Download I. Biopolymers Lipids and Membranes

Department of Chemistry and Biochemistry
University of Lethbridge
Biochemistry 3020
I. Biopolymers
Lipids and Membranes
Cast of Lipid Characters
Fatty acids: principal building blocks of complex lipids
Triaglycerols: membrane precursors
Glycerolphospholipids: as above
Sphingolipids: brain lipids with a weird name
Waxes: you know these
Terpenes: like, turpentine
Steroids: lots of fun here…things that make us crazy
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Lipids: Definitions and Basic Concepts
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Biological molecules distinguished by high solubility in non polar
solvents, low solubility in H2O
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Carbohydrates= C-OH, Lipids = CH2, CH3. Fully reduced form of
carbon.
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When fully oxidized (burned as fuel) get large energy release
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Lipids are amphipathic: critical for use in membranes, a key
function
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Simple versus complex lipids: presence of fatty acid
Fatty Acids
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Composed of hydrocarbon tail (even # of carbons) and charged
head group
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Saturated (carbon-carbon bonds are single) versus unsaturated
(one or more double bonds); mono, poly, etc.
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Nomenclature: common (e.g. stearic) versus systematic name
(octadecanoic = 18CH2 +COOH)
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Typical Saturated and Unsaturated Fatty
Acids
18:1(∆9)
18:2 (∆9,12)
18:3 (∆9,12,15)
Representative Important Fatty acids
Essential: can not
be synthesized by
humans
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All Fats Are Not Equal: Nutrition and
Different Fatty Acids
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essential fatty acids: linoleic and α-linolenic fatty acids; must get
these from plants
“good fats”: high in polyunsaturated Fats. Typical foods include
vegetable oils, like olive, canola, sunflower, etc.
“bad fats”: high in saturated fats. Classic offenders stearic (beef);
palm & coconut oils (found in candy)
“really bad fats”: trans fatty acids, result from partial
hydrogenation of vegetable oils. Margarine has trans fatty acids.
Fatty Acid + Glycerol = Triacylglycerol
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But What's Their Name?
What is special about that carbon?
Triacylglycerols
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Major form of fatty acids: esterified to glycerol. Major energy
reserve in animals.
Simple triacylglycerol: all three FAs are the same
Mixed triacylglycerol: different fatty acids on the glycerol.
Energy yield from burning: 38 kJ/gram, as compared to 17
kJ/gram for carbs.
Its like gasoline!
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Lipids are the most energy rich of all
compounds
Stored metabolic fuel in a 70 kg person
Glycerolphospholipids
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Typically a 1,2 diacylglycerol (the fatty acids) with a phosphate
group at position 3
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Essential components of cell membranes and other cellular
structures
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Issues related to nomenclature and stereochemistry: the use of a
systematic naming system
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The parent molecule is phosphatidic acid
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You can have additional compounds esterified to the phosphate
group
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Prochirality
Glycerol
CH2OH
CH2OH
The D- and L- naming system leads
to ambiguity for glycerol derivatives
C
OH
H
D
CHOH
CH2OH
C
H
OH
Phosphatidic Acid is the parent
phospholipid
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Examples of Glycerolphospholipids
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Phosphatidylcholine
(lecithin) and
phosphatidylethanolamine:
common membrane
constituents
Cardiolipan=
diphosphatidylglycerol (note
two phosphates and extra
glycerol)
Fatty Acids can also be connected to
glycerol through an ether linkage
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Examples of Glycerolphospholipids
Ether lipids
Ether glycerolphospholipids (e.g. platelet
activating factor, an important lipid
signaling molecule)
cis-αβ-unsaturated
Plasmalogens: one of the alkyl-groups is
cis-αβ-unsaturated (not a standard
alkyl group)
Chloroplasts Contain Galactolipids and
Sulfolipids
Galactolipids found in thylakoid
Membranes of chlorolasts. They
Make up about 70% to 80% of the
Total membrane lipids.
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Archaebacteria Contain Unique Membrane
Lipids
The archaebacteria have membrane lipids containing long-chain
(32 carbons) branched hydrocarbons linked at each end to glycerol
In their fully extended form these lipids span the width of the
surface membrane.
ether linkage
Sphingolipids:
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Backbone is based on
sphingosine, an amino alcohol
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If fatty acid is joined to
sphingosine by amide linkage,
get a ceramide
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Sphingomylelins:
phosphorylcholine/ethanolamine
esterified to 1-hydroxy
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Sphingolipids
Complex Gangliosides
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A ganglioside: a complex
glycosphingolipid with a
ceramide + 3 or more sugars
(typically sialic acid)
•Small abundance, key function is
tissue/organ specificity. Also important
in nerve impulse transmission.
Tay-Sachs disease
Remember that one?
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Glycosphingolipids as Determinants of
Blood Groups
Electron micrograph of the
erythrocyte outer membrane
Waxes
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Ester of a FA and fatty alcohol
Waxes are insoluble and water repellent
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Weakly polar head group
Fatty acids are usually saturated
Alcohols are saturated/unsaturated
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Includes sterols
Lanolin and carnuba are examples
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Terpenes
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Lipids are built from
isoprene units rather
than fatty acids
Isoprene is a basic five
carbon unit
Usual linkage is head to tail
More complex terpenes are
built up from multiple isoprene units.
Some Common Terpenes
Monoterpene = C10 (two)
limonene, citronella, menthol
Sesquiterpene= C15 (three)
bisabolene
Diterpene= C20 (four)
phytol, gibberellic acid, all-trans retinal
Triterpene= C30 (six)
squalene, lanosterol
Tetraterpene
β-carotene, lycopene
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Polyprenols
Long chain polyisoprenoids with terminal alcohol.
Ex: dolichols = 16-22 isoprenoids; carry carbohydrate units in
biosynthesis of glycoproteins.
Warfarin
Polyprenols have diverse functions
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As phosphates, carry carbohydrates in the synthesis of
carbohydrates for glycoproteins
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Polyprenol groups anchor proteins in the membrane
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For bacteria, functional homolog of dolichol-P is undecaprenol
(fewer isoprenes, no P)
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Polyprenols are the side chains of important vitamins; coQ, K1, K2
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Steroids
The parent compound
Cholesterol: the key precursor
Cyclopentanoperhydrophenathrene
Steroid Hormones
Glucocorticoids:
Stress hormones Androgens: regulate sexual development
Bile acids:
Detergent
molecules
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Lipid Taxonomy: Review
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Lipids are distinguished by characteristic chemistry
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Fatty acids: carboxylate + saturated vs. unsaturated aliphatic
carbon chain
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Triaglycerols: glycerol + fatty acids (add phosphate)
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Sphingolipids: sphingosine + fatty acids
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Waxes: fatty acid + fatty alcohol
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Terpenes + polyprenols: head-tail joining of five carbon isoprene
unit
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Steroids: based on the cholesterol chemistry
Membranes
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All Living Cells Have Membranes
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Exclusion of certain toxic ions and molecules
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Accumulation of cellular nutrients (food!)
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Energy transduction (cf., mitochondria)
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Cell locomotion
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Reproductive processes (i.e. cell division)
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Signal transduction processes
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Varied interactions with molecules or other cells
Cellular organelles are membrane enclosed
Not shown
are the
mitochondria
which are
also membrane
enclosed
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Monolayers and Micelles
Micelle
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depends on lipid
concentration- when low, get
monolayer, when high, get
micelles.
Depends on critical micelle
concentration (CMC)
Phospholipids form bilayers
Unilamellar and multilamellar
vesicles (liposomes)
Monolayers and Micelles
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Phospholipids form bilayers
Unilamellar and multilamellar
vesicles (liposomes)
Bilayer
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Monolayers and Micelles
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Phospholipids form bilayers
Unilamellar and multilamellar
vesicles (liposomes)
Liposome
The fluid mosaic model
Singer & Nicholson- membranes are dynamic
Structures; a fluid 2D matrix; proteins free to move
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Lets Design an Experiment!
Singer & Nicholson- membranes are dynamic
Structures; a fluid 2D matrix; proteins free to move
Experiment I
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Experiment I
Experiment I
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Experiment II
Explain This Observation:
The motion of a single fluorescenet
lipid molecule in a cell surface is
recorded on video by fluorescence
microscopy. The track shown represents
A molecule followed for 56 ms.
The track begins in the purple area and
Continues through blue, green,
and orange.
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Restricted Motion
Motions of Single Phospholipids in a Bilayer
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Lipids are oriented asymmetrically in
membranes
Memranes Can Undergo Phase Transitions
Paracrystalline state: polar head groups
Are uniformly arrayed, acyl chains nearly
Motionless, packed with regular geometry
Fluid state: acyl chains undergo much
thermal motion, no regular organisatio
Liquid-ordered state: between those two
extremes, allows individual molecules
lateral diffusion.
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Explain This Observation:
Fatty acid composition of E. coli cells cultured at different temperatures
Reading
Chapter 13
PRINCIPLES OF BIOENERGETICS
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