Module 13 PCB

What is cell signaling?

Communication between cells using extracellular messenger molecules (ligands).

What is a ligand?

A first messenger that binds to a receptor.

What is signal transduction?

Conversion of an extracellular signal into an intracellular response.

What are the main steps of signaling?

Reception, Transduction, Response.

What is autocrine signaling?

Cell signals itself.

What is paracrine signaling?

Local signaling (short distance).

What is endocrine signaling?

Long-distance signaling via bloodstream (hormones).

How are signals typically transmitted inside the cell?

Through protein phosphorylation cascades.

What do kinases do?

Add phosphate groups.

What do phosphatases do?

Remove phosphate groups.

What can phosphorylation do to a protein?

Activate/inactivate, Change location, Alter interactions, Trigger degradation.

What are GPCRs?

Receptors with 7 transmembrane domains that activate G proteins.

What are G proteins?

Heterotrimeric proteins: Gα, Gβ, Gγ.

Which subunit activates effectors?

Gα.

What happens when a ligand binds a GPCR?

Gα exchanges GDP → GTP, Gα separates from Gβγ, Gα activates effector (e.g., adenylyl cyclase).

What does adenylyl cyclase produce?

cAMP (second messenger).

What are second messengers?

Small molecules that amplify signals.

Examples of second messengers?

cAMP, Ca²⁺, IP3, DAG, NO.

What does cAMP activate?

Protein kinase A (PKA).

What does PKA do?

Phosphorylates target proteins → cellular response.

How are GPCR signals turned off?

Gα hydrolyzes GTP → GDP, Reassociation with Gβγ.

What is receptor desensitization?

GPCR is phosphorylated + arrestin binds → blocks signaling.

What enzyme splits PIP2?

Phospholipase C (PLC).

What are the products of PIP2 cleavage?

IP3 → releases Ca²⁺, DAG → activates PKC.

Why is Ca²⁺ a good second messenger?

Stored at low levels → rapid increase = strong signal.

Where is Ca²⁺ stored?

ER + extracellular space.

What protein binds Ca²⁺?

Calmodulin.

What happens when Ca²⁺ binds calmodulin?

Changes shape → activates enzymes (kinases, channels).

What activates RTKs?

Ligand binding → dimerization.

What happens after dimerization of RTKs?

Autophosphorylation of tyrosine residues.

What binds phosphotyrosines?

Proteins with SH2 or PTB domains.

What is Ras?

Small GTPase (monomeric G protein).

What are the active and inactive forms of Ras?

Active = GTP-bound, Inactive = GDP-bound.

What activates Ras?

GEF (Sos).

What inactivates Ras?

GAP.

What is the MAPK pathway?

MAPKKK → MAPKK → MAPK → transcription factors.

What is the function of the MAPK pathway?

Controls cell growth, division, differentiation.

What is convergence in signaling?

Multiple signals → same pathway.

What is divergence in signaling?

One signal → multiple pathways.

What is cross-talk in signaling?

Interaction between pathways.

Do plants have RTKs?

No.

What is a key plant hormone?

Auxin.

How does auxin activate transcription?

Promotes ubiquitination of repressors (Aux/IAA), Frees ARF transcription factors → gene expression.

What are key features of apoptosis?

Cell shrinkage, DNA fragmentation, Membrane blebbing, No inflammation.

What enzymes drive apoptosis?

Caspases.

What triggers the intrinsic pathway of apoptosis?

Internal stress (DNA damage).

What is a key event in the intrinsic pathway?

Cytochrome c release from mitochondria.

What triggers the extrinsic pathway of apoptosis?

External signals (e.g., TNF).

How is necroptosis different from apoptosis?

Cell swells, Membrane ruptures, Causes inflammation.

What promotes cell survival?

NF-κB activation.

What is a key concept in cell fate?

Cell fate depends on balance: survival vs apoptosis vs necroptosis.

Which GPCR subunit activates effectors?

Gα.

What activates PKA?

cAMP.

What releases Ca²⁺ from the ER?

IP3.

What activates PKC?

DAG.

What protein directly triggers apoptosis execution?

Caspases.

Which pathway causes inflammation?

Necroptosis.