MCB Ch 14 Intracellular Signaling

Cortisol

steroid hormone derived from cholesterol 

• produced by adrenal cortex 

Effects: adaptation to long term stress by raising blood glucose levels and mobilizing fat

the cortisol receptor is a ____

transcription factor

Signal transduction

relay of an outside signal through an intracellular signaling cascade involving a number of intermediate molecules with diff activities

• pathway is triggers when an external signal molecule binds to surface receptor

G protien

membrane-bound protein complex with three subunits

• activated by GTP

inactivate form of G Protein:

all three subunits (a, B, and y ) are associated and the a-subunit has a GDP bound to it

inactivated form of G protein:

GDP dissociates from the a-subunit and is replaced with a GTP (a nucleotide exchange)
→ the a-subunit dissociates from the B-and y-subunits
→ the B- and y-subunits remain associated and act as a
single unit, the By complex

Epinephrine

produced by adrenal medulla

• stimulates the breakdown of glycogen in anticipation to muscular activity 

• stops production of glycogen

• used to sympathetic neurotransmitter

Epinephrine Receptor

G-protein couple receptor

• activated adenylyl cyclase → catalyzes conversion of ATP into cAMP

• results in elevation of cAMP levels and activation of protein kinase A

Protein Kinase A (PKA) promotes…

glycogen metabolism

Which enzyme isomerizes glucose-1-P into glucose-6-P, which enters glycolysis?

Phosphoglucomutase

Calmodoluin

small Ca²⁺ binding protein that is involved in the modulation of many cellular processes by activating a number of calmodulin-dependent kinases and phosphates 

_______ activate calmodulin

four Ca²⁺

The pathway to the activation of calmodulin begins with the activation of _______

a G protein

Wnt proteins 

large family of secreted signals 

• pathway involved in cell differentiation, cell adhesion, and establishment of embryonic axes

Wnt pathway activates….

transcription factor B-catenin - which is important for the transcription of cell differentiation genes in neighboring cells

If no Wnt signal is present:

a destruction complex forms in the cytoplasm

• complex containing APC  targets B-catenin for degradation

if the Wnt signal is present:

Wnt binds Frizzled which activates Disheveled through a G Protein

RTKs

Enzymic receptors

• form homodimers 

Steps in the activation of RTK:

1. binding of signal as a dimer causes the formation of receptor subunit dimers

2. the cytoplasmic tyrosine kinase domains of the receptor subunits phosphorylate each other 

3. phosphorylated tyrosine become binding sites for signaling proteins that contain an SH2 domain