Molecular and Cellular Biology Unit 2

What do phospholipids and triglycerides have in common? 1) They both contain serine or some other organic compound. 2) They both have three fatty acids. 3) They both have a glycerol backbone. 4) They both have a phosphate.

3) They both have a glycerol backbone.

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? 1) CO2 2) an amino acid 3) glucose 4) K+ 5) starch

1) CO2

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures? 1) The double bonds form kinks in the fatty acid tails, forcing adjacent lipids to be further apart. 2) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes. 3) Unsaturated fatty acids permit more water in the interior of the membrane. 4) The double bonds block interaction among the hydrophilic head groups of the lipids. 5) The double bonds result in shorter fatty acid tails and thinner membranes.

1) The double bonds form kinks in the fatty acid tails, forcing adjacent lipids to be further apart.

Which aspect of phospholipids is most important to the formation of bilayers? 1) They are amphipathic. 2) Their size is large, relative to cholesterol. 3) Their size is small, relative to fats. 4) Their hydrocarbon tails can consist of fatty acids or isoprene subunits.

1) They are amphipathic.

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids? 1) They can move laterally along the plane of the membrane. 2) They frequently flip-flop from one side of the membrane to the other. 3) They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane. 4) They are free to depart from the membrane and dissolve in the surrounding solution. 5) They have hydrophilic tails in the interior of the membrane.

1) They can move laterally along the plane of the membrane.

Which of the following is the best explanation for why vegetable oil is a liquid at room temperature while animal fats are solid? 1) Vegetable oil has more double bonds than animal fats. 2) Vegetable oil has fewer double bonds than animal fats. 3) Animal fats have no amphipathic character. 4) Vegetable oil has longer fatty-acid tails than animal fats have.

1) Vegetable oil has more double bonds than animal fats.

Which of the following crosses lipid bilayers the slowest? 1) a sodium ion 2) a small, polar molecule like water 3) a large, polar molecule like glucose 4) a small, nonpolar molecule like oxygen (O2)

1) a sodium ion

Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold? 1) by increasing the percentage of unsaturated phospholipids in the membrane 2) by increasing the percentage of cholesterol molecules in the membrane 3) by decreasing the number of hydrophobic proteins in the membrane 4) by co-transport of glucose and hydrogen 5) by using active transport

1) by increasing the percentage of unsaturated phospholipids in the membrane

The presence of cholesterol in the plasma membranes of some animals 1) enables the membrane to stay fluid more easily when cell temperature drops. 2) enables the animal to remove hydrogen atoms from saturated phospholipids. 3) enables the animal to add hydrogen atoms to unsaturated phospholipids. 4) makes the membrane less flexible, allowing it to sustain greater pressure from within the cell. 5) makes the animal more susceptible to circulatory disorders.

1) enables the membrane to stay fluid more easily when cell temperature drops.

Which of the following functions do lipids provide in a cell? 1) structural 2) cell identification 3) information storage 4) neither structural, cell identification, nor information storage

1) structural

You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You then double the length of the hydrocarbon tails, and re-measure membrane permeability. You then double the length of the hydrocarbon tails again, and make a third measurement of membrane permeability. You graph membrane permeability as a function of hydrocarbon tail length. Which of the graphs below best represents the data you expect? 1) Linear, positive slope 2) Linear, negative slope 3) Bell curve 4) Linear, horizontal

2) Linear, negative slope

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose? 1) You can't predict the outcome. You simply have to make the measurement. 2) Permeability to glucose will increase. 3) Permeability to glucose will decrease. 4) Permeability to glucose will stay the same.

2) Permeability to glucose will increase.

If you mechanically shook a mixture of amphipathic lipids and water, what would you expect to see when you observe the solution using an electron microscope? 1) The lipids and water will have separated into two distinct layers because the lipids are partially nonpolar. 2) The lipids will have formed tiny vesicles filled with water. 3) The lipids will have formed planar bilayer membranes. 4) The lipids will have completely dissolved in solution because they are partially polar.

2) The lipids will have formed tiny vesicles filled with water.

Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell? 1) Their size probably allows them to diffuse through the plasma membrane. 2) Their lipid nature probably allows them to diffuse through the plasma membrane. 3) Their protein nature probably allows them to diffuse through the plasma membrane. 4) They must require a protein transporter, because the plasma membrane is completely impermeable to molecules.

2) Their lipid nature probably allows them to diffuse through the plasma membrane.

Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes? 1) Cholesterol binds to the outside surface of a membrane, thus blocking the movement of solutes. 2) Because cholesterol is amphipathic, it forms tiny vesicles that trap solutes. 3) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane. 4) Cholesterol has four rings in its structure that can sequester (trap) solutes.

3) Because cholesterol is amphipathic, it fits in between the phospholipids and blocks diffusion through the membrane.

Why are lipids and proteins free to move laterally in membranes? 1) The interior of the membrane is filled with liquid water. 2) There are no covalent bonds between lipid and protein in the membrane. 3) Hydrophilic portions of the lipids are in the interior of the membrane. 4) There are only weak hydrophobic interactions in the interior of the membrane. 5) Molecules such as cellulose can pull them in various directions.

3) Hydrophilic portions of the lipids are in the interior of the membrane.

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? 1) The membrane phospholipids of cold-adapted organisms will have longer hydrocarbon tails. 2) The membrane phospholipids of cold-adapted organisms will have more saturated hydrocarbon tails. 3) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.

3) The membrane phospholipids of cold-adapted organisms will have more unsaturated hydrocarbon tails.

How do phospholipids interact with water molecules? 1) The polar heads avoid water; the nonpolar tails attract water (because water is polar and opposites attract). 2) Phospholipids don't interact with water because water is polar and lipids are nonpolar. 3) The polar heads interact with water; the nonpolar tails do not. 4) Phospholipids dissolve in water.

3) The polar heads interact with water; the nonpolar tails do not.

What preserves the structural integrity of phospholipid bilayers? 1) Peptide bonds form between the phosphate groups of the phospholipids. 2) Sugars associated with the cell membrane covalently cross-link. 3) hydrophobic and hydrophilic interactions between nearby phospholipids 4) van der Waals interactions between the glycerol molecule and fatty acids of a single phospholipid

3) hydrophobic and hydrophilic interactions between nearby phospholipids

Phospholipids can form all of the following structures in water except which one? 1) micelles 2) bilayers 3) monolayers 4) vesicles

3) monolayers

Which of the following types of molecules are the major structural components of the cell membrane? 1) phospholipids and cellulose 2) nucleic acids and proteins 3) phospholipids and proteins 4) proteins and cellulose 5) glycoproteins and cholesterol

3) phospholipids and proteins

In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude? 1) The experiment failed. 2) The water somehow blocked the movement of ions across the membrane. 3) The left side would probably also test negative for ions. 4) Ions cannot cross planar bilayers.

4) Ions cannot cross planar bilayers.

You make a phospholipid bilayer with short, saturated hydrocarbon tails. You measure the permeability of this membrane to oxygen. You are going to change the length of the hydrocarbon tails and re-measure membrane permeability, but first your boss asks you to graph the data you expect if there is no effect of hydrocarbon tail length on membrane permeability (your null hypothesis). Which of the graphs below best represents the data you expect if your null hypothesis is correct? 1) Linear, positive slope 2) Linear, negative slope 3) Bell curve 4) Linear, horizontal

4) Linear, horizontal

Which of the following crosses lipid bilayers the fastest? 1) a sodium ion 2) a small, polar molecule like water 3) a large, polar molecule like glucose 4) a small, nonpolar molecule like oxygen (O2)

4) a small, nonpolar molecule like oxygen (O2)

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules? 1) the presence of double bonds 2) increasing temperature 3) removing cholesterol 4) increasing length of the hydrocarbon chains

4) increasing length of the hydrocarbon chains

Which of the following phospholipid membranes would be most permeable to glycerol? 1) one with long and saturated fatty-acid tails 2) one with long and unsaturated tails 3) one with short and saturated tails 4) one with short and unsaturated tails

4) one with short and unsaturated tails

Lipids that form membranes have what kind of structure? 1) completely nonpolar, because they are lipids 2) completely polar, which allows them to dissolve in water 3) polar heads and nonpolar tails; the nonpolar tails interact with water 4) polar heads and nonpolar tails; the polar heads interact with water

4) polar heads and nonpolar tails; the polar heads interact with water