This powerpoint explains the stages of cells divisions

1. Structure, function and growth of
prokaryote and eukaryote cells
(ii) Cell growth and Cell cycle
• Interphase
• Mitosis
• Mitotic index
• Control of the cell cycle
• Abnormal Cell division: cancer
cells

2. Cell Cycle
When cells reach a certain size, they must
stop growing or divide.
The cell cycle is the period from the
formation of a new cell until that cell
divides itself
The length of the cycle depends on the
cell – but is usually 8 – 20 hours

3. The Cell Cycle
CK

4. The Four Stages of Interphase…
Stage 1: G1 (First Gap Phase)
The longest phase in most cells.
The cell is still young and undergoes rapid
growth until it attains its normal size.
Formation of organelles.
Chemical preparation for DNA Synthesis
(enzymes, deoxyribose sugars, nucleotide
bases, and phosphates synthesized)
Cells that do not divide (e.g., nerve cells)
remain at this stage throughout their life
cycle

5. The Four Stages of Interphase
Stage 2: S phase (synthesis)
Replication of DNA
Chromosomes held together by
centromere
Each chromosome is made up of two
sister chromatids by the end of this stage.
In animals centriole pairs duplicate

6. The Four Stages of Interphase…
Stage 3: G2 (Second gap phase)
Preparation for cell division
Cell builds up energy reserves
The assembly of proteins such as
microtubules happens. It causes the
chromosomes to move during cell
division.

7. Stage 4: Mitosis Phase
The cell undergoes division
The division of the cell nucleus is called
karyokinesis, while the division of cytoplasm is
called cytokinesis.
Cytokinesis in animal cells and other cells without a
cell wall by the inward pinching of the cell
membrane of the cell membrane is called cleavage
furrow formation.
In plant cells and other cells with cell walls,
cytokinesis starts at the middle of the cell and
moves outward is called cell plate formation.

8. Stage 4: Mitosis Phase

9. Mitosis
Compare this to
your SG diagram.
Name the stages
Interphase
Prophase
Prometaphase
Metaphase
Telophase
Cytokinesis
What features
characterize each
stage?

10. STAGES OF MITOSIS
A type of somatic cell division resulting in
two nuclei daughter cells that have
identical genetic material to each other.
This results in two daughter cells having the
same number of chromosomes as the parent
cell called diploid.
Diploid – parent cell containing two sets of
homologous chromosomes (paternal and
maternal chromosome sets) results in two
diploid daughter cells after mitosis.

11. STAGES OF MITOSIS
In mitosis, Homologous
chromosomes (paternal and
maternal chromosomes) in
diploid cells behave
independently upon segregation.
This suggests that the normal body
cell containing 46 chromosomes
undergoes mitosis.
Which produces two genetically
identical daughter cells that contain
the same number of chromosomes.

12. STAGES OF MITOSIS
Mitosis occurs only in eukaryote cells.
It is used by multicellular organisms:
For growth and development.
For tissue repair, and
In asexual reproduction.

13. Stages of Mitosis
Prophase
The condensing of chromosomes and
centrosomes (made from centrioles)
Centrosome – responsible for organizing
microtubules and providing cell, as well as working to
pull sister chromatids apart.
Joins onto
spindle fiber
Chromatids in
condensed form

14. Stages of Mitosis
Prophase
Developing of spindle
fibers.
Spindle fibers (mitotic
spindle)
form a protein structure that
divides the genetic material in a
cell.
Spindle fibers are called mitotic
spindle during mitosis
mitotic spindle are formed
from the cell’s centrioles.

15. Mitosis – prophase cont…

16. Stages of Mitosis
Prometaphase
The breakdown of the nuclear
envelope.
The separation of duplicated
genetic materials of a parent cell
from the nucleus.
Spindle fibers attach to
kinetochore microtubules.
Kinetochore microtubules - are
large protein assemblies that
connect chromosomes to
microtubules of the mitotic
spindle.

17. Stages of Mitosis
Metaphase
The spreading out of the
individual chromosomes in
the cell nucleus.
The nucleus dissolves and
the cell’s chromosomes
condense, and
Begin to align the
equatorial plate in the
center of the dividing cell.
Plant Cell
Animal Cell

18. Stages of Mitosis
Anaphase
During this phase, the
spindle fibers connected
to the two sister
chromatids pull them
apart.
The separated
chromosomes will move
toward the opposite poles
due to of the spindle
fibers.

19. Stages of Mitosis
Telophase
The sister chromatids are
located on the opposite
poles.
A new nuclear membrane
forms around the
chromosomes, which start
to uncoil.
The spindle fibers dissolve
and disappear.
It is important to note that each
chromosome in the resulting
daughter cell is composed of only
one chromatid.

20. Stages of Mitosis
Cytokinesis
Division of the nucleus
(karyokinesis), the cytoplasm
starts to divide.
Only occurs in animal cells.
Other cells without cell walls
start by the inward pinching
of the cell membrane until
the cell is divided into two
cells and this process is
called a cleavage furrow.

21. Stages of Mitosis
Cytokinesis
in plant cells and other cells with a cell wall,
cytokinesis starts at the middle of the cell and moves
outward through a process called cell plate
formation.

22. STAGES OF MITOSIS

23. STAGES OF MITOSIS

24. The Mitotic Catastrophe
Malfunctions of any of the checkpoints at the
G1, S, and G2 phases of the cell cycle and the
checkpoint at the M phase may lead to a mitotic
catastrophe.
Mitotic catastrophe is defined as the failure to
arrest the cell cycle before or at mitosis,
resulting in abnormal chromosome separation.
Under normal conditions, death in these cells
will occur by activation of the apoptotic cycle.
Apoptotic cycle – a type of cell death in which a
series of molecular steps in a cell lead to its death.

25. The Mitotic Catastrophe
Cells that fail to execute the apoptotic cycle are
likely to divide asymmetrically in the next round
of cell division.
This leads to the generation of aneuploid cells
(cells containing abnormal chromosome
numbers).
Thus, a mitotic catastrophe may be regarded as
one of the mechanisms contributing to
oncogenesis (tumor cell development).

27. Mitosis – metaphase cont..
Chromosomes attach to the spindle
fibre by the kinetochore in the
centromere
The arrangement of the chromosomes
across the equator is also known as the
metaphase plate.

28. Mitosis – metaphase cont…

29. Mitosis
Anaphase
Centromeres divide
Sister chromatids separate and the
chromosomes are pulled to the poles

30. Mitosis – anaphase cont…

31. Mitosis
Telophase
Chromosomes begin to de-condense
Nuclear membrane reforms
Spindle disassembles and reassembles
as the cytoskeleton in the 2 new cells

32. Mitosis – telophase cont…

33. Cytokinesis
Dividing of the cytoplasm and organelles
Animals
Cytoplasm is pinched by a ring of contractile
microfilaments (made up of the proteins actin
and myosin)
As the ring gets smaller it forms a cleavage
furrow

34. Cytokinesis cont…

35. Cytokinesis cont…
In plants
Membrane vesicles spread across the
equator of the cell.
They merge to form plasma membrane
The new membranes lay down the cell
wall between the two cells.

36. Cytokinesis cont…

37. Mitotic Index
The fraction (or percentage) in a
microscope field that contain condensed
chromosomes (i.e. Undergoing mitosis)

38. Learning Activities
Look at web animations
www.biozone.co.uk/links.html
Cell biology – Mitosis / Meiosis – How cells divide
Posters
Card sort (pictures / names / descriptions)
Read Dart pg 9-14 and take notes
Use Scholar
Advanced Higher Questions