8 Solutes cross membrane by simple diffusion HYDROPHOBIC COz MOLECULES N2 x If uncharged solutes are small enough benzene they can move down their concentration SMALL gradients directly across the lipid UNCHARGED H2O bilayer by simple diffusion. 多 POLAR urea MOLEcuLEs glycerol Most solutes can cross the membrane LARGE lrDl only if there is a membrane transport UNCHARGED glucose POLAR sucrose protein to transfer them MOLECULES x Passive transport, in the same H+ Na+ direction as a concentration gradient IONS HCO3, K Mo2以 Ca+ c Active transport is mediated by carrier proteins, against a concentration Diffusion of small moecues across synthetic gradient, require an input of energy lipid phospholipid bilayers bilayer
v Solutes cross membrane by simple diffusion Diffusion of small molecules across phospholipid bilayers vIf uncharged solutes are small enough, they can move down their concentration gradients directly across the lipid bilayer by simple diffusion. vMost solutes can cross the membrane only if there is a membrane transport protein to transfer them. vPassive transport, in the same direction as a concentration gradient. v Active transport, is mediated by carrier proteins, against a concentration gradient, require an input of energy
C. Two classes of membrane transport proteins Carrier proteins are responsible for both the passive and the active transport. o Channel proteins are only responsible for passive transport transported molecule channel carrier protein otein lipid ncentration bilayer gradient simple channel- carrier diffusion mediated mediated PASSIVE TRANSPORT ACTIVE TRANSPORT
C. Two classes of membrane transport proteins vCarrier proteins are responsible for both the passive and the active transport. vChannel proteins are only responsible for passive transport
o Carrier proteins bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfer the solute to the other side of the membrane lipid state A state B bilayer OUTSIDE concentration gradient INSIDE carrier protein mediating solute-binding site passive transport
vCarrier proteins bind one or more solute molecules on one side of the membrane and then undergo a conformational change that transfer the solute to the other side of the membrane
Facilitate diffusion: Protein-mediated movement movement down the gradient ②2 OUTSIDE OF CELL Transport protein shifts to alternative Glucose binds conformation Glucose is to binding site released to the open to outside inside and protein returns to its original Glucose conformation INSIDE OF CELL Glucose y Glucose transporter (GluT1) The carrier protein, the Glucose transporter(GluTl) in the erythrocyte PM, alter conformation to facilitate the transport of glucose
The carrier protein, the Glucose transporter (GluT1 ) in the erythrocyte PM, alter conformation to facilitate the transport of glucose. vFacilitate diffusion: Protein-mediated movement, movement down the gradient
Most of the channel proteins are ion channels including three types, with ion channels that they can be opened and closed (A)voltage (B) ligand-gated (C)ligand-gated (D)stress gated (extracellular (intracellular activated ligand) ligand CLOSED CYTOSOL OPEN b n CYTOSOL
vMost of the channel proteins are ion channels, including three types, with ion channels that they can be opened and closed