In early cell cycles there are only two phases M and S Name

In early cell cycles there are only two phases (M and S). Name the protein complex used for the cell cycle phase progression. When is it inactive and active? How is its activity regulated?

Solution

The 2 main proteins complex present in the process are Cyclins & Cyclins dependent protein kinase (Cdks)..

1) the main activity of Cdks are phsphrylation of the molecules i.e adding a negative phosphate gp. This signals the cell that it is ready to be passed to the next step or stage of the cell cycle.. But it\'s activity is dependent upon the other protein called Cyclins..!! When Cyclins binds to the Cdks it makes the Cdks active and which results in the activation of Cdks activity hence start phosphrolyting the molecules of cell cycle..!!

2) the Cyclins are the protein molecules which are continuously made and degraded according to the need for the cell cycle. When the cell cycle starts it forms which goes and combines with the Cdks thus forming a Cdks-Cyclins protein complex which signals the cells to pass to the next stage if everything goes right..

There are different clases of Cyclins which specifically binds to Cdks regulates the passes of cells from a particular stage to another. For eg:- Cyclins A/ Cdks-2 does the transition from G1-S phase..!!