Chapter 6

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.

Hydrocarbons are molecules composed of carbon and hydrogen molecules. The bonds between carbons in these molecules play a key role in the function of hydrocarbons. A single covalent bond between two carbon molecules in a hydrocarbon chain forms what structure?

A single bond between two carbons in a hydrocarbon chain forms a three-dimensional tetrahedron.

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

ATP hydrolysis provides the energy to transport ions against their concentration gradients.

In the illustration, which protein transport mechanism is best represented by the letter "C"? Summary of the Passive and Active Mechanisms of Membrane Transport.

Active transport

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

All of the given answers are correct.

Which of the following is true of cell membranes?

Amphipathic proteins can span the membrane.

Which of the following would decrease membrane fluidity?

An increased level of saturation of fatty acids

Removing butter from the refrigerator and trying to spread it onto a piece of toast right away usually results in putting a hole in the toast because the butter is hard. Which of the following characteristics results in butter being hard after being stored in the refrigerator?

Butter is a saturated lipid with long-chain hydrocarbons. In the cold, saturated hydrocarbon chains have reduced fluidity as a result of hydrophobic interactions between hydrocarbon chains.

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 ATP and copying ribozymes would persist and dominate the population.

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 utilizes 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.

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

Energy is stored in the C-H and C-C bonds. Although these bonds are relatively low-energy bonds, the number of covalent bonds allows for the storage of large amounts of potential energy that can be used to generate ATP in times of need.

Which phospholipid structures affect the permeability of membranes?

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

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.

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.

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.

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

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

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

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

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 substances is an unsaturated lipid?

Safflower oil

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.

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

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 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

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 allows for the phospholipid 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

Approximately 30 percent of all the 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.

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 ATP to add a phosphate group to a protein allows for movement of molecules via __________.

active transport

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

amphipathic

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

The physical state of lipids is varied. The fluidity of lipids is determined by ______.

bond saturation

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

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

chloride

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

In the illustration, which protein transport mechanism is best represented by the letter "A"? Summary of the Passive and Active Mechanisms of Membrane Transport.

diffusion

In the illustration, which protein transport mechanism is best represented by the letter "B"? Summary of the Passive and Active Mechanisms of Membrane Transport.

facilitated diffusion

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

facilitated diffusion

A red blood cell that is placed in distilled water will __________.

gain water and expand

The transmembrane transport protein GLUT-1 transports __________.

glucose

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

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

move into the cell via osmosis

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

osmosis

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 relative to the membrane charge outside the cell

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

What happens when phospholipids are placed into water and agitated?

they form liposomes