Flashcards in Membrane Transport Deck (23):
What is membrane transport?
The transport of molecules across biological membranes.
Membranes are rigid - true or false?
False, membranes are very wobbly
Why is membrane transport important?
It protects metabolic reactions within the cell from the environment.
Communication and exchange of material between the cell and the environment.
Membranes are walls with gates. What are these gates and what do they do?
Gates are transport proteins.
Transport proteins allow and control passage in and out of the cell.
They allow for controlled interaction between the cell and the environment.
Membranes are very hydrophobic and only allow for the passage of other hydrophobic molecules. So why does water get through?
Water molecules are so small that some inevitably get through.
What do transport proteins do to allow larger molecules to pass?
Create a hydrophilic passage
Create a filter
Provide possibility for energy coupling
Provide possibility for regulation
Facilitate diffusion by generating a hydrophilic pore
What is facilitated diffusion?
Transport proteins create a hydrophilic pore that hydrophilic molecules can diffuse through.
What are the two types of force that drive the movement of molecules across membranes.
Chemical gradient (concentration gradient)
Electrical gradient (charge gradient)
What is the electrochemical gradient?
The net driving force for the movement of a molecule resulting from the combination of the chemical and electrical gradient.
What does active transport do?
Moves substances against the electrochemical gradient and requires the input of energy.
What does passive transport do?
Moves substances down the electrochemical gradient and does not require an input of energy.
What are the transport proteins for active transport?
What are the transport proteins for passive transport?
What do pumps do?
Establish an electrochemical gradient which can be used to drive active transport of other molecules
What is energy coupling?
ATPases: transport is coupled to the hydrolysis of ATP
What is conformational change?
Same amino acid, different shape.
Energetically most favourable change
What do co-transport systems do?
Couple the downward movement of one ion (driver) with the uphill movement of another solute (substrate).
What is symport?
Driver ion and substrate move in same direction (piggyback principle)
What is antiport?
Driver ion and substrate move in opposite direction (revolving door principle)
Protein pushes "door" allowing sugar through in the opposite direction.
What does a channel do?
A channel provides an aqueous pore for passage of ions
What does a carrier do?
A carrier undergoes a conformational change that exposes ion binding sites to different sides of the membrane.
What is a selective ion channel?
Select which ions pass through
Some ion channels have a 100 fold higher permeability for K+ than for Na+