Membrane Permeability And Transport Flashcards
What is a semi-permeable membrane?
A layer through which only allowed substances can pass.
What is passive transport dependent on?
It is dependent on permeability and concentration gradient.
Equations for net rate of transport (J).
Given by Fick’s Law: J= P(C1 - C2). P= permeability coefficient, C1 and C2= concentration gradients on side 1 and 2.
What is passive transport?
No energy required, solute moves by diffusion down concentration radiant or electrical gradients.
What is active transport?
Cellular energy required, solute moves across the membrane against its concentration gradient.
Describe bulk flow of water in passive diffusion.
Entire surface of cell membrane, bi-directional flow, water crosses to reach solute equilibrium.
Describe bulk flow of water in pores.
Integral membrane proteins, bi-directional flow, reaches equilibrium rapidly.
What is a uniporter transport proteins?
Transports one substance in one direction. They can be passive or active transport.
What is a symport transport proteins?
Transports two different substances in the same direction, can be passive or active transport.
What is an antiport transport protein?
Transports two different substances in opposite directions, can be passive or active transport.
Uniport vs Co-transport.
Uniport- only one molecule transports at a time per cycle down concentration gradient, can be a channel or carrier protein (GLUT3). Co-transport- usually two (or more) substances transported on a membrane transporter per reaction cycle.
Examples of co-transport systems (antiport)
- Na+-K+-ATPase (1° active transport): maintains cellular concentrations of Na+ and K+. 2. Na+-Ca2+-exchange (2° active transport): inwards flow of sodium ions down a Na+ concentration gradient drives the outward flow of Ca2+ up its concentration gradient. 3. Na+/H+- exchanger (2° active transport): inward flow of Na+ down its concentration gradient leads to cell alkalinisation by removing H+.
Example of co-transport systems (symport).
Na+/glucose co-transport (small intestine and kidney): entry of 1 or 2 Na+ ions provides the energy for the entry of 1 glucose molecule against concentration gradient.
