ch. 8 - EXAM II

which statements are consistent with the known facts about membrane transport? a) active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher b) transport does not involve any pores or channels in membranes c) transport proteins may be involved in bringing substances into cells

A and C

write the structural formula for a triacylglycerol, and name the component parts

Any combination of fatty acids is possible, DRAW IT OUT

suggest a reason why inorganic ions, such as K+ Na+ Ca+ and Mg2+ do not cross biological membranes by simple diffusion

Biological membranes are highly non-polar environments. Charged ions tend to be excluded from such environments rather than dissolving in them, as they would have to do to pass through the membrane by simple diffusion.

which of the following statements is (are) consistent with what is known about membranes? a) A membrane consists of a layer of proteins sandwiched between tow 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 and 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 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 outside of the membrane e) the term mosaic refers to the arrangement of the lipids alone

C and D

suppose that you are studying a protein involved in transporting ions in and out of cells. Would you expect to find the non-polar residues in the interior or the exterior? Why? would you expect to find the polar residues in the interior or the exterior? why?

In a protein that spans a membrane the non-polar 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

Crisco is made from vegetable oils, which are usually liquid. Why is Crisco a solid?

Many of the double bonds have been saturated. Crisco contains "partially hydrogenated vegetable oils"

Briefly discuss the structure of myelin and its role in the nervous system.

Myelin is a multilayer sheath consisting mainly of lipids (with some proteins) that insulates the axons of nerve cells, facilitating transmission of nerve impulses

suggest a reason why the same protein system moves both sodium and potassium ions into and out of the cell

Nature chooses what works. This is an efficient use of a large protein and of the energy of ATP

which is more hydrophilic, cholesterol or phospholipids? defend your answer

Phospholipids are more hydrophilic than cholesterol. The phosphate group is charged, and the attached alcohol is charged or polar. These groups interact readily with water. Cholesterol has only a single polar group, an -OH

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

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

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 membranes in cold climates is an aid to membrane fluidity.

In the preparation of causes that involve mixing water and melted butter, egg yolks are added to prevent separation. How do the egg yolks prevent separation? (egg yolks are rich in phosphatidylcholine [lecithin])

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

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 also removes the natural oils and waxes on the feathers. These oils and waxes must regenerate before the birds can be released.

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

This lipid is a ceramide, which is one kind of sphingolipid.

which of the following lipids are not found in animal membranes? (A) phosphoglycerides (B) cholesterol (C) triacylglycerols (D) glycolipids (E) sphingolipids

Triacylglycerols are not found in animal membranes

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

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

what structural features do a sphingomyelin and a phosphatidyl choline have in common? How do the structures of these two types of lipids differ?

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

write an equation, with structural formulas, for the saponification of the triacylglycerol in question 7

from 7 DRAW OUT saponification of the triacylglycerol

what structural features do a triacylglycerol and a phosphatidyl ethanolamine have in common? How do the structures of these two types of lipids differ?

in both types of lipids, glycerol is esterified to carboxylic acids, with three such ester linkages formed in triacylglycerols and two in phosphatidyl ethanolamine. the structural difference comes in the nature of the third ester linkage to glycerol. in phosphatidyl ethanolamines, the third hydoxyl group of glycerol is esterified not to a carboxylic acid but to phosphoric acid. the phosphoric acid moiety is esterified in turn to ethanolamine

draw the structure of a phosphoacylglycerol that contains glycerol, oleic acid, stearic acid, and choline

see picture and DRAW IT OUT

proteins, nucleic acids, carbohydrates are grouped by common structural features found within their group. What is the basis for grouping substances as lipids?

solubility properties (insoluble in aqueous or polar solvents, soluble in nonpolar solvents). some lipids are not at all structurally related

how does the structure of steroids differ from that of the other lipids discussed in this chapter?

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

succulent plants from arid regions generally have waxy surface coatings. Suggest why such a coating is valuable for the survival of the plant.

the waxy surface coating is a barrier that prevents loss of water

what are the structural features of waxes? what are some common uses of compounds of this type?

waxes and esters of long-chain carboxylic acids and long-chain alcohols. they tend to be found as protective coatings.