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PHGY209 > transport mechanisms > Flashcards

transport mechanisms Flashcards

1
Q

what are the main functions of the cell membrane?

A
  • support distinct compostions of the ICF and the ISF

- be selectively permeable

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2
Q

what is the cell membrane highly permeable to?

A

H20
lipid soluble substances
dissolved gases
small uncharged molecules

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3
Q

is the cell membrane permeable or impermeable to large molecules (macromolecules?)

A

impermeable

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4
Q

what type of movement is exhibited by the phospholipid bilayer?
what is it composed of?

A
  • it exhibits lateral mobility
  • it is amphipathic
  • composed of hydrophilic polar head and hydrophobic tails
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5
Q

what is the role of cholesterol in the bilayer and where does it insert?

A

cholesterol can be found in the phospholipid bilayer and it provides stability and rigidity based on temperature.

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6
Q

by weight, what percentage of the bilayer does cholesterol occupy?

A

around 20%

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7
Q

what type of proteins can be found in the proximity of the bilayer?

A
  • intergral proteins

- peripheral proteins

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8
Q

identify the following type of protein?

closely associated with the phospholipids, mostly cross the membrane
amphipathic
transmembrane
need detergents to be removed

A

integral proteins

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9
Q

identify the following type of protein?

more loosely anchored on the cytoplasmic side of the membrane

A

peripheral proteins

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10
Q

what do the carbohydrates and glycoproteins on the outer side of the membrane constitute?

A

the glycocalyx

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11
Q

what are some of the main function of membrane proteins?

A
  1. allow for selective transport and diffusion of specific molecules in and out of the cell
  2. act as enzymes
  3. serve as a cell receptor which receives and transduce signals from the cell environment
  4. cell surface identity markers (blood groups)
  5. cell to cell adhesion
  6. attachment to the cytoskeleton
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12
Q

what factors affect movement across the cell membrane?

A
  • lipid solubility. a lipid soluble molecule will pass with more ease
  • particle size: smaller particles can move across membranes more easily
  • electrical charges: the interior of the cell is slightly negative and will tend to repulse negatively charged molecules
    4. availability and number of carriers and ion channels
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13
Q

what is an energy independent transport mechanism?

A 
-passive transport
it includes
diffusion
carrier mediated facilitated diffusion
osmosis
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14
Q

what are the energy dependent type of transport mechanisms?

A
  1. carrier-mediated active transport (primary and secondary)

2. pino/phagocytosis

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15
Q

what is diffusion?

A

movement of solute particles resulting from thermal motion.

the net flux goes from [high] to [low]

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16
Q

can diffusion occur even if there is the presence of a mechanical partition?

A

yes, as long as it is permeable to the diffusing molecules

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17
Q

what is fick’s law of diffusion?

what do the variables represent?

A 
J= PA(Co-Ci)
J= net flux
P= permeability of diffusion coefficient
A: surface area of the membrane
Co-Ci: concentration gradient of the diffusion molecules across the membrane
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18
Q

is diffusion effective over long distances? and why?

A

no, its only effective over short distances as the diffusion time increases in proportion to the square of the distance, hence greater distance means a rapid increase in time.

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19
Q

how can diffusion particles penetrate

A
  1. dissolving in the lipid component (used by non polar molecules)
  2. diffusion through channels (used by ions)
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20
Q

what do ion channels consists of?

A

either a single protein or a cluster of proteins

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21
Q

how do ion channels show selectivity?

A

based on diameter as well as on the distribution of charges that line the channel

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22
Q

what factor also affect the movement of ions?

A

the electrical gradient

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23
Q

what is the electrochemical gradient?

A

its the simultaneous existence of the electrical and the concentration gradient for particular ions

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24
Q

what is the charge of the cell at rest? (resting potential)

A

its negative

-90 mV

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25
Q

what states do channels normally exist in?

A

they alter conformation and can either be in an open of closed conformation

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26
Q

what are the 3 ways channels can be gated?

A
  • ligand gated
  • voltage gated
  • mechanically gated
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27
Q

what factors influence the amount of ions flowing through voltage gated channels?
give examples of such channels.

A
  1. the channel conductance
  2. how often its open
  3. how long it stays open for

ex: Na+ channel (in)
K+ channel (out)
Ca2+ channel (in)
Cl- channel (in)

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28
Q

what are some of the fundamental characteristics of mediated transport systems?

A
  • they are specific
  • they can be saturated, at that point carriers reach vMax
  • competition may occur betweens sructurally similar molecules for the binding site
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29
Q

what factors determine the magnitude of mediated transport systems?

A
  1. solute concentration (more concentration will be saturated sooner)
  2. affinity of the transporter for the solute
  3. number of transporters (greater flux)
  4. rate of transporter conformation changes (faster= greater flux.)
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30
Q

what does facilitated diffusion involve?

A

the presence of a carrier molecule which will enable a solute to penetrate more readily than it would in simple diffusion

31
Q

how does facilitated diffusion function?

A
  • solute binds to carrier
  • carrier undergoes conformation changes
  • solute is delivered to other side of membrane
  • reverts to original conformation
32
Q

what are the key properties of facilitated diffusion?

A

it is carrier mediated
passive
net flux is from [high] to [low]

33
Q

what may cause an increase in number and or affinity of transporters in certain membranes?
give an example

A

hormones

Glut 4 transports glucose in muscles increased by insulin.

34
Q

what are the key properties of active transport

A
  • transporter mediated
  • requires supply of energy (hydrolysis of ATP)
  • susceptible to metabolic inhibitors
  • transport against gradient
35
Q

what is primary active transport?

A

involves the hydrolysis of ATP by a carrier and the phosphorylation of the carrier causes for a conformational change and solute binding affinity allowing to transport solute against gradient

36
Q

what happens in the sodium-potassium ATPase?

A

on the intracellular side of the membrane, 3 Na+ bind to the carrier and with hydrolysis of ATP carrier changes conformationand loses its affinity for Na+ causing for 3 Na+ to move to the extracellular side and allowing for 2 K+ to bind to transporter.
reverts to original conformation causing for 2 K+ to move inside the cell

37
Q

what is the function of the Ca2+ ATPase in the body?

A

it enables to keep levels of intracellular Ca2+ low

38
Q

what is the function of H+-ATPase in the body?

A

it allows to maintain a low lysosomal pH

39
Q

what is the function of the H+/K+-ATPase?

A

allows for acidification of the stomach which is useful in digestion

40
Q

what is secondary active transport?

A

its the movement down the electrochemical gradient that is coupled with the transport of another molecule (glucose or AA)

41
Q

explain how secondary active transport functions?

A

Na+ bind to a transporter outside of the cell (high concentration) then a solute molecule binds to the same carrier (often glucose of AA)
through a conformational change both Na+ and the solute are delivered to the inside of the cell.
the conformation of the carrier is reverted and the sodium is pumped out by the Na+/K+-ATPase

42
Q

what is cotransport?

A

when the solute molecule moves in the same direction as sodium

43
Q

what is counter transport?

A

molecules move in opposite directions of each other.

44
Q

give examples of counter transport?

A

Na/H+ exchanger
Na/Ca2+ exchanger
Cl-/HCO3- exchanger

45
Q

give examples of cotransport?

A

Na+-glucose cotransporter

Na-Amino Acid cotransporter

46
Q

what are active transport mechanisms that involve the participation of the cell membrane itself?

A

endocytosis

exocytosis

47
Q

what is endocytosis?

A

the cell membrane invaginate forming a channel, which pinches off to form a vesicle

48
Q

what is exocytosis?

A

an intracellular vesicle fuses with the cell membrane and its contents are released into the ECF

49
Q

What is pinocytosis?

A

ingestion of dissolved materials by ENDOCYTOSIS.
cell membrane invaginate and pinches off placing small droplets of fluid in a pinocytic vesicle.
the liquid contents are slowly transferred to the cytosol

50
Q

what is phagocytosis?

A

ingestion of solid particles by ENDOCYTOSIS
the cell membrane invaginate and pinches off forming a phagosome
the phagosome then fuses with lysosomes and the material gets degraded

51
Q

what are the 2 types of receptor mediated endocytosis?

A
  • clathrin dependent

- potocytosis

52
Q

what is clathrin dependent receptor mediated endocytosis

A

it involves the pinching off of “clathrin coated vesicles” that fuse with endosomes where vesicle contents are sorted

53
Q

what is potocytosis?

A

clathrin independent receptor mediated endocytosis
involves pinching off of tiny vesicles called Caveolae that deliver their contents to the cell cytoplasms directly via channels and carriers.

54
Q

what facilitates the diffusion of water?

A

the presence of aquaprotins that form water permeable channels

55
Q

can water diffuse freely across membranes?

A

yes

56
Q

what is osmosis?

A

it is the net movement of water across a semi-permeable membrane

57
Q

what is a semi permeable membrane

A

permeable to solvent

impermeable to solute

58
Q

what is the osmotic pressure?

A

its the pressure rrquires to prevent the movementof water across the semi-permeable membrane.
its equal to the difference in the hydrostatic pressures of the 2 solutions

59
Q

what is the equation for osmotic pressure?

A 
P=nRT/V
P: osmotic pressure
n: number of particles
R: gas constant
T: absolute temperature
V: volume
60
Q

is the osmotic pressure proportion to the size, charge or conformation of molecule

A

no, its proportion to the number of particles in solution/ unit volume.

61
Q

what is osmolarity (Osm)?

A

its the total solute concentration of a solution
ex: 1 osmol= 1 mol of solute particle
1 mol glucose= 1 osmol
1 mol NaCl = 2 osmol

62
Q

is the osmotic pressure proportional to the osmolarity?

A

yes

63
Q

what can a small difference in # of solute affect the osmotic pressure?

A

it can lead to big differences in osmotic pressure.

64
Q

what is an isosmotic solution?

A

its a solution where the number of osmotically active particles = extracellular solution

65
Q

what is a hypoosmotic solution?

A

solution osmoticall active particles < extracellular

66
Q

what is a hyperosmotic solution?

A

solution osmoticall active particles > extracellular

67
Q

what is needed for particles to be effective in exerting a sustained osmotic pressure?

A

they must be non penetrating

68
Q

what is a hypertonic solution?

what happens to the cell?

A

if solution [non penetrating particles] > 300 mOsm (ICF)

Water will leave the cell causing it to shrink

69
Q

what is a hypotonic solution?

what happens to the cell?

A

if solution [non penetrating particles] < 300 mOsm (ICF)

water will move into the cell causing it to swell

70
Q

what is a isotonic solution?

what happens to the cell?

A

if solution [non penetrating particles] = 300 mOsm (ICF)

no net movement

71
Q

what is the capillary wall?

A

its a single layer of flattened endothelial cells and supporting basement membrane

72
Q

how is transport across capillary wall executed?

A
  1. diffusion through membrane filled channels and across cell membranes
  2. pino/exocytosis: endocytosis and vesicle formation on luminal side followed by exocytosis and vesicle release on interstitial side.
  3. bulkflow: flow of molecules subjected to a pressure difference causing redistribution of extracellular solutions
73
Q

what is filtration?

A

its bulk flow across a membrane that acts as a sieve withholding some particles.

PHGY209 (6 decks)

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