UNIT 3: CELL DIVISION

(MITOSIS)

Campbell and Reece, 2010. Chapter 12 p. 228-243, Edulink and learning guide notes

CHROMOSOMESChapter 12 p. 230

Chromosomes form when the chromatin network in the nucleus of the cell, coils 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 are 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

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

THE PHASES OF THE CELL CYCLECHAPTER 12 P. 231

The cell cycle includes the following phases:

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

Mitosis (divides nucleus)

Cytokinesis (divides cytoplasm)

Growth The result is 2 identical cells.

INTERPHASE

Cell builds up enough energy for division process (preparation).

Nuclear envelope bounds the nucleus

DNA replication occurs (during S phase) – chromosomes not condensed yet

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 (centrosomes) move to opposite poles, with spindle fibers stretching between them (mitotic spindle).

PROMETAPHASE

Chromosomes become even more condensed

Each of two chromatids has kinetochore Specialized protein structure located at

centromere Some microtubules attach to

kinetochores – kinetochore microtubules

Pull chromosomes back and forth

METAPHASE: longest stage

The centrioli reached the opposite poles with the spindle fibers in between.

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

ANAPHASE: shorstest stage

The spindle fibers pull tight. The centromers attaching the

chromatids of the chromosomes split in half.

Daughter chromosomes move to opposite poles as kinetochore microtubules shorten.

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 have 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