Cell divisionCell division

CELL CYCLE, MITOSISCELL CYCLE, MITOSIS

The necessity for cell The necessity for cell division in living organisms.division in living organisms. Most of the cell in our body are Most of the cell in our body are

continuously growing, dividing and continuously growing, dividing and dying. dying.

Dead cells must be replaced with new Dead cells must be replaced with new cells.cells.

Process of every cells making a copy of Process of every cells making a copy of itself through a process called mitosis.itself through a process called mitosis.

In plant : Meristematic tissue (terminal In plant : Meristematic tissue (terminal buds, vascular cambium, cork cambium)buds, vascular cambium, cork cambium)* Cork is dead at maturity and doesn't expand

Vascular cambium

Terminal buds

cork cambiumcork cambium

Cell division

Nuclear division

Cytoplasmic division

( cytokinesis )

Examples :

1. Developing of human zygote

2. Binary fission

Zygote zygote begins to divide

A human zygote developing into a foetus

Binary fission

The significance of The significance of mitosismitosis

Mitosis is the process of nuclear division Mitosis is the process of nuclear division which result in the formation of two which result in the formation of two genetically identical genetically identical daughter nucleidaughter nuclei..

Significant of mitosisSignificant of mitosis

i. essential in replacing dead cells i. essential in replacing dead cells

ii. Allows damage cell to be repaired, ii. Allows damage cell to be repaired, replaced and replaced and

regenerated. regenerated.

iii. Increase the number of cell in living iii. Increase the number of cell in living organismorganism

Chromosomes and Chromosomes and chromosomal numberchromosomal number

Somatic cells Somatic cells mitosis mitosisreproductive cells (gametes) reproductive cells (gametes) meiosis meiosis

Number of chromosomalNumber of chromosomal- onion – 16 chromosomes- onion – 16 chromosomes- Drosophila – 8 chromosomes- Drosophila – 8 chromosomes

Chromosomes in nucleus exist in pairs = Chromosomes in nucleus exist in pairs = diploid.diploid. onion onion 2n = 16 2n = 16

drosophila drosophila 2n = 8 2n = 8

Cells Somatic cellsgametes

chromatid

sentromer

In human, one set of chromosomes consists of In human, one set of chromosomes consists of 23 chromosomes. Hence , our somatic cells have 23 chromosomes. Hence , our somatic cells have 46 chromosomes arranged in 23 pairs or 2n=46.46 chromosomes arranged in 23 pairs or 2n=46.

The two chromosomes in each pairs have the The two chromosomes in each pairs have the same structural features and are referred to as same structural features and are referred to as the the homologous chromosomeshomologous chromosomes. .

Each member of the matching pair is called Each member of the matching pair is called homologue.homologue.

One of the chromosomes is of paternal origin, One of the chromosomes is of paternal origin, whereas the other is of maternal origin. whereas the other is of maternal origin.

Haploid (n) : gametes contains only one set of Haploid (n) : gametes contains only one set of unpaired chromosomes.unpaired chromosomes.

CELL CYCLECELL CYCLE

The cell cycle is the period that The cell cycle is the period that extends from the time of new cell is extends from the time of new cell is produced until the time the cell produced until the time the cell completes a cell division.completes a cell division.

2 major phase : interphase ( G2 major phase : interphase ( G11, S, G, S, G22 ) )

: M phase (mitosis + : M phase (mitosis + cytokinesis)cytokinesis)CELL CYCLE

MITOSIS ANIMATION

INTERPHASEINTERPHASE

Accounts for 90% of cell cycle.Accounts for 90% of cell cycle. GG11 : Chromosomes are extremely : Chromosomes are extremely

fine and cannot be seen under light fine and cannot be seen under light microscope.microscope.

S : Synthesis of DNA occursS : Synthesis of DNA occurs

Prophase Metaphase anaphase telophase Cytokinesis

STAGES OF MITOSIS

The importance of The importance of controlled mitosiscontrolled mitosis

Genetic information carried by the Genetic information carried by the chromosomes is necessary for the proper chromosomes is necessary for the proper funtioning of an organisms.funtioning of an organisms.

To ensure the genetic information content To ensure the genetic information content and the number of chromosomes in the and the number of chromosomes in the parent cells are maintained in the daughter parent cells are maintained in the daughter cells from one generation to the next.cells from one generation to the next.

The rate and timing of cell division in The rate and timing of cell division in animals and plants are important for animals and plants are important for growth, development and maintainace.growth, development and maintainace.

The effects of uncontrolled The effects of uncontrolled mitosismitosis

When a cell divides through mitosis repeatedly, When a cell divides through mitosis repeatedly, without control and regulation, it can produce without control and regulation, it can produce cancerous cells.cancerous cells.

Cancer is a genetic disease cause by Cancer is a genetic disease cause by uncontrolled mitosis due to severe disruption to uncontrolled mitosis due to severe disruption to the mechanism that controls the cycle cells.the mechanism that controls the cycle cells.

Cancerous cell :Cancerous cell :- divides freely- divides freely- compete with the surrounding normal cell to - compete with the surrounding normal cell to obtain sufficient nutrients and energy.obtain sufficient nutrients and energy.- can intrude and spread to other tissue - can intrude and spread to other tissue - can form tumour (an abnormal mass of cell)- can form tumour (an abnormal mass of cell)

Cancer can be caused from :Cancer can be caused from :

- damage to the DNA- damage to the DNA

- mistakes that occurs in the genes- mistakes that occurs in the genes

- certain chemical compounds like tar - certain chemical compounds like tar and tobaccoand tobacco

- carnigenic compound such as - carnigenic compound such as formaldehyde.formaldehyde.

Application on mitosis in Application on mitosis in cloningcloning

CloningCloning Tissue culture techniqueTissue culture technique

Cloning Cloning

Process of producing clones or Process of producing clones or genetically identical copies of a cell, genetically identical copies of a cell, tissue or an organisms through tissue or an organisms through asexual reproduction.asexual reproduction.

Involve the transfer of the nucleus Involve the transfer of the nucleus from a somatic cell to an ovum or from a somatic cell to an ovum or embryonic cell which has the embryonic cell which has the nucleus removed.nucleus removed.

Eg : first cloned Eg : first cloned Dolly (1997) Dolly (1997)

Tissue culture techniqueTissue culture technique

Tissue culture technique involves the Tissue culture technique involves the growth of cells or tissues outside the cell growth of cells or tissues outside the cell in in suitable mediumsuitable medium (contain nutrients (contain nutrients and growth hormone).and growth hormone).

Plant cell divides by mitosis to form Plant cell divides by mitosis to form callus callus (undifferentiated mass of tissue)(undifferentiated mass of tissue)

Callus Callus embryo embryo plantlets. plantlets. CC allusallus

New plantlets (shoots with leaves) are forming.

A mass of callus tissue is formed that is just starting to make new plantlets.

If the conditions are right a small "forest" of plants will develop in the tissue culture container.

ADVANTAGES OF ADVANTAGES OF CLONING CLONING

Allows biotechnologist to multiply Allows biotechnologist to multiply copies of useful genes or clones.copies of useful genes or clones.

Can produced in Can produced in shorter timeshorter time and in and in large number .large number .

Many Many transgenic cropstransgenic crops like wheat, like wheat, soys bean which are resistant to soys bean which are resistant to herbicide, pests and disease have herbicide, pests and disease have been created.been created.

Vegetative reproduction Vegetative reproduction does not does not need the pollinating agentneed the pollinating agent

Shorter period for plant that Shorter period for plant that reproduce from seedreproduce from seed

Certain transgenic bacteria can be Certain transgenic bacteria can be used to control environment used to control environment pollutionpollution

- some bacterial clones which are - some bacterial clones which are able to break down toxic waste able to break down toxic waste material can help clean up toxic material can help clean up toxic waste dump.waste dump.