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Do now: List the phases of the cell cycle

The Cell CycleComposed of 4 phases

G1(gap 1)S (DNA replication/Synthesis)G2 (gap 2)M (Mitosis and cytokinesis)

Interphase

Mitotic phase

Aim: What is the cell cycle?

G1 and G2Phases of cell growth, differentiation (modification

of cell to perform particular functions) and cell activity.

Aim: What is the cell cycle

S (DNA synthesis)Copies of DNA needed for cell division are

made in this phase. (DNA Replication)

Aim: What is the cell cycle

G0Cells that stop growing and dividing leave the

cell cycle and enter this phaseDo you know of any cells that stop dividing?Http://www.youtube.com/watch?v=P9ngTBG2e0EThey are still metabolically active (continue

doing all the chemical processes they need to survive) and viable (alive and useful)

Aim: What is the cell cycle

M (Mitosis and Cytokinesis)Mitosis-nuclear division

Cytokinesis-division of the cell’s cytoplasm. At the end of mitosis and during cytokineses chromosomes uncoil and DNA starts directing protein synthesis

Aim: What is the cell cycle

Continual proliferationIf a cell that should be in G0 is not in G0 goes

into continual proliferationThis means that it continues to grow and

divide uncontrollablyThis can lead to cancer.

Aim: What is the cell cycle

Initiation of MitosisA protein complex called MPF (mitosis promoting

factor) initiates mitosis in the cell cycleMPF is a protein factor made of 2 proteins: an

oscillating protein (constantly increasing and decreasing in amount) called Cyclin B and a constant

kinase called CDC2.A kinase is an enzyme that ads a phosphate to a

protein in a process called phosphorylation.

Because CDC2 only works when Cyclin B is present it is referred to as a Cyclin Dependant Kinase

Aim: What is the cell cycle

P

1. CDC2 remains constantly and inactive in the cell

2. There is an increase of Cyclin B

3. Cyclin B phosphorylates

CDC2(adds 2 phosphates)

Aim: What is the cell cycle

Steps to initiate mitosis1. CDC2 remains constantly and inactive in the

cell2. There is an increase of Cyclin B

3. Cyclin B phosphorylates CDC2(adds 2 phosphates)

4. Another kinase then removes one of the phosphates

5. Mitosis starts

6. Cyclin B is degraded and CDC2 becomes inactive again

Aim: What is the cell cycle

P

1. CDC2 remains constantly and inactive in the cell

2. There is an increase of Cyclin B

3. Cyclin B phosphorylates

CDC2(adds 2 phosphates)

4. Another kinase then removes one of the phosphates

5. Mitosis starts6. Cyclin B is degraded

and CDC2 becomes inactive againAim: What is the cell cycle

Cell Cycle Check PointsMake sure that events have been completed before commencing the next phase.There are 3 major checkpoints1.G1/S checkpoint-checks for cell size and damaged DNA.

S-phase promoting factor is a protein used at this checkpoint to prepare DNA for replication.

Aim: What is the cell cycle

Cell Cycle Check Points2. G2/M checkpoint-checks for proper and

complete DNA synthesis/replication and damaged DNA.

3. M checkpoint-checks spindle fibers formation and attachment to chromatids

Aim: What is the cell cycle

G2/M

Aim: What is the cell cycle

ApoptosisG1/S check detects too much DNA damage

the cell might selfdestruct.Apoptosis is programed cell deathHowever, if among the damaged DNA is the

p53 the call cannot selfdestruct ensuring cancer.

This gene has been linked to colon, breast, lung and many other cancers.

Aim: What is the cell cycle