Biosignaling II

Question 1

Receptor tyrosine kinase structure

Answer 1

dimer structure (2 of each subunit)
alpha subunit ligand binding site
beta subunit integral protein (transmembrane)
enzyme active site on intracellular side with 3 Tyr residues
intrinsic protein kinase activity (to phosphorylate Tyr residues)

Question 2

insulin RTK pathways intrinsic effects and cascade pathway mechanisms

Answer 2

targeted intrinsic effects: peripheral insulin sensitivity (glucose uptake), Beta cell development, and central leptin sensitivity
affects a lot of growth factors

secondary messengers: MAPK and PIP3 signaling cascades

Question 3

activation of RTK

Answer 3

ligand binding causes phosphorylation of Tyrosines on activation loop on intracellular side, which is blocking the binding site
Conformational change of the activation loop leads to opening the binding site, to phosphorylate target proteins

Question 4

function of insulin

Answer 4

regulates metabolic enzymes and gene expression
does not enter cell

Question 5

MAPK pathway for insulin part 1 (up til start of MAPK)

Answer 5

1. Insulin binds RTK and dimers autophosphorylate
2. Insulin RTK phosphorylates IRS-1
3. Grb2 (SH2) binds IRS-1 Tyr
4. Sos binds Grb2
5. Sos binds Ras, ousting GDP for GTP
6. Active Ras binds Raf-1 (MAPKKK)

Question 6

MAPK pathway for insulin part 2 (MAPK pathway)

Answer 6

6. Raf-1 (MAPKKK) phosphorylates 2 Serine residues on MEK
7. Mek (MAPKK) phosphorylates Thr and Tyr residues on ERK (MAPK)
8. ERK (MAPK) moves into nucleus and phosphorylates TF to activate, like Elk1
9. Elk1 and SRF transcription factors stimulate transcription of cell division genes

Question 7

IRS-1

Answer 7

insulin receptor substrate 1
target protein that goes from RTK to MAPK pathway and to PI3K in GLUT transporter pathway/GS (glycogen synthase inactivation)

Question 8

protein phosphorylation mechanism

Answer 8

ATP donates P and transferred to an acceptor protein
catalyzed by protein kinase enzymes
can activate or inactivate the target

Question 9

PIP3 pathway for glucose

Answer 9

1. IRS-1 (from RTK MAPK pathway) binds/activates PI3K enzyme
2. PI3K enzyme converts PIP2 –> PIP3 via phosphorylation (membrane bound)
3. PKB (protein kinase B) binds to PIP3, and is phosphorylated
4. PKB phosphorylates GSK3 to be INACTIVE (so GS stays active, when GSK3 is active, it inactivates glycogen synthesis)
5. PKB stimulates movement of GLUT4 receptors from vesicles to plasma membrane for increased glucose uptake into cell (muscle, fat and heart tissue)

Question 10

PI3K
PIP3

Answer 10

phosphoinositide 3-kinase enzyme
phosphatidylinositol 3,4,5 triphosphate

Question 11

GSK3

Answer 11

Glycogen synthase kinase 3
regulates glycogen synthesis
when inactive (phosphorylated) GS (glycogen synthase) remains active and synthesizes glycogen via phosphorylation by PKB in PIP3 pathway
when active, it phosphorylates GS (inactivating it), prevent glycogen synthesis
very active in muscle and liver tissue

Question 12

where is PIP3 pathway for glucose very common

Answer 12

fat and muscle tissue

Question 13

Structure and function of variations in RTK and growth factors

Answer 13

all have interior tyrosine kinase domains
extracellular receptors differ for each growth factor to bind different ligands

Question 14

INSR kinase

Answer 14

insulin receptor kinase
phosphorylates tyrosine residues on beta-adrenergic receptor amplification of insulin signaling)
also phosphorylates IRS-1 in normal insulin pathways (PI3K and MAPK)

Question 15

internalization of beta-adrenergic receptors due to insulin signaling

Answer 15

insulin receptor kinase (INSR) phosphorylates 2 Tyr on b-adrenergic receptor
Insulin-activated PKB phosphorylates 2 Ser residues on b-adrenergic receptor
result is internalization of beta-adrenergic receptors into vesicles

Question 16

amplification of MAPK signaling with b-adrenergic receptors

Answer 16

INSR kinase phosphorylates b-andrenergic receptor
receptor can then initial MAPK signaling pathway, enhancing insulin signaling x10

Question 17

resting membrane potential

Answer 17

-70 to -50 mV
polarized, depolarized, hyperpolarized
more positive than -50 is threshold potential

Question 18

Na-K Pump

Answer 18

3 Na+ pumped out into extracellular matrix
2 K+ pumped into intracellular matrix
K+ moves with electrical gradient, but against concentration gradient
catalyzed by ATPase

Question 19

How depolarization works

Answer 19

1. Sodium channels depolarize (Na+ pumped in)
2. K+ then depolarize (K+ pumped out)
3. Voltage gated Ca2+ channels open due to depolarization
4. Ca2+ entering cell triggers release of acetylcholine from vesicles
5. Acetylcholine crosses synaptic cleft and binds ligand gated channels
6. Na+/Ca2+ enters new dendrite and depolarization begins anew

Question 20

Dendrotoxins

Answer 20

block repolarization of K+, effectively prolonging action potential

Question 21

hormones travel bound to

Answer 21

serum binding proteins

Question 22

Nuclear receptor mechanism of hormones (steroid, retinoid, thyroid)

Answer 22

1. Hormone diffuses through plasma membrane and enters nucleus
2. Hormone binds to nuclear receptor, causing conformational change
3. forms homo or heterodimers with other hormone-receptor complexes
4. Together bind hormone response elements (HRE) on DNA adjacent to specific genes
5. Receptors attract coactivator/co-repressor proteins to regulate transcription (increasing/decreasing mRNA formation)
6. Altered levels of hormone gene products produced leading to cellular response

Question 23

steroid receptor location

Answer 23

usually cytoplasmic or nuclear
5-10% can be localized to plasma membrane