Describe the relationships between membrane channel proteins, membrane enzyme proteins, direct activation, and indirect activation. Include G proteins

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ncchemist eNotes educator| Certified Educator

Membrane channel proteins are proteins that span the phospholipid bilayer of the cellular membrane.  They form a "channel" between the inside and outside of a cell or organelle that can allow particular chemicals to traverse the membrane.  Enzymes are a type of protein, so membrane enzyme proteins are enzymes that are attached to a cellular membrane.  They perform regular enzyme type functions including the synthesis or breaking down of biomolecules. 

A g-protein is a type of protein the can be thought of as a molecular switch.  An extracellular (outside the cell) stimulus sends a message through a particular type of membrane channel protein called a g-protein coupled receptor that in turn activates a g-protein within the cell.  This g-protein then causes a signalling cascade that has an effect on the cell's function.  Direct activation of a g-protein involves a biochemical attaching to the receptor having a direct effect on the g-protein.  Indirect activation involves a series of signalling events being required to activiate the g-protein.