Chapter 4: Cell Membrane

Membrane carbohydrates:

can be covalently linked to membrane proteins or to membrane lipids.

What are the building blocks of a phosphoglyceride, specifically phosphatidic acid?

glycerol + 1 phosphate group + 2 fatty acids

Signal transduction:

involves the response of a cell to external stimuli, such as specific molecules or light.

An electrochemical gradient:

is determined by the concentration difference of a substance between two compartments and by the difference in charge between two compartments.

Where in a myelinated axon are action potentials generated?

nodes of Ranvier

The movement of water molecules down its concentration gradient and across selectively a permeable membrane is known as _________.

osmosis.

All of the following characteristics are common to facilitated diffusion and active transport EXCEPT for ___________.

the requirement for energy.

Peripheral membrane proteins can be solubilized from the plasma membrane by _________.

Aqueous Salt Solutions

Most of the functions of a cell membrane are performed by ________.

Proteins

Which of the following is a function of the plasma membrane?

Compartmentalization. Responding to external signals. Scaffold for biochemical activities.

How do cells transport small, nonpolar, hydrophobic molecules, such as fatty acids or steroid hormones across the cell membrane?

Such molecules diffuse freely.

What appears to serve as "fences" around portions of the membrane that restrict the distance an integral protein can travel?

The membrane's underlying cytoskeleton

You have fused a mouse cell and a human cell and then treated the cell with specific antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins - green; antibodies to human proteins - red). What does the cell look like about 40 minutes to an hour after fusion?

The red and green labels are uniformly distributed across the entire membrane.

What is TRUE regarding phospholipids?

They are amphipathic.

What is true regarding liposomes?

They are very useful in membrane research. They form spontaneously when a small amount of phosphatidylcholine is dispersed in an aqueous solution. They are fluid-filled spherical vesicles. They can be used to deliver drugs within the body.

What is true about peripheral membrane proteins?

They can either attach or detach from the membrane as needed. They provide mechanical support for the membrane. They may function as enzymes. They may function as an anchor for integral membrane proteins.

Drugs may affect behavior by having which of these effects at the synapse?

They may prevent the reuptake of neurotransmitters from the synaptic cleft. They may prevent release of neurotransmitters from the presynaptic cell. They may block receptors that bind to neurotransmitters. They may mimic the action of neurotransmitters at the synapse.

What is true of the freeze-fracture replication technique?

Tissue is frozen solid and then struck with a knife blade, which fractures the block into two pieces. The fracture plane often follows a path between the two leaflets of the lipid bilayer. Once membranes are split by the fracturing, metals are deposited on their exposed surfaces to form a replica, which can be viewed in the electron microscope. This technique allows investigation of the microheterogeneity of the membrane.

The temperature at which the lipids that compose the lipid bilayer convert from a liquid crystal phase to a crystalline gel in which phospholipid fatty acid chain movement is greatly restricted is called the _________.

Transition temperature

What is true regarding the diffusion of substances through membranes?

Water can diffuse through the lipid bilayer because it is small. Substances with a larger partition coefficient are better able to diffuse through the lipid bilayer. Diffusion across a membrane requires a concentration gradient. A membrane is permeable to a substance that can cross through the lipid bilayer or through an aqueous pore that spans the membrane.

One reason why gene therapy has NOT been successful in the treatment of cystic fibrosis is that:

adenovirus did not integrate its own DNA into the target cell and had to be re-administered frequently, increasing the risk of an inflammatory response.

The fine extension of a neuron that conducts impulses away from the cell body is:

an axon.

Lipid rafts:

are thought to be patches of cholesterol and sphingolipids that tend to float within the more fluid environment of phosphoglycerides.

Aquaporins:

can be regulated by the hormone vasopressin.

An action potential is ultimately caused by:

changes in membrane permeability.

Membranes contain a wide diversity of lipids, including ________.

cholesterol, phosphoglycerides and sphingolipids

Plasma membranes contain a wide diversity of lipids, including _______________.

cholesterol, phosphoglycerides and sphingolipids

The ten alpha-helices in the transmembrane domain:

create a channel through the membrane where the ion binding and transit may occur.

Membrane fluidity can be increased by:

desaturation of fatty acid chains. the presence of two unsaturated fatty acid chains in a single phospholipid molecule. reshuffling of fatty acid chains between glycerol backbones to increase the number of double bonds in the fatty acid chains of membrane phospholipids. forming double bonds between carbon atoms that comprise the fatty acid chain.

Which is true concerning the transition temperature (melting point) of membrane lipids?

double bonds lower it, and increased length raises it

Which organism provided an ideal system for the study of the nicotinic acetylcholine receptor?

electric fish

Diffusion:

eliminates a concentration gradient between two regions.

In the cell fusion experiments of Larry Frye and Michael Edidin of Johns Hopkins University,:

fluorescent dyes were covalently linked to antibodies for membrane proteins. cells from mice and from humans were fused to each other. it was shown that membrane proteins could move within the plane of the membrane. indicated that the mobility of membrane proteins was decreased at lower temperatures.

Saturated fatty acids:

have straight fatty acyl chains.

Acetylcholine:

increases in concentration in the synaptic cleft in the presence of drugs that inhibit acetylcholinesterase.

A symport:

is used to move Na+ and glucose together into the epithelial cells of the intestine.

The major drawback of using fluorescence recovery after photobleaching (FRAP) to follow the movements of molecules in the membranes of living cells is:

it can only be used to follow the average movements of a relatively large number of molecules over a relatively large distance.

The substance a-bungarotoxin possesses all of these characteristics

it causes paralysis. it is a component of snake venom. it binds to nicotinic acetylcholine receptors. it was used to measure the amount of the acetylcholine receptor purified using affinity chromatography.

The plasma membrane of the human erythrocyte is the MOST studied and BEST understood of all the diverse types of membrane because:

it is easily obtained by hemolysis of red blood cells.

If a red blood cell were added to a hypotonic solution:

it would rapidly gain water and swell or burst.

It is thought by some investigators that cholesterol and sphingolipids self-assemble into microdomains within the plasma membrane that are more gelated and highly ordered than surrounding regions that contain primarily phospholipids. It is hypothesized that certain proteins tend to concentrate in these so-called ________, thereby organizing the membrane into functional compartments.

lipid rafts.

Individuals that lack glycophorin A in their red blood cell membranes:

may be protected from the protozoan that causes malaria.

Carbohydrates found on the plasma membrane of the red blood cell:

may be related to certain disease conditions.

Proteins that penetrate the lipid bilayer _________.

may pass entirely through the lipid bilayer and protrude from both the extracellular and cytoplasmic sides of the membrane.

Gated channels may be opened or closed by:

mechanical forces. voltage differences. binding of a ligand.

The sodium-potassium pump, or Na+/K+ ATPase:

moves both Na+ ions and K+ ions across the membrane against their concentration gradients.

Passive transport includes _________.

osmosis. facilitated diffusion. diffusion of a substance directly across the lipid bilayer of the membrane.

Ankyrin and spectrin are peripheral membrane proteins that:

play a major role in determining the biconcave shape of the erythrocyte.

What word below characterizes the amino acids that are found in an α-helical segment that spans a membrane?

predominantly hydrophobic

Tetrahydrocannabinol, the active ingredient in marijuana, binds to receptors located in the ________ terminals of certain brain neurons. It lowers the likelihood that these neurons will release ________.

presynaptic, neurotransmitters

MOST functions of cell membranes are carried out by:

proteins

The temperature at which the lipids that compose the lipid bilayer convert from a liquid crystalline phase to a frozen crystalline gel in which phospholipid-fatty-acid-chain movement is greatly restricted is called the _________.

transition temperature.

What is true regarding the myelin sheath?

It allows saltatory conduction whereby action potentials are generated only at the nodes of Ranvier. It deteriorates in those who suffer from multiple sclerosis. It is composed of layers of lipid-containing membranes. It is composed of Schwann cells or oligodendrocytes.

Which of the following is true about the cholesterol associated with membranes?

It interferes with the movements of the fatty acid tails of the phospholipids.

It is thought by some investigators that cholesterol and sphingolipids self-assemble into microdomains within the plasma membrane that are more gelated and highly ordered than surrounding regions that contain primarily phospholipids. It is hypothesized that certain proteins tend to concentrate in these so-called ________, thereby organizing the membrane into functional compartments.

Lipid Rafts

What is true about membrane proteins?

Lipid-anchored proteins are attached to lipids that are situated within the bilayer. Integral proteins have domains that protrude from both the extracellular and the cytoplasmic sides of the membrane. Integral proteins comprise 25-30% of all encoded proteins. Peripheral proteins are associated with the surface of a membrane by noncovalent bonds.

Which of the following statements is true regarding the mobility of membrane components?

Lipids tend to move more rapidly than proteins within the plane of the membrane.

_________ can be used to trap integral proteins and drag them through the membrane with a known force, using forces generated by a focused laser beam. This yields information about the presence of membrane barriers.

Optical tweezers

Facilitated diffusion:

requires a concentration gradient.

Potassium and sodium cannot move through the cell membrane into the cell on their own because:

these ions are charged.

Integral membrane proteins are difficult to isolate in a soluble form because:

they possess hydrophobic transmembrane domains.

Membranes can be found in all of the following EXCEPT __________.

a ribosome.

On average, how many amino acids engaged in predominantly hydrophobic a- helices does it take to cross the hydrophobic part of the membrane?

about 20 amino acids

The major component of all cell membranes is _________.

A lipid bilayer

Which process REQUIRES input of energy to move materials across a membrane?

Active transport that moves substances against a concentration gradient.

Which of the following compounds can diffuse across a phospholipid bilayer?

H2O

A transport system that moves one solute into the cell and another one out of the cell during a single cycle accompanied by the expenditure of energy through ATP hydrolysis could be called a(n) _______

active antiport

Movement of membrane proteins may be restricted by:

a high density of neighboring proteins embedded in the membrane. interactions with the underlying "membrane skeleton." peripheral proteins situated on the cytoplasmic side of the membrane. interaction of integral membrane proteins with extracellular materials..

Which of the following is NOT a function of membranes?

providing a nonselective permeable barrier

What appears to serve as "fences" around portions of the membrane that restrict the distance an integral protein can travel?

the membrane's underlying cytoskeleton

The ratio of lipids to proteins in a membrane:

varies considerably depending upon the type of cell and membrane, the organism, and the function of the membrane.

The best understood gated channel is:

voltage-gated potassium ion channels.

Under which conditions would a cell membrane be most likely to be in a liquid, crystalline state, in which an individual phospholipid can rotate around its axis or move laterally through the plane of the bilayer?

warmer temperatures around 37°C