They supposed that such mutant forms constituted new species and thus believed that natural selection was not necessary to account for the origin of species. The last influential mutationist was Richard Goldschmidt

TLS Online TPP Program

#Id: 9638

#XL - T Zoology

Sos is a GEF that catalyzes conversion of inactive GDP bound Ras to the active GTP-bound form.

TLS Online TPP Program

#Id: 9639

#XL - T Zoology

GRB2 has- 

Phosphotyrosine-binding SH2 domain

Two SH3 domains, bind to Sos

TLS Online TPP Program

#Id: 9640

#XL - T Zoology

The SH3 domains in GRB2 selectively bind to 

proline-rich sequences in Sos

TLS Online TPP Program

#Id: 9641

#XL - T Zoology

Downstream of Ras is a highly conserved cascade of three protein kinases-

Ras → Raf → MEK → MAP kinase

TLS Online TPP Program

#Id: 9642

#XL - T Zoology

In unstimulated cells, 

Raf is phosphorylated by several cytosolic kinases on two sites:

1. Serine/threonine kinase domain 

2. N-terminal autoinhibitory domain

TLS Online TPP Program

#Id: 9643

#XL - T Zoology

Molecular Handcuff 

Phosphorylation of Raf is recognize by protein 14-3-3 dimer, which locks the autoinhibitory domain in a position where it blocks and inhibits the kinase active site