Question

Describe mechanisms by which ion channels, protein phosphorylation and G-proteins give cells an ON or OFF response for cell signaling.

Describe this for each of these three processes, in the specific prompts below. Be sure be clear about where these mechanisms are distinct from one another. What are the inactive and inactive states? How does signal input activate the system? How is the system returned to inactive state?

Answer 1

Ligand-gated ion channels has a hydrophilic channel in the middle of it and it binds to a ligand to open up. As a ligand binds to the channel's extracellular region, a specific type of ions is allowed to pass through it. This binding of ligand thereby opening the gate for ion depicts “ON” condition. However, sometime the ligand binding closes the gate and do not allow passing of ion. This is referred to as “OFF” condition.

G proteins bind to the nucleotide guanosine triphosphate (GTP). As they attach to GTP, GTP break down through hydrolysis and form GDP. When the G protein attaches to GTP it is said to be in active state or “ON” state. When G protein attaches to the GDP it is said to be in inactive state or “OFF” state. G proteins associate with GPCRs and when they attach to an inactive receptor i.e GDP, then they are in the “OFF” form.

Phosphorylation of Ser and Thr residues activates protein kinase B that regulate cell survival. This is referred to as “ON” condition. While on the other hand when c-Src (proto-oncogene tyrosine-protein kinase) gets dephosphorylate, the regulation of cell growth is turned “OFF”