Mitosis

Mitosis – what is it?

•Mitosis is the division of the genetic material in the nucleus of the cell. (Note: the mitochondria and chloroplast also contain some DNA)

•Cells replicate their genetic material just before mitosis so that when they divide the two ‘daughter’ cells produced are identical to the original ‘parent’ cell

•Mitosis has 4 major stages: prophase, metaphase, anaphase and telophase

•When the nucleus in a cell is not undergoing mitosis it is said to be in interphase

Mitosis – where does it take place?

•Mitosis takes place in body cells, otherwise known as somatic cells.

•Mitosis does not take place in the sex cells (sperm and egg), otherwise known as the gametes

•When an organism wants to grow, or repair its tissue after damage, the cells undergo mitosis

•When an organism reproduces asexually it uses mitosis

Mitosis – where does it take place?

•In mammals mitosis takes place in many part of the body including the skin cells that divide to replace dead skin cells, and in the bone marrow where new blood cells are made.

•In insects mitosis takes place every time they loose their exoskeleton and undergo growth spurts.

•In plants mitosis occurs at the tips of roots and shoots (where the new growth occurs).

Cytokinesis – what is it?•If mitosis is the division of the nucleus only, then there must also be a process by which the rest of the cell divides in order to make two cells rather than one cell with two nuclei.

•Cytokinesis is the division of the cytoplasm and occurs after mitosis.

•During cytokinesis the cell membrane constricts at two points opposite each other and the cell looks like it is pinched. This is known as cleavage.

•The cleavage ‘cuts’ the cell into two.

•Let’s have a look at this process…

Mitosis

cell membrane

nuclear membrane

nucleolus

A simplified cell

nucleus

•Mitosis occurs in the nucleus of cells

centrioles

MitosisInterphase

Cell membrane

Nuclear membrane

DNA

•The cell has replicated its DNA preparing for Mitosis

•The DNA condenses by folding on itself even more than usual

•You can start to see the chromosomes, they look like spaghetti on a plate!

MitosisEarly prophase

•The 6 chromosomes in this nucleus have been colour coded in their homologous pairs so we can follow them in this display; 2xblue, 2xgreen and 2xred

•The coloured pairs are also called homologous chromosomes; one shade is from mum and one shade is from dad

one blue chromosomefrom mum

one blue chromosome from dad

MitosisProphase

•The chromosomes have condensed as much as they can; they now look like the letter ‘H’.

•The two vertical arms of the chromosome are called sister chromatids and they are connected by a centromere

•The centrioles duplicate themselves

centromere

sister chromatids from

mum

from dadHomologous chromosomes

MitosisProphase

•The chromosomes start to line up on the metaphases plate that runs down the centre of the cell

•The centrioles start to move in opposite directions

•The nuclear membrane begins to break down

metaphase plate

Mitosis

Late Prophase

•Centrioles continue to move to opposite ends of the cell

•Nuclear membrane breaks down even more

Mitosis

Late Prophase

•Centrioles arrive at opposite ends of the cell

•Nuclear membrane has completely broken down

Mitosis

Metaphase

•Chromosomes are lined up on the metaphase plate

•Centrioles build spindle fibres

•Centromeres join to spindle fibres

Spindle fibres

Mitosis

Anaphase

•Chromosomes are pulled apart and sister chromatids move to opposite ends of the cell along the spindle fibres

Mitosis

Anaphase

•Sister chromatids continue to pull part

•Cell membrane starts to pinch or cleave

cleavage

Mitosis

Telophase

•Cleavage continues and a cell plate is formed in plants cells only(this becomes the cell wall)

•New nuclear membranes form around the new nuclei

•Cytoplasm divides, this is known as cytokinesis

cell plate forms in plant cells

Mitosis

Telophase

•Chromosomes start to de-condense

•Nuclear membranes properly formed

Mitosis

Interphase

•The nucleolus returns

•Chromosomes are no longer visible

•Two new daughter cells identical to their parent

Mitosis

•So nuclear division, or Mitosis starts from an interphase cell and finishes as an interphase cell.

•Let’s have a look again at the process of Mitosis, this time we won’t stop………….. (click as fast as you like to work the animation!)………..

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Can you guess the order of these cells undergoing mitosis?

1- Anaphase

2. Telophase

3. Interphase

The end