This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Transition from G2 to M phase of the cell cycle is controlled by - 
Select and explain. 
A. Retinoblastoma gene product, B. p53 protein, C. Cyclin E, D. Cyclin B
D: Cyclin B
Answer: D: Cyclin B 
Explanation: o Resting cells are in G0 phase of cell cycle and need to be recruited into the G, stage and beyond in order to replicate. The entry and progression of cells through the cell cycle is controlled by changes in levels and activities of cyclins and cyclin dependent kinases (CDKs), and their inhibitors.