Download 2. Mitosis

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
centrioles
A simplified cell
•Mitosis occurs
in the nucleus
of cells
nucleolus
nucleus
nuclear
membrane
cell membrane
Cell
membrane
Mitosis
Interphase
•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!
Nuclear
membrane
DNA
one blue
chromosome
from mum
Mitosis
Early 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
one blue
chromosome
from dad
•The coloured pairs are
also called homologous
chromosomes; one
shade is from mum and
one shade is from dad
sister
chromatids
centromere
Mitosis
from
mum
Prophase
•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
Homologous
chromosomes
from dad
•The centrioles
duplicate themselves
Mitosis
Prophase
•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
cell plate forms
in plant cells
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
Mitosis
Telophase
•Chromosomes
start to decondense
•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!)………..
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Can you guess the order of these
cells undergoing mitosis?
1- Anaphase
2. Telophase
3. Interphase
The end