13-40 Flashcards
Membranes, Potential, AP
what state do living organisms occupy
steady state, they are in stationary state with minimum entropy production. Living organisms are made up of a great number of subsystems, not all of them are in steady state but most are in TD equilibrium
quasi-equilibrium state
when whole system changes its parameters slowly and w/i time, the subsystems will adapt and quickly change to stationary state
bioenergetics
science of energy formation, transfer and use w/i a biological system
energy
the capacity to perform work, used to synthesise organic materials, drive AT/endocytosis/muscle contractions
Kinetic Energy=process of doing work, energy of motion (heat, light)
Potential energy=energy matter occupies due to its position
cellular metabolism
total sum of chemical activities of cells
obtain chemical energy via degradation of nutrients or by converting molecules into cells
catabolic metabolism
reactions release energy by breaking down complex molecules into simpler compounds EG Respiration
anabolic metabolism
reactions consume energy to build complicated molecules from simpler compounds EG Photosynthesis
ATP
adenine triphosphate, useful free energy currency via spontaneous dephosphorylation reaction that releases lots of free energy
spontaneous reaction
change in S increases, change in free energy decreases
non-spontaneous reaction
change in entropy decreases, change in free energy increases
natural membranes
mainly composed of lipids and proteins
lipids
mainly phospholipids EG phospho-choline/ethanolamine/serine/linositol and sphingomyeline
aren’t uniformly distributed
marks cells for destruction by IS= phosphatidyl serine signals macrophages to remove dying cells
affects membrane permeability=cholesterol increases bilayer strenght and biochemical interactions
bilayer lipid membrane
sheet of lipids 2 molecules thick, hydrophILIc Heads point out, hydrophobic tails point in, longer tailed lipids have increased SA to interact w/ molecules being transported through but decreased mobility
phase transition temp
affected by degree of unsaturation of lipid tails so more UNSAT double bonds= kink= disrupts lipid packing = increases fluid HC medium=extra free space for flexibility
function of lipid bilayer
barrier = hydrophobic core permeable to small Hphobic solutes EG Cholester/Ethanol. Impermeable to inorganic compounds and ions EG AA or Nucleic Acid, proteins, carbohydrates
intrinsic proteins embedded in lipid bilayer so PPC interacts w/ non-polar region
membrane receptor proteins activate phospholipases that cleave selected phospholipids to generate fragments = intracellular signaling molecules
glycerol based lipids
glycosylcerides=highly complex
phopholipids=cell signaling and membrane permeability
cholesterol
regulates membrane fluidity more cholesterol =decreases fluidity by forming microdomains=lipid rafts that are rich in kinks
non-mediated transport
via simple diffusion, driven by potential gradient
mediated transport
via specific carrier proteins, facilitated diffusion
what do substances depend on to diffuse across membranes
substances diffuse at rates proportional to magnitude of gradient and they depend on solubility of membrane’s non polar core
EG of passive transport
osmosis, SD, FD
AT
Low conc to high conc, it is endergonic and relies on coupling to sufficiently exergonic processes for favorable reaction
primary AT
proceeds by chemical reaction EG ATP hydrolysis or Na/K pump
secondary AT
coupled with primary AT EG glycolysis transport is coupled with Na/K transport in intestines
uniport
transports 1 substance in 1 direction
joint transport
simultaneous transport of 2 or more substances by 1 system
antiport
in opposite direction
symport
same direction
electroneutral transport
no change in value to TM potential EG Na+/Cl- in 1 direction or Na+/K+ in opposite directions
electrogenic transport
changes membrane potential 3Na+/2K+ in opposite direction
hypotonic
higher water conc in sol, lower water conc in cell so water moves into cell = swell = bursts
hypertonic
lower water conc in sol, higher water conc in cell so water moves out of cell = shrivels up = dies
electrophoresis
movement of electrically charged particles in electric fields
nenst plank molar flux
describes flux of ions under influence of ionic conc gradient and electric field
from what regions to electrons move
from negative potential to positive potential
membrane permeability
describes diffusion of particles through membranes [cm/s]
FD
Transport by carrier proteins that move larger and polar molecules across membranes
the trasnporters are specific for substrates, transporters are formed by mobile carriers and channels
is FD Saturable process
yes because there are a limited no. of protein channels available that are specific to ions
pores
gap junctions between endothelial/muscle/neuronal cells, maintained in open state and will close if membrane is damaged or metabolic state is depressed. Pores are more open and non-selective structures
EG nuclear pores = proteins and NA enter/leave nucleus
OMM Pores= mitochondrial proteins encoded by nuclear genes leave
ERM Pores=PPC of secretory proteins and PM proteins leave
ionophores
molecules of diverse types that increase permeability of membranes to ions
carrier ionophores=increase permeability by binding to selected ion and diffusing through membranes and releasing ion on other side
EG. Valinomyelin is a mobile ion carrier, K+ binds to central core diffuses across membrane and releases K+ to gradually dissipate K+ gradient
channel-forming ionophores = form TM channel/pore where ions can diffuse
EG. Gramicidin= its dimers form channel/pore in membrane to allow inorganic, non-covalent ions (Na+/K+) to diffuse, this destroy ion conc differences which causes ion leaks in mitochondria to halt ATP production = kills cell
lactose permease
utilises proton gradient across bacterial cell membrane to cotransport proton and lactose to drive ATP synthesis
define diffusion potential
merging of electrolytes w/ different concs that develop into an electric potential gradient
how is diffusion potential formed
different conc of ionic sol to result in an immediate diffusion potential due to difference in ion mobility, this causes a separation of ions to establish a PD at the boundary between the 2 solutions, which can be measured
conditions for observing membrane diffusion potential
different mobility/conc of ions and non-selective membrane
memebran equilibrium potential
neutral solution w/ different conc of ions, the membrane is permeable to a specific ion so that the other ion cannot cross membrane = EG K+ only moves across membrane this causes an increase in charge until it is too big so that there will be no futher K+ movement so flux of K+ is 0 and electric potential is in equil
conditions for establishing equilibrium membrane potenial
different conc of ions, semi-permeable membrane, electric potential is established at equil so it remains constant and doesn’t change over time
donnan potential
electric potential risen due to unequal distribution of ion conc seperated by semi-permeable membrane
effect of electro-neutrality principle
no of +ive charges must be same as no. of -ive charges
osmotic consequences of gibbs-donnan equilibrium
due to movement of ions to preserve electroneutrality, causes a greater osmotic pressure on 1 side = eater will flow from the other side if it is not restrained
SO in plant cells=cell wall to allow for a higher intracellular hydrostatic pressure
in animal cells= uses Na+/K+-ATPase pump to regulate ion conc w/i cells
TM PD arises due to what
TM Ion gradients which are maintained by large outwards K+/Na+ gradient via primary AT in PM
Relative permeability of PM to K+ and Na+ depending on open/closed status if ion-selective membrane channels
goldmann equation
determines reversal potential due to ionic movement
thomas equation
relates ion current and flux
factors contributing to resting potential
gibbs-donnan equilibrium < -10mV to RMP
electrogenic Na/K-ATPase < 5mV in skeletal muscle, more in smooth muscle
electrodiffusion of ions to brin TM electrical PD to equil potential
generation of AP
- Depolarisation = Na+ channels open
- AP
- Repolarisation = Na+channels close spontaneously and K+ open, these take longer to open so requires a greater depolarisation
- Hyperpolarisation = K+ channels close
- Resting potential = VG K+ close so K+ permittivity and PD move back to resting levels
- Failed initiations
how is AP initiated
When PD reaches membrane threshold (about-70mV) voltage-gated Na channels open due to increased permittivity of Na to membranes, this causes depolarization, which activates more VG Na+ channels to open to begin an explosive feedback recruitment of Na+ channels
Hodgkin Cycle
due to increased conductance of Na+, there will be more positive intracellular space so increased membrane potential which will repeat
hyperpolarisation
summed activity of VG and non-gated K channels
salatatory conductions
propagation of AP along myelinated axon from 1 node of Ranvier to the next node, this increases conduction velocity of AP by 10-100x
node of ranvier
gaps where impulse jumps from node to node
VG Conductance
Na+ channels activate when increased conductance of Na due to depolarisation, this shows there is a V induced change in shape of Na channels which will displace the highly charge region and open pore movement
