Biochem Ch. 8 (Exam 2 - Review Exercise)

52) Define omega-3 fatty acids...

An omega-3 fatty acid had a double bond at the third carbon from the methyl end.

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

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

38) Suggest a reason why inorganic ions, such as K+, Na+, Ca2+, and Mg2+ do not cross biological membranes by simple diffusion.

Biological membranes are highly nonploar environments. Charged ions tend to be excluded from such environments rather than dissolving in them. They would have to do to pass through the membrane by simple diffusion.

4) 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 phosphatidyl cholines contain phosphoric acid esterified to an amino alcohol. They differ in the second alcohol to which phosphoric acid is esterified. -Phosphatidyl cholines - the second alcohol is glycerol (which has formed ester bonds to two carboxylic acids) -Sphingomyelins - the second alcohol is another amino alcohol, sphingosine (which has formed an amide bond to a fatty acid)

42) What is the structural relationship between vitamin D3 and cholesterol?

Cholesterol is a precursor of vitamin D3 The conversion reaction involves ring opening

51) A healthy-conscious friend ask weather eating carrots is better for eyesight or for preventing cancer. What do you tell them?

Eating carrots is good for both. Vitamin A, which is abundant in carrots, plays a role in vision. Diets that include generous amounts of vegetables are associated with a lower incidence of cancer.

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

Hydrophobic interactions among the hydrocarbon tails are the main energetic driving force in the formation of lipid bilayers.

34) Suppose that you are studying a protein involved in transporting ions in and out of cells. Would you expect to find the nonpolar residues in the interior of 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 nonpolar residues are the exterior ones. -They interact with the lipids of the cell membrane. The polar residues are in the interior, the lining the channel through which the ions enter and leave the cell

22) 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 associated with diets low in saturated fatty acids.

10) Which is more hydrophilic, cholesterol or phospholipids? Explain

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

36) What role does phosphorylation of tyrosine residues play in the action of receptor proteins?

Phosphorylation of tyrosine residues can activate or deactivate a receptor protein, depending on the specific system.

31) Do all proteins associated with membranes span the membrane from one side to another?

Proteins that are associated with membranes do not have to span the membrane. Some can be partially embedded in it, and some associate with the membrane by noncovalent interaction with its exterior.

1) What is the basis for grouping substance as lipids?

Solubility properties -Insoluble in aqueous or polar solvents -Soluble in nonpolar solvents -Some lipids are not at all structurally related

8) How does the structure of steroids differ from that of other lipids discussed in this chapter?

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

37) What does the hydrolysis of GTP have to do with the actions of receptor proteins?

The action of a number of receptor proteins requires binding of GTP to a specific subunit, followed by subsequent hydrolysis

26) 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 % of unsaturated fatty acids in membranes in cold climates is an aid to membrane fluidity.

28) Are the relative amounts of cholesterol and phophatidylcholine the same in all the kinds of membranes found in a typical mammalian cell?

The relative amount of cholesterol and phosphatidylcholine can vary widely in different types of membranes in the same cell.

13) In the produce department of supermarkets, vegetables and fruits (cucumbers are an example) have been coated with wax for shipping and storage. Why is this done?

The surface wax keeps produce fresh by preventing water loss.

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

The transition temp is lower in a lipid bilayer with mostly unsaturated fatty acids compared with one with a high % of saturated fatty acids is already more disordered than the one with a high % of saturated fatty acids.

5) 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.

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

Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids -natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called saponification (Latin, sapo, soap)mixed \ Phosphoacylglycerols (Phospholipids): When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced -second most abundant group of naturally occurring lipids, and they are found in plant and animal membranes.

50) Why are many vitamin supplements sold as antioxidants?

Vitamin A and E are known to scavenge free radicals, which can do oxidative damage to cells.

39) Which of the 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 substance into cells

a. Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher c. Transport proteins may be involved in bringing substance into cells

18) 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 two layers of lipids b. The composition of the inner and outer lipid layers are the same in any individual membrane c. Membranes contain glyolipids and glycoproteins d. Lipid bilayers are an important component of membranes e. Covalent bonding takes place between lipids and proteins in most membranes.

c. Membranes contain glyolipids and glycoproteins d. Lipid bilayers are an important component of membranes

35) 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 outside of the membrane e. The term MOSAIC refers to the arrangement of the lipids alone

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

17) Which of the following lipids are NOT found in animal membranes? a. Phosphoglycerides b. Cholesterol c. Triacylgylcerols d. Glycolipids e. Sphingolipids

c. Triacylgylcerols are not found in animal membranes.