Question

Describe how protein kinases and phosphates change the activity of downstream proteins and explain what is meant by "kinase cascade" by using the mitogen activated protein kinase pathways as an example.

Answer 1

Kinases and phosphatases are the most important molecules in any living cell.

Kinases are responsible for the addition of phosphate group whereas phosphatases are wallpaper for the removal of a phosphate group.

Both of these molecules work together to regulate a reaction. In some cases, kinases are positive stimulator of a reaction where as in some other cases phosphatases are positive stimulator of a reaction. Both of the enzymes can also work as negative stimulator of a reaction.

Kinases transfer phosphate group from the energy rich molecule ATP to a substrate molecule to convert it into product molecule.

Phosphatases transfer phosphate group from substrate molecule to ADP to convert it into ATP and form a product molecule.

Addition or removal of phosphate group to a protein can either activate it or inactivate it. Both kinases and phosphatases are involved.

Kinase cascade is referred to as a series of reactions where one molecule is phosphorylated by the other which in turn gets phosphorylated by another molecule. A very good example of this series of reactions in a cell is mitogen-activated protein kinase.

The image of this pathway is given above. In this signalling pathway, MAPKKK phosphorylates a substrate molecules to form a product molecule, the product is then phosphorylated by MAPKK, and further the new product is phosphorylated by MAPK. MAPK then enters nucleus to phosphorylate a regulatory molecule which can then control downstream processes.

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