Week 8 Pt I - Membrane Transport Part I Flashcards
What is a major property of a membrane?
Barrier (semi-permeable)
What passes easily through the membrane?
Small non polar molecules
What happens if molecules are charged?
They cannot pass through the hydrophobic part of the membrane e.g. Na+, K+ ions
Why is a protein required?
Has binding side for a molecule that can change between different sides of membrane
On different sides Of membrane it must have different affinities
On the side of membrane where the solute is a high concentration
Low affinity
Who won the Nobel Prize for work on ion channels or channels that move small molecules
Peter Agre
Roderick MacKinnon
What did Peter Agre’s group look at?
Water transport
Worked with cells with high flux of water (kidney cells and red blood cells)
Purified protein and put it in egg cells of toads
Put the cells into hypertonic and hypotonic solution
Low concentration of solute: explode
High concentration of solute: shrivel up
Why is working with membrane proteins extremely difficult?
Very unstable when taken out of the membrane
What did Roderick MacKinnon group work on?
Crystallised the protein KcSa1 from bacteria
It is a potassium channel
What are two kinds of transport?
Down a concentration gradient - Passive Transport
Up a concentration gradient - Active transport
What is diffusion?
A spontaneous movement of material from a region of high concentration to a region of low concentration
Where does the energy come from of solute movement?
Entropy
Where does the energy and change in concentration come from?
The change from a concentrated solution to a more dilute solution
What does change in Gibbs Free Energy during diffusion of non electrolytes depend on?
Concentration gradient
What does change in Gibbs Free Energy during diffusion of electrolytes depend on?
Electrochemical gradient and concentration gradient
What is diffusion?
Exergonic
What do all of our cells contain?
Sodium potassium pump
What is the Faraday constant?
23.06kcal/v mol
What is the electrical potential of all charged solutes?
Delta G = mF delta y
What is the chemical potential of a charged solute?
2.3RT log10 ([Na+]i/[Na+]o)
How does movement of ions occur?
Through ion channels
What are Ion channels?
Selective
Bidirectional
Allowing diffusion in the direction of the electrochemical gradient
Why does PH not change on either side of the membrane?
Aquaporins are present
What is Osmosis?
Water moves from a region of lower solute concentration to a region of higher solute concentration
What serves as water channels?
Aquaporins
What does potassium have?
Solvation shelf
What does each subunit of KcsA Contain?
Two transmembrane alpha helixes (M1,M2) and pore segment (P)
What forms the selectivity filter?
A pentapeptide segment within P segment
Where backbone carbonyl oxygen atoms coordinate to K+ ions
What do all ionic solutes have?
Hydration shell of water molecules
What just a solute be in order to pass through the 3A pore in the ion channel?
Desolvated (dehydrated)
For the smaller Na+, what does the selectivity filter provide?
4 coordination sites
