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Lecture

Membrane & Membrane Function.docx


Department
Biology
Course Code
BIOL 2382B
Professor
Jessica Kelly

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1
Lecture 13 Membrane & Membrane Function
Biomembranes
Basic components:
Lipids
Sterols
Proteins (about 50%)
Phospholipids are amphipathic… they spontaneously form lipid bilayers in aqueous
solutions (energetically favourable)… properties of fatty acids confer properties onto
the bilayers (i.e. how fluid bilayer is = saturation/size of fatty acids)…
Liposomes naturally form as the edges of a bilayer sheet interact unfavourably with
water but favourably with one another (hydrophobic effect)
micelles do not form
readily b/c the fatty acid chains of phosphoglycerides are too bulky to fit in the interior
of the micelle…
Membranes
define what is a cell...
Allow specialized cellular functions to
occur in a localized manner
I.e. provide an internal environment
different in chemical composition from
the external environment

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Fatty acids & Phospholipids
Phospholipid amphipathic molecule composed of a long hydrocarbon chain (fatty acid)
attached to a polar head group
Fatty Acids:
Often use the notation Cx:ywhere x = number of carbon molecules,
y = number of double bonds
No double bonds = saturated
One double bond = unsaturated
More than one double bond = polyunsaturated
Effect of Double Bonds on Structure
Tm (melting temperature) increases with chain length & decreases with
unsaturation…
Saturated chains can be tightly packed numerous van der Waal’s forces due
to regular structure…
Natural occurring double bonds are… commonly cis rarely trans = kinking of
chain… (packing)
Over 100 fatty acids known… only a few common in membranes

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Cell Membrane Components
Phospholipid head group attached via phosphate
2 Main Groups of Phospholipids:
1. Phosphoglycerides
2. Sphingomyelin
Phosphoglycerides derived from glycerol (3 carbon chain) scaffold to which a polar
(hydrophilic) head group is attached to phosphate (attached to glycerol) and 2 acyl chains
also attached to glycerol
Sphingolipids
Sphingolipids - derived from sphingosine (amino alcohol with a long carbon chain
attached)
Sphingomyelin (SM) a phospholipid with sphingosine as a molecular scaffold (instead
of glycerol)
Glucosylceramide (GlcCer ) a glycolipid (sphingolipid with a sugar
(mono/oligosaccharide) as the polar head group)
PE phosphatidylethanolamine
PC phosphatidylcholine
PS phosphatidylserine
PI phosphatidylinositol
All phosphoglycerides but they
differ in the head group that is
attached to the phosphate…
Glycolipids are found most
abundant in nervous tissue…
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