Mitosis and the cell cycle
AS Biology
Mitosis and the cell cycle
• The cell cycle is the
series of events in the
life of a cell.
• The cell is either
actively dividing –
mitosis, or it is
between divisionsinterphase
Interphase
• This used to be called the resting phase
but in fact some important events occur in
interphase
• This stage divides into three sections
G1
S
G2
Still with Interphase
•
G1- the cell enlarges
after division and
organelles like
mitochondria replicate.
• S- the cell commits to
division in this stage
because DNA replicates.
One chromosome
becomes two chromatids
• G2-Reserves of ATP
build up and the
centrioles replicate
Mitosis
• The cell division part of the cell cycle is a
continuous process but it is described in
four named stages
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
During interphase
the chromosomes
have appeared as
diffuse granular
material called
chromatin but now
they begin to
shorten by coiling
up. They appear
as thin threads
Prophase
• The pairs of centrioles move to opposite poles of the cell
and begin to form a spindle of microtubules
• The chromosomes condense and can be seen to be
composed of two identical chromatids held together by
centromeres
Metaphase
• The chromosomes
align at the equator of
the cell and the
centromeres attach to
the microtubules of
the spindle
Metaphase
• On this slide you can
clearly see
chromosomes aligned
at the cell equator
Anaphase
• As the microtubules
shorten the two
chromatids of each
chromosome
separate and are
pulled to opposite
poles of the cell
Anaphase
• The central cell is in
anaphase
• Each cluster of
chromosomes
contains one copy of
each chromosome
Telophase
• Each cluster of
chromosomes becomes
surrounded by a new
nuclear membrane
• The spindle disappears
and the chromosomes
uncoil
• The cytoplasm of the cell
separates into two, a
process known as
cytokinesis
Summary
Importance of Mitosis
• Two new cells are formed from one
original cell
• Each cell is a genetically identical copy of
the original cell –a clone
• Each new cell contains the same number
and type of chromosomes as the original
cell
Where does mitosis happen
In animals mitosis occurs in all tissues in the
embryo, foetus and juvenile for growth.
In adults mitosis is used for replacement of tissues
like skin, hair, blood and mucous membranes,
and for wound healing.
Plants don’t grow all over their bodies like animals
but have regions of cell division called
meristems. These are found at the tips of the
root and main and side shoots, and in woody
plants, in a ring around the stem.
Homework
•
•
•
•
Look at the following web page
www.biology.arizona.edu/default.html
Click on Cell biology and onion root tips
Read the pages and do the activity ( the
kinetochore is part of the centromere)
• Email me the answer (percentage of cells
in each stage of the cell cycle) at
hwellington@stvincent.ac.uk