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A Handbook of Biology

 All organisms,

even the

largest, start

their life from

a single cell

 The growth and

reproduction of

all organisms

depend on the

division and

enlargement of

cells.

 The mechanisms

of division and

multiplication

of cells together

constitute cell

reproduction.

 These newly

formed

daughter cells

can themselves

grow and divide

giving rise to

a new cell

population.

ÇËLL ÇÝÇLË

It is the life period of a cell during

which

a

cell

synthesizes

DNA

(replication), grows & divides into 2

daughter cells.

Cell growth (cytoplasmic increase)

is a continuous process but DNA

synthesis occurs only at a specific

stage.

The sequence of events takes place

in a coordinate way to ensure

correct division and formation of

progeny cells with intact genomes.

These events are themselves under

genetic control.

Duration of cell cycle varies in each

organism and each cell type.

E.g. Duration of a typical eukaryotic

cell cycle (e.g. human cell is about

24 hrs). In Yeasts, it is 90 minutes.

While in bacteria E.coli the cell cycle

is of 20 minutes.

1. PHÅSËS ØF ÇËLL ÇÝÇLË



Cell cycle includes 2 basic phases: Interphase & M Phase.

1. ÏÑTËRPHÅSË (RËSTÏÑG PHÅSË)



It is the phase between two successive M phases.



It includes cell growth and DNA synthesis.



It is the time during which the cell prepare itself for division by undergoing

both cell growth and DNA replication in an orderly manner.