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Membrane Transport Flashcards

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1
Q

Does homeostasis = equilibrium?

A

No

  • ICF and ECF are in osmotic equilibrium
  • chemical and electrical are in disequilibrium
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2
Q

Osmosis:

A

simple diffusion of H2O through selectively permeable membrane

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3
Q

Which direction does osmosis flow?

A

from high [H2O] to low [H2O]

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4
Q

Normal osmolarity for ECF and ICF

A

300 mOsm

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5
Q

Osmolarity equilibrium:

A
  • osmolarity for ECF and ICF have to be equal

- if different, then H2O moves to fix it

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6
Q

Osmotic pressure:

A
  • amount of pressure needed to stop osmosis from happening
  • measured in mmHg
  • 1 mOsm/L = 19.3 mmHg
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7
Q

What monitors osmotic pressure in the body?

A

osmoreceptors in hypothalamus

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8
Q

Oncotic pressure:

A

osmotic pressure of plasma proteins

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9
Q

Isoosmotic can be

A

isotonic / hypotonic

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10
Q

Hyperosmotic can be

A

isotonic / hypotonic / hypertonic

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11
Q

Hypoosmotic can be

A

hypotonic

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12
Q

Tonicity:

A
  • describes volume change of a cell
  • no unit for it
  • affects steady state volume of cell
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13
Q

How is tonicity determined?

A

by # of nonpermeable ECF solutes

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14
Q

How does isotonic solution affect cell?

A

no osmosis, so no change in cell

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15
Q

How does hypotonic solution affect cell?

A

H2O moves into cell and causes swelling / lysis

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16
Q

How does hypertonic solution affect cell?

A

H2O moves out of cell and causes shriveling / crenulating

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17
Q

3 types of transport processes for molecules:

A
  • vesicular: bulk
  • passive: doesn’t need E
  • active: needs E
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18
Q

Vesicular transport:

A
  • bulk
  • moves substance across membrane w/ vesicle
  • membrane will alter to form vesicle
  • uses E by breaking down ATP/GTP
  • needs increase in intracellular [Ca2+]
  • ex: endocytosis, exocytosis, transcytosis
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19
Q

Endocytosis:

A
  • ex of vesicular transport
  • receptors regulate endocytosis
  • infolding of membrane to allow large molecule to enter the cell
  • phagocytosis: brings solids into cell (cell eating)
  • pinocytosis: brings liquid into cell (cell drinking)
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20
Q

Exocytosis:

A
  • ex of vesicular transport
  • fusion of vesicle w/ membrane to eject molecule from cell
  • needs Ca2+ and ATP
  • constitutive: product made and released immediately
  • regulated: product made and stored until signaled for release
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21
Q

Transcytosis:

A
  • ex of vesicular transport

- moves substance across cell

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22
Q

Passive transport:

A
  • doesn’t need E

- uses diffusion and osmosis

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23
Q

Diffusion:

A
  • movement of solutes from high [ ] to low [ ]

- driven by gradients until equilibrium is reached

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24
Q

Where does E for diffusion come from?

A

brownian motion: random thermal motion of atoms/molecule

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25
Chemical gradient is...
difference in [ ] that causes net movement from higher [ ] to lower [ ]
26
Electrical gradient is...
- difference in charge causes net movement | - like charges repel and unlike charges attract
27
What is the electrochemical gradient?
a combination of electrical and chemical gradient
28
Simple diffusion
- carrier independent - substance moves through membrane / channel - lipid soluble: moves between membrane - non-lipid soluble: moves through membrane via channels and pores
29
T/F: simple diffusion uses active transport
F, uses passive transport
30
Channel proteins:
- transmembrane protein w/ central H2O passage / pore - aquaporins: H2O channels used for osmosis - gated ion channels: allow channel to open (permeable) /close (nonpermeable)
31
Gated ion channels are classified by:
- selectivity to one or more ions - conductance - rectification
32
Selectivity of ions are based on:
- diameter of ion - shape of channel - electrical charge of channel
33
What does conductance measure?
measures how readily an ion moves through channel
34
Rectification is...
- the directional ease of movement through channel - inward rectifier: movement of ions into cell is easier than out - outward rectifier: movement of ions out of cell is easier than in
35
Types of gated channels:
- leak - voltage gated - ligand - mechanical - intracellular messenger
36
Leak gated channels:
- spontaneously open and close - mostly for H2O - high probability for opening
37
Voltage gated channels:
- responds to alterations in membrane potential | - change in charge polarity will cause it to open
38
Ligand gated channels:
- open by binding to signaling molecule | - ex: neurotransmitters, hormones, drugs
39
Mechanically gated channels:
- responds to physical conformation | - ex: stretch or pressure
40
Intracellular messenger gated:
- responds to change in intracellular signal | - ex: increase in intracellular Ca2+/cAMP
41
Facilitated diffusion:
channel/carrier dependent (for molecules too big/polar for pores)
42
Carrier proteins:
- transmembrane protein w/ binding sites for molecule to be moved - undergoes conformational change
43
Ability of carrier proteins to move molecules is affected by...
- competitive inhibition - non-competitive inhibitions - saturation: not as many carriers as molecules - specificity: carriers are specific to molecules
44
Competitive inhibtion:
something else attaches to binding site instead of substrate
45
Non-competitive inhibition:
something else attaches to different area on carrier and changes shape so substrate can't bind
46
Flick's law determines...
- net movement when there's no electrical or pressure difference - J=PA[C1-C2] or J= - DA[change in C/change in X]
47
Net flux is inversely proportionate to...
- molecular weight | - higher the molecular weight = lower speed
48
Net flux is directly proportionate to...
- temp: higher temp = higher brownian movement | - lipid solubility: higher solubility = higher diffusion rate b/c higher area for exchange
49
What is the impact of electrical charge:
- affect ions that diffuse through ion channels according to electrical/electrochemical differences - not accounted for by Flick's Law - rate affected by # of protein channels present in membrane
50
Nernst equation is used to determine...
- electrochemical equilibrium potential of any ion | - also the electrical difference across the membrane where ion will reach its dynamic equilibrium
51
Nernst equation:
- assumes free permeability of ion | - Eion=[-61.5/z]log([ioninside]/[ionoutside])
52
Diffusion trapping:
- alteration of solute after it's moved across membrane, which preserves gradient - allows for increased diffusion and increased rate of diffusion
53
Active transport:
- movement of substance across membrane against electrochemical gradient - needs a pump type of carrier protein
54
Primary active transport:
- all transported molecule are moving against the gradient | - needs pump powered by ATP
55
T/F: primary active transport get E indirectly from hydrolysis of ATP
F, gets E directly from hydrolysis of ATP
56
Secondary active transport:
- uses carrier that has binding sites for two molecules - one molecule is moved with the gradient and drives the transport (Na+) - the other is linked and moves against its gradient
57
Secondary active transport gets E ______ from hydrolysis of ATP
indirectly | - Na+ gets pumped back out of cell w/ Na+/K+ ATPase
58
Types of pumps and exchangers:
- uniporters - symporters - antiporter/exchanger
59
Uniporters:
- is a primary active transporter - bind and transport only one substance against gradient - ex: Ca2+ ATPase and SERCA
60
Symporters:
- binds 2+ different substances on same side of membrane - both move in same direction - secondary active transporter: one will move with its gradient and one will move against its gradient
61
Symporters are also called...
cotransporters
62
Antiporter/exchanger:
- binds 2 substances from different sides of membrane - can use both primary and secondary active transport - primary: both against gradient - secondary: one w/ gradient and one against
63
Antiporter/exchanger is also called...
countertransporters
64
Na+/K+ ATPase
- most common antiporter/exchanger - establishes RMP - primary active transport - 3 Na+ moves out and 2 K+ moves in - accounts for 1/3 of body E supply - decrease in activity = more positive membrane potential
65
Resting membrane potential (RMP):
- cellular proteins that are stuck inside cell usually have net negative charge - inhibits movement of cations (K+) out of cell - favors movement of anions (Cl-) out of cell
66
Excitable cells:
- nerve and muscle | - have lower RMP than non-excitable cells
67
Examples of tissues that are excitable:
- skeletal muscle - spinal nerves - cardiac ventricular myocytes - neurons of CNS - smooth muscle
68
Factors that contribute to RMP:
- difference in permeability of membrane to ions b/c of large conductance of K+ via leak channels - proteins trapped in cell and act as anions, which makes inside more negative - electrogenic pump (Na+/K+ ATPase) - equilibrium potential of all permeant ions (increase in permeant ions = increase in ability to force membrane)
69
Membrane potential is weighted average of _____
equilibrium of potential of all permeant ions | - Na+, K+, and Cl- are important
70
Weighting factor:
accounts for relative permeability of ion

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