CH8

fatty acids

-carboxyl group at the polar end and a hydrocarbon chain at the nonpolar tail. -amphipathic compounds because the carboxyl group is hydrophilic and the hydrocarbon tail is hydrophobic.

Phosphoacylglycerols

-one of the alcohol groups of glycerol to be esterified by a phosphoric acid molecule rather than by a carboxylic acid. -two fatty acids are also esterified to the glycerol molecule. compound is called a phosphatidic acid -Fatty acids are usually monoprotic acids with only one carboxyl group able to form an ester bond, but phosphoric acid is triprotic (H3PO4) and thus can form more than one ester linkage. One molecule of phosphoric acid can form ester bonds both to glycerol and to some other alcohol, creating a phosphatidyl ester. -are important components of biological membranes.

Write an equation, with structural formulas, for the saponification of the triacylglycerol in

Aqueous NaOH glycerol 3 carboxylate salts

Lauric Acid

CH3(CH2)10COOH

Myristic Acid

CH3(CH2)12COOH

Palmatic Acid

CH3(CH2)14CO2H

Typical Naturally occurring Unsaturated Fatty Acids

POL LA PALMITOLEIC oleic linoleic linolenic arachidonic

lipids

1 gr. -open-chain compounds with polar head groups and long nonpolar tails: fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, and glycolipids. 2 gr. fused-ring compounds, the steroids; an important representative of this group is cholesterol.

FROM HOME

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Write the structural formula for a triacylglycerol, and name the component parts.

Any combination of fatty acids is possible.

Suggest a reason why the cell membranes of bacteria grown at 20°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.

Suggest a reason why inorganic ions, such as K+1, Na+1, Ca+2, and Mg+2, do not cross biological membranes by simple diffusion.

Biological membranes are highly nonpolar 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.

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 phosphatidylcholines 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 phosphatidylcholines, 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.

stearic acid

CH3(CH2)16CO2H

Arachidic Acid

CH3(CH2)18CO2H

arachidonic acid 20

CH3(CH2)4CH=CH(CH2)4(CH2)2CO2H 20:4 -d 5,8,11,14

linoleic acid 18

CH3(CH2)4CH=CH(CH2)CH=CH(CH2)7CO2H 18:2-d9,12

Palmitoleic Acid 16

CH3(CH2)5CH=CH(CH2)7COOH 16:1-d 9

oleic acid 18

CH3(CH2)7CH=CH(CH2)7CO2H 18:1 -d9

Linolenic acid 18

CH3(CH2CH=CH)3(CH2)7CO2H 18:3-d9,12,15

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

DRAW KEEPING IN MIND THE SPECIFIC POSITION OF EACH 1. POSITION MUST BE SATURATED 16=18 C 2. POSITION MUST BE UNSATTURATED 16-18C 3 .CHOLINE

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 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 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.

What structural features do a triacylglycerol and a phosphatidylethanolamine 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 phosphatidylethanolamines. The structural difference comes in the nature of the third ester linkage to glycerol. In phosphatidylethanolamines, the third 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.

Typical Naturally occurring saturated Fatty Acids

LMP SA Lauric Myristic Palmatic STEARIC Arachidic

lipids

Lipids are marginally soluble (at best) in water but readily soluble in organic solvents, such as chloroform or acetone.

Crisco is made from vegetable oils, which are usually liquid. Why is Crisco a solid? Hint: Read the label

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

Glycolipids

Membrane carbohydrates that are covalently bonded to lipids. -a carbohydrate bound to an alcohol group of a lipid by a glycosidic linkage -are often found as markers on cell membranes and play a large role in tissue and organ specificity.

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?

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 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.

Proteins, nucleic acids, and 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.

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.

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.

Statements (a) Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher and (c) Transport proteins may be involved in bringing substances into cells are correct; statement (b) is not cor rect because ions and larger molecules, especially polar ones, require channel proteins.

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.

Statements (c) Some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane. and (d) Carbohydrates are covalently bonded to the outside of the membrane. are correct. Transverse diffusion is only rarely observed [statement (b)], and the term mosaic refers to the pattern of distribution of proteins in the lipid bilayer [statement (e)]. Peripheral proteins are also considered part of the membrane [statement (a)].

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 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.

Statements (c) Membranes contain glycolipids and glycoproteins. and (d) Lipid bilayers are an important component of membranes are consistent with what is known about membranes. Covalent bonding between lipids and pro- teins [statement (e)] occurs in some anchoring motifs, but is not widespread otherwise. Proteins "float" in the lipid bilayers rather than being sandwiched between them [statement (a)]. Bulkier molecules tend to be found in the outer lipid layer [statement (b)].

How does the structure of steroids differ from that of the 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 membranes in cold climates is an aid to membrane fluidity.

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

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.

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.

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

Waxes are esters of long-chain carboxylic acids and long-chain alcohols. They tend to be found as protective coatings.

saponification-an hydrolysis rxn that takes place outside of the organims

When a base such as sodium hydroxide NaOH or potassium hydroxide KOH is used, the products of the reaction, are glycerol and the sodium or potassium salts of the fatty acids. These salts are soaps.

Steroids

a fused-ring system consisting of three six-membered rings and one five-membered ring ex: sex hormones ( testosterone, progesterone , estradiol) cholesterol

triacylglycerol

a lipid formed by esterification of three fatty acids to glycerol; triesters of glycerol incorporating fatty acids When all three of the alcohol groups of glycerol form ester linkages with fatty acids, the resulting compound is a triacylglycerol; -they accumulate in adipose tissue -concentrated stores of metabolic energy

Waxes

are complex mixtures of esters of long-chain carboxylic acids and long- chain alcohols. They frequently serve as protective coatings for both plants and animals. In plants, they coat stems, leaves, and fruit; in animals, they are found on fur, feathers, and skin.

lipases.

enzymes that hydrolyze lipids the ester linkages of triacylglycerols are hydrolyzed