Life sciences

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 centromerethat 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 CYCLECHAPTER 11 P. 164

The cell cycle includes the following phases:

Interphase (include G1- , S- [DNA synthesis] and G2 phase)

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

BioFlix: Mitosis

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

CANCERChapter 11 p.170-171

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

Credit to J.Williamson

E.Pretorius

P. Stewart

R Drevale

K.Segui