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Y1 - ICPP > Lecture 3 - Membrane Permeability And Transport Of Ions And Small Molecules > Flashcards

Lecture 3 - Membrane Permeability And Transport Of Ions And Small Molecules Flashcards

1
Q

What is a semi-permeable membrane?

A

A layer through which only ALLOWED substances can pass through

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2
Q

Normally, what is the charge distribution either side of a membrane?

A

Outside = POSITIVE
Inside = NEGATIVE

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3
Q

What is meant by solute equilibrium?

A

When the concentration of solute is equal on either side of the membrane

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4
Q

What is the main phospholipid in erythrocytes?

A

Phosphatidylserine

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5
Q

What are the 4 classes of molecules that may try and cross the phospholipid bilayer?

A

Hydrophobic molecules
Small uncharged polar molecules
Large uncharged polar molecules
Ions

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6
Q

What is the phospholipid bilayer permeable to and describe their relative permeability (passive diffusion)?

A

Hydrophobic molecules = very high permeability
Small uncharged polar molecules (high permeability)

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7
Q

What molecules is the phospholipid bilayer not permeable to and what is their relative permeability?

A

Large uncharged polar molecules = low permeability
Ions = extremely low permeability

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8
Q

Give some examples of hydrophobic molecules:
Why do they have a very high permeability?

A

Oxygen
Carbon dioxide
Nitrogen
VERY SMALL so can pass through small gaps

Benzene

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9
Q

Give some examples of small uncharged polar molecules

A

H2O
Urea
Glycerol

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10
Q

Give some examples of large uncharged polar molecules:

A

Glucose
Sucrose
(Sugars and large amino acids)

NORMALLY REJECTED

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11
Q

Give some examples of ions:

A

Na+
K+
Ca2+
Mg2+
Cl-
HCO3-
H+
(NORMALLY REJECTED)

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12
Q

What is passive transport?

A

Transport that does not require energy to take place, particles flow in direction of concentration gradient

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13
Q

What 2 factors does rate of passive transport depend on?

A

Permeability of molecule
Concentration gradient

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14
Q

Using Ficks law, how does rate of passive transport change as concentration gradient increases?

A

Increases linearly

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15
Q

What is facilitated diffusion?

A

Where a membranes protein is required for transport across the membrane to occur

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16
Q

What sort of relationship exists between the concentration of highly permeable substances and the rate of simple diffusion?

A

Directly proportional

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17
Q

What limits the rate of facilitated diffusion when concentration of substance is increased?

A

Number of available transporter proteins

After certain conc, Vmax is reached since transporters get fully saturated

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18
Q

What are the methods water uses in order to enter cells?

A

Passive diffusion
AQUAPORINS

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19
Q

How does water travel during passive transport into a cell?

A

Uses entire surface of cell membrane
Bidirectional flow
Water crosses to reach solute equilibrium

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20
Q

What are aquaporins?

A

Integral membrane proteins with aqueous centre

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21
Q

How does water enter into cells via aquaporins?

A

Rapid movement so equilibrium reached very quickly

Bidirectional flow

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22
Q

What is passive transport?

A

Solute moves by diffusion down concentration or electrochemical gradients using NO ENERGY

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23
Q

What is active transport?

A

Solute moves across the membrane against its concentration gradient using the energy from the cell

24
Q

Does simple diffusion use membrane proteins?

25
What membrane proteins can facilitated diffusion happen across?
Channel proteins Carrier proteins
26
What type of transport is facilitated diffusion?
PASSIVE TRANSPORT
27
What type of membrane proteins carry out active transport?
Carrier proteins
28
What are the 2 types of membrane channels/pores?
Gated or Non gated
29
What type of protein channel/pore is conditionally open?
Gated ion channels
30
Why type of channel is always open?
Non gated ion channels
31
What are the 2 types of gated ion channel?
Ligand gated ion channel Voltage gated ion channel
32
What is the property to the centres of the channel proteins that allow hydrophilic molecules through?
The centres = hydrophilic
33
What is bidirectional transport and what type of channel does this occur across?
Substances can move back and forth Non gated pores (always open)
34
Give an example of facilitated diffusion via a a gated ion channel (ligand)
Ligand gated ion channels at neuromuscular junctions Ach binds to channel causing conformational change opening channel Na+ can pass through depolarising membrane
35
Where is the example of ATP sensitive K+ ion channels for facilitated diffusion applicable?
B cell of pancreas
36
How does facilitated diffusion across the ATP sensitive K+ channel occur in the B cell?
Influx of ATP in cell ATP binds to the ATP sensitive K+ ligand gated ion channel Conformational change closes the channel K+ accumulates in cell since it cant leave Causes depolarisation (more +)
37
How does the Ca2+ voltage gated ion channel in the B cell work?
Depolarisation of cell as a result of build up of K+ makes inside of cell more positive This causes conformational change opening the channel causing Ca2+ influx
38
What ion is the CFTR channel protein a channel for?
Cl- Chloride ions
39
How does the CFTR channel normally function to produce normal mucus?
Chloride ions transported onto apical membrane of cell via CFTR Chloride draws 5 water molecules out of cell onto apical surface Produces correct consistency mucus
40
What condition does a mutated CFTR gene cause?
Cystic fibrosis
41
What happens when the CFTR protein is mutated in cystic fibrosis?
Cl- not pout on cell surface Water not drawn out so mucous membrane snot moistened THICK STICKY MUCUS = HARD TO BREATHE
42
What toxin does cholera produce?
Protein kinase A
43
How does cholera cause diarrhoea?
Toxin protein kinase A Phosphorylates CFTR causing it to always be open Cl- constantly moved through CFTR into lumen of gut, lots of water constantly drawn into gut = diarrhoea
44
How do carrier proteins carry out facilitated diffusion?
Molecule binds causing conformational change (closes to outside of cell) Molecule released causing conformational change (opening to inside of the cell)
45
Why can only a limited number of substances by moved via facilitated diffusion through a carrier protein?
The speed of the conformational changes can not be changed
46
What are the 3 types of carrier protein transporters?
Uniporter Cotransporters : - Symporters - Antiporters
47
What is a uniporte?
Carrier protein that only moves 1 substance at a time
48
What is the definition of uniport?
Only 1 molecule transported at a timer per cycle down the concentration gradient (channel or carrier protein)
49
What is co-transport?
2 or more substances transported on a membrane transporter per reaction cycle
50
What is symport?
2 or more substance moving in the same direction
51
What is antiport?
2 or more substances move in the opposite directions
52
What type of transport is Na+/K+ ATPase? What is its role?
Cotransport Antiport Maintains cell concs of Na+ and K+
53
What type of transport is Na+/Ca2+ exchange? What is its role?
Cotransport Antiport Expels Ca2+ from cell during cell recovery (repolarisation)
54
What type of transport is SGLT (Na+/glucose transporter)?
Symport
55
What type of transport is Na+/H+ exchanger? What is its role?
Antiport Alkaliniisation of cell since it removes H+
56
What are the general roles of transport process in the body?
Maintain ionic comp Maintain intracellular pH Regulates cell vol COnc of fuels Expulsion of waste and toxic substance Generating ion gradients for muscles and nerves

Y1 - ICPP (23 decks)

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