RAS oncogene

Question 1

what is RAS?

Answer 1

protein family of small GTPases

Question 2

how is Ras activiated normally?

Answer 2

through the Ras/Map kinase pathway
growth factor binds to receptor tyrosine kinase causing the receptor to change shape allowing dimerisation of two receptors
autophosphorylation then occurs allowing the recruitment of GRB2 and SOS proteins to the membrane
SOS protein activates Ras through the conversion of GDP to GTP
Ras then activated MAP kinases (ERK1 and ERK2) which travel to the nucleus and phosphorylate/ activate transcription factors to induce the expression of genes

Question 3

what are the genes that are activated by ERK1 and ERK2 involved in?

Answer 3

survival 
cell proliferation 
migration 
angiogenesis 
differentiation

Question 4

what are the isoforms of Ras?

Answer 4

HRAS
NRAS
KRAS

Question 5

at which codons do mutations in Ras usually occur?

Answer 5

12
13
61

Question 6

which isoform of Ras is commonly mutated in colorectal cancer?

Answer 6

KRAS

Question 7

what is the most common type of mutation in colorectal cancer and why?

Answer 7

missense

causes change in amino acid and so most likely to cause a gain in function