M&R 2 - Permeability Barriers Flashcards
What is the relationship between the rate of passive transport and increasing concentration gradient.
The rate of passive transport increases linearly with increasing conc gradient.
How do non polar molecules travel across bilayers?
They diffuse across the hydrophobic domain
How does water travel across the membrane?
Water diffuses passively down the osmotic gradient
In some cells the moment of water is also facilities by aquaporins
Why is the movement of ions and hydrophilic molecules important?
Maintains intracellular pH
Maintains ionic composition
Regulates cell volume
What are the two thermodynamically viable mechanisms of facilitated diffusion?
Carrier molecules (ping pong) Protein channels (pores)
What is the difference between active and passive transport?
Active needs energy passive is spontaneous.
What are the three ‘currencies’ of free energy used for active transport?
ATP
electron transport
Light
What is a co-transporter?
This is when the transport of one substance is linked to concentration of another.
What is a uni port?
One solute molecule from one side -> the other side
What is co transport in the same direction called? And what is different?
Same - symport
Different - anti port
What are the features of a Na+/K+ ATPase pump?
Plasma membrane pump that uses ATP to pump 3 sodium out and 2 potassium in.
Necessary for electrical excitability
Drives secondary active transport that leads to -
The control of pH, regulation of cell volume etc
Why do calcium levels need to be controlled in cells?
Ca2+ is toxic to cells. (See MoD)
What are the features of the PMCA pump?
Expels Ca2+ from the cell in exchange for H+ (anti port)
Uses ATP.
It has a high affinity for calcium but a low capacity
What are the features of the SERCA pump?
Accumulates Ca2+ in the ER in exchange for H+ (antiport)
Uses ATP, also has a high affinity low capacity
What are the features of the NCX pump?
Uses the Na+ gradient set il by the sodium potassium pump
(Secondary active transport)
Removes most Ca2+
Electrogenic - as current flows in direction of sodium gradient