Hormone action

Question 1

steps in GPCR singling through IP3 and Ca (7)

Answer 1

1. hormone binds to specific receptor
2. occupied receptor causes GDP to be replaced by GTP on Gq-alpha
3. Gq-alphae bound to GTP moves to phospholipase C (PLC) and activates it [membrane bound]
4. activated PLC cleaves PIP2 into IP3 (inositol triphosphate) and diacylglycerol (DAG)
5. IP3 binds to a specific receptor-gated calcium channel, releasing sequestered calcium
6. DAG and Ca activate protein kinase C at the surface of the plasma membrane
7. phosphorylation of cellular proteins by PKC produces some of the cellular responses to the hormone

Question 2

what are the 2 products of PIP2 cleavage?

Answer 2

IP3 and DAG

Question 3

what molecule cleaves PIP2?

Answer 3

PLC

Question 4

which G-alpha subunit activates PLC?

Answer 4

Gq-alpha

Question 5

where is DAG located?

Answer 5

membrane bound

Question 6

where is IP3 found?

Answer 6

free in cytoplasm

Question 7

hormones may use more than one G-protein. true or false?

Answer 7

true

Question 8

why is singling through GPCR complex?

Answer 8

use can change during development and use can change depending on hormone concentration or in different tissues

Question 9

what are the two types of receptors involved with tyrosine kinase?

Answer 9

1. receptors with an integrated (intrinsic) kinase activity

2. receptors that recruit a kinase

Question 10

what is a tyrosine kinase?

Answer 10

kinase that specifically phosphorylates tyrosine residue on a protein

Question 11

which are the most studied RTK?

Answer 11

insulin receptor and IGF-1 receptor

Question 12

which type of RTK are the insulin receptors and IGF-1 receptors?

Answer 12

receptors with intrinsic tyrosine kinase activity

Question 13

what is the structure of the insulin receptor?

Answer 13

hetero-tetrameric structure 2 alpha and 2 beta chains held together by disulphide bonds
=> 2 types of subunits, 4 subunits in total

Question 14

how is the insulin receptor synthesized?

Answer 14

from a single precursor protein

Question 15

where are insulin receptors most abundant?

Answer 15

adipocytes and hepatocytes

Question 16

what is the series of events after insulin binding? (3)

Answer 16

1. autophosphorylation (intrinsic kinase activity) of intracellular domain of receptor (carboxylic end)
2. docking and phosphorylation of IRS-1 or IRS-2 (insulin receptor substrate)
3. activation of 2 major signal pathways MAPK and PIP3

Question 17

which signaling pathways does insulin binding trigger?

Answer 17

MAPK and PIP3

Question 18

steps involved in Insulin receptor signaling through MAPK pathway (7)

Answer 18

1. insulin receptor binds insulin and undergoes autophosphorylation on its carboxyl-terminal Tyr residues
2. insulin receptor phosphorylates IRS-1 on its tyrosine residue
3. SH2 domain of Grb2 binds to phosphorylated-Tyr of IRS-1, Sos binds to Grb2, then to Ras, causing GDP release and GTP binding to Ras
4. activated Ras binds and activates Raf-1
5. Raf-1 phosphorylates MEK on two Ser residues, activating it. MEK phosphorylates ERK on a Thr and a Tyr residue, activating it
6. ERK moves into the nucleus and phosphorylates nuclear transcription factors such as Elk1, activating them
7. phosphorylated Elk1 joins SRF to stimulate the transcription and translation of a set of genes needed for cell division

Question 19

what are adaptor proteins? give examples (4)

Answer 19

1 protein comes and adapts to a multiprotein conglomeration complex
ex: Grb2, Sos, Ras, Raf-1

Question 20

Ras acts like a G protein, why?

Answer 20

GDP replaced by GTP

Question 21

role of Raf-1

Answer 21

kinase that activates MEK

1st protein of MAPK pathway

Question 22

what is the cellular response of the MAPK pathway

Answer 22

changes in gene expression - targets are transcription factors

Question 23

steps involved in Insulin receptor signaling through PIP3 pathway (5)

Answer 23

1. IRS-1, phosphorylates by the insulin receptor, activates PI3K by binding to its SH2 domain. PI3K converts PIP2 to PIP3
2. PKB bound to PIP3 is phosphorylated by PDK1. Thus activated, PKB phosphorylates GSK3 on a Ser residue, inactivating it
3. GSK3, inactivated by phosphorylation, cannot convert glycogen synthase (GS) to its inactive form by phosphorylation, so GS remains active
4. synthesis of glycogen from glucose is accelerated
5. PKB stimulates movement of glucose transporter GLUT4 from internal vesicles to the plasma membrane, increasing the uptake of glucose

Question 24

PIP2 is involved in 2 signaling pathways. which are they?

Answer 24

GPCR pathway and IRS through PIP3 pathway

Question 25

what is the difference between PIP2 in GPCR and PIP3 pathway?

Answer 25

in GPCR: PIP2 converted to DAG and IP3 by PLC | in PIP3: PIP2 is phosphorylated by PI3-K into PIP3

Question 26

what is the difference between IP3 and PIP3

Answer 26

in IP3 - 1st carbon is phosphorylates in PIP3 - PIP2 isn't cleaved, a phosphate is just added to 3rd carbon + IP3 is cleaved off into cytoplasm where as PIP3 is still membrane bound

Question 27

what is the distinct feature of GSK3 and Glycogen synthase involved in PIP3 signaling pathway

Answer 27

GSK3 and GS are active when it is NOT phosphorylated => when phosphorylated by PKB -> inactivation => when phosphorylated by GSK3 -> inactivation

Question 28

when can glycogen synthesis happen?

Answer 28

when GSK3 is phosphorylated because this will inactivate GSK3 and prevent phosphorylation (inactivation) of GS rendering GS active -> glycogen synthesis

Question 29

which hormones have receptors with recruited tyrosine kinase activity?

Answer 29

growth hormone prolactin leptin

Question 30

characteristics of GH signaling pathways

Answer 30

- GH has 2 binding sites and binds sequentially to 2 receptor molecules forming a dimeric complex - > dimerization of the cytoplasmic regions initiates signal transduction

Question 31

what are the 2 first steps of GH signaling pathway?

Answer 31

1. binding of GH and dimerization | 2, recruitment of JAK-2 [tyrosine kinase]

Question 32

what are the 3 branches possible when recruiting JAK protein?

Answer 32

1. activation of the transcription regulatory proteins STAT 2. activation of the MAPK pathway (as insulin, but JAK2 plays role of IRS1) 3. activation fo PIP3 pathway (instead of IRS we have JAK2)

Question 33

what kind fo activity does JAK have?

Answer 33

intrinsic kinase activity -> phosphorylates itself, the receptor and other proteins

Question 34

what are STAT proteins?

Answer 34

transcription regulatory proteins - transcription factors that translocate from membrane to nucleus -> change in gene expression

Question 35

steps in JAK-STAT pathway (5)

Answer 35

1. binding of interferon cross-links adjacent receptors, and JAKs cross-phosphorylate each other on tyrosine (intrinsic tyrosine kinase activity) 2. activated JAKs phosphorylate receptors on tyrosine residues 3. After STATs dock on specific phosphotyrosines on the receptor, the JAKs phosphorylate them 4. STATs dissociate from receptor and dimerize via their SH2 domain 5. STATs translocate to nucleus where they act as transcription factors (bind to DNA and other gene regulatory proteins)

Question 36

which hormones bund to a family of intracellular receptors?

Answer 36

steroid hormones and thyroid hormones

Question 37

where are intracellular receptors located?

Answer 37

in cytoplasm or nucleus

Question 38

what is the function of the intracellular receptors?

Answer 38

transcription factors

Question 39

Response of intracellular receptors is fast since transcription and translation of proteins is necessary. True or false?

Answer 39

False! SLOW response

Question 40

for intracellular receptors to have a typical function, what must their nuclear receptor domain have? (3)

Answer 40

1. DNA-binding domain (DBD) 2. Nuclear localization signal (NLS) - for translocation into nucleus 3. ligand binding domain (LBD)

Question 41

once the hormone binds to the nuclear receptor and is activated, which sequence does it recognize on the DNA?

Answer 41

hormone response element

Question 42

if the nuclear receptor is a homodimer, what is the particularity of their HRE?

Answer 42

HRE sequence is the same for both

Question 43

what are co-repressors?

Answer 43

involved in repression of gene transcription | associated with nuclear receptor bound to DNA but not bound to ligand - inhibitory to transcription

Question 44

histone acetylation is involved with .....

Answer 44

gene expression

Question 45

histone deacetylation is involved with ....

Answer 45

repressed/lowered gene expression