Steroids and Cholesterol Plasma (Cell)Membranes Lipids Phospholipids Steroids and Cholesterol Plasma (Cell)Membranes

Phosphoglycerides Most abundant lipids in cell membranes Control cell permeability FATTY ACID glycerol PO4 Amino alcohol

Lecithin Abundant in brain and nerve tissues Found in egg yolk, what germ, yeast

Sphingolipids Esters of an 18-carbon alcohol sphingosine FATTY ACID PO4 Amino alcohol

Sphingomyelin Found in the myelin sheath CH3(CH2)12CH=CH –CH–OH O sphingosine ‖ fatty acid CH–NH –C –(CH2)14CH3 ‖ + CH2 –O –P –O –CH2CH2 –N–(CH3)3 ‖ O– choline

Steroids Steroid nucleus 3 cyclohexane rings 1 cyclopentane ring

Cholesterol Most abundant steroid in the body Add methyl CH3- groups, alkyl chain, and -OH to steroid nucleus

Cholesterol in the Body Cellular membranes Myelin sheath, brain, and nerve tissue Bile salts Hormones Vitamin D

Bile Salts Synthesized in the liver from cholesterol Stored in the gallbladder Secreted into small intestine Mix with fats to break them part Emsulsify fat particles

Example of a Bile Salt

Steroid Hormones Chemical messengers in cells Sex hormones Androgens in males (testosterone) Estrogens in females (estradiol) Adrenocorticosteroids from adrenal glands mineralocorticoids (electrolyte balance) glucocorticoids regulate glucose level

Sex Hormones

Plasma Membranes Surround cells Lipid bilayer pf phospholipids Nonpolar hydrocarbon tails in center Polar (hydrophilic) sections on outside Some unsaturated fatty acids give flexibility Keep aqueous contents inside Allow certain biochemicals to pass through

Diagram of a Plasma Membrane Polar sections Nonpolar tails

Other Structures in Membranes Cholesterol molecules add strength Glycolipids on surface communicate with other cells Proteins embedded in bilayer move certain substances (water, K+, Cl-, HCO3-) across the cell membrane Proteins on surface act as receptors for hormones and other biochemicals

Learning Check PL1 Identify each lipid as: (1) phospholipid (2) steroid (3) triglyceride (4) sphingolipid A. Cholesterol Glycerol, 2 fatty acids, phosphate, and choline Glyceryl tristearate Sphingosine, fatty acid, phosphate, and choline Estradiol Bile salts Most of plasma membranes

Solution PL1 A. 2 steroid B. phospholipid C. 3 triglyceride D. 4 sphingolipid E. 2 steroid F. 2 steroid G. 1 phospholipid