Bio 2415- Module 3
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Bio 2415- Module 3
what are the 5 main membrane functions?
define boundaries and serve as permeability barriers
2. membranes are
sights of specific proteins
and therefore specific functions
3. membrane proteins
regulate the transport of solutes
proteins detect and transmit electrical and chemical signals
5. membrane proteins mediate
what is the difference between plasma membrane and intracellular membrane?
plasma membrane surrounds the whole cell
intracellular membranes compartmentalize functions within the cell
what is the function of specific enzymes associated with particular membranes?
used as markers
to identify the membranes during isolation
how are substances transported through the membrane?
diffuse directly across membranes
others must be
moved by specific transporters
mechanisms by which signals are transmitted from the outer surface to the interior of the cell
how is cell-to-cell contacts important for animals?
critical in animal development
and are often mediated by cadherins
: have extracellular sequences of amino acids
that bind calcium
promote adhesion between similar types of cells
in a tissue
limit the passage of molecules and ions
through the space between cells.
most materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue.
block the movement of integral membrane proteins
hold cells together
are intercellular channels that
permit the free passage between the cells of ions and small molecules
changes in membrane potential to pass from cell to cell.
The fluid mosaic model is thought to be descriptive of all biological membranes. What are the 2 key features?
fluid lipid bilayer that is constant motion
mosaic of macromolecules
with diverse functions that are attached to or embedded in the bilayer
3 reasons why lipids are considered a macromolecule
have a high molecular weight
are important in cellular structures
made by dehydration reaction
monomers form polymers by releasing water as a product
formed through this chemical reaction
what are the 6 classes of lipids?
Fatty acids (physical and chemical characteristics)
are building blocks of some lipids
long amphipathic, unbranched hydrocarbon chain with a carboxyl group at one end
polar carboxyl group is the head
non-polar hydrocarbon chain is tail
highly reduced, upon oxidation will absorb energy?
difference between saturated and unsaturated fatty acids.
saturated fatty acid
: each carbon atom in the chain is
bonded to the maximum number of hydrogen atoms
; have long straight chains that
pack together well
unsaturated fatty acid
one more double bonds
; the chains have
bends that prevent packing
Triacylglycerol (physical and chemical characteristics)
glycerol molecule attached to three fatty acids
that very in length and degree of saturation
what is glycerol and how are fatty acids linked to it?
glycerol is a
3-carbon alcohol with a hydroxyl group on each carbon
fatty acids linked to glycerol, one at a time, by
ester bonds formed by removal of water
phospholipids (physical and chemical characteristics)
and are vital to membrane structure
polar head due to a negatively charged phosphate group linked to a positively charged group
2 nonpolar hydrocarbon tails
form the "rail road" track appearance under EM
what are the 2 forms of phospholipids?
in most membranes
based on the structure of phosphatidic acid,
which has 2 fatty acids (one saturated and one unsaturated) and a phosphate group attached to a glycerol
small hydrophilic alcohol linked to the phosphate by an
indicated by the "R"
alcohol is usually serine
, ethanolamine, choline or inositol
which contributes to
of phospholipid head group
based on the
which has long
hydrocarbon chain with a single site of unsaturation near the polar end
"R" group may or may not contain phosphate group
can form an
to a long-chain fatty acid resulting in ceramide
glycolipids ( physical and chemical characteristics)
specialized membrane components
lipids containing a carbohydrate
instead of a phospholipid and are
often derivatives of sphingosine and glycerol
carbohydrate groups attached to glycolipids may be
1-6 sugar units
D-glucose, D-galactose and/or N-acetyl-D-galactosamine
steroids (physical and chemical characteristics)
functions in membrane and as hormones
derivatives of a 4-ringed hydrocarbon skeleton
, which distinguishes them from other lipids
Terpenes (physical and chemical characteristics)
synthesized from isoprene
(5-carbon compound) and are sometimes called
what are polyisoprenoids and dolichol?
are found in membranes of archaea
and some electron carriers are isoprene derivatives found in organelle membranes
The hydrophobic effect
force water to form a cage-like structure
because cage is
highly organized, it costs energy to form
energy cost minimized if the hydrophobic molecules cluster together instead and limit the contact of water
to the smallest possible number of molecules
the hydrophobic effect is important for 4 reasons:
the formation of lipid bilayer
the insertions of membrane proteins into the nonpolar lipid environment
protein-small molecule interactions
Heterogeneous lipids all share the following 3 characteristics:
, thus little affinity for water (hydrophobic effect)
readily soluble in nonpolar solvents
relatively few polar groups
, but some are amphipathic, having polar and nonpolar regions
3 lipids form the basic structure of the lipid bilayer, what are they?
what is Thin-layer chromatography (TLC) and why is important?
separates different kinds of lipids based on their relative polarity
important technique for separating lipids and analyzing the lipid composition of membranes
membrane components are amphipathic
(having both polar and non-polar) what 5 things occur?
spontaneously form bi-layers
hydrophilic regions face the water
hydrophobic regions make up the central core
never have a free end due to cohesion
spontaneously reseal, able to self-heal
fuse with other membrane structures
Fatty acids of phospholipids are essential to membrane structure and function, how?
sizes of fatty acids
range between 12-20 carbons long, which is optimal
for bilayer formation
and dictates the usual thickness of membranes
hydrocarbon tails provide a barrier to the diffusion of polar solutes
The membranes of most eukaryotes contain significant amounts of sterols. what is the main sterols found in animal, plant and fungal cell membranes?
needed to stabilize and maintain membrane
, similar to cholesterol
what are the effects of sterols on membranes?
decrease the permeability of membranes to ions and small polar molecules
fill spaces between the hydrocarbon chains
of phospholipids which blocks the routes
what are 3 ways that phospholipids move within the membrane?
about their axis
can move within the monolayer via
exchange from one leaflet to another (
Transverse diffusion occurs with assistant, how?
some membranes, in particular the Smooth ER membrane, have
proteins called phospholipid translocators
catalyze the flip-flop of membrane lipids
what are the 2 things that membrane fluidity depends on?
: membrane fluidity
decreases as temperature falls
and vice versa
temperature at which the membrane changes fluidity is dependent on the types of lipids
that go into composition (length of fatty acid and degree of saturation)
Every lipid bi-layer has a characteristic transition temperature, Tm what is it and the effect on the membrane?
temperature at which it becomes fluid
change of state is called a
(solid to liquid)
below the Tm, any function that rely on the membrane fluidity will be disrupted
The level of fatty acid saturation impacts the temperature at which the membrane changes fluidity, which fatty acid is more fluid and why?
saturated fatty acids pack together well in the membrane
unsaturated fatty acids have one or more double bonds that have bends in the chains that prevent proper packing
unsaturated fatty acids are more fluid and have lower Tms
How does the length of fatty acid chains also influence the fluidity of the membrane?
longer the chains, the more neighbouring chains interact with one
decreases fluidity and increases rigidity