MITOSIS A&P I

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MITOSIS



MITOSIS

Mitosis is the nuclear division

of somatic, or body cells.This process divides the

chromosomes found in the

nucleus. It results in two nuclei,which are identical.



MITOSIS

Mitosis occurs in theM phase of the cell cycle.



MITOSIS

Chromosomes were first

observed by Walter Fleming

in 1882. He was observingthe dividing cells of a

salamander larvae. It was

Fleming who first used theterm mitosis.



CHROMOSOMES

Chromosomes are composed

of both DNA and histoneproteins. This complex of DNA

and histone proteins is about

50% DNA and 50% proteins.



CHROMOSOMES



CHROMOSOMES

A typical human chromosome

contains about half billionnucleotides in one long DNA

helix that would be about 5

centimeters if laid out in astraight line.



CHROMATIN-CHROMOSOMES

When our DNA-histone protein

molecule is long and uncoiled,it is termed chromatin. However,

when it becomes coiled and

condensed it is termed a chromosome.




Chromatin is present during

interphase and the C phaseof the cell cycle. Chromosomes

are present during the M phase

of the cell cycle.



CHROMOSOMES

Chromosomes exist in somatic

cells as two nearly identical

copies of each other calledhomologous chromosomes, or

homologues. Cells that have

two of each type of chromosomeare called diploid cells.



CHROMOSOMES

During the s subphase of

interphase, each of the two

homologues chromosomesreplicate. This results in two

identical copies called sister

chromatids. The chromatidsare joined at a site called the

centromere.



CELL CYCLE



INTERPHASE

During interphase the cell is not dividing.

Interphase is divided into phases. G1 phase isthe time when the cell carries out basic

functions and performs specialized activities.The cell produces energy and grows. The

duration is extremely variable. This phasecontains a restriction checkpoint when the

cell “decides” to divide, enter a quiescentphase, G0 , or die.



INTERPHASE

The G0 Phase can replace the G1 Phase ifthe cell maintains its specialized

characteristics, but does NOT divide.Examples of this in the human body

include neurons and muscle cells.



INTERPHASE

S Phase - cell replicates

chromosomes &synthesizes proteins.



INTERPHASE

G2 Phase –The cellsynthesizes additional

proteins and assemblesmembrane materials.Also the centriolesreplicate.



MITOSIS

The process of mitosis occurs during theM Phase of the cell cycle. Mitosis is

one continuous event. However,for the ease of study it is

divided into 4 stages: prophase, metaphase, anaphase,

and telophase.



PROPHASE

1. The chromatincondenses and forms areplicated chromosome.

2. The nuclear enevlopeopens.

3. The nucleolus degrades.



PROPHASE

4. The centrioles migrateto opposite ends of thecell.

5. The mitotic apparatusforms from thecytoskeleton.

6. The replicatedchromosomes attach tothe spindle fibers usingtheir kinetochore fibers.



METAPHASE

1. The replicatedchromosomes movetoward the center of themitotic apparatus.

2. The replicatedchromosomes alignthemselves in the centerof the mitotic apparatus.



ANAPHASE

1. The centromere, whichis composed of twokinetochores, splits andthe sister chromatidsseparate.

2. The sister chromatids“travel” toward the polesof the mitotic apparatus.



ANAPHASE

3. The cleavage

furrow begins to form.



TELOPHASE

1. The sister chromatidsarrive at the poles of themitotic apparatus.

2. The mitotic apparatusis degraded and reformsthe cytoskeleton of thecell.



TELOPHASE

3. The nuclear envelopereforms from the roughE.R.

4. The nucleolus reforms.

5. The chromosomes begin

to uncoil and lengthen toreform chromatin.



CYTOKINESIS

Cytokinesis is the divisionof the cell’s cytoplasm after

mitosis. It results in two cells.



CYTOKINESIS

1. The cleavage furrowdeepens using

microfilaments.

2. The contraction

continues until the cellis literally pinched intwo.



Cytokinesis in

animal cells



MITOSIS and CYTOKINESIS

Mitosis followed by cytokinesis leads toincrease in the number of cells, growth,with each cells having the same numberof chromosomes and the same genetic

information.



CANCER

Cancer (loss of cell cycle control) is a

condition resulting from excess celldivision or deficient apoptosis.



CANCER

Characteristics of Cancer Cells:

can divide uncontrollably

are heritable & transplantablelack contact inhibition

readily metastasize

exhibit angiogenesisexhibit genetic mutability



CAUSES OF CANCER

1. Over-expression of oncogenesOncogenes are genes that trigger

limited cell division.2. Inactivation of tumor suppressor

genes

Tumor suppressor genes prevent a cellfrom dividing or promote apoptosis.



CAUSES OF CANCER

Normal functioning of oncogenes & tumorsuppressor genes may be affected by

environmental factors:

Carcinogens Radiation

Viruses Diet exercise habits

MITOSIS A&P I

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