Cell Division and Mitosis

One parent cell giving rise to two identical daughter cells

What is Mitosis?

Mitosis is the process of duplication of chromosomes and division of the nucleus prior to cell division.

5 Phases of Mitosis

InterphaseProphaseMetaphaseAnaphaseTelophase

Interphase

Includes the time that the cell is not actively dividing so may last a long time

The cell carries out its normal life functions during this phase

DNA is in the form of chromatin – long threadlike strands, not visible with light microscope

Late Interphase

Chromosomes have replicated.

Nuclear membrane is still intact

Nuclei stained blue; Nuclei stained blue; Center and right cell in Center and right cell in

interphaseinterphasePublic Domain: Public Domain: http://en.wikipedia.org/wiki/File:HeLa_cells_stained_with_Hoechst_33258.jpg

Interphase

= Chromatin= Chromatin

Prophase

Chromatin coils into chromatids and become easily visible with light microscope.

Duplicate chromosomes are attached at the centromeres.

Fluorescence microscope image of two

mouse cell nuclei in prophase (scale bar is 5 µm).

http://en.wikipedia.org/wiki/Prophase

Prophase

In the cell:Centrioles move to opposite ends of the

cell (animal cells)Spindle formsNucleolus disappearsNuclear membrane breaks down

Different Forms of Chromosomes

(1) Chromatin during interphase with centromere. (2) Condensed chromatin during prophase. (Two copies of the DNA molecule are now present) (3) Sister chromatids from the end of prophase through anaphase.

Image modified from Image modified from http://commons.wikimedia.org/wiki/File:Chromatin_chromosome.png

Prophase

http://en.wikipedia.org/wiki/Prophase

Chromosomal components:(1) Chromatid(2) Centromere(3) Short arm(4) Long arm

http://en.wikipedia.org/wiki/Centromere

Metaphase

The chromosomes have aligned along the equator of the cell attached to the spindle fibers by the centromeres

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Metaphase

http://en.wikipedia.org/wiki/Metaphase

Anaphase

Each centromere splits allowing identical sister chromatids to separate and move along the spindle fibers toward opposite ends of the cell.

Anaphase

Early Anaphase: The chromosomes are starting to migrate toward opposite poles.

Late Anaphase: The contraction of the spindle fibers has moved the separate masses of chromatids farther from the equator.

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Onion Root TipOnion Root Tip

Whitefish eggWhitefish egg

Anaphase

http://en.wikipedia.org/wiki/Anaphasehttp://en.wikipedia.org/wiki/Anaphase

Telophase

The chromatids have reached the poles. The chromatids uncoil back into chromatin.

Each set of chromosomes becomes incorporated in a new nucleus as the nuclear membrane reforms.

Cytokinesis or cell division now occurs.

http://en.wikipedia.org/wiki/Telophasehttp://en.wikipedia.org/wiki/Telophase

Daughter Cells in Interphase

After cytokinesis: Cells may enter a prolonged period of

interphase when all the processes that normally take place in the cell occur, except for cell division.

Cells may repeat the steps of mitosis and divide again

Phases of Mitosis – Another Look

Public Domain: http://commons.wikimedia.org/wiki/File:Interphase_and_Mitosis.svgPublic Domain: http://commons.wikimedia.org/wiki/File:Interphase_and_Mitosis.svg

Mitosis in Onion Root Tip

http://http://commons.wikimedia.org/commons.wikimedia.org/wiki/wiki/File:Onion_root_mitosis.jpgFile:Onion_root_mitosis.jpg

Can you find:Can you find:

ProphaseProphase

MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

http://commons.wikimedia.org/wiki/File:Mitosis_schematic_diagram-en.svghttp://commons.wikimedia.org/wiki/File:Mitosis_schematic_diagram-en.svg