What would happen if the kinase that adds the inhibitory phosphate to cdk were defective?

If the kinase that adds the inhibitory phosphate to cdk were defective then the M phase would begin prematurely. Of the many proteins involved in cell cycle control, cyclin-dependent kinase (CDKs) are among the most important. They are a family of multifunctional enzymes that can modify various protein substrates involved in cell cycle progression. M-phase promoting Factor is a complex of a cyclin and cyclin dependent kinase that, when activated, phosphorylates a number of specific proteins needed to intiate mitosis in eukaryotic cells. The cyclin sub-unit regulates the formation of the MPF dimer; the kinase subunit catalyzes the phosphoryation of other proteins to start M phase.

Six amino acids have side chains that are polar but not charged. these are serine (ser), threonine (thr), cysteine (cys), asparagine (asn), glutamine (gln), and tyrosine (tyr). these amino acids are usually found at the surface of proteins, as discussed in the proteins 2 module.