Cell Cycle. What can I say?

For clarification, most of the lines have either an arrowhead or yellow cross in place of an arrowhead.  Lines that do not have either are binding to the molecule whose action line they intersect.  A yellow cross as an endpoint indicates the source of that line is inhibiting the action of the line they cross (i.e. there is a red line that ends in a yellow cross from G1-Cdk that crosses Rb's action line=G1-Cdk inhibits Rb).