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Diffusion Flashcards

1
Q

what is a fundamental physical feature of molecules of any substance?

A

continuous state of movement or vibration

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2
Q

collisions

A

in solutions, rapidly moving molecules undergo millions of collisions per second
collisions alter the direction of molecule movement

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3
Q

nature of molecules movement

A

random

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4
Q

where does energy for movement come from?

A

heat - warmer substances move more rapidly

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5
Q

simple diffusion

A

random thermal motion redistributes solute from higher concentrations to lower concentrations

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6
Q

flux

A

amount of material crossing a surface in a unit of time

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7
Q

what does flux depend on?

A

concentration of molecules

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8
Q

net flux

A

difference between 2 one way fluxes

determines net gain and net flux

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9
Q

diffusion equilibrium

A

2 one way fluxes are equal in magnitude and opposite in direction
net flux is 0
concentrations are equal
no further change in concentrations

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10
Q

3 types of fluxes

A

2 one way fluxes

net flux

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11
Q

factors affecting magnitude of net flux

A

temperature
mass of molecule
surface area
medium through which molecules are moving

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12
Q

diffusion and distance

A

diffusion times increase in proportion to the square of the distance

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13
Q

how can rate of diffusion be measured?

A

monitoring rate at which intracellular concentration approaches diffusion equilibrium with its concentration in extracellular fluid

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14
Q

Fick diffusion equation

A

J = PA(Co - Ci)

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15
Q

major factor affecting diffusion through membrane

A

hydrophobic interior of lipid bilayer slows it

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16
Q

polar and non-polar molecules diffusing through membranes

A

non-polar molecules diffuse rapidly across plasma membrane because they can diffuse in non-polar regions of the membrane occupied by fatty acid chains

polar molecules diffuse very slowly or not at all due to their low solubility in membrane lipids

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17
Q

different cells and permeabilities

A

different cells have different permeabilities to ions, but nonpolar substances have similar permeabilities across all cells

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18
Q

artificial lipid bilayers

A

containing no proteins - impermeable to polar molecules

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19
Q

ion channels

A

allow ions to diffuse across the membrane
hole in middle provides channel
several proteins may aggregate
small size of channel prevents larger molecules from entering

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20
Q

selectivity of ion channels

A

selectivity based on channel diameter, charged and polar surfaces of the protein subunits and the number of water molecules associated with ions

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21
Q

membrane potential

A

separation of electrical charge across plasma membranes (millivolts)

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22
Q

effect of electrical charge on attraction of ions

A

if inside of cell has a net negative charge compared to the outside, there’s an electrical charge attracting positive ions into the cell and repelling negative ions

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23
Q

electrochemical gradient

A

concentration difference and electrical difference

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24
Q

opposition of conc difference and electrical difference

A

could be opposed - net movement of ions depends on magnitudes of forces

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25
channel gating
process of opening and closing ion channels
26
3 factors affecting channel protein conformation
ligand gated channels voltage gated channels mechanically gated channels
27
ligand gated channels
binding of specific molecules to channel proteins directly or indirectly producing an allosteric or covalent change in the shape ligands often chemical messengers
28
voltage gated channels
changes in membrane potentials causes movement of certain charged regions on a channel protein, altering its shape
29
mechanically gated channels
physically deforming/stretching the membrane affects the conformation
30
molecules like amino acids and glucose
too polar to diffuse through lipid bilayer and too large to diffuse through channels
31
transporters
integral membrane proteins mediate the passage of molecules and the non diffusional movements of ions
32
mediated transport
movement of substances through a membrane by transporters - depends on conformational changes in these transporteeres
33
process of mediated transport
transported solute binds to a specific site on a transporter portion of transporter changes shape, exposing the same binding site to the solution on the opposite side of the membrane substance dissociates from transporter binding site
34
similarities in transporters and ion channels
membrane proteins and specificity
35
differences in transporters and ion channels
number of molecules or ions crossing the membrane ion channels move more because they can remain open to support continuous flow without a change in conformation transporters move less because they have to change their conformation for each molecule
36
3 factors affecting magnitude of solute flux through a mediated-transport system
saturation of transporter binding sites - solute concentration and affinity of transporters for the solute number of transporters rate of conformational change in transport protein
37
diffusion and energy
simple and facilitated diffusion aren't directly coupled to energy derived from metabolism, so they can't produce a net flux of solute from a lower to a higher concentration
38
intra and extracellular concentration of glucose
intracellular concentration is lower than the extracellular concentration because it's metabolised to glucose-6-P very quickly
39
GLUT transporters
each GLUT is coded for by a different genes, and the genes are expressed in different types of cells
40
insulin and GLUTs
insulin affects the type of transporter expressed in skeletal and cardiac muscle and adipose tissue increases recruitment of transporters from intracellular vesicles to plasma membrane
41
type 1 diabetes mellitus
insulin is not available muscle and adipose cells can't transport glucose into cells efficiently accumulation of glucose in ECF
42
active transport
uses energy to move a transport a substance uphill across a membrane requires transporter - pumps
43
2 means of coupling energy to transporters
primary active transport - direct use of ATP | secondary active transport - electrochemical gradient across a membrane drives process
44
primary active transport
hydrolysis of ATP by a transporter transporter is an enzyme called ATPase that catalyses the breakdown of ATP and phosphorylates itself changes the conformation of the transporter and affinity of the solute binding site
45
Na+/K+ -ATPase pump
moves sodium ions from the ICF to ECF potassium ions from ECF to ICF against concentration gradients transporter has an associated molecule of ATP binds 3 sodium ions at high affinity sites on the ICF surface of protein 2 binding sites exist for potassium but they're in low affinity state binding of sodium activates inherent ATPase activity of transporter protein causing phosphorylation of cystolic surface, releasing 1 ADP conformational change exposes sodium to ECF and reducing affinity of binding sites for sodium increased affinity of binding sites for potassium - binding results in dephosphorylation to original conformation
46
major primary active transport proteins
Na+/K+ -ATPase Ca2+ -ATPase H+ -ATPase H+/K+ -ATPase
47
Ca2+ cytosol concentration
greater in ECF than ICF
48
secondary active transport
movement of an ion down its electrochemical gradient is coupled to the transport of another molecule
49
transporters mediating secondary active transports
have 2 binding sites, one for an ion (typically Na+) and one for the cotransported molecule
50
secondary active transport process
other solute being cotransported must move against its concentration gradient high affinity binding sites for Na+ on extracellular surface of transporter binding of Na+ increases affinity for other molecule conformational change exposes both binding site to intracellular side of membrane Na+ moves into ICF by simple diffusion affinity of solute binding site decreases, releasing it into ICF
51
primary and secondary transport
if production of ATP is inhibited, primary transport of Na+ can't occur, which stops secondary transport
52
cotransport
movement of solute into the cell
53
countertransport
movement of solute out of cell
54
different types of carriers
uniport - single substance symport - 2 substances in same direction antiport - 2 substances in opposite direction
55
GLUT4
in skeletal and adipose tissues
56
GLUT1
present in many cells, including brain, where it transports glucose across blood-brain barrier via facilitative diffusion
57
GLUT1 deficiency syndrome
very rare mutations in gene encoding GLUT1 less functional GLUT1 - reduces amount of glucose available to brain cell symptoms: seizures, microcephaly, developmental delay
58
ATP7B protein
Cu2+ -ATPase present in liver that transports copper into bile
59
Wilson's disease
rare disorder mutations in ATP7B gene deposition of copper in liver and other tissue symptoms: liver disease, tremor, Kayser-Fleischer rings in eyes
60
SGLT1
transports glucose and galactose from the intestinal lumen into blood and sodium
61
glucose-galactose malabsorption
very rare mutations in SGLT1 less functional SGLT1 - malabsorption symptoms: chronic severe diarrhoea, dehydration, failure to thrive
62
communication between cells
signalling molecules e.g. hormones, neurotransmitters and growth factors
63
receptor types
intracellular - steroid hormones | cell-surface - peptide hormones
64
secondary messengers
cAMP, IP3, DAG, Ca2+ - amplification
65
example of ligand-gated ion channels
cholinergic nicotinic receptors
66
G protein-coupled receptors
alpha and beta adrenoceptors protein phosphorylation
67
enzyme-linked receptors
insulin receptors protein and receptor phosphorylation
68
intracellular receptors
steroid receptors protein phosphorylation and altered gene expression
69
G proteins
integral part of G-protein coupled receptors on cell membrane surfaces
70
cholera
vibrio cholerae bacteria produce cholera toxin crosses cell membrane modifies subunit of G protein increased adenylate cyclase activity increased second messenger (cAMP) levels stimulates transporters in cell membrane of intestinal cells secretion of ions and water into gut
71
cystic fibrosis
1 in 25 carriers | mutation in CFTR protein
72
CFTR protein
chloride channel found in many tissues, e.g. pancreas, lungs, skin abnormal function -> sticky, viscous mucus
73
drugs targeting membrane transporters
cardiac glycosides proton pump inhibitors loop diuretics thiazide diuretics
74
cardiac glycosides
digoxin | act on Na+/K+ -ATPase in cardiac muscle cells
75
proton pump inhibitors
omeprazole | H+/K+ -ATPase in gastric parietal cells
76
loop diuretics
furosemide | NKCC2 cotransporter in thick ascending limb of loop of Henle
77
thiazide diuretics
Bendroflumethiazide | act on NCC cotransporter in distal tubule

Membranes (2 decks)

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