Ras Pathway

[biologybuzz]

I need some help on this question!!!! I've been trying to find an answer for hours and have gone nowhere...any help would be appreciated!

Use diagrams and brief explanations to show how the cell cycle in the budding yeast, Saccharomyces cerevisiae, is temporarily halted during mating. Be sure to specify the role of MAP kinase pathway(s) in this process.

The following questions focus on experimental observations that are related to determining the sequence in which two key components of the Ras pathway interact with each other.

(a) When epidermal growth factor (EGF) is added to epithelial cells, the Ras and Raf proteins are both activated. From this observation by itself, what conclusion can you draw about the relationship between Ras and Raf?
(b) In mutant cells containing a permanently inactivated Ras protein, addition of EGF does not activate the Raf protein as much as it does in normal cells. What conclusion can you draw from this observation?