Question

Describe two proteins phosphorylated by the M phase cyclin-dependent kinase (M-Cdk). What does the phosphorylation of that protein cause?

Answer 1

M phase cyclin dependent kinases, once activated by dephosphorylation drives the entry of cell in mitotic phase.. M-cdk alone does almost all the work necessary for mitosis.

Following are 2 primary targets of M cdk during mitosis

Condensins

Condensins are class of proteins responsible for condensation of chromatins. Condensins can form a ring like structure and use energy obtained from ATP hydrolysis in compacting sister chromatids.

M- CDK helps in condensation of sister chromatids by phosphorylating condensin subunits and hence triggers the coiling and condensation of DNA led by phosphoylated condensin proteins.

Lamin proteins

Lamins are important fibrous proteins. They are responsible for structural rigidity of nuclear membrane. Lamins are also responsible for degradation and reassembly of nuclear membrane along with positioning of nuclear pores.

Dismantling of nucler membrane is another key step during cell division. M-cdk triggers dissolution of cell membrane by phosphorylating laminin proteins and thereby triggereing it's depolymerization.

Apart from these proteins M- cdk also plays pivotal role in assembly and stabilization of spindle fibres. Therefore it is M cdk which triggers sismantling of nuclear membrane, condensation of sister chromatids alongwith assembly of spindle fibres.