Download Cell Division (Mitosis)

Cell Division
(Mitosis)
Section 10-2
Chromosomes

In our cells the
genetic information
that is carried from
one generation to
the next is carried
by chromosomes
– Chromosomes are
made up of DNA
– Every organism has
a specific number of
chromosomes
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Fruit Fly =8 (4 pair)
Human = 46 (23 pair)
Carrot = 18 (9 pair)
Chromosomes
– Chromosomes are not
visible in most cells
except during cell
division
– Before cell division,
each chromosome is
replicated, or copied
– Because of this, at the
beginning of cell
division each
chromosome consists
of two identical sister
chromatids

Each pair of
chromatids are
attached at an area
called a centromere
Replicated Chromosomes
Centromere
Sister Chromatids
The Cell Cycle

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During the cell cycle, a
cell grows, prepares for
division, and divides to
form two daughter
cells, each of which
then begins the cycle
again
The cell cycle consists
of two distinct phases
– Interphase
– M (Mitotic)-phase
The Cell Cycle (Mitosis)
Interphase

Interphase is broken down into three
different steps (This is not necessarily
part of mitosis)
– G1(Gap1)Phase

This is a period in which the cell does most of
its growing
– S (Synthesis)Phase

This is when the chromosomes are replicated
– G2(Gap2) Phase

The organelles and other molecules required
for cell division are produced
Cell Cycle

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When the events of G2
are complete the cell is
ready to enter the M
(mitotic)-Phase
Mitosis can be divided
into four different
phases:
– Depending on the type
of cell:
– the four phases of
mitosis can last a few
minutes or several days
1. Prophase
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The longest phase of
mitosis
The chromosomes
become visible
Centrioles, which are
two tiny structures
located in the
cytoplasm near the
nuclear envelope,
separate and move to
opposite sides of the
nucleus
Prophase

The spindle fibers form
– These are fanlike
microtubule structure that
helps to separate the
chromosomes

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Chromosomes
become attached to the
spindle fibers at the
centromere of each
chromatid
Nucleolus (ribosomes
are made here)
disappears as does the
nuclear envelope
Prophase
2. Metaphase

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Second phase of
mitosis
Lasts only a few
minutes
The
chromosomes
line up across the
center of the cell
Metaphase
3. Anaphase

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Third phase of mitosis
The centromeres that
join the sister
chromatids separate
Allows the chromatids
to separate and
become individual
chromosomes
These chromosomes
continue to move until
they have separated
into two groups on
opposite sides of the
cell
Anaphase
4. Telophase

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Fourth phase of
mitosis
Everything that
happened during
prophase is reversed
The spindle fibers
disappear
Two new nuclear
membrane are formed
Chromosomes are
wrapped up
Chromosomes turns
back into chromatins
Telophase
Cytokinesis
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At the end of mitosis,
two nuclei--each with
a duplicate set of
chromosomes--are
formed
All that remains to
complete the cell cycle
is cytokinesis, the
division of the
cytoplasm
Cytokinesis usually
occurs at the same
time as telophase
Cytokinesis

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Cytokinesis can
take place in a
number of ways
In animal cells the
cell membrane is
drawn inward until
the cytoplasm is
pinched into two
nearly equal parts
– Each part contains
its own nucleus and
organelles
Cytokinesis in Animal Cells
Cytokinesis
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In plants a cell
plate forms
midway between
the divided nuclei
The cell plate
gradually develops
into a separating
membrane
A cell wall then
begins to appear
in the cell plate
Cytokinesis in Plant Cells
Mitosis in Onion Root Tip