Chapter 1. CELL DIVISION• INTRODUCTION:

Cell Division means the division of a cell for following functions like Growth, Repair, Replacement Reproduction, and Regeneration.

Cell Division takes place through cell cycle. Cell Cycle consist of Interphase and Mitosis or Meiosis.consist of Interphase and Mitosis or Meiosis.

Interphase has 3 phases / stages:

(1). G 1 (Growth Phase / Gap 1)(2). S - phase (Synthesis Phase

(3). G 2 (Gap 2)

If the cells are of somatic type or body cells then it undergoes Mitosis and if the cells are germ cells or reproductive cells then it undergoes Meiosis.

INTERPHASE• It is the longest phase in a Body (Somatic) cells & in

Germ (Reproductive) cells. The Eukaryotic cellspends majority of time in this phase. It preparesitself for cell division.

• Interphase is also considered to be the 'living' phaseof the cell, in which the cell obtains nutrients, grows,reads its DNA, and conducts other "normal" cellfunctions.functions.

• Before dividing, each cell has to attain the same sizeas its mother cell.

• It has 3 sub-stages:a). G-1 Phaseb). S Phase (Synthesis Phase)c). G-2 Phase

G-1 PHASE• It’s an initial growth phase or first growth

phase of the cell.• The cell grows (to about double its original

size) - more organelles are produced,increasing the volume of the cytoplasm.

• The amount of cytoplasm increases and cyto-plasmic organelles like mitochondria etc….replicates.replicates.

S-PHASE (Synthesis PHASE)- Chromosomes are duplicated by the

synthesis of more DNA (Replication of DNA:Semi-conservative replication takes place)

- Also known as SWANSON Phase

CELL CYCLE

• In addition, some cells that do not divideoften or ever, enter a stage called Go (Gapzero), which is either a stage separate fromInterphase or an extended G1 phase, whichfollows the restriction point, a cell cyclecheckpoint found at the end of G1.

• The duration of time spent in Interphaseand in each stage of Interphase is variableand depends on both the type of cell andand depends on both the type of cell andthe species of organism it belongs to. Mostcells of adult mammals spend about 20hours in Interphase, this accounts forabout 90% of the total time involved in celldivision. (Mader, S. S. 2007)

• Body (Somatic) cells, or normal

diploid cells, go through Mitosis in

order to reproduce through cell

division, whereas diploid Germ cells

(i.e., primary spermatocytes and

primary oocytes) go throughprimary oocytes) go through

Meiosis in order to create haploid

gametes (i.e., sperm and ova) for

the purpose of sexual reproduction.

G-2 PHASE• This growth phase is shorter.

• Proteins required for cell division are synthesized.

• Cell increases in size.

• Cells prepares itself to enter the next phase of division“Mitosis”

• The nucleus of cell enlarges and a definite number offine, coiled thread like structures called chromosomesfine, coiled thread like structures called chromosomesbecome visible.

• In fact at the beginning of mitosis the nuclear materialhas already doubled. This stage is calledINTERPHASE, also called the Resting Stage (butactive) when in fact the cell is synthesizing thechromatin substance.

Cell Division

• When the cell has reached certain level ofgrowth it enters the division phase

• Where through a sequence of events themature parent cell divides into two daughtercells.

• These phases are of various durations indifferent cells, but the basic outline ofdifferent cells, but the basic outline ofsequences is the same.

• Cell division consists of two major stages:1). Karyo-kinesis: Nuclear division where

nucleus divides into two.2). Cyto-kinesis: Entire cells splits separating

each nuclei.