MITOSISMITOSISThe nature of replicating cellsThe nature of replicating cells

Reproduction: Not as simple as it looks.

Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny)

I

II

III

IV

= one bit ofgenetic information

= one bit ofgenetic information

The information transfer problem becomes more challenging as more bits of information are incorporated into the organism

One of life’s solutions to this challenge: “Package” the

bits of information into single units called chromosomes

= one bit ofgenetic information

chromosomes

Packaging of genetic material in prokaryotes and eukaryotes

prokaryote cell

eukaryote cell

Fig 2.4 The structure of a highly condensed, replicated chromosome.© 2003 John Wiley and Sons Publishers

A Chromosome

BASIC GENETICSBASIC GENETICS

• Each cell in the human body contains two sets of 23 chromosomes

• Mitosis identically replicates this information

• Each cell therefore has the same genetic material

• Reproductive cells only have one set of chromosomes. These combine to make a new person with different genetic material to both parents

The cell cycle.

© 2003 John Wiley and Sons Publishers

Mitosis

The The SStages of the tages of the CCell ell CCycleycle

M stageM stageMitotic Stage

The nucleus and cytoplasm split to make two new cells

known as DIPLOID cells

Every dividing tissue cell in the body is always at a stage of the cell cycle. Whether it is at :-

STAGES OF MITOSISSTAGES OF MITOSIS

Cytokinesis

Thus enabling the body

to continuously make

new body tissue for

growth and repair.

Diagram showing the Stages of

Mitosis

Prophase

MetaphaseAnaphase

Telophase

Interphase

Prophase

Metaphase

Anaphase Telophase

The The Stages Stages

of of MMitosisitosisInterphase

The SpindleThe Spindle

A spindle is a web type structure made up of microtubule fibres. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division.

Mitotic centre

MicrotubuleA cell at metaphase a spindle

Chromosomes attached to spindle during nuclear division

INTERPHASEINTERPHASE

After a cell has divided, the two

new cells begin the process again,

the cells at this stage are in

Interphase.

Cell cycle

It is divided into three mini stages:- G1

S

G2

Eukaryotic chromsome replicating

PROPHASEPROPHASE• The chromatin (unravelled DNA)

in the nucleus, condenses to form pairs of chromosomes.

• The centrioles move to opposite ends of the nucleus.

• As this is happening the nucleolus

begins to break down

• Nuclear membrane begins to break down

Prophase

• Chromatin condenses (remember that chromatin/DNA replicate during Interphase), the nuclear envelope dissolves, centrioles (if present) divide and migrate, the spindle forms.

METAPHASEMETAPHASE

• The spindle becomes fully developed

• The nuclear membrane has completely gone

• The chromatid pairs place themselves onto individual fibres and are aligned along the centre of the spindle

ANAPHASEANAPHASE

• The chromatid pairs are split into two

(This is done by movement of the spindle fibres)

• The pairs then travel to opposite ends of the spindle

• The halved chromatids are now called chromosomes

TELOPHASETELOPHASETwo new nuclei are formed when the chromosomes reach the opposite poles of the cell

The nuclear membrane is formed- the nucleolus reappears

The chromosomes disperse in the nucleus

REMEMBER!REMEMBER!

IInterphase

PProphase

MMetaphase

AAnaphase

TTelophase

IPMAIPMATT

Mitosis in animal cells.

© 2003 John Wiley and Sons Publishers

CYTOKINESISCYTOKINESIS

Literally means, division of the

cytoplasm

Mitosis is the splitting of the nucleus.

Cytokinesis is the splitting of cytoplasm

It usually begins during ANAPHASE

Observed with place contrast microscopy.

The work of Shinya Inoue and Rudolf Oldenbourge.The Mitosis World Website.

The work of Mr Paul Maddox. The Mitosis World website.

Kangaroo epithelial kidney cell going through mitotic division.

Mitosis and cell plate formation in a flattened endosperm cell of the African bloodlily Haementhus Katherininae.

Cell Turnover - Cell Turnover - The speed of The speed of mitosismitosis

Although you may have seen a speeded up video of mitosis in action. One full cycle can vary between a couple of minutes to days.

For example skin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away.

Cells which make up organs such as the eye and the brain, need not multiply as often once they reach adult size.

Click here for movies

Organs which need to produce new cells continuously have the highest turnover.

For example:- Bone marrow-

producing replacement

blood cells

The testes - producing

semen

TumoursTumours

Abnormalities can sometimes occur in cells which reproduce at a rapid rate, this in turn may lead to the formation of tumours.

Tumours of any type should be considered serious.

Although benign tumours do not usually cause a threat to a persons life, they can cause great inconvenience if not treated.

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