cell DIVISION.ppt

7/31/2019 cell DIVISION.ppt

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CELL DIVISION

CHAPTER 5


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Significance of mitosis

Growth- allows a zygote to produce morecell in order to grow

Repair and replacement- allow themulticellular organism maintain its tissues,

example skin cells and blood

Asexual reproduction- clone


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Somatic cells have 2sets of chromosomes:

contains a diploid

number of

chromosomes (2n).

1 set inherited fromeach parent

Human: have 23 pairsof chromosome.

2n = 46

Homologous chromosomes


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Cell Cycle

Cell cycle - The periodthat extends from thetime a new cell isproduced until the timethe cell completes a cell

division. Mitosis: nuclear division Cytokinesis: cytoplasmic

division

The cell cycle is divided

into two major phases:1. Interphase2. Mitosis

Cell grows

Cell prepares to divide


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Interphase

The period between division, divided into 3sub phases (G1, S and G2):

i.G1- cells grow rapidly and new organelleare synthesis

ii.S - synthesis of DNA and chromosomes

are replicatediii.G2 - cells prepare for mitosis, synthesisprotein and mitotic spindle begin to form


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Mitosis

Mitosis is a division of the nucleus to producetwo new daughter cells containingchromosomes identical to the parent cell.

Mitosis is a continuous process and dividedinto 4 main phases based on the appearanceand behavior of the chromosomes.

1. Prophase, P

2. Metaphase, M3. Anaphase, A

4. Telophase, T


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Prophase

Early prophase Chromosome condense and appear

shorter and thicker and become visiblein a light microscope

Each chromosome now consists of apair ofsister chromatids joined

together at centromere. Nucleolus disappears & nuclear

membrane disintegrates.

Paired centrioles move to oppositeends of the cell

Late prophase

Nuclear membrane disappears Spindle form

Centrioles

Centromere


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Metaphase

Spindle fibres are fullyform

Sister cromatids line up at

the spindle equator/metaphase plate.

Two sister chromatids arestill attached to oneanother at thecentromere.

At the end of metaphase,the centromers divide.


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Anaphase

Anaphase begin with theseparation of the centromers

The sister cromatids are drawnto opposite poles of the cell byshortening of spindle fibres.

Once separated, chromatidsare referred to as daughterchromosome.

End anaphase: the poles of the

cell have complete andequivalent sets ofchromosome.


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Telophase

Telophase begin when the twosets of daughter chromosomeshave reached the two poles of thecell.

The spindle fibres disintegrate, the

nuclear membrane forms aroundeach set of daughterchromosomes and the nucleolireappear.

The nucleolus also re-forms ineach nucleus.

The chromosomes uncoil andbecome less visible under the lightmicroscope.

Mitosis process is now completed.


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The importance of controlled

mitosis

Controlled mitosis: the ability of the cell todivide at its own rate and time.

Crucial to normal growth, development andmaintenance for the perpetuity of living things.

Eg: in plants controlled mitosis occurs atshoots results in growth of plants.

in human Malphigian layer of skin divides

actively to replace dead and damaged cells.


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The effects of uncontrolled mitosis

in living things

Mutation is the change in the DNA structure of

the cell.

This change in the DNA corrupts the codedgenetic instructions for mitosis control.

This leads to uncontrolled mitosis, which is the

non-stop division of cells, producing a mass of

new daughter cells, called tumour.


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Uncontrolled mitosis


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Tumor cells that remain at original site.

Can be removed surgically or killed by radiation,

usually eliminating any further cancer development at

that site.

BENIGN TUMOUR


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Some tumor cells send out signals that tell the body to

produce a new blood vessel at the tumor site.

These cells not only have their own food and oxygen

supply, they also have an avenue forescape to a new

part of the body - through the new blood vessel and intobloodstream.

MALIGNANT TUMOUR


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Cells that break away from the tumor begin to spreadto surrounding tissues (via the bloodstream or lymph)

and start new tumors.

The person concerned is said to be suffering fromCANCER

Usually surgery is performed to remove the tumor,

followed by radiation and chemotherapy.


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Causes of Cancer

Genetic- some forms of cancer like prostate, colon,breast, skin, ovary are suspected to be inherited fromthe parents

Carcinogens- these are chemicals which affectgenetic activity and cause cancer, e.g. of carcinogen adiesel exhaust, cigarette smoke, hair dyes, soot,arsenic, benzene and formaldehyde.

Radiation- excess exposure to x-ray, gamma-rays andultra violet rays lead to increase cancer risk.

Viruses- some viruses (such as the HPV and HIV-1)cause cancer.


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LEUKAEMIA

is caused by mutation (change in genetic information)

The mutation causes the bone marrow to produce redblood cells and platelets at a rate that is much slower

than normal

Hence, a leukaemia patient suffers from insufficientoxygen, weakness and diificulty in blood clotting


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INTESTINES CANCER


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Application of Mitosis in Cloning

Mitosis is used to improve the quality, toproduce new species and to ensure

uniformity in the traits. Cloning: process of artificially creating a new

individual that is genetically identical to an

existing individual.

Technique in application of mitosis in cloning tissue culture.


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Application on mitosis in cloning

Plant tissue

Skin tissue

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