BIO-235 Signal Transduction

Which toxin affects the Gs subunit and what is the resulting effect on cAMP?

Cholera Toxin (CTX) makes the Gs subunit sensitive, preventing the hydrolysis of GTP, which raises cAMP levels indefinitely.

Which toxin affects the Gi subunit and what is the resulting effect on cAMP?

Pertussis Toxin (PTX) affects the Gi subunit. By inhibiting the "inhibitor," it ultimately raises cAMP levels.

Which reaction is catalyzed by Adenyl Cyclase?

It converts ATP into the second messenger cAMP (cyclic Adenosine Monophosphate).

What occurs to the G-protein heterotrimer after GTP binds to the alpha subunit?

The α(Gs)  -GTP complex dissociates from the    subunits to interact with downstream effectors.

What makes the Gz subunit unique compared to other Gi proteins?

Gz is the only Gi-type protein known to be insensitive to Pertussis Toxin (PTX); it is specifically involved in opioid signaling.

What is the role of IP3 once it is released into the cytosol?

It travels to the ER (Endoplasmic Reticulum) and binds to receptors to trigger the release of  Ca²+  ions.

What is the primary function of the Gs G-protein subunit?

The Gs (stimulatory) subunit stimulates Adenyl Cyclase (AC), which leads to an increase in cAMP levels.

What is the primary function of the Gq G-protein subunit?

The Gq subunit activates Phospholipase C (PLC), triggering the phosphoinositide signaling pathway.

What is the primary function of the Gi G-protein subunit?

The Gi (inhibitory) subunit inhibits Adenyl Cyclase (AC), which leads to a decrease in cAMP levels.

What is the primary downstream target of cAMP in the Adenyl Cyclase pathway?

PKA (Protein Kinase A).

What is the direct enzymatic target of α(Gs)  -GTP?

It targets and activates Adenyl Cyclase.

What enzyme is responsible for reversing the phosphorylation effects caused by PKA?

PPP (Protein Phosphatase).

What are the two products formed when PLC cleaves the membrane phospholipid PIP₂?

IP3 (Inositol trisphosphate) and DAG (Diacylglycerol).

What are the primary functions of the Go G-protein subunit?

The Go subunit opens ion channels and is sensitive to Pertussis Toxin (PTX).

What are the known roles of the Gβγ (beta-gamma) complex in signaling?

The Gβγ dimer can open ion channels and acts as a yeast scaffolding protein.

In the Phospholipase Pathway, which enzyme is activated by  α(Gq) -GTP?

PLC (Phospholipase C).

In the Adenyl Cyclase Pathway, which molecule is bound to the G-protein in its inactive state?

The G-protein is inactive when the alpha subunit (  ) is bound to GDP.

In the Adenyl Cyclase Pathway, what event triggers the activation of the G-protein?

A ligand binds to the GPCR (G-protein Coupled Receptor), causing the alpha subunit to exchange GDP for GTP.

How does Cholera Toxin (CTX) specifically alter the Adenyl Cyclase Pathway?

It blocks the GTPase activity of the    subunit, preventing the conversion of GTP back to GDP and locking the pathway in the "on" position.