lec 21

Question 1

phospholipase C (PLC) path overview

Answer 1

breaks down PI 4,5- bisphosphate (PIP2) into diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3)

Question 2

Do DAG and IP3 act as a 2nd messenger?

Answer 2

Yes

Question 3

What do IP3 and DAG do?

Answer 3

IP3 binds to ER Ca2+ channels
- causes release of Ca2+ which causes PKC to translocate to membrane
DAG activates PKC when it gets to the membrane
- PKC can phosphorylate various target molecules

Question 4

PLC path

Answer 4

1. activating ligand bind to GPCR
2. GPCR changes conformation and induces activation
   - exchange of GDP to GTP bound to alpha of associated trimeric G protein
3. Activated trimeric G protein diffuses w/n the membrane to activate the target, PLC
4. PLC cleaves PM-associated phospholipid PIP2 into its IP3 and DAG
5. DAG and IP3 = 2nd messenger
6. DAG stays w/ PM
7. IP3 binds to Ca2+ channels in membrane of ER
   - opens and Ca2+ = released into cytosol
8. Ca2+ binds to PKC
   - causes it to translocate to PM
   > allows PKC to bind to DAG which activates PKC
9. PKC phosphorylate downstream target proteins
   - mediate effector func

Question 5

enzyme-linked receptors

Answer 5

either enzyme or it associates directly with/ enzyme
ligand binding triggers enzymatic activity

Question 6

recept tyrosine kinases (RTKs)

Answer 6

1. class of enzyme-linked cell surface
2. many subfamilies
3. recept diverged over time
4. all have intracellular kinase domains
   - most = x1 pass TM proteins that form dimers upon ligand binding
   ligands = growth factors (GF) and hormones

Question 7

ligand binding to RTKs causes

Answer 7

1. dimerization
2. cross-phosphorylation
   - activates recept in 2 ways:
   i. phosphorylation of tyrosine INSIDE RTK kinase domain increases kinase activity
   ii. phosphorylation of tyrosine OUTSIDE kinase domain making high affinity docking sites for intracellular signaling proteins

Question 8

Ras (RTK) -MAPK path overview

Answer 8

ligand binding to RTK activates Sos (Ras-GEF)
Ras = monomeric GTPase
Ras activates the MAP kinase serine/threonine phosphorylation module

Question 9

What happens after Ras activates MAP kinase?

Answer 9

Ras phosphorylates Mek
- phosphorylates Erk
> phosphorylates downstream and gene regulatory proteins in the nucleus

Question 10

Ras-MAPK path

Answer 10

1. activating ligand binds to recept tyrosine kinases which spans the PM
2. ligand binding induces recept dimerization and cross phosphorylation of intracellular domains of dimerized receptors on tyrosine residues
3. residues serve as binding sites for adaptor protein, Grb2
4. Grb2 binds to intracellular domain of the RTK and GEF
5. Sos is brought closer to the cytosolic side of PM
   - allows to act as GEF for Ras
6. Sos facilitates exchange of GDP to GTP bound to Ras which activates Ras
7. Ras activates kinase Raf
8. Ras phosphorylates and activates Mek
9. Mek phosphorylates and activates Erk
10. Erk phosphorylates various downstream target proteins, which mediate effector function

Question 11

specialized growth factor receptor

Answer 11

1. hedgehog GF binds to patched recept
2. Wnt GF binds to frizzled recept

Question 12

Wnt Signal transduction path (no Wnt)

Answer 12

1. Beta-catenin = phosphorylated by GSK destruction complex
2. phosphorylation targets Beta-catenin for ubiquitylation and destruction by proteosome