PLease help! I have an oncology(cancer biology) assignment to be finished by tom

Question

PLease help!

I have an oncology(cancer biology) assignment to be finished by tomorow... need help really.

Please explain

1) Ras -> Raf -> MAP kinase pathway

2) PI3 kinase pathway: controls inositol lipids and the Akit/PKB kinase.

3) Ral(distant cousin of Ras) pathway

in detail, and long explanations please:) My professor only gives good grades if I organize the answers into very clear, organized way and long....

Please explain their detailed pathways, mechanism, and its contribution to cell proliferation and cancer forming.

Explanation / Answer

1. Ras -> Raf -> MAP kinase pathway is also known as MAPK/ ERK pathway.

Kinase linked receptors respond mainly to protein and enzyme mediators. A single transmembrane helix connects the extracellular binding domain to the intracellular domain. Eg: insulin, growth factors.

The binding of growth hormone to the receptor causes dimerisation (by the activation of Janus kinase 2, JAK2) of the receptor (conformational change) that result in autophosphorylation of tyrosine residues. The binding of SH2-domain (src homology) protein (Grb-2) to the phosphorylated tyrosine residues stimulates cell growth through a cascade of protein phosphorylations.

Grb- 2 recruits a protein called SOS, which activates Ras by binding to it (Ras binds to GTP). Finally, the activated Ras causes phosphorylation of other proteins including Raf kinase. This results in the activation of MEK 1 and MEK 2, which activates mitogen activated protein kinase by phosphorylation, finally gene transcription occurs in the nucleus.

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