Cell Membrane Transport: Facilitated Diffusion Flashcards
Define: Facilitated Diffusion
Facilitated diffusion is membrane protein-mediated movement of a substance across a membrane that does not require energy because the ion or molecule being transported is being moved down an electrochemical graient
Define: Carrier Proteins
Membrane bound proteins that bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfers the solute to the other side of the membrane
Define: Channel Proteins
membrane bound proteins that for hydrophilic channels through the membrane that allow the passage of solutes without a major change in the conformation of the protein
Describe two types of channel proteins
Porins/Aquaporins - which allow selected hydrophilic solutes (H2O) with molecular solutes with molecular weights of about 600 to diffuse across the membrane
Ion channels - allow ions to pass through the membrane without help from ATP
Define : Alternating Conformation Model
The carrier protein is an allosteric protein that alternates between two conformational states
Define : Competitive Inhibition
a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa
What is a uniporter?
when a carrier protein transports a single solute across the membrane
Define : Coupled Transport
when two solutes are transported simultaneously
Coupled Transport:
What is a symport?
What is an antiport?
when two solutes are moved in the same direction
when solutes are moved in opposite directions
One specific type of carrier protien in erythrocytes is the glucose transporter (GLUT).
Describe the steps the protein takes to move glucose across the cell.
- D-glucose collides with and binds to GLUT1 in the T1 conformation
- GLUT1 shifts to the T2 conformation
- The conformational change causes the release of glucose
- GLUT1 returns to the T1 conformation
(this is also a reversible process determined by solute concentration inside and outside the cell)
Why is the erythrocyte anion exchange protein called the “ping-pong” mechanism?
the anion exhange protein is throught to function by alternating between two conformational states
First state: binds to chloride ion on one side
Second state: chloride is moved across the membrane
Back to first state when bicarbonate binds to the protein
How does the anion exchange protein play a central role in the process by which waste CO2 produced in metabolically active tissues is delivered to the lungs to be expelled?
Tissues: CO2 diffuses into RBC and carbonic anhydrase turns it into bicarbonate ions. increase in bicarbonate concentration in cell moves it out of the cell
Lungs: the process is reversed, bicarbonate goes into RBC and converted to CO2 by carbonic anhydrase
Net result is the movement of carbon dioxide from the tissues to the lungs
Define: transmembrane channels
protein channels that allow specific hydrophilic solutes to move across the membrane directly
What are ion channels?
a tiny pore lined with hydrophilic atoms, selectively allowing ions to flow through the membrane
What are the three main types of gated ion channels?
Describe them.
Voltage Gated channels - open and close in response to some changes in the membrane potential
Ligand-Gated Channels - triggered by the binding of specific substances to the channel protein
Mechanosensitive Channels - respond to mechanical forces that act on the membrane
