Signalling Through Cell Surface Receptors

These flashcards cover the key concepts from the lecture on signalling through cell surface receptors, focusing on receptor types, mechanisms, and cellular responses.

What are the three classes of cell surface receptors?

• Ion channel coupled receptors

• G-protein coupled receptors (GPCRs)

• Enzyme coupled receptors.

What distinguishes G-protein coupled receptors (GPCRs) from other receptor types?

They are 7 pass transmembrane proteins that interact with G-proteins.

What is the primary function of ion channel coupled receptors?

They alter membrane permeability to ions.

What is the role of cAMP in cell signalling?

cAMP acts as a secondary messenger in many signalling pathways.

What condition is associated with an autoimmune response to nicotinic acetylcholine receptors?

Myasthenia gravis.

Who were awarded the Nobel Prize in Physiology or Medicine in 1994?

Alfred G. Gilman and Martin Rodbell for their discovery of G-proteins.

Types of G-proteins

• Monomeric - Transduces signals from enzyme linked receptors

• Trimeric - Transduce signals from G-protein linked receptors

What do trimeric G-proteins consist of?

Three heterologous subunits (alpha; a GTPase, beta and gamma)

They bind GDP in a resting state and exchange it for GTP upon receptor activation.

How do G-proteins become activated?

Signal binding induces a conformational change

The alpha subunit releases GDP and is replaced by GTP.

The three subunits dissociate, and the G protein can activate and interact with other G proteins to relay the signal.

How do G-proteins get inactivated?

• The alpha sub-unit binds onto a target protein

• This causes the hydrolysis of GTP to GDP

• The alpha sub-unit reassociates to the beta-gamma subunit and the protein returns to the inactive state.

What are the two key proteins activated by trimeric G-proteins?

Adenylyl cyclase and phospholipase C.

What does adenylyl cyclase convert ATP into?

Cyclic AMP (cAMP).

What second messengers does phospholipase c produce?

Inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG).

How does protein kinase A (PKA) transmit information down the signalling pathway?

• cAMP binding to PKA causes a conformational change

• The catalytic subunits are released and activated

What is the significance of phosphorylation in cellular signaling?

Phosphorylation can switch proteins on and off.

What role does GTP play in the cell?

• Nucleic acid synthesis

• Signal transduction

  • cGMP and G-protein activation (GTP)

  • cAMP and phosphorylation (ATP)

• Carrying energy

What is the mechanism of epinephrine's effect in the 'fight or flight' response?

It activates G-protein coupled receptor signalling leading to glucose release.

What is the amplification effect of epinephrine in the cell?

Amplification ensures a rapid response by increasing the concentration of cAMP and activated proteins.