Growth signals with broken parts
Cultured mammalian cells divide only when a growth factor binds its receptor tyrosine kinase (RTK). The active receptor phosphorylates itself, adaptor proteins help Ras swap GDP for GTP, and Ras-GTP starts the MAP kinase cascade (Raf → MAP kinase kinase → MAP kinase), which switches on genes for division. Each strain below carries the stated mutation in every copy of the gene and is otherwise normal. Cells are grown with no growth factor, a normal dose, or ten times the normal dose.
For each strain, predict whether the division signal reaches the nucleus under each condition.
Wild type
No growth factorNormal growth factor10× growth factorReceptor binds growth factor but has no kinase activity
No growth factorNormal growth factor10× growth factorRas that can't hydrolyse GTP
No growth factorNormal growth factor10× growth factorRas that can't bind GTP
No growth factorNormal growth factor10× growth factorReceptor active without ligand, plus Ras that can't bind GTP
No growth factorNormal growth factor10× growth factorConstitutively active MAP kinase kinase, receptor gene deleted
No growth factorNormal growth factor10× growth factor
| Row | No growth factor | Normal growth factor | 10× growth factor |
|---|---|---|---|
| Wild type | |||
| Receptor binds growth factor but has no kinase activity | |||
| Ras that can't hydrolyse GTP | |||
| Ras that can't bind GTP | |||
| Receptor active without ligand, plus Ras that can't bind GTP | |||
| Constitutively active MAP kinase kinase, receptor gene deleted |
Answer every part to submit.