1. CELL DIVISION

2. CELL DIVISION
Why do cells need to divide?
-To allow an organism to
grow
-To pass on genetic material
-To assist an organism’
survival

3. CELL DIVISION
2 types of cell division
Mitosis
Meiosis
-daughter
cells are
genetically
identical
-daughter
cells are
genetically
different

4. CELL DIVISION
Mitosis
5 stages:
- Literally refers
to the division
of the nucleus
Interphase
Prophase
Metaphase
Anaphase
Telophase

5. CELL DIVISION
Interphase
- Cell is not dividing but
also not dormant
- Cell is active and
growing and also
preparing for division
- Sometimes called
resting phase but this
is inaccurate (real
resting phase is G0)
- DNA/chromosomes
not visible (unwound)

6. CELL DIVISION
Interphase: 4 stages
Gap 0 (G0):
- Cell rest cycle
- may be temporary
or permanent (where
cells are functional
but no new cells are
produced (i.e.
neuron)
G0

7. CELL DIVISION
Interphase: 4 stages
Gap 1 (G1):
- Rapid growth (4hr)
- cell takes in
nutrients for energy,
growth, repair
- Cells either go into S
or G0 after G1
G0

8. CELL DIVISION
Interphase: 4 stages
S phase (S):
- 10 hrs
- DNA synthesis/
replication
- the cell duplicates
its genetic material to
make an identical
copy of its DNA
G0

9. CELL DIVISION
Interphase: 4 stages
Gap 2 phase (G2):
- 3-4hr
- second period of
growth in preparation
for cell division
-cell grows larger in
size
G0

10. CELL DIVISION
S phase (S): Let’s take a closer look
DNA replication
DNA
duplication
Normally
After duplication

11. CELL DIVISION
How does all of the DNA remain organized in the nucleus?
Why does it not tangle?

12. CELL DIVISION
DNA strands are wrapped around histone proteins which act
as “spools”

13. CELL DIVISION
Histone proteins that have been wrapped with DNA form
“nucleosomes”

14. CELL DIVISION
Moving into mitosis…
After interphase, the cell may enter
mitotic (M) phase:
-
A process by which somatic cells grow
and divide
-
Cells come from pre-existing cells
-
Parent cell divides to produce two
new identical daughter cells
-
Cell division occurs through:
- A) Mitosis – process of dividing
nuclear material
- B) Cytokinesis – Process of
separating the cytoplasm and its
contents into equal parts

15. CELL DIVISION
Prophase
- nuclear membrane breaks down
- chromosomes shorten and
thicken
- Other structures important for
mitosis are also forming (i.e. the
centrioles)

16. CELL DIVISION
Prophase
- chromosomes
shorten and thicken
into X-shaped things

17. CELL DIVISION
Prophase
- A centromere holds two copies of the same chromosome together
- Each copy of a chromosome is called a chromatid

18. CELL DIVISION
Prophase
- A centromere holds two copies of the same chromosome
together
- Remember, every chromosome has been duplicated during the S
phase of interphase.
Colors are not accurate
- Recall this:
Mitosis
Mother’s
side
Mother’s
side
Mother’s
side

19. CELL DIVISION
Prophase

20. CELL DIVISION
Metaphase
- Proteins attach to the
centromeres creating the
kinetochores.
- Microtubules (spindle fibres)
attach at the kinetochores
and the chromosomes move
to the centre (the metaphase
plate)

21. CELL DIVISION
Metaphase

22. CELL DIVISION
Anaphase
- Paired chromosomes separate
at the kinetochores and move
to opposite sides of the cell
- Motion results from
kinetochore movement along
the spindle microtubules

23. CELL DIVISION
Telophase
- Chromatids arrive at opposite
poles of cell
- New membranes form around
the daughter nuclei
- Chromosomes disperse and
are no longer visible under the
light microscope
- spindle fibres disperse

24. CELL DIVISION
Cytokinesis
- Animal cells: the
cell membrane
pinches (forming
a cleavage furrow)
into two daughter
cells, each with
one nucleus

25. CELL DIVISION
Cytokinesis
- In plant cells, a
cell plate (made
of rigid cellulose)
is synthesized
between the two
daughter cells.

26. CELL DIVISION
Mitosis and cytokinesis: Review