diffusion and active transport Flashcards
what is diffusion?
A process by which a gas or substance in solution expands to fill all the available volume, where molecules spread from regions of high concentration to areas of low concentration.
what do molecules need to be to diffuse through the lipid bilayer passively?
Small and Uncharged (most important qualities)
Lipophilic (hydrophobic)
describe the speed of lipophilic and lipophobic gases through the lipid bilayer:
Lipophilic gases like O2 and N2 pass faster than Lipophobic gases like CO2 through it.
what are channel mediated transporter proteins?
they’re integral/transmembrane proteins that provide an aqueous pathway across the membrane for the simultaneous diffusion of water and ions.
channel mediated transporter proteins only allow the passage of what?
mineral ions such as Na+ and K+, Cl-, Ca2+ and H+ accompanied by H2O while molecules such as glucose are too large to go through.
what is the main channel that is permanently open to water diffusion to the inside of the cell?
aquaporin
what type of channels do ions use to cross the membrane?
gated - which remain closed until an electrical/chemical/mechanical stimulus cause a conformational change in the configuration of the channel proteins which leads them to open.
what are the two types of gated channels?
Voltage gated channels
Ligand gated channels
What are voltage gated channels? where are they found?
Open/close in response to alterations in the membrane electrical potential
(charge difference on either side of the membrane).
Found extensively in muscle and nerve cells.
What are ligand gated channels?
open/close when a chemical such as neurotransmitter/hormone binds to a receptor binding site on the channel protein.
Multitasking membrane proteins – act as both receptor & transporter
What is the direction of diffusion dependent upon?
the concentration/chemical gradient and, in the case of charged particles, the electrical gradient
Combined together they are called the electrochemical gradient
Sometimes these forces co-operate, sometimes they oppose each either.
Net direction of movement depends on the dominant force.
When is the electrochemical gradient reached?
when the chemical and electrical gradients are in balance.
What are carrier-mediated transport proteins (or transporters)?
They are proteins that transport large molecules like glucose, they bind the molecule then undergo a change in shape which exposes the opposite side binding site, leading the molecule into the cell.
How does the electrochemical gradient affect the transportation of molecules through Carrier-mediated transport proteins?
If the electrochemical gradient favours the direction of movement, movement occurs by facilitated diffusion and no energy input is required.
If the electrochemical gradient opposes the direction movement then energy (ATP) is required to move the molecule against this gradient (active transport).
In these cases the carrier protein also functions as an enzyme (ATPase) as it hydrolyses ATP to release energy.
What is active transport?
Movement of molecules through transport proteins against their electrochemical gradients while using energy in the form of ATP.
