Oils and fats. The definition of a lipid The definition of a lipid is based on solubility ---...
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Transcript of Oils and fats. The definition of a lipid The definition of a lipid is based on solubility ---...
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