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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?

A

No

25
Q

What membrane proteins can facilitated diffusion happen across?

A

Channel proteins
Carrier proteins

26
Q

What type of transport is facilitated diffusion?

A

PASSIVE TRANSPORT

27
Q

What type of membrane proteins carry out active transport?

A

Carrier proteins

28
Q

What are the 2 types of membrane channels/pores?

A

Gated or Non gated

29
Q

What type of protein channel/pore is conditionally open?

A

Gated ion channels

30
Q

Why type of channel is always open?

A

Non gated ion channels

31
Q

What are the 2 types of gated ion channel?

A

Ligand gated ion channel
Voltage gated ion channel

32
Q

What is the property to the centres of the channel proteins that allow hydrophilic molecules through?

A

The centres = hydrophilic

33
Q

What is bidirectional transport and what type of channel does this occur across?

A

Substances can move back and forth

Non gated pores (always open)

34
Q

Give an example of facilitated diffusion via a a gated ion channel (ligand)

A

Ligand gated ion channels at neuromuscular junctions

Ach binds to channel causing conformational change opening channel
Na+ can pass through depolarising membrane

35
Q

Where is the example of ATP sensitive K+ ion channels for facilitated diffusion applicable?

A

B cell of pancreas

36
Q

How does facilitated diffusion across the ATP sensitive K+ channel occur in the B cell?

A

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
Q

How does the Ca2+ voltage gated ion channel in the B cell work?

A

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
Q

What ion is the CFTR channel protein a channel for?

A

Cl-
Chloride ions

39
Q

How does the CFTR channel normally function to produce normal mucus?

A

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
Q

What condition does a mutated CFTR gene cause?

A

Cystic fibrosis

41
Q

What happens when the CFTR protein is mutated in cystic fibrosis?

A

Cl- not pout on cell surface
Water not drawn out so mucous membrane snot moistened
THICK STICKY MUCUS = HARD TO BREATHE

42
Q

What toxin does cholera produce?

A

Protein kinase A

43
Q

How does cholera cause diarrhoea?

A

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
Q

How do carrier proteins carry out facilitated diffusion?

A

Molecule binds causing conformational change (closes to outside of cell)
Molecule released causing conformational change (opening to inside of the cell)

45
Q

Why can only a limited number of substances by moved via facilitated diffusion through a carrier protein?

A

The speed of the conformational changes can not be changed

46
Q

What are the 3 types of carrier protein transporters?

A

Uniporter
Cotransporters :
- Symporters
- Antiporters

47
Q

What is a uniporte?

A

Carrier protein that only moves 1 substance at a time

48
Q

What is the definition of uniport?

A

Only 1 molecule transported at a timer per cycle down the concentration gradient (channel or carrier protein)

49
Q

What is co-transport?

A

2 or more substances transported on a membrane transporter per reaction cycle

50
Q

What is symport?

A

2 or more substance moving in the same direction

51
Q

What is antiport?

A

2 or more substances move in the opposite directions

52
Q

What type of transport is Na+/K+ ATPase?
What is its role?

A

Cotransport
Antiport

Maintains cell concs of Na+ and K+

53
Q

What type of transport is Na+/Ca2+ exchange?
What is its role?

A

Cotransport
Antiport

Expels Ca2+ from cell during cell recovery (repolarisation)

54
Q

What type of transport is SGLT (Na+/glucose transporter)?

A

Symport

55
Q

What type of transport is Na+/H+ exchanger?
What is its role?

A

Antiport

Alkaliniisation of cell since it removes H+

56
Q

What are the general roles of transport process in the body?

A

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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