Mitosis And Cytokinesis

What is mitosis?

The process of nuclear division.

What does mitosis ensure?

That both daughter cells when a parent cll divides are genetically indentical, except in the rare events where mutations occur.

What will each new cell produced by mitosis have?

An exact copy of the DNA present in the parent cell and the same number of chromosomes.

When is mitosis necessary?

When all the daughter cells have to be identical. This is the case during growth, replacement and repair of tissues in multicellular organisms such as plants, animals and fungi.

Why else is mitosis necessary?

For asexual reproduction.

What is asexual reproduction?

The production oof genetically identical offspring from one parent in multicellular organisms including animals, plants and fungi.

Why can’t prokaryotes undergo mitosis?

They do not have nuclei.

How do prokaryotic organisms reproduce?

Asexually, by binary fission.

What must happen before the cell can undergo mitosis?

All of the DNA must be duplicated (during interphase).

What is DNA (chromosomes) convered to?

Two identical DNA molecules, called chromatids.

Where are the two chromatids joined together?

At the centromere.

Why is it neccessary to keep the chromatids together during mitosis?

So that they can be precisely manoeuvered and segregated equally, one each into one of the two new daughter cells.

What are the four stages of mitosis?

Prophase, metaphase, anaphase and telophase.

What happens during prophase?

• Chromatin fibres begin to coil and condense to form chromosomes that will take up stain to become visible under a light microscope.

• The nuclear membrane begins to break down.

• Spindle fibres begin to emerge from the centromeres

• The spindle fibres attach to specific areas on the centromeres and start to move the chromosomes into the correct positions before division

• By the end of prophase, the nuclear envelope has dissapeared

What happens during metaphase?

• The chromosomes are moved by the spindle fibres to form a plane in the middle of the cell - the metaphase plate, and then held in position.

What happens during anaphase?

• The centromeres holding together the pairs of chromatids in each chromosome divide.

• The chromatids are seperated - pulled to opposite poles of the cell by the shortening spindle fibres.

What happens during telophase?

• The chromatids have reached the poles and are now called chromosomes.

• The two new sets of chromosomes assemble at each pole and the nuclear envelope (re)forms around them.

• The chromosomes start to uncoil and the nucleoulus is formed.

What takes place after mitosis?

Cytokinesis

What is cytokinesis?

Division of the cytoplasm.

How does cytokinesis take plae in animal cells?

• A cleavage burrow forms around thr middle of the cell.

  • The cell-surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle, forming two cells.

How does cytokinesis take place in plane cells?

• Vesicles from the golgi apparatus begin to assemble in the same place as where the metaphase plate was formed.

• The vesicles fuse with each other and the cell surface membrane, dividing the cell into two.

Why can’t plant cells form a cleavage burrow?

Because they have cell walls, unlike animal cells.