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Semester 2 MR > W2-Membrane Permeability > Flashcards

W2-Membrane Permeability Flashcards

(57 cards)

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1
Q

What are the two types of passive transport?

A

Simple diffusion

Facilitated diffusion

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2
Q

What does a black film form?

A

When painted with phospholipids, a lipid bilayer form and turns the membrane black

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3
Q

Which molecules cannot pass through the bilayer?

A

Large, uncharged, polar molecules- glucose and sucrose.

Ions- Na+, Mg2+, Ca2+, K+, Cl-, H+, HCO3-

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4
Q

What is passive transport dependent on?

A

Permeability and concentration gradient

Passive transport increases linearly with increasing concentration

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5
Q

Name 3 things transport proteins are important for.

A

Maintenance of ionic composition/ ion gradients for electrical excitability
Maintenance of cellular pH
Control of cell shrinkage/swelling (cell volume)

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6
Q

What are the two models of membrane transport proteins?

A

Ping-pong transport- gated pore

Ion channel

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7
Q

What is quicker- gated pore or ion channel?

A

Ion channel- they are selective though

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8
Q

Name examples of LGIC that effect Na+ flow and K+ flow?

A

Na+ is effected by nicotinic ACh R
K+ flow by KATP channels

Both are by facilitated diffusion

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9
Q

Give an example of a LGIC that binds ACh.

A

Nicotinic ACh R- ACh binds leading to an influx of Na+ into the cell

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10
Q

Explain how VGNa+ channels work

A

Voltage sensor domain recognises membrane depol/ change in excitability so Na+ can enter cell.
(Usually -ve intside and +ve outside a cell)

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11
Q

Are all transport proteins saturable?

A

Yes they all show Michaelis Menton kinetics- Km and Vmax (define these)- all have max rate of activity

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12
Q

Do membrane proteins increase the permeability of membranes?

A

Yes greatly, allow larger, charged molecules through

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13
Q

Does active transport require energy? Why?

A

Yes, it requires energy to work against a c.g. or electrical gradient

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14
Q

What two things does active transport depend on?

A

Concentration ratio IE. Against c.g

Membrane potential IE. Against electrical gradient

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15
Q

What is the Na+ conc inside and outside the cell?

A 
EC= 145mM
IC= 12 mM

HIGHER EC CONC FOR NA+

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16
Q

What is the EC and IC conc of K+?

A

EC= 4mM
IC=155mM

HIGHER IC CONC FOR K+

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17
Q

What is the IC and EC concs of Cl-?

A 
EC= 123mM
IC= 4.2mM

HIGHER EC CONC FOR CL-

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18
Q

What is the EC and IC concs of Ca2+?

A

EC=1.5mM
IC=0.1uM

GREATER OUTSIDE- Ca2+ conc kept very low in cells to remove toxic effects of CaP forming

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19
Q

What does the plasma membrane Ca2+ATPase (PMCA) do?

A

Example of primary active transporter
Binds ATP and hydrolyses it to pump Ca2+ AGAINST c.g
Requires Mg2+ for ATP hydrolysis

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20
Q

What happens when active transport is in the reverse mode?

A

ATP synthetase- gradient generated by H+ extrusion from MT matrix used to generate ATP from ADP and Pi.

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21
Q

Define co-transport. Name the two types

A

When more than one molecule is being transported at the same time through a membrane proteins per cycle.

Symporter and antiporter

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22
Q

What defines a transporter as a pump?

A

If it uses ATP for energy or not

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23
Q

Explain how the Na+/K+ ATPase (Na+ pump) works.
What type of co-transport is used?
What is its function?

Study These Flashcards
A

3NA+ are REMOVED from the cell in exchange for 2K+ and the hydrolysis of ATP (overall 1 removed)

Antiporter- 25% BMR used for this - ACTIVE TRANSPORT

Functions to maintain resting membrane potentials

24
Q

Why is the Na+/K+ ATPase also called a P-type pump?

Study These Flashcards
A

ATP phosphorylates aspartate

Phosphoenzyme intermediate produced

25
Name the two subunits of the Na+/K+ ATPase and state what they do
Alpha- Na+, K+, ATP and ouabain binding sites | Beta- glycoprotein, directs pump to surface (would otherwise stay in ER)
26
What type of molecules can freely diffuse through a lipid bilayer? Name them
Hydrophobic molecules. 02, CO2, N2, benzene. | Small, uncharged polar molecules- H20, glycerol, urea
27
How does the Na+/K+ ATPase contribute to the RMP?
It generates the high conc of K+ IC- THE GRADIENT IS SET (Contributes only -5-10mV) K+ diffusion through generates the rest of the -7-mV
28
Explain how KATP channels work
Facilitated diffusion of K+ ions: KATP channel is normally open allowing K+ to flow out of the cell If ATP conc in cytoplasm high, it binds channel causing closure so K+ flow stops. E.g. Couples glucose metabolism to insulin release
29
What are the 4 roles for NA+K+ATPase in secondary active transport?
Control of pH Regulates cell volume and Ca2+ conc Absorption o Na+ in epithelia Nutrient uptake eg. Glucose from SI
31
Name the primary and secondary active transporters for Ca2+ and explain how they work.
Primary- Ca2+-Mg2+-ATPase removes Ca2+ from cell (High affinity, low capacity) Secondary- NCX- Ca2+ out, 3Na+ in (antiporter) (Low affinity, high capacity)
31
Name the three types of co-transport systems
Na+-glucose NCX NHE
32
Explain how the NHE works
Secondary active transport: Relies on Na+/K+ ATPase to set gradient Na+ enters cell and H+ is removed (antiporter) cell alkilistation
33
Explain how the Na+-glucose transporter works.
Secondary active transport: Na+/K+ATPase sets gradient Entry of Na+ through exchanger provides energy for glucose to enter (symporter)
34
In CF, what are the implications of the defective CFTR?
Cl- does not leave cell Na+2Cl-K+ transporter allows Cl- into cell usually Na+K+ATPase restores balance IC, K+ leaves via K+ channels But Na+ does not follow Cl- out of cell Water does not follow, thickened mucus occurs
35
Where does energy for active transport come from?
``` ATP hydrolysis (-31kJ mol-1) either directly or indirectly Some cells its 30-50% energy expenditure ```
35
What role does CFTR play during diarrhoea?
Allows Cl- to leave cell, water follows in gut epithelia Cholera toxin up regulates CFTR Excess water leaves leading diarrhoea
36
Where in a cell can Ca2+ be stored at high concentrations?
SR
37
Which 4 proteins contribute to resting Ca2+ IC conc?
PMCA SERCA (both primary transporters) NCX MT Ca2+ uniports (both secondary transporters)
38
What does PMCA (Ca2+ATPase) do?
Removes 1Ca2+ in exchange for 1H+ High affinity, low capacity Hydrolyses ATP
39
What does SERCA do?
Pumps Ca2+ into SR Exchanges 1Ca2+ for 1H+ High affinity, low capacity
40
What do MT uniports do?
Put Ca2+ into MT | Operate at high concs to buffer potentially toxic Ca2+
41
What does electrogenic mean?
The current flows in the direction of the gradient
42
Is the activity of NCX membrane potential dependent?
Yes Depolarised membrane potential reverses mode of operation Leads to high IC Ca2+ conc which can be toxic eg. In ischemia Contributes to cardiac a.p.
43
Name 2 acid extruders and state how they work
NHE NBC- exchanges H+ and Cl- for Na+ and HCO3- into the cell (Removing H+ increases alkalinity of cell) ELECTRONEUTRAL Regulate cell volume also and activated by GFs
44
Name the base extruders and describe how it works.
AE- HCO3- leaves in exchange with Cl | HCO3- makes the cell alkaline but there is NO charge difference
45
What does amiloride inhibit?
NHE
46
Do bicarbonate transporters regulate cell volume?
Yes- movement of Na+ or Cl- affects movement of water
47
Do all cells express Na+/K+ATPases?
Yes
48
How is IC pH regulated?
Held at set point | Drift away corrected by increased activity of either Na+-H+ or Cl--HCO3- exchangers
49
Describe how a cell may resist swelling
Extrude ions e.g. K+ and Cl- through respective channels so water follows NO CHANGE IN m.p
50
Explain how a cell may resist shrinking.
Influx ions- eg. Na+ and Ca2+ through channel so that water follows
51
Explain how bicarbonate is reabsorbed in the PCT of kidney. Explain how you can intervene in hypertension
``` Broken down into H20 and CO2 via carbonic anhydrase Converted back in cell to H2CO3 Broken down to H+- goes to lumen via NHE And HCO3- which goes into blood via AE (Na+ via NHE and sodium pump into blood) ```
52
Where do loop diuretics work?
Thick ascending limb-NKCC2 | Blocks Na+ reabsorption so water lost in urine
53
Where do thiazides work?
DCT- NCCT- block Na+ reabsorption and hence water too
54
Where does amiloride work?
DCT- blocks ENaC so blocks Na+ reabsorption and hence water
55
Where does spironolactone act?
Cortical collecting duct Mineralocorticoid R antag Treats overproduction of aldosterone leading to too many aquaporins
56
Why is all Na+ and HCO3- usually reabsorbed?
To retain base for pH buffers

Semester 2 MR (4 decks)

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