Question

Explain how RAs is normally regulated and what the function of Ras is when activated

Answer 1

Regulaion of Ras is done by Sos mediated positive feedback system.Ras, a small G - protein is inactive in GDP bound condition. For it's activation Sos (Son of sevenless), a guanine nucleotide exchange factor binds to ras GTPase and relese ras GDP and add GTP . Once ras is active it activates downstream cascade Raf which is a serine theronine kinase. Raf adds phosphate group over Mek, a serine tyrosine kinase, which in turn activates Erk, a map kinase by phosphorylation. A scaffold protein holds three kinases & after activation Erk immediately leaves the scaffold, moved to nucleus and activates early and late gene which proceed cell cycle to next phase.