Question

What proteins are considered the “most important cell cycle regulators”? Briefly describe how these proteins are activated.

Under normal cell circumstances, proteins of the type you described in (b) above are most frequently activated/inhibited (highlight one of the two preceding terms) by proto-oncogenes and activated/inhibited (highlight one of the two preceding terms) by tumor suppressors.

Answer 1

Positive Regulation of the Cell Cycle

Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.

A conserved set of cyclin-dependent protein kinases (Cdks) initiate or regulate events through phosphorylation of intracellular proteins, thus controlling cell cycle progression, terminal differentiation, and apoptosis.

Cyclins are named such because they undergo a constant cycle of synthesis and degradation during cell division. When cyclins are synthesized, they act as an activating protein and bind to Cdks forming a cyclin-Cdk complex. This complex then acts as a signal to the cell to pass to the next cell cycle phase.

Cdk activation requires two steps. First, cyclin must bind to the Cdk. In the second step, CAK must phosphorylate the cyclin-Cdk complex on the threonine residue 160, which is located in the Cdk activation segment. In both humans and yeast, cyclin binding is the rate limiting step in the activation of Cdk.

Cdk activation inhibited by tumour suppressor protein

Under normal cell circumstances, proteins of the type described in above are most frequently

activated by proto-oncogenes and this genes activate cell division and cell proliferation

inhibited by tumor suppressors like p53 gene and this gene inhibit cell proliferation

Thank You!