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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
what states do channels normally exist in?
they alter conformation and can either be in an open of closed conformation
26
what are the 3 ways channels can be gated?
- ligand gated - voltage gated - mechanically gated
27
what factors influence the amount of ions flowing through voltage gated channels? give examples of such channels.
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)
28
what are some of the fundamental characteristics of mediated transport systems?
- they are specific - they can be saturated, at that point carriers reach vMax - competition may occur betweens sructurally similar molecules for the binding site
29
what factors determine the magnitude of mediated transport systems?
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.)
30
what does facilitated diffusion involve?
the presence of a carrier molecule which will enable a solute to penetrate more readily than it would in simple diffusion
31
how does facilitated diffusion function?
- solute binds to carrier - carrier undergoes conformation changes - solute is delivered to other side of membrane - reverts to original conformation
32
what are the key properties of facilitated diffusion?
it is carrier mediated passive net flux is from [high] to [low]
33
what may cause an increase in number and or affinity of transporters in certain membranes? give an example
hormones | Glut 4 transports glucose in muscles increased by insulin.
34
what are the key properties of active transport
- transporter mediated - requires supply of energy (hydrolysis of ATP) - susceptible to metabolic inhibitors - transport against gradient
35
what is primary active transport?
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
what happens in the sodium-potassium ATPase?
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
what is the function of the Ca2+ ATPase in the body?
it enables to keep levels of intracellular Ca2+ low
38
what is the function of H+-ATPase in the body?
it allows to maintain a low lysosomal pH
39
what is the function of the H+/K+-ATPase?
allows for acidification of the stomach which is useful in digestion
40
what is secondary active transport?
its the movement down the electrochemical gradient that is coupled with the transport of another molecule (glucose or AA)
41
explain how secondary active transport functions?
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
what is cotransport?
when the solute molecule moves in the same direction as sodium
43
what is counter transport?
molecules move in opposite directions of each other.
44
give examples of counter transport?
Na/H+ exchanger Na/Ca2+ exchanger Cl-/HCO3- exchanger
45
give examples of cotransport?
Na+-glucose cotransporter | Na-Amino Acid cotransporter
46
what are active transport mechanisms that involve the participation of the cell membrane itself?
endocytosis | exocytosis
47
what is endocytosis?
the cell membrane invaginate forming a channel, which pinches off to form a vesicle
48
what is exocytosis?
an intracellular vesicle fuses with the cell membrane and its contents are released into the ECF
49
What is pinocytosis?
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
what is phagocytosis?
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
what are the 2 types of receptor mediated endocytosis?
- clathrin dependent | - potocytosis
52
what is clathrin dependent receptor mediated endocytosis
it involves the pinching off of “clathrin coated vesicles” that fuse with endosomes where vesicle contents are sorted
53
what is potocytosis?
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
what facilitates the diffusion of water?
the presence of aquaprotins that form water permeable channels
55
can water diffuse freely across membranes?
yes
56
what is osmosis?
it is the net movement of water across a semi-permeable membrane
57
what is a semi permeable membrane
permeable to solvent | impermeable to solute
58
what is the osmotic pressure?
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
what is the equation for osmotic pressure?
``` P=nRT/V P: osmotic pressure n: number of particles R: gas constant T: absolute temperature V: volume ```
60
is the osmotic pressure proportion to the size, charge or conformation of molecule
no, its proportion to the number of particles in solution/ unit volume.
61
what is osmolarity (Osm)?
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
is the osmotic pressure proportional to the osmolarity?
yes
63
what can a small difference in # of solute affect the osmotic pressure?
it can lead to big differences in osmotic pressure.
64
what is an isosmotic solution?
its a solution where the number of osmotically active particles = extracellular solution
65
what is a hypoosmotic solution?
solution osmoticall active particles < extracellular
66
what is a hyperosmotic solution?
solution osmoticall active particles > extracellular
67
what is needed for particles to be effective in exerting a sustained osmotic pressure?
they must be non penetrating
68
what is a hypertonic solution? | what happens to the cell?
if solution [non penetrating particles] > 300 mOsm (ICF) | Water will leave the cell causing it to shrink
69
what is a hypotonic solution? | what happens to the cell?
if solution [non penetrating particles] < 300 mOsm (ICF) | water will move into the cell causing it to swell
70
what is a isotonic solution? | what happens to the cell?
if solution [non penetrating particles] = 300 mOsm (ICF) | no net movement
71
what is the capillary wall?
its a single layer of flattened endothelial cells and supporting basement membrane
72
how is transport across capillary wall executed?
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
what is filtration?
its bulk flow across a membrane that acts as a sieve withholding some particles.

PHGY209 (6 decks)

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