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Biophysics > 13-40 > Flashcards

13-40 Flashcards

Membranes, Potential, AP

1
Q

what state do living organisms occupy

A

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

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2
Q

quasi-equilibrium state

A

when whole system changes its parameters slowly and w/i time, the subsystems will adapt and quickly change to stationary state

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3
Q

bioenergetics

A

science of energy formation, transfer and use w/i a biological system

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4
Q

energy

A

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

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5
Q

cellular metabolism

A

total sum of chemical activities of cells

obtain chemical energy via degradation of nutrients or by converting molecules into cells

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6
Q

catabolic metabolism

A

reactions release energy by breaking down complex molecules into simpler compounds EG Respiration

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7
Q

anabolic metabolism

A

reactions consume energy to build complicated molecules from simpler compounds EG Photosynthesis

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8
Q

ATP

A

adenine triphosphate, useful free energy currency via spontaneous dephosphorylation reaction that releases lots of free energy

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9
Q

spontaneous reaction

A

change in S increases, change in free energy decreases

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10
Q

non-spontaneous reaction

A

change in entropy decreases, change in free energy increases

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11
Q

natural membranes

A

mainly composed of lipids and proteins

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12
Q

lipids

A

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

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13
Q

bilayer lipid membrane

A

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

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14
Q

phase transition temp

A

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

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15
Q

function of lipid bilayer

A

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

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16
Q

glycerol based lipids

A

glycosylcerides=highly complex

phopholipids=cell signaling and membrane permeability

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17
Q

cholesterol

A

regulates membrane fluidity more cholesterol =decreases fluidity by forming microdomains=lipid rafts that are rich in kinks

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18
Q

non-mediated transport

A

via simple diffusion, driven by potential gradient

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19
Q

mediated transport

A

via specific carrier proteins, facilitated diffusion

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20
Q

what do substances depend on to diffuse across membranes

A

substances diffuse at rates proportional to magnitude of gradient and they depend on solubility of membrane’s non polar core

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21
Q

EG of passive transport

A

osmosis, SD, FD

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22
Q

AT

A

Low conc to high conc, it is endergonic and relies on coupling to sufficiently exergonic processes for favorable reaction

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23
Q

primary AT

A

proceeds by chemical reaction EG ATP hydrolysis or Na/K pump

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24
Q

secondary AT

A

coupled with primary AT EG glycolysis transport is coupled with Na/K transport in intestines

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25
Q

uniport

A

transports 1 substance in 1 direction

26
Q

joint transport

A

simultaneous transport of 2 or more substances by 1 system

27
Q

antiport

A

in opposite direction

28
Q

symport

A

same direction

29
Q

electroneutral transport

A

no change in value to TM potential EG Na+/Cl- in 1 direction or Na+/K+ in opposite directions

30
Q

electrogenic transport

A

changes membrane potential 3Na+/2K+ in opposite direction

31
Q

hypotonic

A

higher water conc in sol, lower water conc in cell so water moves into cell = swell = bursts

32
Q

hypertonic

A

lower water conc in sol, higher water conc in cell so water moves out of cell = shrivels up = dies

33
Q

electrophoresis

A

movement of electrically charged particles in electric fields

34
Q

nenst plank molar flux

A

describes flux of ions under influence of ionic conc gradient and electric field

35
Q

from what regions to electrons move

A

from negative potential to positive potential

36
Q

membrane permeability

A

describes diffusion of particles through membranes [cm/s]

37
Q

FD

A

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

38
Q

is FD Saturable process

A

yes because there are a limited no. of protein channels available that are specific to ions

39
Q

pores

A

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

40
Q

ionophores

A

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

41
Q

lactose permease

A

utilises proton gradient across bacterial cell membrane to cotransport proton and lactose to drive ATP synthesis

42
Q

define diffusion potential

A

merging of electrolytes w/ different concs that develop into an electric potential gradient

43
Q

how is diffusion potential formed

A

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

44
Q

conditions for observing membrane diffusion potential

A

different mobility/conc of ions and non-selective membrane

45
Q

memebran equilibrium potential

A

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

46
Q

conditions for establishing equilibrium membrane potenial

A

different conc of ions, semi-permeable membrane, electric potential is established at equil so it remains constant and doesn’t change over time

47
Q

donnan potential

A

electric potential risen due to unequal distribution of ion conc seperated by semi-permeable membrane

48
Q

effect of electro-neutrality principle

A

no of +ive charges must be same as no. of -ive charges

49
Q

osmotic consequences of gibbs-donnan equilibrium

A

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

50
Q

TM PD arises due to what

A

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

51
Q

goldmann equation

A

determines reversal potential due to ionic movement

52
Q

thomas equation

A

relates ion current and flux

53
Q

factors contributing to resting potential

A

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

54
Q

generation of AP

A
  1. Depolarisation = Na+ channels open
  2. AP
  3. Repolarisation = Na+channels close spontaneously and K+ open, these take longer to open so requires a greater depolarisation
  4. Hyperpolarisation = K+ channels close
  5. Resting potential = VG K+ close so K+ permittivity and PD move back to resting levels
  6. Failed initiations
55
Q

how is AP initiated

A

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

56
Q

Hodgkin Cycle

A

due to increased conductance of Na+, there will be more positive intracellular space so increased membrane potential which will repeat

57
Q

hyperpolarisation

A

summed activity of VG and non-gated K channels

58
Q

salatatory conductions

A

propagation of AP along myelinated axon from 1 node of Ranvier to the next node, this increases conduction velocity of AP by 10-100x

59
Q

node of ranvier

A

gaps where impulse jumps from node to node

60
Q

VG Conductance

A

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

Biophysics (4 decks)

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