Which of the following statements is true of cyclin-dependent kinases? o o o o o they regulate the cell cycle by phosphorylating other proteins they serve as receptors in signal-transduction pathways. they bring about apoptosis within cancer cells. they add methyl groups to histone proteins to assist in gene regulation. they speed up the cell cycle and cause abnormal cell proliferation. which of the following statements is true of cyclins? o o o o o the levels of cyclin oscillate during the course of the cell cycle. they add methyl groups to histone proteins to assist in gene regulation. they regulate the cell cycle by phosphorylating other proteins. they normally speed up the cell cycle and cause abnormal cell proliferation. they function via an intracellular domain to which a signaling molecule can bind.