Kinase (enzyme) -linked receptors

Question 1

describe phosphorylation

Answer 1

the phosphorylation of PROTEINS activates or inactivates them

affecting their affinity, localisation, interactions with other proteins

undergone via atp dephosphorylation to adp

Question 2

impact of phosphorylation on target proteins

Answer 2

affects their affinity, localisation, interactions with other proteins

Question 3

name the three amino
acids involved in protein phosphorylation

Answer 3

serine, threonine and tyrosine

Serine and threonine are phosphorylated by the ame protein kinases

Question 4

classify kinase-linked receptors with example(s)

Answer 4

tyrosine kinase-associated receptor
EXAMPLE: cytokine receptors

receptor tyrosine kinase
EXAMPLE: insulin receptor, epidermal growth factor receptor

Question 5

Explain the kinase cascade of receptor kinase signalling

Answer 5

1. Once GrB2 binds to tyrosine residue and phosphorylates
2. SOS binds to GrB2 to facilitate GTP–>GDP exchange
   3.RAS is activated to turns GTP to GDP
3. Free phosphate molecules are used to produce a phosphorylation cascade Raf–>Mek–>MAPK
4. MAPK translocates into the nucleus
5. Phosphorylates transcription factors and modulates gene transcription

Question 6

What Kinases are active in the kinase cascade

Answer 6

serine and threonine kinases

Question 7

describe the structure of the insulin receptor

Answer 7

Dimer in absence of ligand binding
- (αβ)2 (a dimer of heterodimers)
- extracellular α subunit and intracellular β subunit are linked by disulfide bonds

Question 8

describe the activation of the insulin receptor

Answer 8

• unliganded - access of substrates to the active site is blocked due to activation loop inhibition
• liganded - inhibition removed
• phosphorylation of tyrosine in the activation loop

Question 9

describe the structure and activation of insulin receptor mediated signalling

Answer 9

3 major pathways
1. Insulin receptor
substrate (IRS) –> Grb2 –>SOS–>Ras–>Raf–>MEK–>MAPK
2. Insulin receptor
substrate (IRS) –>PI3K–>AKT
3. APS–>CAP–>c-CBL

Question 10

GLUT4-mediated glucose uptake

Answer 10

GLUT4 increase the amount glucose taken up by the cell

Question 11

explain the use of fluorescent proteins to study insulin-stimulated translocation of GLUT4

Answer 11

Fluorescent EGFP and immuno-fluorescent antibodies allow for the visualisation of GLUT4 translocation

• When in basal state the GLUT4 float in the cell
• When activated GLUT4 fuse with the cell membrane exposing myc-tag externally
• This is tracked by immunofluorescence as insulin antibodies bind to the extracellular myc-tag and display fluorescent formation along the cell wall

Question 12

explain the use of small molecule tyrosine kinase inhibitors to treat cancer

Answer 12

Epidermal growth factor receptor are over expressed when cells are affected by cancer

Tyrosine kinase inhibitors prevent the binding of ATP preventing tyrosine kinase phosphorylation, inhibiting growth.