Membrane structure and transport Flashcards
membranes functions
keep its molecules of life from dissipating awya (DNA and RNA)
keep out foreign molecules
Selective permeability
amphipathic phospholipids are used to block certain molecules out of cell (polar, big molecules, ions)
leaflets membrane
asymmetrical
glycolipids on extracellular leaflet so that the carbohydrate of the glycolipid protudes into extracellular medium
lateral movements vs flipflop
lateral movement: occurs relatively often
Flipflop: rare, because does not occur spontaneously, needs energy imput
ways to control membrane fluidity
lenght of FA:
Shorter leads to fewer stabilizing interactions leads to more fluid membrane
double bonds in acyl tail:
double bond makes a kink, prevents close packing of hydrocarbon tails and reduces hydrophobic interactions, so makes it more fluid
sterols through membrane:
cholesterol stabilizes membrane at low temperature (acts as spacer between FA) and keeps fluidity
at high temperature, hydroxyl group of cholesterol reacts with hydrophilic tails of phospholipids, makes it less fluid
lipids raft
regions of phospholipids with enriches sterols and membrane protiens
play important role for signal transduction
membrane protiens types
integral
covalent attachment of lipid to an amino acid within a protein, done post-translationally (after polypeptide is created)
transmembrane
goes through bilayer
Peripheral proteins
do not interact with the hydrophobic interior of the phospholipid bilayer
non-covenlantly bound to regions of integral membrane or to the polar head groups of phospholipids
typically bound to membrane by hydrogen or ionic bond
membrane proteins functions
transport
enzymatic activity
signal transduction
cell-to-cell recognition
intercellular joining
attachement to cytoskeleton
cell-cell junctions
anchoring junctions (anchor cells to cytoskeleton)
tight junctions (nothing gets through)
gap/communicating junctions (allows for commucation)
plasmodesmata (for plants because of cell wal)
Extracellular matrix
main ingredients are glycoproteins secreted by cells
components:
fibers: made of glycoprotein collagen (looks like tubes)
proteoglycan: 95% carbohydrates (looks like filaments)
fibronectin: adhesive that attaches the ECM to the plasma membrane of the cell
integrins: bouds to the ECM on one side and to the microfilaments of the cytoskeleton on the other
diffusion
molecules diffuse outwards from regions of high concentrations to lower ones
continues until homogenous
diffusion occurs when a system not at equilibrium
passive process (steeper the gradient (greater the different) high the net rate of solute movement)
larger the particle of solute, slower rate of diffusion
higher temperature faster rate of diffusion (since depends on kinetic energy)
increases entopy
simple diffusion vs facilitated diffusionWAAS
simple diffusion: small, nonpolar molecules passes throigh lipid bilayer
facilitated diffusion: transport of hydrophilic molecules facilitated by proteins
facilitated diffusion
done through:
polar protein channels (tunel), quick, usually for ions
carrier proteins: bonds to a specific solute and undergoes a series of conformational change (ex: uniport: moves 1 molecule)
is specific to only certain ions/moelcules
it saturates if all relevant carrier protiens are being used
still passive, uses gradient
internal glucose
body keeps its internal glucose level by immideatly attaching phosphate (if not, by osmosis cell will explode) and then it becomes highly charged and cant pass though the membrane again
gated channels
gated chanels: most channels have a gate to control its permeability ex Ligand-gated channels.
can also be done through intracellular protein that will activate the gate
some gates controled by reglatory proteins ex: phosphorylate gated chanel, chloride channels (openend by phosphorylation)
can also be volatge gated, response to electric gradient ex sodium and potassium nerve channels
can also me mechano sensitive (sensitive in changes in membrane tension) ex ability to hear depends on this
active transport
require energy imput, goes against gradient
major factor of cell meintaining internal concentrations
primary: uses atp, ex sodium-potassium pump
secondary: uses energy in set up gradient to move something against the gradient, ex: high sodium concentration outside cell, will want to move inside but will have to be coupled with low concentration surcrose outside the cell to allow the trasnport to pass it through
symporter/cotransport (trasnports 2 molecules or more agaisnt gradient, same dirrection), antiporter (trasnports 2 or more molecules agaisnt gradient, different dirrection)
sodium-potassium pump
3 sodium go out the cell, 2 potassion go in
universal in animal cells
maintaints voltage different accros nerve cell membranes
drives other transporters
electrogenic pump
any pump which moves net electrical charges across membrane
sodium-potassium pump: as exchange not equal (3 Na+ leaving 2K+ coming), it creates a difference in the net charge accros the membrane surface called the membrane potential (interior is a bit negative)
bulk transport
large molecules usually cross bilayer through bulk transport using vesicles
also requires energy
excosytosis: secretes out of cell, ex insulin
endocytosis: into cell
phagocytosis
pinocytosis
receptor-mediated endocytosis
exo-endo are likend and are in a sort of cycle to maintainsurface area and volume
phagocytosis
cellular eating
cell wraps a peudopodia around it and packages it inside a sac
sometimes goes to lysosome to be destroyed
unspecific
pinocytosis
cellular drinking
takes external fluid gulp, with all its solutes
unspecific
receptor-mediated endocytosis
receptors activate intake
ex: LDL intake
osmosis
water diffuses to where there is more solute throigh a semipermeable membrane (water gradient)
osmolarity: total solute concentration
depends on ions and dissasociation (NaCl=Na + CL so doule the osmolarity than initially)
iso-osmotic: same osmolarity
hyperosmotic: solution with a high osmolarity than another
hyposmotic: solution with a lowerosmolarity than another
osmotic pressure: indirredt measure of the pressure that must be exterted ona side of the selective permeanle membrane containing more solute to prevent diffusion of water from the side containg less solute
as osmotic pressure increases, osmolarity increases
as water concentration decreases, ormotic pressure increases
water will flow up an osmotic pressure gradient
tonicity
measure of how a soluton affect cell colume
depends on solute concentration and solute permeability across semi permeable membrane
isotonic: solution does not alter cell volume
hypertonic: solution that causes cells to shrink (more concentrated outside)
hypotonic: solution that causes cells to swell (less concentrated outside)
in plants tonicity
hypotonic: water vacule is full and cell is turgid (turgor pressure: force within the cell that pushes the plasma membrane against the cell wall)
isotonic: poper cell wall support, vacuole is not exterting too much pressure
hypertonic: water seeks to exit cell, vacuole empty, no rigidity in wall
osmoregulation
urinary system and endrocrine system play major role in making sure we have good blood osmosis
paramecium are usually hypertonic relative to theur envritonment, so contractile vacuole will pump water out of cell
