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Question 1

state two mechanisms of signaling via enzyme-coupled receptors

Answer 1

• Phosphorylation: signal perception triggers activation of receptor kinases or receptor-associated kinases
• Proteolysis: signal perception triggers protein cleavage or degradation

Question 2

is proteolysis only for degradation?

Answer 2

no; can also be used in signaling

Question 3

receptor tyrosine kinases are essential in

Answer 3

mammals

Question 4

what is the function of receptor tyrosine kinases?

Answer 4

mediate diverse functions

Question 5

describe the shared structure of RTKs

Answer 5

• Different extracellular domains bind different ligands
• Transmembrane domain
• Intracellular tyrosine kinase domain phosphorylates different targets at tyrosine residues

Question 6

kinase insert region

Answer 6

RTKs sometimes have these couple of extra amino acids

Question 7

how are RTKs activated?

Answer 7

by ligand binding and transautophosphorylation

Question 8

why is transautophosphorylation

Answer 8

trans = on different RTK molecules
auto = RTKs act on RTKs

1. signal protein binds to inactive RTK
2. receptor is activated and forms a dimer, causing the tyrosine kinase domain to phosphorylate the neighbouring tyrosine kinase domain. they both phosphorylate each other at the same time, activating the kinase domains
3. both sides will phosphorylate each other at specific tyrosines, generating binding sites for signaling proteins

Question 9

what happens if one side of the RTK is not working?

Answer 9

neither of them works

Question 10

what is the function of an activated RTK?

Answer 10

can act as a scaffold protein and OFTEN activates Ras-GEFs

Question 11

what are two ways in which signaling proteins can bind to RTKs?

Answer 11

via SH2 or PTB domains

Question 12

describe the structure of the SH2 domain and its functional important

Answer 12

has 2 binding sites:
1. recognises the phosphorylated tyrosine
2. recognises nearby amino acids

these ensure that SH2 domains bind specific phosphorylated proteins

Question 13

what do Ras-GEFs do when activated by RTK?

Answer 13

causes exchange of GDP into GTP by Ras protein, causing it to become active.

Question 14

there are —- different Ras-GEFs; so there are —– different Ras proteins

Answer 14

many

Question 15

what are Ras family proteins related to?

Answer 15

other monomeric GTPases

Question 16

MAP kinase

Answer 16

mitogen-activated protein kinase

Question 17

what is the effect of activated Ras on MAP kinase cascades?

Answer 17

Activated Ras can activate MAP kinase cascades

Question 18

function of MAP kinases

Answer 18

• MAP kinases can convert a short-term RTK activation at the cell surface to a stable/long-term change in gene expression
• MAP kinases also provide
  negative feedback

Question 19

describe a MAP kinase cascade

Answer 19

active Ras protein activates MAP kinase kinase kinase (Raf) which phosphorylates/activates MAP kinase kinase (Mek) which phosphorylates/activates MAP kinase (Erk) which then causes changes in protein activity and changes in gene expression

Question 20

mitogen

Answer 20

substance that generates mitosis

Question 21

humans have ~ —– MAPKKKs, —— MAPKKs, and —– MAPKs. They all operate with different ——

Answer 21

7; 7; 12; specificities

Question 22

what do Raf, Mel, and Erk stand for?

Answer 22

names of the proteins in humans

Question 23

what is the function of scaffold proteins in relation to MAP kinase cascades?

Answer 23

they can provide specificity; they ensure the particular kinases stay together so you can only have one particular pathway occurring for a particular stimulus

Question 24

what was the first discovery of RTK signaling?

Answer 24

drosophila sevenless signaling

Question 25

describe drosophila eyes

Answer 25

- Drosophila compound eyes are made of ommatidia - Each ommatidia has 8 photoreceptor cells (R1-R8) - The R7 cells is required to detect UV light

Question 26

what experiment did scientists conduct to better understand the developmental signaling pathway for drosophila eyes?

Answer 26

To understand the developmental signaling pathway, scientists screened for Drosophila mutants that cannot sense UV light and characterized the signaling pathway components they identified

Question 27

describe sevenless signnaling

Answer 27

In the R8 cell, a transmembrane ligand called Boss is present. Boss signals to the neighboring cell (the future R7) by binding and activating the Sevenless receptor tyrosine kinase. Activation of Sevenless recruits the adaptor protein Grb2 (called Drk in Drosophila), which then brings in Sos, a Ras-GEF. Sos promotes GDP–GTP exchange on Ras, activating Ras. Active Ras triggers the downstream signaling cascade required for the cell to differentiate into an R7 photoreceptor.

Question 28

Drk =

Answer 28

downstream of receptor kinase

Question 29

describe the process of RTKs signaling through phosphoinositides (PIPs)

Answer 29

1. RTK activated by a survival factor 2. RTK activates PI 3-kinase 3. PI 3-kinase converts PI(4,5)P2 to PI(3,4,5)P3 4. PDK1 & Akt bind PI(3,4,5)P3 5. PDK & mTORC2 phosphorylate Akt 6. Akt phosphorylates Bad to release Bcl2 to inhibit apoptosis (lecture 11)

Question 30

what is the relationship between RTK and GPCR signaling?

Answer 30

there can be crosstalk between RTK and GPCR signaling

Question 31

when do pathways signal via tyrosine kinase associated receptor? what mechanisms are used?

Answer 31

- Some receptors have no kinase activity (e.g. cytokine receptors) - These associate with cytoplasmic tyrosine kinases to signal - The mechanisms of transautophosphorylation and protein binding to the phosphorylated receptor remain similar

Question 32

describe structure of receptor serine/threonine kinases

Answer 32

- Extracellular ligand binding domain - Transmembrane domain - Intracellular kinase domain - Multiple receptors associate in response to signals

Question 33

what do receptor serine/threonine kinases do?

Answer 33

kinase domains phosphorylate serine and/or threonine residues in targets

Question 34

give an example of contact-dependent signaling

Answer 34

Delta-Notch

Question 35

what two signaling processes does Notch involve?

Answer 35

- Signaling via endocytosis - Signaling via proteolysis

Question 36

what does active notch consist of?

Answer 36

one protein that is cleaved into two pieces

Question 37

describe the formation of Notch

Answer 37

1. notch protein is made in the ER 2. notch is cleaved into two pieces in the Golgi 3. the two pieces stay together and move to the plasma membrane

Question 38

describe what happens to Notch after it interacts with Delta

Answer 38

1. The extracellular part of Notch directly interacts with Delta on the surface of the other cell 2. Delta-Notch is endocytosed into the Delta-expressing cell 3. The remainder of Notch is cleaved at two more sites 4. The cytosolic ”tail” of Notch moves to the nucleus 5. The Notch tail promotes transcription of Notch target genes 6. Delta is repressed in this cell 7. The cell with active Notch target genes does not differentiate

Question 39

no hedgehog signal

Answer 39

1. Patched is active in the cilium 2. Active Patched inhibits Smoothened and keeps Smoothened out of the primary cilium 3. SuFu binds and inhibits Gli2 & Gli3 4. GPCR (Gpr161) is active 5. Active Gpr161 promotes cAMP synthesis 6. cAMP activates PKA 7. PKA phosphorylates Gli3 8. Gli3 phosphorylation causes Gli3 proteolytic processing 9. The remaining fragment of Gli3 moves to the nucleus to repress expression of hedgehog target genes

Question 40

hedgehog signal

Answer 40

1. Hedgehog binds and inactivates Patched 2. Smoothened is active and moves to the tip of the primary cilium 3. Gpr161 and PKA are inactive (not shown) 4. Gil3 is not proteolytically processed so it does not inhibit hedgehog target genes 5. SuFu and Gli2 move along microtubules to the tip of the primary cilium 6. Smoothened releases Gli2 from SuFu 7. Gli2 moves along microtubules from primary cilium to nucleus 8. Gli2 activates hedgehog target genes

Question 41

what is the similarity between Notch and Hedgehog?

Answer 41

both involved in multiple processes and signaling pathways