L27-28 Signal Transduction

Q: What is signal transduction?

A: It is the process by which a cell converts an external signal into a functional internal response.

Q: Why do cells need signal transduction?

A: To detect and respond to environmental changes, regulate gene expression, and coordinate cell functions.

Q: Name four types of bacterial signal transduction systems.

A:

1. Two-component systems (2CS)

2. One-component systems (1CS)

3. ECF sigma factors

4. Class III adenylyl/guanylyl cyclase

Q: What is the key difference between 1CS and 2CS systems?

A: 2CS uses two separate proteins with His-Asp phosphotransfer; 1CS uses a single protein without this transfer.

Q: What are ECF sigma factors?

A: Alternative sigma factors that respond to stress signals and redirect RNA polymerase to specific promoters.

Q: What happens to ECF sigma factors in the absence of a stimulus?

A: They remain inactive, bound by cognate anti-sigma factors.

Q: What is the role of adenylyl cyclase in bacteria?

A: Converts ATP to cAMP, a secondary messenger important in signaling.

Q: What are the three major eukaryotic signal transduction pathways?

A:

1. Receptors with intrinsic protein kinase activity

2. Receptors that interact with kinases

3. Receptors that interact with G proteins

Q: What activity do most receptor kinases have?

A: Tyrosine kinase activity.

Q: What does ligand binding do to receptor kinases?

A: Induces dimerization, activates kinase activity, and leads to autophosphorylation.

Q: What are the types of protein kinases based on specificity?

A:

1. Tyrosine kinases

2. Serine/threonine kinases

3. Dual specificity kinases

Q: What is the JAK-STAT pathway?

A: A simple signal pathway where a receptor activates JAK, which phosphorylates STAT. STAT dimerizes and activates transcription.

Q: What are the components of the JAK-STAT pathway?

A:

1. Receptor

2. JAK kinase

3. STAT transcription factor

Q: What type of receptors interact with G proteins?

A: 7-transmembrane (serpentine) receptors.

Q: What causes activation of a G protein?

A: Ligand binding leads to GDP-GTP exchange on the α subunit, which then activates effectors.

Q: What are the three subunits of a G protein?

A: α, β, and γ.

Q: How does cAMP affect transcription in eukaryotes?

A: It activates protein kinase A, which phosphorylates CREB, allowing it to bind to CRE and activate transcription.

Q: What is CREB?

A: cAMP Response Element-Binding protein, a transcription factor activated by PKA.

Q: What is a CRE?

A: A cAMP Response Element—a DNA sequence that CREB binds to stimulate transcription.

Q: What is Ras and how is it activated?

A: A monomeric G protein activated by GEFs; inactivated by GAPs.