Mitosis

The division of the nucleus

© 2010 Paul Billiet ODWS

Conception

All animals begin as a fertilised egg cell (a zygote)

Image Credit: Zygote

Then it divides…

Image Credit: www.ehd.org/

… and divides

Released into the Public Domain by Jrockley

Until it becomes an embryo

Image Credit: www.scienceclarified.com

But what actually happens when a cell divides?

http://video.google.com/videoplay?docid=-5522357274832025243&q=mitosis&total=368&start=0&num=10&so=0&type=search&plindex=2

http://www.johnkyrk.com/mitosis.html http://www.bio.unc.edu/faculty/salmon/lab/mit

osis/mitosismovies.html

Image Credit: www.bioweb.uncc.edu/

Interphase: In between cell divisions

The working cell It grows in size (protein synthesis) It copies it’s genetic material (replication)

Nucleus

Nucleus envelope

Centriole

Nucleolus

Cytoplasm

Plasma membrane

© 2010 Paul Billiet ODWS

Image Credit: www.bioweb.uncc.edu/

Prophase: Division begins

Centriole divides

Treads appear in the nucleus =

Chromosomes condensing

Nucleus swells

Nucleolus disappears

© 2010 Paul Billiet ODWS

End of prophase: The nucleus disappears

Nucleus envelope breaks down

Spindle fibres grow out from the ends of the cell

CentromereSister chromatids

Chromosomes appear as two threads (the chromatids) joined by a constriction (the centromere)

© 2010 Paul Billiet ODWS

Image Credit: www.bioweb.uncc.edu/

Metaphase: The chromosomes are organised

Chromosomes line up across the equator of the spindle

Joined to fibres by their centromeres

© 2010 Paul Billiet ODWS

Image Credit: www.bioweb.uncc.edu/

Anaphase: The chromosomes split

The sister chromatids of each chromosome split

The spindle pulls one to each pole

© 2010 Paul Billiet ODWS

Image Credit: www.bioweb.uncc.edu/

Telophase: The end of mitosis The nuclei reform Each one contains a complete set

of chromosomes A new nuclear envelop forms The chromosomes uncoil

The cytoplasm divides in two to form two identical daughter cells

The cells goes back to work

© 2010 Paul Billiet ODWS

Chromosomes and cell division

Multicellular organisms copy their chromosomes before cell division

They must grow to a mature size

The nucleus divides, distributing the chromosomes into two equal groups

Interphase

The cytoplasm then divides each part taking a nucleus

Mitosis

Cytokinesis

© 2010 Paul Billiet ODWS

The cell cycle

G1 + S + G2 = INTERPHASE

First growth phase.Varies in length

Copying of chromosomes

Some cells may stay in this stage for over a year

Second growth period

M

G1

S

G2

G0

Cytokinesis division of the cytoplasm

© 2010 Paul Billiet ODWS

Cell cycles are not uniform

Cell type Cell cycle / h

Bean root tip 19.3

Mouse fibroblast 22

Chinese hamster fibroblast 11

Mouse small intestine epithelium 17

Mouse oesophagus epithelium 181

© 2010 Paul Billiet ODWS