L11- Membrane transport Flashcards
What are the two types of facilitated diffusion?
- Mediated by transmembrane transport proteins
2. Mediated by carrier proteins
How do transmembrane proteins carry out facilitated diffusion?
- Contain solute binding site
- Alternates between two conformation so the binding site is available on both sides of membrane
- Solutes move down the concentration gradient so no energy is required
What is an example of a transmembrane transport protein?
GLUT1- glucose transporter 1
• Uniporter
• Increases glucose diffusion rate by x50,000
• 492 aa residues, 12 membrane spanning helices
• D glucose transported more readily than L glucose
What is the difference between facilitated and passive diffusion?
- FT has a much higher transport rate but is saturable because:
- Limited number of membrane pores or carriers
- Each pore or carrier is limited to accommodating a certain number of molecules at a time
What are ion channels?
Integral membrane proteins that span the entire membrane to form an aqueous pore across the bilayer that is permeable to ions.
Molecules travel faster via electrochemical gradient
How does carrier-facilitated transport work?
- A membrane permeant protein molecule binds substance to be transported at one side of membrane
- Transmembrane protein carries substance through the membrane and deposits it at the other side.
What is active transport?
Transport of substances against a concentration gradient via:
• Ion pumps
• Co-transport systems
• Modification
How do ion pumps carry out active transport?
Direct coupling of ATP hydrolysis to ion transport e.g
•Na/K pump- 3Na+ moved out for every 2K+ moved into cell and requires hydrolysis of ATP to occur to change conformation of pump (notes)
What is the concentration of Na inside and outside cells?
Inside= 10mM Outside= 140mM
What is the concentration of K inside and outside cells?
Inside= 100mM Outside= 5mM
How does a co-transport system work?
Movement of a substance through the membrane is coupled to the spontaneous transport of another substance (symport). e.g glucose/sodium transport
How does glucose-sodium transport work?
Glucose-sodium symport harvests energy stored in the sodium gradient to pump glucose into cells of the gut lumen lining.
Binding of one molecule makes binding of the other more effective, symporter undergoes a conformational change
How much energy is needed for the transport of one molecule of glucose?
+11.9 kj/mol
How many mol Na needed to transport one mol glucose?
2 (atleast) per glucose molecule
How does transport by modification occur?
A molecule moves into a cell by passive or facilitated diffusion and is chemically modified so that it can no longer pass back through the membrane.
Result= quantities of the modified molecule accumulate within the cell. e.g bacterial uptake of sugars by phosphorylation
