Cell division

Made by : Hoor el Bakry

How do you think you grow?

For organisms to grow and function properly, their cells go through a duplication process then a division phase. This is collectively known as the cell

cycle.

Why do we need mitosis?

•cells wear out, die and need to be replaced• new cells are needed to repair damaged tissues• It allow a body to grow. Mitosis makes it possible for new skin tissues, bone tissues and muscle tissues to be made.

Interphase

.The first part of the cell cycle, in which the cell grows and cytoplasmic organelles are replicated is known as Interphase.

.It makes about 90% of the whole cycle.

.The other 10% is made up of the mitotic phase and cytokinesis.

*G1 *S

*G2

The Interphase stage can be mainly divided into three

parts:

G1 : Gap 1

.This phase ,which is also called the growth phase or the first gap, is the one prior to the synthesis of DNA (the S phase).

.During this period the cell is carrying out its normal functioning, however, it is growing in size.

Note: if the checkpoint system realizes a default with the DNA it inhibits the cell

from progressing

.This second phase (along with a part of G1)is a major checkpoint during the cycle.

.The DNA replicates itself and prepares for the next step

S : Synthesis

. G2 phase is the last stage of interphase and previous to the mitotic phase.. Throughout the phase the cell grows increasingly and the organelles are replicated. The cell prepares for division.

Note: It is too late for the cell to go back once it reached G2

G2 : Gap 2

G1 , S and G2

Then mitosis starts…

The process of nuclear division is complex and highly regulated.Cell division is a term that describes the separation process of one cell into two ‘daughter’ cells which involves two steps :.mitosis. & cytokinesis

Mitosis is the process of dividing the duplicated

DNA into two new nuclei then into two new cells

However within mitosis there are many different stages (which are then followed by cytokinesis): *prophase *metaphase *anaphase *telophase

Prophase

.It is the first phase within mitosis. During prophase the nucleolus and the nuclear membrane begin to slowly breakdown.

.As prophase progress the DNA condenses to form chromosomes. Also the mitotic spindles (made ofmicrotubules) begin to form.

Metaphase

. By the time metaphase starts the spindles are fully formed and connected by the centrioles at the poles of the cell.. The chromosomes then line up vertically across the cell preparing for their pullingin the next stage.

AnaphaseDuring this phase the microtubules shorten as they draw the chromatids towards a centriole.

The unattached microtubules, as they are being pulled , result in stretching the cell.

TelophaseSince the centrioles now reached the end of the cell the nuclear membrane begins to reform around each group of chromatids which are now chromosomes.

.The nucleolus starts to reappear within each membrane while the chromosomes relax and unwound, therefore become invisible

Then cytokinesis starts…

Cytokinesis

The final step in cell replication is the cytokinesis. It is during this step where the cell is finally being divided into two ‘daughter’ cells.

How long is mitosis ?!

Mitosis lasts about one hour in human cells Prophase takes about 15 minutes. Metaphase is the longest stage, 20 minutes, Anaphase last for three minutes andTelophase and Cytokinesis last for less than 10 minutes.

Summary of mitosis

How does mitosis link to

today’s problems ?One of today’s most crucial issues

is Cancer. Scientists had discovered the basic problem that results in this dangerous disease .

They realized that mitosis plays the biggest role in the cause of Cancer

( therefore in the future developments can result in a cure).

Mitosis is the process responsible for cell replication whereas cancer is caused by an uncontrolled cell division. So once a tumor in a cell occurs and mitosis fails in reacting normally cancer is caused as this tumorous cell keeps replicating and spreading in the body.

A detailed video of mitosis:

http://www.youtube.com/watch?v=C6hn3sA0ip0

Bibliography :. www.biology-online.org/dictionary/Cell_division

.http://biology.about.com/od/mitosis/ss/mitosisstep.htm

. www.en.wikipedia.org/wiki/S_phase

.www.users.rnc.com/jkimball.ma.ultranet/BiologyPages/C/CellCycle.html

.http://cantorsbiologyblog.blogspot.com.au/2011/02/mitosis-somatic-cell-division.html

. www.cellsalive.com/mitosis.htm . http://en.wikipedia.org/wiki/G2_phase