Bio Chapter 6

Which phospholipid structures affect the permeability of membranes?

Fatty acid tail length and the degree of saturation of fatty acid tails

The freeze-fracture technique was used to resolve the debate about membrane structure with respect to the placement of proteins. Which of the following statements about membrane structure did the freeze-fracture technique elucidate?

Freeze fracture and scanning electron microscopy allowed researchers to see in between the two lipid bilayers.

Which of the following was evidence for the fluid-mosaic model of membrane structure?

Freeze fracture followed by scanning electron microscopy showed pits and mounds.

Aquaporins are membrane proteins that act as a channel to allow water to cross the plasma membrane 10 times faster than it does in the absence of aquaporins. What types of functional groups face the interior of the aquaporin pores?

Hydrophilic functional groups, in particular carbonyl groups, face the interior of the aquaporin pore.

If a solution surrounding a cell is hypertonic relative to the inside of the cell, how will water move?

It net movement of water will be out of the cell via osmosis.

The concentration of K+ ions is higher inside a cell than outside the cell. What type of transport system is needed to move K+ ions in and out of the cell?

K+ can move into the cell by active transport and out of the cell by facilitated diffusion.

Which type of molecule moves across a cell membrane most easily?

Lipid-soluble, nonpolar molecules, such as oxygen and carbon dioxide

Describe, on a molecular level, how you would expect these lipids to behave in water. Lipids would aggregate in lipid bilayer on the surface of water. Lipids would aggregate in little micelles. Lipids would float on the surface of the water, or collect in droplets suspended in water, reducing their interaction with water to a minimum. Lipids would dissolve in the water. They would not aggregate, reducing their interaction with water to a minimum.

Lipids would float on the surface of the water, or collect in droplets suspended in water, reducing their interaction with water to a minimum.

Which of the following membranes would have the least permeability? (A) A membrane made with 50 percent cholesterol and 20 percent unsaturated phospholipids (B) A membrane made with 20 percent cholesterol and 20 percent unsaturated phospholipids (C) A membrane made with 20 percent cholesterol and 30 percent saturated phospholipids (D) A membrane made of 0 percent cholesterol and 30 percent saturated phospholipids

Membrane A would be the least permeable.

Place the following molecules in order of permeability to a lipid bilayer from low permeability to high permeability: Na+, O2, sucrose, and H2O.

Na+ < sucrose < H2O < O2

How does a pump differ from a channel or a carrier?

Pumps require energy for transport, but channels and carriers do not use energy.

Which of the following is true regarding saturated fats?

Saturated fats contain the maximum number of hydrogen atoms that can attach to the carbon skeleton.

Is lipid structure in foods you eat linked to heart disease? The media is full of advice on what you should and should not eat, but these recommendations often change from year to year. You may have heard that polyunsaturated fats are heart-healthy and saturated fats are not, but is it really that simple? How is the chemical structure of saturated fats different from that of unsaturated fats?

Saturated fats have fatty acid tails with only C−C bonds while unsaturated fats have one or more C=C bonds in the tails.

Which of the following correctly matches the lipid with its description? Fats consist of three fatty acids linked to a hydrophobic head. Phospholipids have three fatty acids and a phosphate-containing region. Saturated fats contain a high degree of double bonds. Steroids have a distinctive four-ring structure with variable side groups attached.

Steroids have a distinctive four-ring structure with variable side groups attached.

Liposomes made by using only cholesterol and phospholipids in phosphate-buffered saline are moved to a hypotonic solution. What will result?

Swelling of the liposome and lysis

A trout moves from a warm environment into a cold environment. Predict how the saturation status of hydrocarbon chains might change to ensure proper membrane fluidity in the new cold environment.

The hydrocarbons would become less saturated to increase the fluidity of the membrane.

Proteins are amphipathic molecules that contain nonpolar (hydrophobic) amino acids and polar (hydrophilic) amino acids. Where would the hydrophobic and hydrophilic amino acid residues of a transmembrane protein be found?

The hydrophobic amino acids would come into contact with the hydrocarbon tails of the phospholipid bilayer, whereas the hydrophilic amino acids would interact with the polar phospholipid heads and the intracellular and extracellular environments.

The term facilitated diffusion refers to which of the following?

The passive transport of substances using a transport protein

The degree of saturation of phospholipids in a membrane will affect which of the following functions of phospholipids?

The permeability of the membrane

Is lipid structure in foods you eat linked to heart disease?The media is full of advice on what you should and should not eat, but these recommendations often change from year to year. You may have heard that polyunsaturated fats are heart healthy and saturated fats are not, but is it really that simple?How you prepare food can affect the amount of saturated fats that you eat. For example, if you cook meat on a grill, the product will have less saturated fat than if you were to eat the same meat raw. What occurs during the process of cooking the meat on a grill that would explain this result?

The saturated fat in meat undergoes a change in its physical state as it is heated −− from a semisolid consistency to a liquid. When meat is grilled, the liquefied fat drips off, resulting in less saturated fat in the final product.

The permeability of a membrane refers to which of the following?

The tendency of a given substance to pass through it

Region A has a low-solute concentration. Region B has a high-solute concentration. They are separated by a selectively permeable membrane that is impermeable to the solute but allows the passage of water. Which of the following is true?

Water moves from region A to region B via osmosis.

The three types of lipids found in cells (fats, steroids, and phospholipids) are insoluble in water because they all possess __________.

a significant hydrocarbon component

Changes in protein structure caused by phosphorylation or other protein modifications are referred to as conformational changes. The use of adenosine triphosphate (ATP) to add a phosphate group to a protein allows for movement of molecules via __________.

active transport

One of the roles of plasma membrane proteins is to____.

allow passage of select molecules that could not otherwise cross the lipid bilayer

Ion channels are specialized membrane proteins that facilitate the movement of ions across membranes. Both the concentration of ions on either side of the membrane and the net charge on either side of the membrane affect the movement of ions. Together, these two features are referred to as __________.

an electrochemical gradient

Glucose transporter 1, or GLUT-1, facilitates the movement of glucose across membranes. GLUT-1 is a __________.

carrier protein

The selective permeability of the plasma membrane and the proteins involved in active and passive transport allow __________.

cells to create an internal environment that is different from the external environment

The lipid bilayer is essentially impermeable to solutes that are

charged

Lipid structures vary widely; however, phospholipids and fats are similar in that they both _________.

contain glycerol

Detergents are useful for isolating membrane proteins because __________.

detergents are amphipathic

Dissolved molecules and ions, or solutes, have thermal energy and are in constant random motion in solution. These dissolved substances will spontaneously demonstrate an increase in entropy in the absence of any outside influence. Thermal energy in the form of kinetic energy thus allows for the movement of solutes or ions in solution, resulting in __________.

diffusion

The movement of molecules through a plasma membrane channel protein is always _____.

down the electrochemical gradient

Molecules that move down a concentration gradient and require transport proteins to cross a membrane use __________.

facilitated diffusion

In fat synthesis,________and fatty acids combine to make fats plus________.

glycerol; water

In the reaction that builds a fat,________ groups react with ________ groups.

hydroxyl; carboxyl

Lipid vesicles are formed containing pure water. If these vesicles are transferred to a solution that contains a rather high concentration of solutes, the solution outside the vesicle is said to be_____.

hypertonic

Unlike animal cells, bacteria have a porous cell wall surrounding their plasma membrane. The cell wall may help bacteria survive in a(n) __________ environment.

hypotonic

Lipids are organic compounds characterized by their _____.

insolubility in water and their solubility in organic solvents

A food company hydrogenated a barrel of fat. The treatment ...

made the fat less fluid.

Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of _____.

more fluid bilayers

If a solution surrounding a cell is hypotonic relative to the inside of the cell, the water will _______.

move into the cell via osmosis

Integral membrane proteins are anchored in lipid bilayers. Which of the following groups of amino acid residues would likely be found in the portion that crosses the lipid bilayer?

nonpolar

Diffusion of water through a selectively permeable membrane is known as _________.

osmosis

Facilitated diffusion is a type of _______.

passive transport

The presence of many C-C and C-H bonds causes fats to be ...

rich in energy and insoluble in water.

Which of the following substances is an unsaturated lipid?

safflower oil

Solutes that can rapidly cross a lipid bilayer are typically

small and nonpolar

Solutes that are ___________ can cross a lipid bilayer, but not as quickly.

small and polar

A voltage-gated ion channel that permits the movement of potassium from inside the cell to outside the cell may be opened when __________.

the membrane charge on the inside of the cell is positive compared with the membrane charge outside the cell

The most unsaturated fats have ...

the most double bonds.

The separation of life from nonlife by the formation of the plasma membrane was important because __________.

the plasma membrane kept damaging compounds out of the cell and allowed entry of needed compounds into the cell by selective permeability

Lipids are not considered polymers because _________.

they are not composed of monomer subunits.

Fats consist of three fatty acid tails that are attached to a glycerol head group. Which of the following reactions occurs to generate fats?

A dehydration reaction

Channel proteins are selective. Each channel protein has a structure that permits only a particular type of ion or small molecule to pass through it. To what does the term gated channel refer?

A gated channel is opened or closed in response to a signal and is not always open or always closed.

In the illustration, which membrane transport mechanism is best represented by the letter "C"?

Active Transport

How does the sodium-potassium pump work to transport sodium and potassium against their concentration gradients?

Adenosine triphosphate (ATP) hydrolysis provides the energy to transport ions against their concentration gradients.

What type of chemical interactions do phospholipids have with their environment?

Amphipathic

Which of the following is true of cell membranes?

Amphipathic proteins can span the membrane.

Fish such as mackerel, cod, and haddock often live in deep, very cold water in the ocean. What is one way that their membranes are able to remain more fluid in cold temperatures?

By increasing the percentage of unsaturated phospholipids in the membranes

Triglycerides vary with respect to the number of ...

C atoms in the tails, double bonds in the tails.

Fats and phospholipids are composed of long-chain fatty acids. These molecules store large amounts of energy in the body of animals. How do these molecules store energy?

C-C and C-H bonds have high potential energy because the participating atoms have low electronegativities and share the electrons equally. The large number of these covalent bonds in long-chain fatty acids allows for the storage of large amounts of potential energy that can be used to generate adenosine triphosphate (ATP) in times of need.

Is lipid structure in foods you eat linked to heart disease? The media is full of advice on what you should and should not eat, but these recommendations often change from year to year. You may have heard that polyunsaturated fats are heart-healthy and saturated fats are not, but is it really that simple? What physical property is often associated with these chemical differences?

C=C bonds normally result in kinks that increase the spacing between fats and thus make unsaturated fats more fluid than saturated fats.

An industrial process called hydrogenation is used to convert vegetable oil into a semisolid compound called margarine. Explain why hydrogenation is an appropriate term for this process. Match the words in the left column to the appropriate blanks in the sentences on the right. Hydrogenation is used because the process is likely to involve converting ____ bonds into ____ bonds by ____ hydrogens. Fats with only _______ bonds (i.e., _____) tend to be semisolid at room temperature.

C=C, C-C, adding, C-C, Saturated

Natural selection during the early evolution of the cell would allow for which of the following cells to proliferate and survive more efficiently than others?

Cells with particularly efficient and selective membrane proteins that imported molecules required for manufacturing adenosine triphosphate (ATP) and copying ribozymes would persist and dominate the population.

In terms of structure, how do channel proteins differ from carrier proteins?

Channel proteins form pores in the membrane, and carrier proteins undergo conformational changes to shuttle molecules across the membrane.

In terms of structure, how do channel proteins differ from carrier proteins?

Channel proteins, have different functional groups in the interior of the pore that function, as a molecular filter form pores in the membrane are open or close in response to a signal Carrier proteins change shape to shuttle molecules or ions across the membrane undergo conformational changes caused by the binding of the specific molecules

Which of the following statements correctly describes the specificity of these transport proteins for the solutes they transport?

Channels typically transport water or inorganic ions, whereas carrier proteins typically transport small polar molecules such as sugars or amino acids.

Cystic fibrosis is a disease associated with the inability to properly transport which ion?

Chloride

A hypothetical cell has a higher concentration of sodium ions outside the cell than inside the cell but an equal amount of chloride outside the cell and inside the cell. Based on its electrochemical gradient, which direction would chloride ions move across the cell membrane?

Chloride ions would move from inside the cell to outside down its electrochemical gradient.

Steroids are a family of lipids that have a bulky four-ring structure. Which of the following is an important lipid for plasma membrane structure?

Cholesterol

Which of the following lipids is classified as a steroid?

Cholesterol

Isolation of membrane proteins uses detergents to separate transmembrane proteins from membrane phospholipids. What property of detergents allows for this activity?

Detergents are small amphipathic molecules with hydrophobic tails that interact with both the hydrophobic phospholipid tails of membrane phospholipids and with the hydrophobic portions of transmembrane proteins.

Which statement best describes the results of an experiment designed to test whether the protein cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel?

Electric current flowed only in the presence of CFTR, indicating the movement of chloride ions.

Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? No, because they have no polar end to interact with water. Yes, because lipids always aggregate to form a membrane in water solution. No, because energy is needed to form a membrane. Yes, because membrane phospholipids may have unsaturated hydrocarbon chains as well.

No, because they have no polar end to interact with water.

A liposome has a selectively permeable phospholipid bilayer. For a particular solute, can the phospholipid bilayer be selectively permeable in only one direction?

No, selective permeability of a phospholipid bilayer is the same in both directions.

Is lipid structure in foods you eat linked to heart disease?The media is full of advice on what you should and should not eat, but these recommendations often change from year to year.You may have heard that polyunsaturated fats are heart healthy and saturated fats are not, but is it really that simple?To study the effect of food on heart disease, researchers fed a variety of diets to mice and then examined them for atherosclerosis −− the narrowing of arteries that is a leading cause of heart attacks. Data observed from mice fed with trans fats are provided below. Do these data identify the cause of atherosclerosis in the mice? No. The data show that there is a correlation between blood levels of trans fats and atherosclerosis, but these data do not show the cause. No. The data show that there isn't a correlation between blood levels of trans fats and atherosclerosis, so these data do not show the cause. Yes. The data show that there is a correlation between blood levels of trans fats and atherosclerosis, thus a high level of trans fats in the blood can cause atherosclerosis. Yes. The data show that there is a causation between blood levels of trans fats and atherosclerosis, thus a high level of trans fats in the blood can cause atherosclerosis.

No. The data show that there is a correlation between blood levels of trans fats and atherosclerosis, but these data do not show the cause.

Which of the following statements best describes the fluid-mosaic model of membrane structure?

The phospholipid bilayer contains diverse proteins, including some embedded amphipathic proteins that span the bilayer.

Which of the following features of phospholipids in a phospholipid bilayer allows for the phospholipids to interact with the aqueous environment in the extracellular media and the intracellular cytosolic environment?

The presence of a polar or charged head group attached to the phosphate

When solutes are diffusing through a membrane from high concentration on one side to low concentration on the other side, what happens when equilibrium is reached?

The rate of diffusion in one direction is the same as the rate of diffusion in the opposite direction.

Approximately 30 percent of all the adenosine triphosphate (ATP) generated in the human body is used to drive the Na+ /K+ -ATPase cycle. Which of the following statements best describes the activity of the Na+ /K+ -ATPase?

The sodium-potassium pump converts energy from ATP to generate an electrochemical gradient across the membrane that favors a flow of anions out of the cell and a flow of cations into the cell.

The spontaneous formation of micelles, liposomes, and phospholipid bilayers does not require the input of energy even though entropy decreases. What does this suggest about the stability of lipids in aqueous solutions compared to their stability in micelles, liposomes, and phospholipid bilayers?

The stability of lipids in aqueous solution is less than in micelles, liposomes, and phospholipid bilayers.

What do DNA, proteins, and fats have in common?

They contain carbonyl groups.

Use of planar lipid bilayers in experiments allowed researchers to do which of the following?

They could determine the temperature at which phospholipid bilayers became permeable for particular substance. They could understand the effect of cholesterol concentration of lipid bilayer structures. They could test to see if different types and concentrations of phospholipids allowed different solutes to cross the membrane.

What happens when phospholipids are placed into water and agitated?

They form liposomes.

How do the phospholipids in archaea differ from those in other cells? They have isoprenoid tails instead of fatty acid tails. They have tails made of unsaturated fatty acids instead of saturated fatty acids. They do not contain hydrocarbon chains. They have two hydrocarbon chains instead of three hydrocarbon chains.

They have isoprenoid tails instead of fatty acid tails.