Phases of the Cell Cycle

The cell cycle is:

is a series of events that leads to a single cell replicating into two.

Three distinct steps of cell cycle:

interphase, mitosis, cytokinesis

Interphase

cell increases in size and doubles its DNA

Mitosis

cell equally seperates its chromosomes

cytokinesis

cell divides completely into two

M phase

cytokinesis overlaps with mitosis

Interphase can be further subdivided into 3 stages

G1,S and G2

G1 (Gap 1):

The cell grows, generates more organelles, and increases its production of proteins to prepare for DNA synthesis (longest step)

s (Synthesis)

cell replicates its DNA

G2 (Gap 2):

the cell grows and prepares for mitosis

Transition through the cell cycle is regulated by:

cyclins, cyclin-dependant kinases (CDKs), and tumor suppressors

Stage specific cyclins are synthesized at each phase of the cell cycle and they

bind and activate specific CDKs

Cyclin-CDK complexes

phosphorylate target proteins to signal transition to the next phase of the cell cycle

Tumor suppressors in the ____ and _____ families inhibit cell cycle progression. These halt the cell cycle by:

cip/kip; INK4

binding cyclin-CDK complexs or CDKs respectively

The tumor suppressor ____ is activated in response to DNA damage

P53

Activated P53

wil halt the cell cycle at the S-phase to allow time to repair DNA before synthesis

________________ ensure that the cell has met necessary requirements before proceeding to the next phase so the cell doe snot pass on damaged DNA

Cell-cycle checkpoints

Cell-cycle checkpoints during:

G1-cell decides whether to divide, continue growth, or rest

G2-cell checks for and repairs DNA damage

M-quality of mitosis is assessed to allow cytokinesis initiation

G0 (Gap 0)

cell can permanently or temporarily leave cell cycle. during this stage the cell can differentiate to perform its required functions