56 terms

ch 5 membrane transport and cell

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functions of cell membrane
-communication with other cells -receive nutrients -eliminate wastes
proteins and phospholipids are mobile within the
what is mobile within the cm
proteins move
moves slowly, laterally or rotate
groups of certain proteins or certain lipids
associate in long lasting specialized patches
as temp cools membranes switch from
membranes switch from fluid to solid state
the temp at which a membrane solidifies depends on
depends on types of lipids
membrane remains fluid to a lower temp if
if is rich in phospholipids with unsaturated hydrocarbon tails
membranes must be fluid to work properly
usually about as fluid as salad oil
the steroid cholesterol has different effects on
has different effects on membrane fluidity at different temp
at warm temps (37c) cholesterol
cholesterol restrains movement of phospholipids
at cool temps cholesterol
cholesterol maintains fluidity by preventing tight packing
variations in lipid composition of cell membranes of many species appear to be
appear to be adaptations to specific environmental conditions
ability to change the lipid compositions in response to temp changes has evolved in
evolved in organisms that live where temp vary
phospholipids
the membranes foundation, most abundant lipid in most membranes, other components are arranged in this layer
phospholipids components
glycerol, fatty acid tails
glycerol
3c alcohol + PO4, polar
fatty acid tails
2, nonpolar
amphipathic molecules
hydrophobic and hydrophilic regions
a phospholipid bilayer can exist as a stable boundary between
between two aqueous compartments
hydrophobic tails
avoid water, stay within the cm, membrane interior
hydrophilic heads
cell and its environment are mostly water, heads face out, need doorways for passage of carbs, aa, protein
a membrane is a collage of
different proteins grouped together, embedded in the fluid matrix of the lipid bilayer
many membrane proteins are
amphipathic
membrane proteins reside in
reside in bilayer with their hydrophilic portions protruding
proteins determine most of membranes
membranes specific functions
transmembrane proteins
integral, peripheral
integral proteins
penetrate bilayer, transmembrane proteins go across cm, hydrophobic regions consist of one or more stretched of nonpolar amino acids often coiled into alpha helices, nonpolar, stays in membrane bc outside membrane is polar
peripheral proteins
do not penetrate the bilayer, lack hydrophobic regions, move along membrane tied to phospholipid, nonpolar regions attach protein to phospholipid
transporters
channels, carriers
protein channels
allow molecules to pass through
protein carriers
bind with molecules to help them cross the cm
enzymes
aid metabolism, attached to pm
cell surface receptors
protein markers for recognition
cell to cell adhesion proteins
homotypic and heterotypic binding
homotypic binding
cells bind together via the same molecule both on cm, most tissues form this way
heterotypic binding
cells with different proteins bind together
attachments to the cytoskeleton
linking proteins connect surface proteins to cytoskeleton,
spectrin, and clathrin
spectrin
maintains shape
clathrin
anchors proteins, cell surface markers
glycolipids: tissue recognition
abo blood groups
glycoproteins: tissue recognistion
extend from cell surface, differ amongst species, individual, cell types
microdomains
regions within pm with specific lipid and protein make up
membrane structure results in
results in selective permeability
cell must regulate transport of substances across
across cellular boundaries
plasma membranes are selectively permeable regulating the cells
regulating the cells molecular traffic
selective permeability of a biological membrane
materials move down concentration gradient, small molecules pass through cm, the more hydrophobic the faster they go, hydrophilic molecules do not pass through the cm through simple diffusion
transport proteins allow passage of
allow passage of hydrophilic substances across the membrane
some transport proteins (channel proteins) have
hydrophilic channel that certain molecules or ions can use as a tunnel
aquaporins
channel proteins that facilitate the passage of water
carrier proteins
transport proteins that bind to molecules and change shape to shuttle them across the membrane
transport proteins is specific for the
substance it moves
passive transport is diffusion of
a substance across a membrane with no energy investment
diffusion
tendency for molecules to spread out evenly into the availiable space although each molecule moves randomly
diffusion of a population of molecules may be
directional
diffusion, movement is from
high to low concentration
dynamic equilibrium
as many molecules cross the membrane in one direction as the other