Final answer:
The PI 3-kinase/Akt pathway is a signaling pathway that regulates cell survival, growth, and metabolism. It involves activation of a cell-surface receptor, phosphorylation of phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 3,4,5-trisphosphate (PIP3), activation of Akt, regulation of downstream target proteins, and inhibition of apoptosis. This pathway plays a critical role in normal cellular functions and is implicated in various diseases.
Step-by-step explanation:
The PI 3-kinase/Akt pathway is a signaling pathway that plays a critical role in cell survival, growth, and metabolism. Here are the steps of this pathway:
- Activation: The pathway is initiated when a signaling molecule, such as a growth factor, binds to a cell-surface receptor. This binding activates the receptor, causing it to change shape and activate its kinase activity.
- Phosphorylation: The activated receptor phosphorylates a molecule called phosphatidylinositol 4,5-bisphosphate (PIP2), converting it into phosphatidylinositol 3,4,5-trisphosphate (PIP3). This step is catalyzed by an enzyme called phosphoinositide 3-kinase (PI 3-kinase).
- Activation of Akt: PIP3 recruits a protein called Akt (also known as protein kinase B) to the cell membrane. Akt is then phosphorylated and activated by another kinase.
- Cellular responses: Activated Akt phosphorylates and regulates various downstream target proteins involved in cell survival, growth, and metabolism. Examples of these targets include mTOR, which promotes protein synthesis, and glycogen synthase kinase-3 (GSK-3), which regulates glucose metabolism.
- Inhibition of apoptosis: The PI 3-kinase/Akt pathway also inhibits programmed cell death, or apoptosis, by phosphorylating and inactivating pro-apoptotic proteins.
This pathway is essential for normal cellular functions and is often dysregulated in diseases like cancer, diabetes, and neurodegenerative disorders.