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Chapter 8 Lipids

SAME solubility
not water soluble
1. Fatty Acids
Open chain
Carboxylic acid
2. Triacylglycerols
ESTER of glycerol + 3 fatty
Saponification via boiling triglycerides
with NaOH
3. Phosphoacylglycerols (Phospholipids)
Glycerol – 1 phosphate – alcohol
phosphatidic acid is produced.
o Esters composed of long chain carboxylic
acids with long alcohols
o Used as protective coating for plants + animals
Myricyl cerotate
Carnauba wax
- used for floor and car wax!
Cetyl palmitate
Spermaceti (taken from whales)
- used for cosmetics
Sphingolipids = contains a long chain amino alcohol known as sphingosine!
(does NOT contain glycerol)
 Found in plants and animals, abundant in nervous system
 structurally similar to phospholipids
Glycolipids = compound where a carbohydrate is bound to an (OH) of a lipid
 Most often found as sugar (Glucose or Galactose)
 Derived from ceramides
 Glucocerebroside is an example!
 Gangliosides = Glycolipids with complex carbohydrate moiety that
contains more than 3 sugars.
Steroids = group of lipids that have fused ring structure of 3 six membered rings
and ONE five-membered ring
 Cholesterol – must know how to draw! (easter egg)
Sex Hormones
 Androgens are MALE sex hormones
o synthesized in the testes
o responsible for the development of male secondary sex
o one example is our good friend testosterone!
Estrogens are FEMALE sex hormones
o synthesized in the ovaries
o responsible for the development of female secondary sex
characteristics and the control of the menstrual cycle.
Lipid Bilayers
 polar surface of the bilayer contains charged groups
 hydrophobic tail is found in the INTERIOR of the bilayer
Biological Membranes
 Every cell has a cell membrane
 Molecular basis of membrane structure is in the lipid component(s):
o Polar head groups are in contact with the aqueous environment
o Nonpolar tails are inside
o The major force driving the formation of lipid bilayers is
hydrophobic interactions
o The arrangement of hydrocarbon tails in the interior can be…
 RIGID = saturated fatty acids
 FLUID = unsaturated fatty acids
Effect of Double Bonds on the Conformation of Fatty Acids
 KINK in hydrocarbon chain
 Causes DISORDER in packing against other chains
 Greater fluidity in the membranes because of the abnormal packing
o look at CIS double bonds and the saturated fatty acid chains!
Biological Membranes (animal versus plant)
 Plant membranes have a higher percentage of unsaturated fatty acids than
animal membranes.
 Cholesterol is found in animals RATHER than plant membranes.
 Animal membranes are LESS fluid (more rigid) than plant membranes
 Prokaryotes contain no steroids and are MOST fluid
Cholesterol Reduces Fluidity by stabilizing extended chain formations of fatty
acid hydrocarbons tails.
 hydrophobic interactions
Membrane Layers
 Inner + outer layers of bilayer membrane contain mixtures of lipids.
 Compositions on inside and outside of lipid bilayer can be different.
o This is what distinguishes the layers.
Temperature Transition in Lipid Bilayer ( heat = disorder in membranes )
 Rigid = transition temperature
 Heat increases the mobility of the lipid chains dramatically.
 Fluid = transition temperature
Membrane Proteins – two types, peripheral and integral.
1. Transport substances ACROSS membrane
2. Act as receptor sites
3. Site of enzyme catalysis
Peripheral Proteins (outside)
bound by electrostatic interactions
Can be removed by raising the ionic strength
Integral Proteins (both / inside)
bound tightly to the interior of the membrane
can be removed by detergents
removal generally denatures the protein
Proteins can be anchored to membranes
 N-myristoyl- and S-palmitoyl anchoring motifs
 Anchors can be via N-terminal Gly
 Thioester linkage with Cys
Fluid Mosaic Model : lateral motion of components in the membrane
 Fluid: lateral motion of components in the membrane
o Proteins “float” in the membrane
and can move along its plane.
 Mosaic: components in the membrane
exist side by side, but are separate
 The structure is that of a lipid bilayer with NO complexes!
Membrane Function: Membrane Transport
Passive Transport = passive diffusion of uncharged species from high
concentration to low concentration via carrier protein (NO energy required)
 Simple diffusion: molecule or ion moves through an opening in membrane
 Facilitated diffusion: molecule or ion is carried across a membrane via
carrier / channel protein.
Active Transport = a substance is moved AGAINST the concentration gradient
 Primary active transport: transport is linked to the hydrolysis of ATP or
other high energy molecule
o NA+/K+ ion pump
 Secondary active transport: transport is driven by the H+ gradient
Membrane Receptors
 Generally oligomeric proteins
 binding of a biologically active substance to a receptor initiates an action
within the cell
Lipid-Soluble Vitamins
 divided into two classes: water soluble and fat soluble (lipid)
 4 different vitamins – A, B, E and K
Vitamin A
 Vitamin A ( retinol ) occurs only in the animal world.
 Extensively unsaturated hydrocarbon (B-carotene)
 Vitamin A is found in the plant world in the form of
a provitamin in a group of pigments called
carotenes (yellow +orange pigmented food)
 Enzyme-catalyzed cleavage of B carotene followed by reduction gives 2
molecules of Vitamin A (retinol)
 The best understood role of vitamin A is its participation in the visual cycle
in rod cells
 The active molecule is retinal (vitamin A aldehyde)
 Retinal forms an imine with an –NH2 groups of the protein opsin to form
the visual pigment called rhodopsin
 The primary chemical even of vision in rod cells is absorption of light by
rhodopsin followed by isomerization of the 11-cis double bond to the 11trans double bond.
Vitamin D
 A group of structurally related compounds that are involved in the
regulation of calcium and phosphorous metabolism
 The most abundant form in the circulatory system is VIT D!!
Vitamin E
 The most active form of vitamin E is alpha tocopherol
 Vitamin E is an antioxidant; traps H00· and ROO· radicals formed as a result
of oxidation by O2 of unsaturated hydrocarbon chains in membrane
Vitamin K
 Vitamin K has an important role in BLOOD clotting
 Long unsaturated hydrocarbon side chain consists of repeating isoprene
 Prostaglandins: a family of compounds that have the 20-carbon skeleton
of prostanoic acid
 First detected in seminal fluid from prostate.
 The metabolic precursor is arachidonic acid
 Production of prostaglandins from arachidonic acid occurs in several steps.
 Compounds also derived from arachidonic acid.
 Found in white blood cells
 Consists of 3 conjugated double bonds
 An important property is constriction in smooth muscles, ESPECIALLY the