Which of the following statement is NOT true?Cell cycle cyclin dependent kinases (CDKs) are synthesized and degraded in every cell cycleO Activity of the S phase CDKs rise in the S phase and drops in the G2 and mitotic phaseAPC/C proteasome activity increases during mitotic phase and drops towards the end of theG1 phaseG1/S cyclin protein amount rises in the G1 phase< PreviousNext >

The cell is the basic functional unit of all biological entities. The cell cycle is a process involving a series of steps in which the parent cell and its contents double and divide to form a daughter cell. The doubling of the cellular content is done to ensure that each daughter cell possesses the genetic material of the parental cell. There are mainly 4 phases of the cell cycle namely,G1 phase ( growth phase)S phase (synthesis phase)G2 phase ( second growth phase involving preparation of the cell to undergo mitosis)M phase (Mitosis phase)Let's understand each statement one by one to determine which one is incorrect.Statement 1:- CDKs are synthesized and degraded in every cell cycle.Cell-dependent kinases (or CDKs) are the proteins that regulate the progression of different cell cycle stages. These CDKs are synthesized and their levels increase or decrease according to their role in a particular phase of the cell cycle. After every cell cycle, to ensure proper regulation and control of cell growth and division, these CDKs are degraded. Therefore this statement is true.Statement 2:- Activity of S phase CDKs rises in the S phase and decreases in the G1 and M phases.The S-CDKs are responsible for phosphorylating the proteins that are involved in replication, such as the Origin Recognition Complex (ORC) to prevent rereplication in the cell, so its activity is higher in the G1 and Mitotic phase. Therefore this statement is not true.Statement 3:- APC/C proteasome activity increases in the M phase and drops at the end of the G1 phase.APC/C proteasome or the Anaphase-promoting complex/cyclosome is a ubiquitin complex that is responsible for ubiquitination in the mitosis phase. So its concentration remains higher in the Mitotic phase and then lowers in the G1 and S phases. Therefore, this statement is true.Statement 4:- G1/S Cyclin protein rises in the G1 phasethe G1/S cyclin protein is responsible for the transition of G1 phase to S phase, so its levels start to rise at the end of the G1 phase toward the start of the S phase. Therefore this statement is true.Hence, option B given as "activity of S phase CDKs rises in S phase and decreases in G1 and M phase" is the most appropriate answer selection to this question because this is the only incorrect statement.