Chapter 6 Textbook Questions *NOT ON TEST*

Integral membrane proteins are anchored in lipid bilayers. Which of the following groups of amino acid residues (see Figure 3.2) would likely be found in the portion that crosses the lipid bilayer? a. acidic c. polar uncharged b. basic d. nonpolar *see definition for figure 3.2*

(insert figure 3.2) D.

The leading health organizations support the claim that saturated fats are linked to heart disease. Why is it not ideal to purchase food that is labeled only as vegetable or animal fat?

Some vegetable fats, such as palm kernel oil, coconut oil, and palm oil, primarily contain saturated rather than unsaturated fats. Therefore, for someone who wants to avoid saturated fats for a healthy living, just the information "vegetable fat" is not enough.

What is not a property of lipids but determines the bilayer structure of biological membranes? a. hydrophobic tails packed together b. negatively charged polar heads interacting with water c. hydrocarbon chains that are non-polar and cannot interact with water d. phospholipids that form large polymers

D.

If a solution surrounding a cell is hypertonic relative to the inside of the cell, how will water move? a. It will move into the cell via osmosis. b. It will move out of the cell via osmosis. c. It will not move, because equilibrium exists. d. It will evaporate from the cell surface more rapidly.

B.

Suppose a cell is placed in a solution with a high concentration of potassium and no sodium. How would the cellular sodium- potassium pump function in this environment? a. It would stop moving ions across the membrane. b. It would continue using ATP to pump sodium out of the cell and potassium into the cell. c. It would move sodium and potassium ions across the membrane, but no ATP would be used. d. It would reverse the direction of sodium and potassium ions to move them against their gradients.

B.

What is the structural property that makes olive oil liquid and butter solid at room temperature?

Butter and olive oil consist of satu- rated and unsaturated hydrocarbon chains, respectively. Saturated hydrocarbon chains allow a tighter packing of the lipid molecules,so butter is solid at room temperature. Double bonds between carbons in unsaturated fats like olive oil result in "kinks" in the hydrocarbon chains, preventing the lipids from stacking tightly.

In an experiment, you create two groups of liposomes in a solution containing 0.1 M NaCl—one made from red blood cell membranes and the other from frog egg cell membranes. When the liposomes are placed in water, those with red blood cell membranes burst more rapidly than those made from egg membranes. Evaluate each of the following statements and identify those that could explain these results. • *T/F* The red blood cell liposomes are more hypertonic relative to water than the frog egg liposomes. • *T/F* The red blood cell liposomes are more hypotonic relative to water than the frog egg liposomes. • *T/F* The red blood cell liposomes contain more aquaporins than the frog egg liposomes. • *T/F* The frog egg liposomes contain ion channels, which are not present in the red blood cell liposomes.

F, F, T, T. The first two responses are false because the interior solution in both sets of liposomes is the same. The third is true because aquaporins allow for an increased rate of water transport. The fourth is true because if the Na or Cl ions can cross the membrane in frog eggs, then osmosis may be reduced or even be prevented from occurring.

What two conditions must be present for osmosis to occur?

For osmosis to occur, a concentration gradient and a membrane that allows water to pass, but not the solute, must be present.

Anindustrialprocesscalledhydrogenationisusedtoconvert vegetable oil into a semisolid compound called margarine. Explain why hydrogenation is an appropriate term for this process.

Hydrogenation is used because the process is likely to involve converting C=C bonds into C-C bonds by adding hydrogens. Fats with only C-H bonds (i.e., saturated) tend to be semisolid at room temperature.

Examine the experiment in Figure 6.14 to determine what would happen to a cell placed in a 0.5M NaCl solution. What would happen if it were placed in distilled water?

In a 0.5M NaCl solu- ADP K + P+ i Glucose gradient tion, the cell would be hypotonic and water would shrink the cell while moving out as it tries to equilibrate the concentration of Cl− and Na+ ions inside and outside the cell. Distilled water would have the opposite effect. As the cell is hypertonic and ions cannot move freely across membranes, water would flow into the cell through osmosis leading to the swelling of the cell.

What are the major sources of saturated and trans fats in the human diet? How are these two fats structurally similar?

Meat and dairy products are the major sources of satu- rated fats in the human diet. Margarine and hydrogenated vegetable oils are the sources of trans fats. Saturated fats have "straight" hydrocarbon chains. Trans fats originate from unsaturated fats that contain hydrocarbon chains with "kinks", but the process of hydrogenation straightens the chains.

Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Describe, on a molecular level, how you would expect these lipids to behave in water.

No, because they have no polar end to interact with water. Instead, these lipids would float on the surface of water, or collect in droplets suspended in water, reducing their interaction with water to a minimum.

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. Explain what conclusions you can draw from the following graph. Discuss what additional experiments you would perform to ascertain your conclusion. (Note that "causation" means that one event is responsible for the occurrence of the other, while "correlation" means that the two events appear to occur together). *see definition for graph*

The graph represents a direct correlation between the concentration of trans fats in the blood and the percent- age of artery atherosclerosis. Such experiments should be accompanied by other experiments where sex, age, weight, and other variables remain constant so that the only variability studied is the amount of trans fats in the blood.

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. When the meat is raw, all the saturated fat remains.

A side effect of hydrogenation is that a small percentage of oil lipids retain their double bonds, but instead of causing kinks, they straighten out the hydrocarbon chain. These are called trans fats based on the configuration of the double bond (cis bonds generate kinks [see Figure 6.1b, right], but trans bonds do not). How do trans fats complicate the previous description of saturated and unsaturated fats?

Trans fats are unsaturated because they have one or more double bonds, but they have physical charac- teristics similar to saturated fats due to the trans double bond that straightens the hydrocarbon chain.