Hand in your homework please!
• Detach the first section (including exam
questions) and put your name on it!
• Homework for MONDAY:
Complete the section on ‘Methods of
studying cells’ INCLUDING exam questions to
hand in on MONDAY.
The Cell Cycle and Mitosis
Cell Division
• Mitosis is a type of cell division that produces
genetically identical copies of cells.
• Not all cells can divide.
• What types of cells DO divide?
• Cells that can divide go through a CELL CYCLE.
The Cell Cycle
Mitosis is only a small part of the ‘life’ of a cell. The
process from one cell division to the next is known
as the cell cycle.
There are 4 parts to the cell cycle:
Gap 1
These stages are all parts of
Synthesis
interphase.
Gap 2
Mitosis
The cell cycle
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Can you think of 3 reasons why
mitosis is important?
A bit of background…
• A chromosome is a strand of DNA.
• After S-phase (DNA replication), identical
copies of chromosomes remain attached –
SISTER CHROMATIDS joined at the
CENTROMERE.
DNA replication
Chromosome
Centromere
Sister chromatids
Reminder:
• The chromosomes
can’t be seen most
of the time – they
are tangled strands
of DNA.
• During cell division,
the chromosomes
condense – they
coil up, aided by a
number of proteins.
Mitosis
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Interphase
• The cell is
engaged in
metabolic activity
in preparation for
mitosis
• Chromosomes
are not visible
under the light
microscope
Prophase
• Chromosomes
condense and become
visible under the light
microscope
• The nucleolus
disappears
• Centrioles begin moving
to opposite ends of the
cell and spindle fibres
extend from the centrioles
Metaphase
• The nuclear
membrane
dissolves, marking
the beginning of
metaphase.
• Spindle fibres
attach to the
centromere of
each chromosome.
Metaphase
• Spindle fibres align
the chromosomes
along the equator of
the cell
• This helps ensure that
during the next phase,
when the
chromosomes are
separated, each new
nucleus will receive
one copy of each
chromosome
Anaphase
• The sister
chromatids
separate at the
centromeres and
move to opposite
sides (poles) of
the cell
Telophase
• Chromatids arrive at
opposite poles of the
cell, and nuclear
membranes form
around them
• The chromosomes
are no longer visible
under the light
microscope
Another way to remember the
stages…
Invisible
Apart
Present
Middle
Two
CYTOKINESIS
• The cytoplasm divides so two cells are
formed.
• The two daughter cells are genetically
identical to each other, and to the parent
cell.
Try to identify the stages of mitosis in the
two photomicrographs on the back of your
sheet.
Write a sentence for each one to explain
how you reached your answer.
Stages of the cell cycle
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