Question

The restriction point is defined best as the point in the cell cycle

	a.	at which G1 ends and S-phase begins
	b.	where cells stop progressing through the cell cycle regardless of the stress they experience
	c.	after which mitogens can promote cell cycle progression
	d.	after which withdrawal of mitogens will not prevent cell cycle progression
	e.	before which mitogens can not influence cell cycle progression

Answer 1

The G1 phase of the cell cycle is the first phase of the cell division cycle and the first phase of the cell division requires some extra growth factor known as mitogen to occurs. But these mitogen are required untill until the cell reach the specific state in the G1 phase. If mitogen are removed before that state cell cycle get arrested. Once the cell has passed that state it is completely independent of mitogen and does not care whether mitogen is present or not. This state is known as restriction point (generally in late G1 phase). Once the restriction ponit is passed cell is destined to undergo mitosis irrespective of presence or absence of mitogen. Hence option D is right answer.