Phospholipids And Steroids

Lipids Phospholipids Steroids and Cholesterol Plasma (Cell)Membranes

1

Phosphoglycerides • Most abundant lipids in cell membranes • Control cell permeability FATTY ACID FATTY ACID

glycerol

PO4

Amino alcohol 2

Lecithin • Abundant in brain and nerve tissues • Found in egg yolk, what germ, yeast O CH2 O C (CH2)14CH3 O CH O CH2

C O

(CH2)14CH3

+ O P O CH2CH2N(CH3)3 O-

choline, an amino alcohol 3

Sphingolipids Esters of an 18-carbon alcohol sphingosine

FATTY ACID sphingosine

PO4

Amino alcohol 4

Sphingomyelin Found in the myelin sheath CH3(CH2)12CH=CH –CH–OH O sphingosine

‖

fatty acid

CH–NH –C –(CH2)14CH3 O ‖ + CH2 –O –P –O –CH2CH2 –N–(CH3)3 ‖

5

Steroids • Steroid nucleus • 3 cyclohexane rings • 1 cyclopentane ring

steroid nucleus

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Cholesterol • Most abundant steroid in the body • Add methyl CH3- groups, alkyl chain, and -OH to steroid nucleus CH3 CH3 CH 3

HO

CH3 CH 3

7

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

8

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

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Example of a Bile Salt cholic acid, a bile acid CH3 OH CH3 CH3

HO

O C N CH2 COO- Na+ H gycine, an amino acid

OH sodium glycocholate, a bile salt 10

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 11

Sex Hormones CH 3 OH CH3

O

CH 3 OH CH 3

HO testosterone

estradiol

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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 13

Diagram of a Plasma Membrane Polar sections

Nonpolar tails

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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 15

Learning Check PL1 Identify each lipid as: A. D. E. F. G. H. I.

(1) phospholipid (3) triglyceride

(2) steroid (4) sphingolipid

Cholesterol Glycerol, 2 fatty acids, phosphate, and choline Glyceryl tristearate Sphingosine, fatty acid, phosphate, and choline Estradiol Bile salts Most of plasma membranes 16

Solution PL1 A. B. C. D. E. F. G.

2 steroid phospholipid 3 triglyceride 4 sphingolipid 2 steroid 2 steroid 1 phospholipid 17