Cyclins modulate the progression of cells through the cell c

Cyclins modulate the progression of cells through the cell cycle by 1) directly activating G proteins. 2) inducing synthesis of constitutively active forms of growth cell receptors. 3) activating protein kinases that are critical regulators of cell division. 4) degrading histones. 5) increasing the production of DNA polymerases. The protein(s) that facilitate the unfolding of chromatin fibers ahead of the replication fork is (are) 1) helicase. 2) scaffold proteins. 3) chromatin remodeling proteins. 4) replisomal proteins. 5) both choices helicase and scaffold proteins

Solution

Ans: option (3)

Reason:- The timing of cell cycle is regulated by a family of protein kinases with activities that change in response to cellular signals. By phosphorylating specific proteins at precisely times intervals, these protein kinases orchestrate the metabolic activities of cell to produce orderly cell division.in absence of cyclin the catalytic subunit is inactive virtually. There are about 8 CDKs which act in various combinations at specific points in cell cycle.

Ans: option(1)

Reason:

DnaB helicase is key protein in initiation of replication. As a replicative helicase DnaB migrates along the single stranded DNA in 5\' to 3\' direction unwinding DNA as it travels. The DnaB helicase loaded onto the two DNA strands thus travel opposite directions creating two potential replication forks.