Lipids

FOB Chapter 2, pages 27-29

FOB Chapter 9, pages 219-236

MCB Chapter 2, pages 26-29

Molecular Structure and Behavior of Lipids

Lipids are hydrophobic

•They are rich in nonpolar hydrocarbon regions and have relatively few polar groups

•Some are amphipathic, having both a polar and a nonpolar region

•Have a strong tendency to associate together through noncovalent bonds

Lipids can be grouped into five different categories:

Fatty Acids

Triglycerides

Phospholipids

•Sphingolipids

•Steroids

Fatty Acids

•Simplest Lipids

•Constituents of several more complex lipids

•Basic Structure

    –Hydrophilic carboxylate group attached to

    –Hydrocarbon chain

    –FOB Table 9-1

    –FOB Fig. 9-1

Triglycerides

•The true fats

•Consist of a glycerol molecule with three fatty acids linked to it by ester bonds

•Primary purpose is to store energy

•FOB Fig. 9-2 page 222 for example

•Adipocytes and adipose tissue

Fat storage in animals serves three distinct functions:

1.Most fat in most animals is oxidized for the generation of ATP, to drive metabolic processes

2. Some specialized cells (in “brown” fat of warm-blooded animals, for example) oxidize the triglycerides for heat production rather than to make ATP.

3.In animals that must live in a cold environment, layers of fat cells under the skin serve as thermal insulation.

Wax

•Consist of a long chain of fatty acid is esterified to a long-chain alcohol

•Waxes are completely insoluble

•Serve as water repellents and energy storage in some animals and plants

•The hardness of waxes is determined by chain length and degree of hydrocarbon saturation

Phosphoglycerides

•The major component of biological membranes

•Major class of naturally occurring phospholipids

•FOB Fig. 9-3, 9-4

•The simplest are phosphatidic acids

•FOB Table 9-2

DPPC

•Major lipid of lung surfactant

•DPPC molecules resist compression thus preventing the complete collapse of the alveolar space

Sphingolipids

•Also major membrane components

•Contain the alcohol sphingosinerather than glycerol

•sphingosine can form an amine bond to a long chain fatty acid, resulting in ceramide.

Sphingomyelin

•Found in the myelin sheath that surrounds and electrically insulates the axons of nerves

Steroids

•Mostly of eukaryotic origin

•Derivatives of cyclopentanoperhydro-phenanthrene

•Steroids play a variety of roles in the cells of higher organisms but are not present in bacteria

•Include a number of important hormones (including sex hormones)

•The most common steriod is cholesterol

Cholesterol

•Weakly amphipathic

•Fits awkwardly into membrane lipids and tends to disrupt regularity in membrane structure

•Cholesterol is the most abundant steroid in animals and is the precursor for the synthesis of many hormones

Steroid Hormones

•Classified according to the physiological responses they evoke:

    –Progesterone

    –Male and female sex hormones
    –Glucocorticoids
    –Mineralocorticoids

Vitamin D

•Derivatives in which the steroid B ring is disrupted between C9 and C10

•Increases serum Ca²⁺ by promoting the intestinal absorption of dietary Ca²⁺

•Vitamin D deficiency produces rickets in children

•Vitamin D accumulates in the fatty tissue

Lipid Mobility in Bilayers

•Lipids cross the bilayer through transverse diffusion

•Lipids are highly mobile in the plane of the bilayer – lateral diffusion