Flashcards in M&R 2.1 - Role Of Membranes As Permeability Barriers Deck (20):
What is the definition of passive transport?
The passage of a molecule through a membrane without any assistance
What are the depending factors of passive transport? Describe the relationship between the factors and the rate
- Dependent on membrane permeability and concentration gradient
- The relationship is linear I.e. Increased rate of transport = increased concentration gradient
How are transport processes important? Give 6 reasons
- Maintain ionic processes and composition
- Maintain intracellular pH
- Regulate cell volume
- Maintain concentration of metabolic fuels etc
- Remove waste products and toxic substances
- Generate an ion gradient
How does a transporter pick up a substrate and transport it across the membrane?
'Ping pong transport'
- Uses a gated pore
- Binding of the molecule causes a conformational change
- Substrate is released on the other side
Give an example of a ligand gated ion channel
Nicotinic acetylcholine receptors
- Stimulation of receptor by nicotine causes release of acetylcholine
What is an ion channel?
A pore that selective to specific ions
What happens when ATP binds to ATP sensitive K+ channels? Why is this significant?
- Binding causes the channel to close
- Stops efflux of K+
- Significant when couple glucose metabolism to insulin release
What is a voltage gated ion channel?
An ion channel that recognises electrical potentials across a membrane
A change in the electrical field causes the protein to move therefore opening to ions
How do transport processes contribute to the control of transport of molecules in and out of the cell?
- Integration of specific proteins in the membrane
- Increases the permeability of what would be available from simple diffusion
Describe active transport
Allows the transport of ions/molecules against an unfavourable concentration/electrical gradient using the direct or indirect hydrolysis of ATP
Describe the energy changes when movement is dependent on a concentration gradient
- Passive = negative change in free energy therefore discharging gradient and releasing energy
- Active = positive change in free energy therefore charging gradient and using energy
Describe the energy changes when movement is dependent on membrane potential
- Passive = negative change in free energy so moving from positive to negative
- Active = positive change in free energy so moving from negative to positive
When would movement be membrane potential dependent rather than concentration gradient dependent?
When there is an equal distribution of concentrations on either side of the membrane
What are the external and internal Na+ concentrations and which way is the gradient?
- 145mM outside, 12mM inside
- Electrical and chemical gradient is INWARDS
What are the external and internal K+ concentrations and which way is the gradient?
- 4mM outside, 155mM inside
- Electrical and chemical gradient OUTWARDS
What are the external and internal Cl- concentrations and which way is the gradient?
- 123mM outside, 4.2mM inside
- Concentration gradient INWARDS
- Electrical gradient OUTWARDS
What are the external and internal Ca2+ concentrations and which way is the gradient?
- 1.5mM outside, 10-4mM inside
- Electrical and chemical gradient INWARDS
More than one type of ion or molecule maybe transported on a membrane transporter per reaction cycle
What are the two types of cotransporter? Describe them
- Symport = transport of 2 ions/molecules in one direction
- Antiport = transport of one substance inwards and one substance outwards in one cycle