chapter 6 a/b
What physical property is often associated with these chemical differences? C=C bonds normally form less hydrogen linkages which increase the spacing between fats and thus make unsaturated fats more fluid than saturated fats. C=C bonds normally form more hydrogen linkages which decrease the spacing between fats and thus make unsaturated fats less fluid than saturated fats. C=C bonds normally result in more compact structure that decreases the spacing between fats and thus makes unsaturated fats less fluid than saturated fats. C=C bonds normally result in kinks that increase the spacing between fats and thus make unsaturated fats more fluid than saturated fats.
C=C bonds normally result in kinks that increase the spacing between fats and thus make unsaturated fats more fluid than saturated fats.
Which statement most accurately explains why cholesterol and phospholipids are amphipathic but fats are not? See Section 6.1 (Page 121) . Cholesterol and phospholipids are primarily hydrophilic; fats are primarily hydrophobic. Cholesterol and phospholipids are primarily hydrophobic; fats are primarily hydrophilic. Cholesterol and phospholipids contain both hydrophilic and hydrophobic regions; fats are primarily hydrophobic. Cholesterol and phospholipids contain both hydrophilic and hydrophobic regions; fats are primarily hydrophilic.
Cholesterol and phospholipids contain both hydrophilic and hydrophobic regions; fats are primarily hydrophobic.
Which of these is NOT a lipid? phospholipid RNA steroids wax cholesterol
RNA
What do fats, steroids, and waxes have in common? (a) Moderate polarity. (b) Low solubility in water. (c) They occur in membranes. Both (a) and (c). Both (b) and (c).
(b) Low solubility in water.
Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal? Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient. Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell. Sodium and glucose compete for the same binding site in the cotransporter. A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose. The cotransporter can also transport potassium ions.
A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
Which statement best explains the effect on membrane permeability of cholesterol and/or temperature? See Section 6.2 (Page 124) . Adding cholesterol reduces permeability because its steroid rings fill gaps in the hydrophobic membrane interior. Adding cholesterol increases permeability because its steroid rings increase the density of the hydrophobic membrane interior. Increasing temperature increases permeability because it increases the strength of hydrophobic interactions in the membrane interior. Adding cholesterol increases permeability because its steroid rings decrease the density of the hydrophobic membrane interior.
Adding cholesterol reduces permeability because its steroid rings fill gaps in the hydrophobic membrane interior.
Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes? Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane. Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes. Cholesterol has four rings in its structure that can sequester ("trap") solutes. Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes.
Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.
Which statement most accurately describes the relationship between the permeability and fluidity properties of phospholipid bilayers and their structure? See Section 6.2 (Page 124) . Bilayers are most permeable but least fluid when they consist of shorter, unsaturated hydrocarbon tails. Bilayers are most permeable and most fluid when they consist of longer, unsaturated hydrocarbon tails. Bilayers are most permeable and most fluid when they consist of longer, saturated hydrocarbon tails. Bilayers are most permeable and most fluid when they consist of shorter, unsaturated hydrocarbon tails.
Bilayers are most permeable and most fluid when they consist of shorter, unsaturated hydrocarbon tails.
The presence of many C-C and C-H bonds causes fats to be ... (a) rich in energy. (b) insoluble in water. (c) low in energy. Both (a) and (b). Both (b) and (c).
Both (a) and (b).
Triglycerides vary with respect to the number of ... (a) hydrocarbon tails. (b) C atoms in the tails. (c) double bonds in the tails. Both (b) and (c). All of the above.
Both (b) and (c).
Which statement most accurately describes how the structures of fats, steroids, and phospholipids compare? See Section 6.1 (Page 121) . Steroids contain fatty acids whereas fats and phospholipids do not Fats and phospholipids contain glycerol whereas steroids do not.
Fats and phospholipids contain glycerol whereas steroids do not.
If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell? Hypertonic Osmotic Isotonic Hypotonic
Hypotonic
Which of the following is a characteristic feature of a carrier protein in a plasma membrane? It requires the expenditure of cellular energy to function. It is a peripheral membrane protein. It exhibits a specificity for a particular type of molecule. It has no hydrophobic regions. It works against diffusion.
It exhibits a specificity for a particular type of molecule.
Gramicidin is an antibiotic that increases the permeability of bacterial cell walls to inorganic ions. What is the most likely mode of action of gramicidin? It forms a channel in the membrane. It causes membranes to fuse with one another. It removes electrical charges from solutes. It acts by active transport.
It forms a channel in the membrane.
Which statement accurately summarizes a feature of passive transport? See Section 6.4 (Page 131) . It makes the cell interior and exterior more different from one another. It involves no change in entropy. No membrane proteins are involved. It is a spontaneous process.
It is a spontaneous process.
If a solution surrounding a cell is hypotonic relative to the inside of the cell, how will water move? It will move out of the cell via osmosis. It will not move, because equilibrium exists. It will move into the cell via osmosis. It will evaporate from the cell surface more rapidly.
It will move into the cell via osmosis.
Cooking oil consists of triglycerides made of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Yes, because membrane phospholipids may have unsaturated hydrocarbon chains as well. No, because they have no polar end to interact with water. No, because energy is needed to form a membrane. Yes, because all lipids always aggregate to form a membrane in water solution.
No, because they have no polar end to interact with water.
How is the chemical structure of saturated fats different from that of unsaturated fats? Saturated fats have one long fatty acid tail while unsaturated fats have one or more short tails. Saturated fats have fatty acid tails with only C=C bonds while unsaturated fats have one or more C−C bonds in the tails. Saturated fats have fatty acid tails with only C−C bonds while unsaturated fats have one or more C=C bonds in the tails. Saturated fats have one long fatty acid tail with only C−C bonds while unsaturated fats have several short tails with one or more C=C bonds.
Saturated fats have fatty acid tails with only C−C bonds while unsaturated fats have one or more C=C bonds in the tails.
If you mechanically shook a mixture of phospholipids and water, what would you expect to see when you observe the solution using an electron microscope? Some lipids will have formed tiny vesicles filled with water. All the lipids will have formed planar bilayer membranes. The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. Most lipids will have completely dissolved in solution because they are partially polar.
Some lipids will have formed tiny vesicles filled with water.
You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be true about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments? The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. The membrane phospholipids of cold-adapted organisms will have longer hydrocarbon tails. The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.
Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell? They must require a protein transporter, because the plasma membrane is completely impermeable to molecules. Their size probably allows them to diffuse through the plasma membrane. Their protein structure probably allows them to diffuse through the plasma membrane. Their lipid nature probably allows them to diffuse through the plasma membrane.
Their lipid nature probably allows them to diffuse through the plasma membrane.
Why are lipids and proteins free to move laterally in membranes? There are only weak hydrophobic interactions in the interior of the membrane. The interior of the membrane is filled with liquid water. Hydrophilic portions of the lipids are in the interior of the membrane. Lipids and proteins repulse each other in the membrane. Molecules such as cellulose can pull them in various directions.
There are only weak hydrophobic interactions in the interior of the membrane.
Describe, on a molecular level, how you would expect these lipids to behave in water. These lipids would float on the surface of the water, or collect in droplets suspended in water, reducing their interaction with water to a minimum. These lipids would dissolve in the water. They would not aggregate, reducing their interaction with water to a minimum. These lipids would aggregate in lipid bilayer on the surface of water. These lipids would aggregate in little micelles.
These 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 is true of membrane lipids? See Section 6.1 (Page 121) . Both the head group and the tail(s) are hydrophobic. They contain a hydrophobic head group and a hydrophilic tail(s). Both the head group and the tail(s) are hydrophilic. They are amphipathic molecules.
They are amphipathic molecules.
What do DNA, proteins, and fats have in common? They contain nitrogen. They contain phosphorus. They are polar. They are polymers. They contain carbonyl groups
They contain carbonyl groups
True or false? Osmosis is a type of diffusion.
True (Osmosis is the diffusion of water across a selectively permeable membrane.)
Which of the following factors would tend to increase membrane fluidity? a lower temperature a greater proportion of saturated phospholipids a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses a relatively high protein content in the membrane a greater proportion of unsaturated phospholipids
a greater proportion of unsaturated phospholipids
Which of the following crosses lipid bilayers the fastest? a small, polar molecule like water a sodium ion a small, nonpolar molecule like oxygen (O2) a large, polar molecule like glucose
a small, nonpolar molecule like oxygen (O2)
A membrane protein that spans the phospholipid bilayer one or more times is _____. an associated protein a transmembrane protein a glycoprotein a peripheral protein an integrin
a transmembrane protein
One of the roles of plasma membrane proteins is to____. See Section 6.4 (Page 131) . dissolve the lipids in the membrane allow passage of select molecules that could not otherwise cross the lipid bilayer form one side of the membrane bilayer provide a structure on which the membrane lipids can assemble a bilayer
allow passage of select molecules that could not otherwise cross the lipid bilayer
For a protein to be an integral membrane protein, it would have to be _____. completely covered with phospholipids hydrophilic exposed on only one surface of the membrane hydrophobic amphipathic, with at least one hydrophobic region
amphipathic, with at least one hydrophobic region
Which of the following allows water to move much faster across cell membranes? peripheral proteins ATP aquaporins the hydrophobic interior of a cell membrane the sodiumpotassium pump
aquaporins
Steroids are considered to be lipids because they _____. contribute to atherosclerosis are not soluble in water are made of fatty acids are essential components of cell membranes are hydrophilic compounds
are not soluble in water
A function of cholesterol that does not harm health is its role _____. as the primary female sex hormone In calcium and phosphate metabolism All of cholesterol's effects cause the body harm the most abundant male sex hormone as a component of animal cell membranes
as a component of animal cell membranes
Molecules that are amphipathic must contain _____. See Section 6.1 (Page 121) . glycerol carbon rings both carbohydrates and lipids both hydrophilic and hydrophobic regions
both hydrophilic and hydrophobic regions
A "mystery molecule" was isolated in a laboratory and scientists found that the molecule readily crossed artificial membranes. Which of the following molecules can be ruled out as the "mystery molecule?" See Section 6.2 (Page 124) . CO2 H2O chloride ion O2
chloride ion
Cooking oil and gasoline (a hydrocarbon) are not amphipathic molecules because they _____. are highly reduced molecules have hydrophobic and hydrophilic regions do not have a nonpolar region do not have a polar or charged region
do not have a polar or charged region
The movement of molecules through a plasma membrane channel protein is always _____. See Section 6.4 (Page 131) . down the molecule's electrochemical gradient against the molecule's electrochemical gradient toward the inside of the cell "paid for" by an expenditure of cellular energy
down the molecule's electrochemical gradient
which of the following building blocks are not used to build very large polymers? amino acids monosaccharides fatty acids nucleotides
fatty acids
In fat synthesis,________and fatty acids combine to make fats plus________. glucose; phosphate phosphate; glycerol esters; phosphate esters; water glycerol; water
glycerol; water
In the reaction that builds a fat,________ groups react with ________ groups. carboxyl; amino hydroxyl; phosphate sulfhydryl; carboxyl hydroxyl; carboxyl phosphate; amino
hydroxyl; carboxyl
Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? the presence of double bonds removing cholesterol increasing temperature increasing length of the hydrocarbon chains
increasing length of the hydrocarbon chains
Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____. and the salt solution are both hypertonic to the cells of the celery stalks and the salt solution are both hypotonic to the cells of the celery stalks is isotonic and the salt solution is hypertonic to the cells of the celery stalks is hypotonic and the salt solution is hypertonic to the cells of the celery stalks is hypertonic and the salt solution is hypotonic to the cells of the celery stalks
is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of _____. See Section 6.2 (Page 124) . more fluid bilayers cholesterol glycerol a bilayer with decreased permeability to CO2
more fluid bilayers
Which of these is rich in unsaturated fats? lard beef fat a fat that is solid at room temperature butter olive oil
olive oil
Which of the following types of molecules are the major structural components of the cell membrane? proteins and cellulose phospholipids and proteins nucleic acids and proteins phospholipids and cellulose glycoproteins and cholesterol
phospholipids and proteins
Lipids that form membranes have what kind of structure? polar heads and nonpolar tails; the nonpolar tails interact with water polar heads and nonpolar tails; the polar heads interact with water polar heads and polar tails, which allows them to interact with water on both sides of the membrane completely polar, which allows them to dissolve in water
polar heads and nonpolar tails; the polar heads interact with water
Where would you most likely find an integral membrane protein? spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell floating freely in the cytoplasm on the inside surface of the cell membrane on the outside surface of the cell membrane
spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell
The most unsaturated fats have ... the shortest hydrocarbon tails. the fewest double bonds. the most double bonds. the highest ratio of H to C. the longest hydrocarbon tails.
the most double bonds.
What region of a steroid is hydrophilic? the long hydrocarbon chain the methyl (CH3) groups the ring structures the terminal hydroxyl group
the terminal hydroxyl group
Ions diffuse across membranes through specific ion channels down ________. their electrical gradients their chemical gradients their concentration gradients the osmotic potential gradients their electrochemical gradients
their electrochemical gradients
Consider a molecule that can diffuse across a lipid bilayer. At equilibrium ____. See Section 6.3 (Page 128) . the molecules no longer move due to a loss of thermal kinetic energy the molecules (solutes) spontaneously form a micelle or vesicle the membrane is no longer permeable to the molecules and restricts their movement there is no change in the concentration of the molecule on either side of the membrane
there is no change in the concentration of the molecule on either side of the membrane
Lipids are insoluble in water because_____. See Section 6.1 (Page 121) . they contain multiple hydroxyl groups they are very large with many carbon atoms they contain nonpolar C-C and C-H bonds The statement is not true. Lipids are soluble in water.
they contain nonpolar C-C and C-H bonds
true or false; all four types of macromolecules always contain carbon (c), hydrogen (h), and oxygen, but NOT all of them contain nitrogen (n)
true
Under what circumstances does membrane transport require energy? whenever a solute is moved against its electrochemical gradient wherever large molecules are moved within a cell whenever oxygen moves through a phospholipid bilayer membrane whenever an ion moves through a phospholipid bilayer membrane
whenever a solute is moved against its electrochemical gradient
