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Biomembrane Structure & Function, Curvature, e.g., rarely form, form…
Biomembrane Structure & Function
Structure
PL bilayer
Non-covalent :raised_hands: interactions
Fluidity & flexibility (fluid mosaic model)
Dynamic :runner: processes (membrane
budding
& fusion)
Typical shapes of
organelles
:black_circle_for_record:
Golgi
Most common PL in membranes:
phosphoglycerides
Classified acc. to
Head group :speaking_head_in_silhouette:
Variation in lipid composition
Several contributing factors
relative % of
phosphoglycerides
and
sphingolipids
PGs
ER membranes
sphingolipids
Golgi membranes
movement
of membranes from one cellular compartment to another
Response to
environment
:pregnant_woman:
Intestinal tract: harsh environment
More sphingolipids, less PGs
Sphingosine's free –OH group = more H bonding
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Fluidity
long FA chains
+++ Van der Waals interactions
gel-like state
fluidity decreased
straight (saturated) FA chains
Cholesterol
:ring::sunny:
Effect on tails depends on concentration
Normal concentrations
Immobilize lipids
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Restricts movement of heads
bile acids
steroid hormones
vitamin D
++ to Hedgehog :baby_bottle:
Thickness
Curvature
head size
small
cone :icecream:
curve :tada:
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large
cylindrical :oil_drum:
flat :oil_drum::oil_drum::oil_drum:
tail length
long
proteins
Variety of cell shapes
Different cell functions
PL: polar head, 2 FA tails
amphipathic
:!!:
fatty acyl chains aggregate and
exclude
water molecules from the “core” :red_cross::droplet:
PLs dispersed in aqueous solution
sheet-like phospholipid bilayers
Van der Waals
2 faces :silhouettes:
Cytoplasmic
Exoplasmic
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depends on:
length of the fatty acyl chains in the hydrophobic tail :straight_ruler:
natural
FA chains generally too bulky
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temperature :thermometer:
degree of saturation (# of C—C bonds) :bow_and_arrow:
spherical micelles :tennis:
a FA tail is removed by
phospholipase
hydrolysis
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if
FA
not removed but instead of ester linkage
ether
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detergent / soap
liposomes :doughnut:
spontaneous formation of
SEALED
,
closed
compartments
NO EDGES!!! :triangular_ruler:
aqueous central compartment :pregnant_woman:
sphingolipids :face_with_head_bandage:
some (but not all) are PLs:
SM
:speaking_head_in_silhouette:
most abundant in nervous tissue
GlcCer
,
gangliosides
sterols :ring::mushroom:
hydroxyl
group (-ol) on one ring
Membrane proteins
Unique functions :point_left:
Integral
Lipid-anchored
Peripheral (indirect)
Contact with cytoskeleton :muscle:
Function
Defines the cell :frame_with_picture:
Separates the inside from the outside :door:
Permeability barrier
Water-soluble substances :sweat_drops: :red_cross:
Maintain characteristic
differences
:silhouettes: between inside & outside
Defines intracellular organelles :frame_with_picture:
Same basic architecture
PL bilayer & proteins embedded
Embedded proteins allow
specific
functions
Regulated transport
Cell specific :point_left:
Explain how membranes are
structured
and how they affect different aspects of cell
function
.
Curvature
e.g.
rarely form
form if
other lipids
e.g.
Sphingolipid - Phosphoglycerides - Cholesterol = 1:1:1
Effect(s) on membrane
Increases
:red_cross:
e.g.
:building_construction:
Classified as
borders the..
how? :o
precursor for
abundant in
complementing