Review of Cell cycle & Cell division

1. Cell Cycle
Cell Division
&

2. Why do cells divide?
GROWTH
REPAIR
REPRODUCTION

3. Cell cycle

4. Cell cycle
Sequence of self-regulated events
that controls cell growth and cell division

5. Cell cycle (contd.)
M phase
G2 phase
S phase
G1 phase

6. Cell cycle (contd.)
Interphase: G1
 Gap between mitosis & DNA replication
 Gather nutrients
 Synthesizes RNA & proteins necessary for DNA synthesis and
replication

7. Cell cycle (contd.)
Interphase: S
 Period of DNA synthesis
 Replication of DNA
At the beginning of this phase,
The chromosome number is (2n), and
The DNA content is also (2d)
At the end of this phase,
The chromosome number remains the same (2n), and
The DNA content doubles to (4d)

8. Cell cycle (contd.)
Interphase: G2
 Gap between DNA replication & next mitosis
 Growth of cell
 Reorganization of cellular organelles

9. Cell cycle (contd.)
G0
 Leaves the cell cycle

10. Cell cycle (contd.)

11. Cell division
MITOSIS
MEIOSIS
&
Equational division
Reduction division

12. CHROMATIN
CHROMATID
CHROMOSOME

13. Mitosis

14. Mitosis
Mitosis is a process of
chromosome segregation and nuclear division
followed by cell division
that produces two daughter cells
with the same chromosome number and
DNA content as the parent cell

15. Mitosis
Mitosis is a process of chromosome segregation and nuclear division
followed by cell division that produces two daughter cells with the
same chromosome number and DNA content as the parent cell

16. Mitosis (contd.)
Prophase
 Replicated chromosomes condense and become visible
 The centrioles separate and migrate to opposite poles of the cell
 The nucleolus disappears
 Microtubules of the mitotic spindle appear between the two
centrosomes
 Microtubules of the developing mitotic spindle attach to the
chromosomes

17. Mitosis (contd.)
Metaphase
 The chromosomes are moved to the equatorial plane of the cell.

18. Mitosis (contd.)
Anaphase
 The sister chromatids separate from each other
 They are slowly pulled at their kinetochores toward opposite spindle
poles.

19. Mitosis (contd.)
Telophase
 The two sets of chromosomes are at the spindle poles and begin
reverting to their decondensed state.
 Nuclear envelope begins to reappear around each set of daughter
chromosomes.
 A belt-like contractile ring produce cleavage furrow, containing actin
and myosin filaments, develops in the peripheral cytoplasm at the
equator of the parent cell.
 It progresses until the cytoplasm and its organelles are divided in
two daughter cells, each with one nucleus.

20. Mitosis (contd.)

21. Meiosis

22. Meiosis
Meiosis is a process involving
two sequential nuclear divisions
followed by cell division
that produce gametes
containing half the number of chromosomes and
half the DNA found in parent cells

23. Meiosis
Meiosis is a process involving two sequential nuclear divisions
followed by cell division that produce gametes
containing half the number of chromosomes and
half the DNA found in parent cells

24. Meiosis (contd.)
Meiosis I
Meiosis II
&

25. Meiosis (contd.)
Why this reduction is necessary?
To maintain
a constant number of chromosomes
In a given species

26. Meiosis (contd.)
Prophase I
 Double-stranded chromosomes condense, and homologous
chromosomes (normally one inherited from the mother and one
from the father) are paired at
 Recombination of genetic material between the maternal and
paternal chromosome pairs may occur.

27. Meiosis (contd.)
 Leptotene
Condensation of chromatin and by the appearance of chromosomes.
 Zygotene
Synapsis, the close association of homologous chromosomes, begins at this stage
and continues throughout pachytene.
 Pachytene
Crossingover occurs that involves transposition of DNA strands between two
homologous chromosomes.
 Diplotene
Homologous chromosomes begin to separate from each other and
appear to be connected by newly formed junctions between
chromosomes called chiasmata.
 Diakinesis
The homologous chromosomes condense and shorten to reach their maximum
thickness, the nucleolus disappears, and the nuclear envelope disintegrates.

28. Meiosis (contd.)
Metaphase I
 Metaphase I is similar to the metaphase of mitosis except that the
paired chromosomes are aligned at the equatorial plate with one
member on either side.
 In late metaphase chiasmata are cleaved and chromosomes are
separated.

29. Meiosis (contd.)
Anaphase I & Telophase I
 Anaphase I and telophase I are similar to the same phases in mitosis
except that the centromeres do not split.
 A maternal or paternal member of each homologous pair, now
containing exchanged segments, moves to each pole.

30. Meiosis (contd.)
Meiosis II
After meiosis I, the cells quickly enter meiosis II without passing through an
S phase.
Meiosis II is an equatorial division and resembles mitosis.

31. Meiosis (contd.)

32. Meiosis (contd.)

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