Cell Biology Exam 2 | Session 12 +13

1. Muscle cells express ____ gene(s) but not the ____ gene(s)

2. Neurons express _____ gene(s) but not the _____ gene(s)

1. Muscle myosin gene, GPCR genes

2. GPCR genes, muscle myosin

how is gene expression often controlled through (dna itself)

open/closed chromatin

what amino acid does kinases/phosphatases usually target (3)

Ser, Thr or Tyr

What is RTK and what is special abt it

receptor tyrosine kinase, special bc rtk acts as a kinase but also a receptor

How do all types of RTKs activate

dimerization

How does RTK dimerization work? make sure the specify which part of

1. ligand binds to ligand-binding region on each RTK (exterior)

2. The RTKs dimerize and associate w each other

3. Dimerization causes the activation loops (inside cytosol) to be phosphorylated

4. Phorsphorylation of one loop causes additional tyrosine residues to be phosphorylated

What is trans-P

when the dimerized RTK’s activate/phosphorylate each others protein tyrosine kinases

why are more tyrosine residues activated

they become binding sites for downstream components of the pathway

What is negative regulation in RTK signal

PTP dephosphorylates tyrosine residues

How is RTK degraded/recycled

RTK uses early and late endosomes to be sent for degradation in lysosome

What is the difference in degradation of ligand bound rtk vs non-igand bound in terms of speed

ligand bound rtk is slower to recycle/degrade and unbpind receptors tend to recycle faster

What is the difference in degradation of ligand bound rtk vs non-igand bound in terms of vesucke

ligand bound - clathrin-mediated endocytosis

nonligand bound - regular vesicles

what is a common domain that proteins have that allow them to bind to RTK kinases (RTK-P)

SH2 domain

what domain in RTK does Sh2 domains bind to

SRC

what is an example of a ligand that uses RTK signaling

FGF (fibroblast growth factor)

What is GRB2

complex of SH2 and Sh3

After FGF binds to the RTKs what happens (3)

1. GRB2 binds to the phosphorylated SRC domain

2. SOS binds to CRB2

3. Sos promotes dissociation of GDP from Ras and GTP binds and Ras dissociates from Sos

After Ras is activated, go through the steps of the pathway (4)

1. Active Ras recruits and binds to and activates Raf (Raf is phosphorylated, not necessarily through Ras)

2. GTP hydolysis leadds to Ras (GTP —> GDP) and dissociation from Raf

3. Raf looses its 14-3-3 binding and activates MEK (Phosphoyrlation)

4. MEK (kinase) activates MAPK (phosphorylation)

What does MAPK do? (general)

goes to nucleus and activates many transcription factors

what is the example of how MapK activates transcription (done in two steps)

1. MapK phosphorylates TCF transcription factor

2. MapK phosphorylates p90 which then phosphorylates SRF factor

what type of protein is ras

monomeric g-protein

What does a Monomeric G-protein need to be activated into its GTP state

GEF proteinWh

In the FGF growth factor pathway with RTK what acts as the GEF

Sos protein

What are two ways that a Ras protein can be made to be constitutively active (2)

Overall hydrolysis of GTP needs to not happen

1. mutation in Ras and GAP binding (GAP is the one helping with hydrolysis)

2. Mutation that changes the inactivity of Ras so that even though it binds to GAP —> no hydrolysis

what is wnt signaling used for (4)

bone development, musculoskeletal system, skin/hair, stem cell

how is the Wnt signal modified and how is its structrue maintained through

1. lipid modified

2. structrue is maintained through 10+ disulfide bonds

What is the main receptor that we discussed that is associated with Wnt signal and what kind of receptor is it

frizzled, type of GPCR

What makes frizzled different than typical gpcrs

dont interact with heterotrimeric g-proteins

In canonical Wnt signaling what is the role of frizzled and LRP

once wnt binds to frizzled, lrp also binds to Fzd

How do the following proteins work to create B-catenin destruction complex:

1. Axin

2. APC

3. CK1 and GSK3B

4. BTrCP

1. Axin and APC bind to eachother

2. Axin binds to ser-thr kinases (Ck1 and Gsk3B)

3. Phosphorylated B-catenin is bound by BTrCp and ubiquinated

How does B-catenin bind to the destruction complex (2)

1. binds to Axin/APC and is phosphorylated by the CK1 and GSK3B

2. BTrCP binds to phosphorylated B-catenin and ubiquinates it

What does ubiquitation of B-catenin do to it

sends it to be degraded in protosome

when is B-catenin degraded

no wnt signal

what happens to the destruction complex + B-catenin when there is a wnt signal

1. wnt binds to fzd and fzd binds to DVL

2. CK1and GSK3B phosphorylates LRP (coreceptor)

3. B-catenin is able to go to nucleus where it activates transcription factors (TCF/LEF1)