Cell cycle

Why must cells divide

To allow an organism to grow and for tissues to be repaired.

What must cells do before they divide

They must grow larger, produce new organelles and replicate DNA.

What are the 3 phases of the cell cycle

Interphase, mitosis, cytokinesis

Interphase

Cells grow and synthesise new proteins, produce organelles and replicate DNA in preparation for nuclear and cell division.

Mitosis

Nuclear division to produce two genetically identical nuclei.

Cytokinesis

Division of cytoplasm to produce two daughter cells.

Why are the daughter cells genetically identical but not just identical

Because the have the same genetic information, however they may contain different numbers of organelles.

What are the 3 phases of interphase

G1 (first growth), S (synthesis), G2 (second growth)

G1 phase

The cell grows in size and synthesises more proteins and membranes and produces more organelles. The cellular contents, excluding chromosomes, are duplicated.

S phase

The DNA is replicated.

G2 phase

Cell growth and protein synthesis continues, and the replicated DNA is checked for any errors. The cell also prepares for mitosis as centrioles replicate.

What occurs at a checkpoint

Progression through the cell cycle is halted until all necessary conditions are met.

What are the 3 major checkpoints of the cell cycle

G1/S, G2/M, M

G1/S checkpoint

Ensures any DNA damage is repaired, the cell is large enough and the environment is suitable for the cell to divide (otherwise the cell may enter G0).

G2/M checkpoint

Checks the DNA has been accurately replicated and repairs any errors. The cell will enter mitosis if it is large enough and the environment is suitable.

M checkpoint

Ensures all chromosomes are attached to the mitotic spindle.

Cyclins

Proteins which are produced to activate enzymes called cyclin-dependent kinases (CDKs).

Cyclin-dependent kinases

Enzymes which are activated at particular checkpoints in the cell cycle and control each step.

How can the cell cycle be stopped

By the production of other proteins that bind to a CDK.

What occurs at the G1/S checkpoint if the DNA is too damaged

Apoptosis (programmed cell death) is triggered.

What could a failure to control the cell cycle or repair damaged DNA result in

Uncontrolled cell division resulting in a tumour.

G0 phase

A resting phase when a cell leaves the cell cycle.

What may a cell undergo in the G0 phase

Apoptosis or senescence (loss of a cell's power of division and growth).

Why might a cell enter G0 temporarily

The environment is unsuitable for division.

Why might a cell enter G0 permanently

The cell is fully differentiated.