origin of life researchers are interested in modeling what the first membranes may have been like. What types of molecules might these researchers consider to be the original building blocks of cell membranes?

amphipathic molecules

Acetylcholine stimulates cells in the pancreas to secrete enzymes that aid in digestion of sugars. It does so by activating GPCRs that stimulate the membrane-bound enzyme phospholipase C (PLC).PLC then triggers which of these downstream events?

an elevation of Ca2+ concentrations, which leads to the activation of protein kinase C (PKC)

The first step in a signaling pathway that responds to a molecule that stays in the extracellular space is

binding of the signal molecule to a receptor.

When activated by the binding of Ca2+, calmodulin relays the Ca2+ signal onward by doing what action?

binding to Ca2+/calmodulin-dependent protein kinases

What is required for PKC activation?

binding to DAG and continuing presence of Ca2+

Steroid hormones trigger transcription of target genes by

binding to nuclear receptors that act as transcription factors for specific genes.

You join a laboratory to study muscle function. You decide to inhibit the pumping of Ca2+ into the sarcoplasmic reticulum to determine how excess cytosolic Ca2+will affect muscle function. Which of the following strategies would be effective in blocking Ca2+ pumping?

block the phosphorylation of the conserved aspartate in the Ca2+ pump

Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell.How might a cell actively engineer this phospholipid redistribution?

by activating a scramblase and inactivating a flippase in the plasma membrane

What determines the direction that glucose is transported across the membrane, through a glucose transporter?

concentration gradient

When activated by a GPCR, what does adenylyl cyclase do?

converts ATP to cAMP

Which of the following inhibits inorganic ions, such as Na+ and Cl-, from passing through a lipid bilayer?

the hydrophobic interior of the lipid bilayer

During an action potential, which of the following actions does not help return the membrane to its resting potential?

the opening of voltage-gated Na+ channels

In the α helices of transmembrane proteins, the hydrophobic side chains face which direction?

the outside of the membrane-spanning helix

Why must all living cells carefully regulate the fluidity of their membranes?

to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules,to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides,to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell

Which of the following mechanisms prevents osmotic swelling in plant cells?

tough cell walls

One of the two types of GTP-binding proteins, often called G-proteins, are membrane bound. These are the

trimeric GTP-binding proteins.

Certain mutant Ras proteins cannot hydrolyze their bound GTP to GDP, and therefore cannot do which of the following?

turn themselves off

Which type of ion channel plays the major role in propagating electrical signals in nerve cells?

voltage-gated

In a lipid bilayer, where do lipids rapidly diffuse?

within the plane of their own monolayer

Consider the following image and then answer the question.Glucose enters the cell by which process?

facilitated diffusion

Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains?

hydrophobic

Which characteristic describes the tails of phospholipids?

hydrophobic

Phospholipids assemble into in a membrane using

hydrophobic forces.

In a 2018 article (Budin, et al., Science vol. 362) researchers probed how membrane fluidity affects electron transport chain activity and ATP production in E. coli by manipulating membrane fluidity and measuring respiration. How could researchers have increased membrane fluidity?

increase the proportion of phospholipids with unsaturated fatty acids

Organisms that live in cold climates adapt to low temperatures by doing which of the following?

increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid???? not sure

PI 3-kinase acts by phosphorylating what molecule(s)?

inositol phospholipids

Which of the following would be a plausible strategy for reducing the activity of the Ras protein?

introducing a mutation that enhances the protein's affinity for GDP

Which is a mechanism for restricting the movement of proteins in the plasma membrane?

it is definitely not coating proteins with carbohydrates. not sure about the rest ???

Enzymes that add a phosphate group to a switch protein are called

kinases.

Auditory hair cells in the ear depend on what type of ion channel to detect sound vibrations?

mechanically-gated

What is a functionally specialized region of a cell membrane, typically characterized by the presence of specific proteins, called?

membrane domain

What is the voltage difference across a membrane of a cell called?

membrane potential

What type of cell response would take the longest amount of time (on the scale of minutes to hours) to execute?

one that involves a change in gene expression

Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest?

oxygen, glucose, sodium ions

Many of the extracellular signal molecules that regulate inflammation are released locally at the site of infection. What form of cell-cell signaling is being used?

paracrine

Proteins that are associated with the membrane by noncovalent interactions with other membrane proteins are called ___________ proteins.

peripheral membrane

Of the following scenarios regarding the lipid bilayer, which one would produce the most fluid lipid bilayer?

phospholipids with tails of 18 carbon atoms and two double bonds

A group of researchers wanted to sort different white blood cell types (monocytes, lymphocytes, and granulocytes) apart from each other based on size differences and to remove unwanted contaminating red blood cells. After a particular manipulation, the red blood cells lysed. The remaining white blood cells increased in size and, more importantly, the size differences among cells increased, allowing for size-based sorting (which requires minimum size differences among cells). What manipulation did the researchers use to increase cell size?

placing cells in an environment with a lower solute concentration than that in the cells

Which term describes a coupled transporter that moves both solutes in the same direction across a membrane?

symport

What is the name of the specialized junction between a neuron and a target cell?

synapse

What makes it possible for a combination of signal molecules to evoke a response that differs from the sum of the effects that each signal could trigger on its own?

the ability of different intracellular relay systems to interact

In eukaryotic cells, phospholipids are synthesized by enzymes bound to which of the following?

the cytosolic face of the endoplasmic reticulum

The following graphs show the number of adherent leukocytes found on the blood vessel wall in control conditions and after adding a selectin inhibitor, which blocks the function of selectin. Which of the following graphs correctly shows the effect of a selectin inhibitor on adherence of leukocytes to the vessel wall?

Graph B

On what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located?

the extracellular side

In fungi, plants, and bacteria, which pump helps to drive the import of solutes?

H+ pumps

Multipass transmembrane proteins can form pores across the lipid bilayer. The structure of one such channel is shown in the diagram.In this figure, what do the areas shown in red represent?

the hydrophilic side chains of the transmembrane α helices

Your friend is attempting to study the function of the Na+-K+ pump and has created spherical liposomes that contain only the Na+-K+ pump. She has inserted the pumps so that the extracellular side of the pump is also outside the liposome. She has added different ions and energy sources to the beaker with the liposomes, but no pumping of ions occurs. You explain that components must be in the proper location inside or outside the liposome for the pump to work. Help her by adding the proper components to the inside or outside of the liposome so that proper pumping occurs. Place unneeded components in the unneeded box. The figure shows a spherical liposome formed from phospholipids.

INSIDE: ATP, Na+, OUTSIDE: K+, UNNEEDED: GTP, Cl-

Cells, compared with the extracellular fluid are

slightly negatively charged.

Consider the following illustration of membrane transport and then answer the question.Which of the following is supported by the information in the figure?

A. Nucleotides enter the cell by facilitated diffusion. B. Sodium and potassium are involved in co-transport.

A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)?

A. long, saturated fatty acid tails

How does diacylglycerol (DAG) function in the inositol phospholipid pathway?

Along with Ca2+, it recruits and activates PKC at the plasma membrane.

Consider the following illustration of the Na+-K+ pump and then answer the question.Which of the following are consistent with the Na+-K+ pump and the illustration?

B. K+ ions are pumped against their chemical gradient. C. Na+ ions are pumped against their chemical gradient. D. Na+ ions are pumped against their electrical gradient.

When an action potential reaches a nerve terminal, what type of voltage-gated channels are opened and result in the fusion of synaptic vesicles with the cell membrane?

Ca2+

The concentration of free Ca2+ in the cytosol of an unstimulated cell is kept low compared with its concentration in both the extracellular fluid and the endoplasmic reticulum. Which of the following help to maintain this difference?

Ca2+ pumps in the ER membrane, Ca2+ pumps in the plasma membrane

How do transporters and channels select which solutes they help move across the membrane?

Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.

Carbohydrates on the surface of leukocytes play an important role in responding to infection or inflammation. Place the following steps of the response in the correct order.

Cytokines are released at sites of infection or inflammation and stimulate endothelial cells, endothelial cells express selections on their plasma membrane, selections bind to carbohydrates on the surface of leukocytes, leukocytes roll along vessel walls, leukocytes crawl out of vessel into adjacent tissue

Alterations in signaling in the pituitary gland can lead to human disease. The GH-releasing hormone (GHRH) stimulates release of growth hormone (GH) from the pituitary gland by binding to GHRH receptors, which are G-protein-coupled receptors. Excessive activity of the GHRH signaling pathway leads to excessive release of growth hormone, which can lead to acromegaly, a form of gigantism. Some patients can reach more than 8 feet tall as they continue to grow even in adulthood.Consider steps that could be taken to reduce GH release. Sort each of the following interventions into the proper category.

DECREASES: inhibit interaction of G with receptor, block ligand binding to receptor, activate phosphorylation of the receptor by GRK kinase, INCREASES: block binding of arresting to the receptor, block hydrolysis of GTP

When scientists were first studying the fluidity of membranes, they did an experiment using hybrid cells. Certain membrane proteins in a human cell and a mouse cell were labeled using antibodies coupled with differently colored fluorescent tags. The two cells were then coaxed into fusing, resulting in the formation of a single, double-sized hybrid cell. Using fluorescence microscopy, the scientists then tracked the distribution of the labeled proteins in the hybrid cell.Which best describes the results they saw and what they ultimately concluded?

Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer.

When activated phospholipase C cleaves an inositol phospholipid, what happens to the small signaling molecules the enzyme produces?

Inositol 1,4,5-trisphosphate (IP3) is released into the cytosol, while diacylglycerol is retained in the membrane.

In skeletal muscle cells, epinephrine (adrenaline) stimulates the breakdown of glycogen by activating a GPCR. In the signaling pathway shown here, which step does not amplify the original signal?

NOT activation of a G protein by an activated GPCR, NOT activation of glycogen phosphorylase by activated phosphorylase kinase. not sure ????

The signaling pathways shown below integrate information provided by signal 1 and signal 2 to activate the transcription of a target gene and trigger a cell response. The intracellular signaling molecules in the pathway are only active when they receive an activating signal (→) from an upstream signaling molecule and are not being inhibited (—I) by any upstream signaling molecule. Given this information, under what conditions will the target gene for this signaling network be expressed?

NOT the target gene will be expressed only when signal 1 is present, and NOT the target gene will be expressed only when both signals are present. not sure????

Lipid bilayers are highly impermeable to which molecule(s)?

Na+ and Cl-

Most sports drinks contain both carbohydrates and salts. The carbohydrates replace glucose burned during exercise and the salts replace salts lost in sweat. The salt also helps the small intestine absorb glucose. Pick the answer that accurately describes which salt is most beneficial for glucose absorption.

NaCl, because Na+ is needed for glucose entry.

Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but lipids can be labeled too.How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?

The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence.

Why do phospholipids form bilayers in water?

The hydrophilic head is attracted to water, while the hydrophobic tail shuns water.

Your friend now has the pumps successfully pumping ions. She added an equal concentration of both ions to the correct sides of the liposomes along with an excess of the energy source. She is surprised when the pumps stop working after a short time. Which of the following could explain why the transporter stopped pumping ions?

The pump ran out of Na+ to pump because it pumps 3 Na+out for every 2 K+ pumped in.

Under what condition will a target cell always respond quickly to an extracellular signal?

The response does not require changes in gene expression.

Calcium ion release triggers all of the following biological processes EXCEPT

action potential transmission along an axon.

Which response to GPCR stimulation would be most rapid?

activation of a G protein that regulates the opening of an ion channel

Consider the following illustration and then answer the question.Each of these mechanisms of transport, as illustrated above, is best categorized by which term?

active transport

The movement of an ion against its concentration gradient is called what?

active transport

IP3 signaling helps regulate sweating, which is important for regulating body temperature. Anhidrosis, the inability to sweat normally, can be caused by genetic and environmental factors. A rare mutation has been identified in a family with several children suffering from anhidrosis. The mutation inactivates the protein that IP3 binds on the ER membrane. Suppose cells were isolated from affected family members and exposed to different treatments. Which of the following treatments would be able to repair the signaling defect in cells isolated from these patients?

addition of high amounts of Ca2+ in the cytosol

Detergent molecules are ___________ in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane.

amphipathic

Which term correctly describes the entire phospholipid molecule?

amphipathic

Which of the following form tiny hydrophilic pores in the membrane through which solutes can pass by diffusion?

channels

Ras is activated by a Ras-activating protein that does what?

causes Ras to exchange GDP for GTP

The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called what?

cell cortex

The plasma membrane is involved in which activities?

cell growth and motility, cell signaling, cell recognition, import and export of nutrients and wastes

Which factors determine the force driving the passive transport of charged solutes across the membrane?

electrochemical gradient

Which of the following types of cell signaling is long range and uses hormones as signals?

endocrine

Which organelle is important for controlling the concentration of calcium ions in the cytosol?

endoplasmic reticulum

Which type of cell-surface receptor(s), when activated, catalyze(s) a reaction inside the cell?

enzyme-coupled receptors

Following the binding of an extracellular signal molecule, receptor tyrosine kinases (RTKs) do which of the following?

form dimers in which each polypeptide chain cross-phosphorylates the cytoplasmic tail of its partner.

Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what?

pump protons out of the cell to generate a proton gradient across the plasma membrane

Ca2+ is an intracellular messenger involved in which of these processes?

release of neurotransmitters, secretion of hormones, triggering of embryonic development after fertilization, initiation of muscle contraction

What type of protein moves randomly selected phospholipids from one monolayer of a lipid bilayer to the other?

scramblase

What are small intracellular signaling molecules often called?

second messengers

Ion channels contain a selectivity filter that

selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel.

RTKs can activate the enzyme phosphoinositide 3-kinase, which phosphorylates inositol phospholipids. These phospholipids then do what?

serve as docking sites that recruit specific intracellular signaling proteins to the plasma membrane

When cells respond to an extracellular signal, they most often convert the information carried by this molecule from one form to another. What is this process called?

signal transduction