Biochemistry Chapter 8

Which statements are consistent with the known facts about membrane transport? (a) Active transport moves a susbtance from a region in which its concentration is lower to the one in which its concentration is higher. (b) transport doe snot involve any pores or channels in the membrane (c) transport proteins may be involved in bringing substances into cells

(a) & (c)

Which of the following states is (are) consistent with what is known about membranes? (a) a membrane consists of a layer of proteins sandwiched between two layers of lipids (b) the compositions of the inner and outer lipid layers are the same in any individual membrane (c)Membranes contain glycolipids and glycoproteins (d) lipid bilayers are an important component of membranes (e) covalent bonding takes place between lipids and proteins in most membranes

(c) & (d)

Which statements are consistent with the fluid mosaic model of membranes? (a) all membrane proteins are bound to the interior of the membrane (b) both proteins and lipids undergo transverse (flip-flop) diffusion from the inside to the outside of the membrane. (c) Some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane (d) carbohydrates are covalently bonded to the oustide of the membrane (e) the term mosaic refers to the arrangement of the lipids alone

(c) & (d)

Which of the following lipids are not found in animal membrane? (a) phosphoglycerides (b) cholesterol (c) triacylglycerols (d) glycolipids (e) sphingolipids

(c) triacylglycerols

A membrane consists of 50% protein by weight and 50% phosphoglycerides by weight. The average molecular weight of the lipids is 800 Da, and the average molecular weight of the proteins is 50,000 Da. Calculate the molar ratio of lipid to protein.

50g lipid x (1mol lipid/800g lipid) = 0.0625 mol lipid 50g protein x(1mol protein/50,000 protein) = 0.001 mol protein Ratio 62.5:1

Suggest a reason why the cell membranes of bacteria grown at 20 degrees Celsius tend to have a higher proportion of unsaturated fatty acids than the membranes of bacteria of the same species grown at 37 degrees Celsius. In other words, the bacteria grown at 37 degrees celsius have a higher proportion of saturated fatty acids in their cell membranes.

At lower temperature, the membrane would tend to be less fluid. The presence of more unsaturated fatty acids would compensnate by increasing the fluididty of the membrane compared to one at the same temperature with a higher proportion of saturated fatty acids.

Suggest a reaosn why inorganic ions, such as K+, Na+, Ca2+, and Mg2+, do not cross biological membranes by simple diffuion.

Charged. biological membranes are highly nonpolar environments.

What structural features do triaglycerol and phosphatidyl ethanolamine have in common? How do the structures of these two types of lipids differ?

In both, glycerol is esterified to carboxylic acids, with three such ester linkages formed in triacylglycerols and two phosphatidul ehtanolamines. The differences comes in the nature of the third ester linkage to glycerol. In phosphatidyl ethanolamines, the htird hydroxyl group of glycerol is esterified not to a carboxylic acid but to phosphoric acid. The phosphoric acid moiety is esterified in turn to ethanolamine.

Why does the American Heart Association recommend the use of canola oil or olive oil rather than coconut oil in cooking?

Less heart disease is assoicated with diets low in saturated fatty acids

Briefly discuss the structure of myelin and its rol ein the nervous system

Myeline is a multilayer sheath consisting maily of lipids that insulates the axons of nerve cells, facilitating transmission of nerve imulses

Do all proteins associated with membranes span the membrane from one sdei to another

No, some can be paritally embedded in it, and some associate iwth the membrane by noncovalent ineractions with its exterior

Which is more hydrophilic, cholesterol or phospholipids? Defend your answer.

Phospholipids because the phosphate group is charged and the attached alcohol is charged or polar. These groups interact readily with water.

What is the basis for grouping substances as lipids?

Solubility properites (insoluble in aqueous or polar solvents, soluble in nonpolar solvents)

You have just isolated a pure lipid that contains only sphingosine and a fatty acid. To what class of lipids does it belong?

Sphingolipid - specificaly ceramide

What structural features does a sphingolipid have in common with proteins? Are there functional similarities?

Sphingolipids contain amide bonds like proteins. Both have hydrophobic and hydrophilic parts. both occur in cell membranes but their functions are different

How does the structure of steroids differ from that of other lipids?

Steroids contain a characteristic fused-ring structure, which other lipids do not

Suggest a reason why animals that live in cold climates tend to have higher proportions of polyunsaturated fatty acid residues in their lipids than do animals that live in warm climates.

The higher percentage of unsaturated fatty acids in the memrbanes in cold climates is an aid to membrane fluicity

In the preparation of sauces that involved mixing water and melted butter, egg yolks are added to prevent separation. How do the egg yolks prevent separation?

The lecithin in the egg yolks serves as an emulsifying agent by forming closed vesicles. the lipids in the butter are retained in vesicles and do not form a separate phase.

What structural feature do a sphingomyeline and a phosphotidyl choline have in common? How do the structures of these two types of lipids differ?

They both contain phosphirc acid esterified to an amino alcohol, which must be choline in the case of phosphatidylcholine and may be choline in the case of a sphingomyeline. They differ in the second alcohol to which phosphoric acid esterified. In phosphatidylcholines, the second alcohol is glycerol, which has also formed ester bonds to two carboxylic acids. In sphingomyelines, the second alcohol is another amino alcohol, sphingosine, which as formed an amide bond to a fatty acid.

What are the main structural features of prostaglandins?

carboxylic acids that include a five membered ring in their structure

What are the main structural features of leukotrienes?

carboxylic acids with three conjugated double bonds

Egg yolks conaiin high amount of cholesterol, but they also contain a high amount of lecithin. From a diet and health standpoint, how do these two molecules complement each other?

cholesterol is not very water-soluble, but lecithin is a good natural detergent, which is actually part of lipoproteins that transport less soluble fats through the blood

Define glycoprotein and glycolipid

glycoprotein is formed by covalent bonding between a carbohydrate and a protein, whereas a glycolipid is formed by covalent bonding between a carbohydrate and a lipid

What is the energetic driving force for the formation of phospholipid bilayers?

hydrophobic interactions among the hydrocarbon tais

In lipi bilayers, there is an order-disorder transition similar to the melting of a crystal. In a lipid bilayer in whihc most of the fatty acids are unsaturated, would you expect this transition to occur at a higher temperature, a lower tempearture, or the same temperature as it would in a lipid bilayer in which most of the fatty acids are saturated? Why?

lower temperature

Crisco is made from vegetable oils, which are usually lipids. Why is crisco solid?

many of the double bonds have been saturated. crisco contains "partially hydrogenated vegetable oils."

Suppose that you are studying a protein involved in transporting in and out of the cell. Would you expect to find the nonpolar residues in the interior or the exterior? Why? Would you expect to find the polar residues in the interior or the exterior? Why?

nonpolar residues are the exterior ones; they interact with the lipids of the cell membrane. the polar residues are in the interior lining the channel through which the ions enter and leave the cell

List two classes of compounds derived from arachidonic acid. Suggest some reason for hte amount of biomedical research devoted to these compounds.

prostaglandins and leukotrienes. they play a role in inflammation and in allergy and asthma attacks

Outline a possible connection between the material in this chapter and the integrity of blood platelets.

prostaglandins in blood platelets can inhibit their aggregation.

When water birds have had their feathers fouled with crude oil after an oil spill, they are cleaned by rescuers to remove the spilled oil. Why are they not released immediately after they are cleaned.

the removal of the oil removes the natural oils and waxes on the feathers. these oils and waxes must regenerate before birds can be released