In: Biology
Describe how positive and negative controls regulate the cell cycle. Your response should include a definition of positive and negative control, and an example of each
Positive control helps in regulation of the cell cycle whereas in negative control cell cycle is halted. An example of positive control is Cyclin CDK complex while negative control is protein retinoblastoma.
Timing and all events of cell cycle is regulated by a heterotrimeric protein complex called cyclin CDK where cyclin is the regulatory subunit and bound to CDK and activate them. CDK (cyclin dependent kinase) is the catalytic subunit and cyclin bound CDK becomes active and act as serine threonine kinase and phosphorylate target proteins. During cell division cyclins are periodically synthesized and degraded by specific proteases whereas concentration of CDK remain constant.
Retinoblastoma in an active form blocks cell cycle progression. Due to inactivation of protein retinoblastoma a transcription factor called E2F becomes active that stimulate transcription of cyclin E CDK 2 complex as the cell approaches G1 to S transition. Loss of functional mutation in both copies of genes of protein retinoblastoma associated with tumor because retinoblastoma is tumor suppressor gene.