23. Enzyme Linked and Intracellular Receptors

Question 1

Describe the mechanism of RTKs?

Answer 1

1. Ligand binds to outside of the cell
   Receptors dimerise
   Tyrosine tail is phosphorylated
2. Grb2 is an adapter protein
   One arm recognised a phosphotyrosine on an active receptor (SH2 domain)
   Other arm recognises proline on signalling molecules (SH3 domain)
3. Ras is a G protein required to transmit RTK cell signalling
   SoS acts to activated Ras by binding to it and removing GDP
   Ras binds GTP
4. Active Ras triggers activation of cell signalling pathways
   Changes in protein activity and gene expression
   Cell proliferation

Question 2

What happens to a ligand-gated ion channel when a hormone binds to it?

Answer 2

Channel opens and activates an influx of ions

Direct coupling of receptor and channel

Question 3

Name an example of a nuclear receptor

Answer 3

Glucocorticoid receptor

Question 4

Describe the mechanism of nuclear receptors

Answer 4

1. Steroid hormone enters via cell membrane
   Receptor in cytosol is bound to a molecular chaperone
   Hormone binding to the receptor causes dissociation of the molecular chaperone
2. Steroid hormone and receptor translocate to the nucleus
3. Binds to DNA-associated receptor to initiate gene expression programmes
4. Gene expression profile of the cell changes due to initiation of transcriptional programme triggered by steroid-receptor complex