Why is the plasma membrane called a selectively permeable membrane?
Why is the plasma membrane called a selectively permeable membrane?
The plasma membrane falls under a family of membranes called semipermeable membranes. This is because they permit only movement of solvent molecules across a concentration gradient to equalise concentration and minimise osmotic pressure.
Selectively permeable membranes go a step further. They do not always behave under the diktats of a concentration gradient. For instance, the plasma membrane is dotted with protein channels that permit only specific molecules to pass through them. These molecules are recognised by structural complementarity. For instance, valinomycin permits the entry of potassium ions. Galactoside permease permits the entry of lactose.
So in addition to being semipermeable, the plasma membrane is also selectively permeable in its permission to different molecular species during entry or exit.
The plasma membrane falls under a family of membranes called semipermeable membranes. This is because they permit only movement of solvent molecules across a concentration gradient to equalise concentration and minimise osmotic pressure.
Selectively permeable membranes go a step further. They do not always behave under the diktats of a concentration gradient. For instance, the plasma membrane is dotted with protein channels that permit only specific molecules to pass through them. These molecules are recognised by structural complementarity. For instance, valinomycin permits the entry of potassium ions. Galactoside permease permits the entry of lactose.
So in addition to being semipermeable, the plasma membrane is also selectively permeable in its permission to different molecular species during entry or exit.
