Ion Channnels And Pores

Question 1

What is a semi permeable membrane?

Answer 1

A layer through which only allowed substances can pass

Question 2

What is Diffusion?

Answer 2

Movement from high to low concentration down the concentration gradient until they come to an equilibrium.

Each substance diffuses down its own concentration gradient, independent of the concentration gradient of the substances.

Pg 4

Question 3

What is passive transport dependant on?

Answer 3

Permeability and concentration gradient

• Rate of passive transport increases linearly with increasing concentration gradient

Question 4

What molecules are permeable to the lipid bilayer?

Answer 4

Hydrophobic molecules e.g. O2, CO2, N2, Benzene

- Small uncharged polar molecules e.g. H20, Urea, Glycerol

Question 5

What molecules aren’t permeable to the lipid bilayer?

Answer 5

• Large uncharged polar molecules e.g. glucose and sucrose
• Ions e.g. hydrogen, sodium, potassium, calcium, magnesium, chloride

Pg 7-8

Question 6

What are the important roles that transport processes have?

Answer 6

• Maintenance of ionic composition
• Maintenance of intracellular pH
• Regulation of cell volume
• Concentration of metabolic fuels and building blocks
• The extrusion of waste products of metabolism and toxic substances
• The generation of ion gradients necessary for the electrical excitability of nerve and muscle

Question 7

Facilitated diffusion - Ping Pong transport

Answer 7

• the substrate enters the membrane from one side, binding to the transport protein and the the transport protein changes information and the substrate moves to the other side of the membrane.

Pg 12

Question 8

Facilitated diffusion - ion channel

Answer 8

• channel opens due to stimulus and then ions move down their ionic gradients across the membrane.

Question 9

Facilitated diffusion - ligand gated ion channels, what are the two examples?

Answer 9

• binding of a ligand (ACH) to the channel and it opens and allows ions (sodium) to cross the membrane.

E.g. nicotinic acetylcholine receptor

Another example is an ATP sensitive potassium channel

• These are open at rest and allows the influx of the ion into the cell
• the channel is sensitive to energy status in the cell, so when ATP binds to the channel it prevents movement of potassium.

Pg 14

Question 10

Facilitated diffusion - ion channels - voltage gated ion channels

Answer 10

• Cells always have a membrane potentialIf there is a change in the membrane potential and it becomes depolarised
• This would be a driving force of the voltage sensors to move away from the positive charge and move upwards towards the outside
• This can be sufficient to cause a conformational change in the protein to allow the channel to open for ions to flow.

Pg 16

Question 11

What is active transport?

Answer 11

• Active transport allows the transport of ions or molecules against an unfavourable concentration and /or electrical gradient
• Energy is directly or indirectly from ATP hydrolysis

Question 12

How does water move across the membrane?

Answer 12

• Water move relatively readily across the hydrophobic
• Small and uncharged : despite the dipole created by the electron distribution
• Moves by diffusion through the dynamic bilayer environment
• Driven by osmotic gradient of solutes

Question 13

What is the typical inorganic ion concentration in the intracellular fluid?

Answer 13

Na+ : 12mM

K+ : 140mM

Cl- : 4mM

Ca2+: 10-7mM

Question 14

What is the Typical inorganic ion concentration in interstitial water?

Answer 14

Na+ : 145mM

K+ : 4.5mM

Cl-: 123mM

Ca2+ : 1.5mM

Question 15

What are the different types of tonicity?

Answer 15

Isotonic - equal solute, equal water

Hypotonic - less solute, more water

Hypertonic - more solute, less water

Question 16

What is the direction of osmosis determined by?

Answer 16

• by comparing total solute concentration.

The net movement of water
Hypotonic - Isotonic - Hypertonic

Question 17

What happens to Animal cells in Hypotonic and Hypertonic solutions ?

Answer 17

1. Hypotonicity - animal cell will gain water, swell and possibly burst (cytolysis)
2. Hypertonicity - animal cells will lose water, shrivel, shrink and lyse

Pg 34-36

Question 18

What is the importance of osmolality in osmosis?

Answer 18

• As water can move freely through the cell membrane and blood capillary wall there is no osmotic disequilibrium among different fluid compartments.
• So under normal conditions osmolality of plasma = interstitial fluid = intracellular fluid
• which is 280-310 mosm/kg or 280-310 mmol/L

Question 19

What is osmolality determined mainly by in Extracellular fluid?

Answer 19

Na+ and Cl- (80%)

Pg 37

Question 20

What does Osmole mean?

Answer 20

• The measure of solution’s ability to create osmotic pressure and thus affect the movement of water.
• Osmole is proportional to the number of osmotic particles in solution

Pg38 check

Question 21

What does osmolality mean?

Answer 21

• When the concentration of solution is expressed in osmoles per kilogram of water, the Osmolar concentration for a solution is referred to as its osmolality

Pg 38

Question 22

What is the definition of osmosis?

Answer 22

• The diffusion of water from a hypotonic solution to hypertonic solution
• across a semi-permeable membrane

Question 23

What is osmotic pressure?

Answer 23

• The pressure required to stop the flow of water.

Pg 40

Question 24

What are Aquaporins?

Answer 24

• water channels
• Integral membrane proteins: tetrameric (4 subunits)
• 13 or more isoforms
• not ion channels
• permits rapid water diffusion above the rate of passive diffusion through the bilayer
• Distinct isoform distribution suggest important and specific roles in different cells/organs

Question 25

How does water move through aquaporin channels?

Answer 25

• Depends on the solute concentration gradient.
• Hydrophilic pore
• Single file passage of water
• Positively charged residues in pore
  
  • preventing movement of charge ions e.g. protons
  • H+ ion gradient not disrupted, so pH is not disrupted