Cell Division

Cell Division Cell Division - Start

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Cell Division

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Cell Division


Cell Increase and Decrease

Cell division increases the number of somatic cellsConsists of mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm)Apoptosis, programmed cell death, decreases the number of cells


The Cell Cycle

Cell cycle: orderly set of stages that take place between the time a cell divides and the time the resulting cells also divide.


The Stages of Interphase

Most of the cell cycle is spent in interphaseIn between episodes of mitosisCell carries on its usual functionsPrepares to divide (grows larger, number of organelles doubles, amount of DNA doubles)Lasts 20 hours in mammals


The Stages of Interphase

3 stagesG1 occurs before DNA synthesis S includes DNA synthesisG2 occurs after DNA synthesisG = growthS = synthesisM = mitosis


The Stages of Interphase

G1 stageCell doubles its organellesAccumulates materials needed for DNA synthesis


The Stages of Interphase

S stageDNA replication occursAt the beginning of stage, each chromosome is composed of one DNA molecule (chromatid). At the end, each chromosome consists of two identical DNA molecules (sister chromatids)DNA replication has resulted induplicated chromosomes


The Stages of Interphase

G2 stageCell synthesizes proteins needed for cell divisionG0 stage“Resting stage”Cell is neither dividing nor preparing to divideEx. nerve cells


The Mitotic Stage

Sister chromatids of each chromosome separate, becoming daughter chromosomes that are distributed to two daughter nucleiAfter cytokinesis, two daughter cells are leftAbout 4 hours in mammal cells


Control of the Cell Cycle

Controlled by internal and external signals.Growth factors: hormones that act as external signals that regulate mitosis


Control of the Cell Cycle

The stop signs represent checkpoints when the cell cycle can possibly stop


Control of the Cell Cycle

Cyclin: protein that control the progression of cells through the cell cycleMust be present from G2 to M, and G1 to S


Control of the Cell Cycle

G1 checkpoint: cell cycle will stop if DNA is damaged In mammals, protein p53 stops cell cycle at G1.If p53 cannot repair DNA, will bring about apoptosis


Control of the Cell Cycle

G2 checkpoint: Cell cycle stops if DNA has not finished replicatingIf DNA is damaged, stopping the cell cycle allows time for damage to be repaired


Control of the Cell Cycle

M checkpoint: Mitosis stops if chromosomes not properly aligned



Programmed cell deathCell fragments engulfed by white blood cells or neighbouring cells



Cells harbour the enzymes that bring about apoptosis

Held in check by inhibitors

Unleashed by internal or external signals

“Initiators” receive signal to activate “executioners” which activate enzymes that dismantle cell

ex. executioners turn on enzymes that tear apart the cytoskeleton and enzymes that chop up DNA.







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