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Chapter 8 Lipids

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CHAPTER 8
unstable
Lipid
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.
Waxes….
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
Sphingosine
Ceramide
Sphingomyelin
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
characteristics
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.
Functions
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
entities
 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.
 NO ENERGY
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
 NEEDS ENERGY
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
phospholipids.
Vitamin K
 Vitamin K has an important role in BLOOD clotting
 Long unsaturated hydrocarbon side chain consists of repeating isoprene
units
Prostaglandins
 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.
Leukotrienes
 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
lungs!
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