CELL DIVISION (MITOSIS)

CHROMOSOMES*Chromosomes form when the chromatin network in the

nucleus of the cell, coil up, shortens and thickens.

*Each organism has a specific amount of chromosomes.

*All humans have 46 chromosomes.

*These chromosomes are arranged in identical pairs called homologous chromosome pairs –

*Therefore humans have 23 homologous pairs of chromosomes.

*These chromosomes is only visible during cell division processes.  

*One chromosome consist of 2 chromatids and one centromere that attach the chromatids together.

* Each chromatid consist of genes which in turn consist of DNA.

* CHROMOSOMESTRUCTURE

X and Y chromosomes: gonosomes/sex-chromosomes

Colored bands represents different genes

THE PHASES OF THE CELL CYCLE

The cell cycle includes the following phases:

*Interphase

*Mitosis

*Cytokinesis

*Growth

The result is 2 identical cells.

*Why is Mitosis important?

*Allow an organism to grow.

*Repairs damaged cells/tissue.

*Replace dead cells/tissue.

*Reproduction in some simple organisms.

* Where does Mitosis take place?

*In all somatic cells (include all body cells and excludes the sex cells – sperm/egg cells)

*The process of Mitosis.

*CONSIST OF A FEW PHASES:

*INTERPHASE

*PROPHASE

*METAPHASE

*ANAPHASE

*TELOPHASE

*INTERPHASE*Cell builds up enough energy for division

process.

*DNA replication occurs

*Cell look normal, like before division

*PROPHASE

*Nuclear envelope and nucleolus disappear.

*Chromatin become more tightly coiled, and condenses into individual chromosomes. Chromosomes arrange randomly in the cell.

*Centrioli move to opposite poles, with spindle fibers stretching between them.

*METAPHASE*The centrioli reached the opposite poles

with the spindle fibers in between.

*The chromosomes arrange randomly on the equator, each single chromosome attaching to a separate spindle fiber by means of the centromere.

*ANAPHASE

*The spindle fibers pull tight.

*The centromers attaching the chromatids of the chromosomes split in half.

*Daughter chromosomes move to opposite poles.

*EARLY TELOPHASE – KARYOKINESIS (DIVISION OF

NUCLEUS*Daughter chromosomes reach poles.

*Nuclear envelope surrounds chromosomes.

*Nucleolus reappear at each pole.

*Chromosomes become less condense forming chromatin.

*Two identical nuclei has been formed

*LATE TELOPHASE – CYTOKINESIS (DIVISION OF THE CYTOPLASM)

*Invagination of the cytoplasm and plasma membrane occurs. (Cleavage furrow forms in animal cells and a cytoplasmic plate forms in plant cells)

*Continues until the cell in divided into 2 separate cells. (Identical to one another and to the original cell)

*MITOSIS PROCESS

*Summary of the different phases in mitosis

*CANCER

*Cancer is caused by the loss of cell cycle controls in cancer cells.

*Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells called a tumor.

*Malignant tumors invade surrounding tissues and can metastasize exporting cancer cells to other parts of the body, where they may form secondary tumors.

*They do not exhibit anchorage dependence or density dependent inhibition.

* Ovarian cancer cells Breast tumor

Ovarian cancer cells dividing