Oils and fats

The definition of a lipid

The definition of a lipid is based on solubility--- marginally soluble in water and soluble in organic solvents

Classification:Group I: open-chain compounds with polar head groups and long nonpolar tails fatty acids triacylglycerols waxes sphingolipids phosphoacylglycerols glycolipids

Group II: fused-ring compounds (steroids)

The chemical natures of the lipid types

Fatty acids(1) Amphipathic(2) Unstaurated vs. saturated(3) Different melting points(4) Rarely found free in nature

trans vs. cis

Fatty acids

(1) Amphipathic(2) Unstaurated vs. saturated(3) Different melting points(4) Rarely found free in nature

Triacylglycerols

(1) Formed from glycerol and fatty acids(2) Not as components in membrane, but accumulate in adipocytes as stores of metabolic energy

Phosphoacylglycerols --- (1) important components in membrane(2) amphipathic

Structures of somephosphoacylglycerols

PE

PC

PS

PI

Structures of some waxes and sphingolipids

Abundant in the nervous system

Wax from whales

Glycolipid

(1) Often found as markers on cell membranes(2) Important in tissue and organ specificity(3) Abundant in the nervous system

Structures of several important gangliosides

Structures of some steroids

(1) Cholesterol is widespread in biological membranes, but not in prokaryotic cell membranes

The nature of biological membranes

(1) Made up by lipids and proteins

(2) Separate cells from the external environment

(3) Transport of specific substances into/out of cells

(4) Enzymes in membranes with specific functions

Lipid bilayers

Lipid bilayer asymmetry

Effects of unsaturated side chains on the packing of the phospholipids

Stiffening of the lipid bilayer by cholesterol

Effect of temperature on the fluidity of lipid bilayer

Flip-flop migration of lipid molecules

Membrane Proteins

Peripheral proteinIntegral protein

Lipid anchors

Glycine residue Cysteine residue

Fluid mosaic model of membrane structure

Membrane structure revealed by freeze-fractured technique

Electron micrograph of a freeze-fractured membrane

Membrane Function

Membrane transport

(1) Passive transport

(a) simple diffusion

(b) facilitated diffusion

(2) Active transport

(a) primary active transport

(b) secondary active transport

Glucose transport

The sodium-potassium pump

Primary active transport

Secondary active transport

Galactoside permease

high

low

low

high

Membrane Receptors

Low-density lipoprotein (LDL) – principle carrier of cholesterol

Lipid-soluble vitamins

Reaction of vitamin A

The formation of rhodopsin from 11-cis-retinal and opsin

Anti-oxidant --- free radicals

Reaction of vitamin D

Vitamin K

Role of vitamin K in blood clotting

Postaglandins and Leukotrienes

Postaglandins(1) produced by prostate gland(2) synthesized from arachidonic acid(3) control of blood pressure, stimulation of smooth muscle contraction induction of inflammation(4)aspirin, cortisone

Leukotrienes

(1) formed in leukocytes (white blood cells)(2) synthesized from arachidonic acid(3) stimulation of smooth muscle constriction especially in the lungs (Asthma)

COOH

H2C CH COO-

S +NH3

Triene

Cysteine