Question

Which of the following about cell cycle control is true?

		The concentration of cyclins changes as Cdk concentration changes.
		Decreasing cyclin concentrations would increase progression through cell cycle check points.
		Cyclins help activate cdks by phosphorylating them.
		Phosphorylation of retinoblastoma will increase progression through the G1/S cell cycle check point.
		Bipolar attachment of chromosomes to the spindle controls the transition from G1 to S.

Answer 1

Phosphorylation of retinoblastoma will increase progression through the G1/S cell cycle check point is true

as retinoblastoma binds to E2F when not phosphorylated, E2F activates gene involved in DNA syntheis

others are false becuase

in first cyclin concentration changes according to different phase of cell cycle and CDK concentration remains almost same

2 decreasing cyclins will not increase progression through checkpoints as decrease in one cyclin is accompanied by increase in other cyclin through the cell cycle

cyclins dont have kinase activity

attachment of chromosomes to spindle take place in mitosis phase of cell cycle in metaphase