Celldivision mee

1. The Cell Cycle and How Cells Divide
E-CLIP EIS Teaching – Learning Strategies / Procedures
Biology Secondary 6, duration 60 min.
Teacher: Mr.Wichai Likitponrak

2. 2
Look at this Picture!
What
is
this?

3. 3
Introduction by this VDO!!!
https://www.youtube.com/watch?v=vA8aMpHwYh0

4. 4
Phases of the Cell Cycle
 The cell cycle consists of
◦ Interphase – normal cell activity
◦ The mitotic phase – cell divsion
INTERPHASE
Growth
G 1
(DNA synthesis)
Growth
G2

5. 5
Cell Division
 An integral part of the cell cycle
 Results in genetically identical daughter cells
 Cells duplicate their genetic material
◦ Before they divide, ensuring that each daughter
cell receives an exact copy of the genetic
material, DNA
20 µm100 µm 200 µm
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
(b) Growth and development.
This micrograph shows a
sand dollar embryo shortly after
the fertilized egg divided, forming
two cells (LM).
(c) Tissue renewal. These dividing
bone marrow cells (arrow) will
give rise to new blood cells (LM).

6. 6
Structure of Chromosomes

7. 7
Chromosome Duplication
0.5 µm
Chromosome
duplication
(including DNA
synthesis)
Centromere
Separation
of sister
chromatids
Sister
chromatids
Centrometers Sister chromatids
A eukaryotic cell has multiple
chromosomes, one of which is
represented here. Before
duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosome
consists of two sister chromatids
connected at the centromere. Each
chromatid contains a copy of the
DNA molecule.
Mechanical processes separate
the sister chromatids into two
chromosomes and distribute
them to two daughter cells.

8. 8
Structure of Chromosomes
 The centromere is a constricted region of the
chromosome containing a specific DNA sequence, to
which is bound 2 discs of protein called kinetochores.
 Kinetochores serve as points of attachment for
microtubules that move the chromosomes during cell
division:
Metaphase chromosome
Kinetochore
Kinetochore
microtubules
Centromere
region of
chromosome
Sister Chromatids

9. 9
Phases of the Cell Cycle
 Interphase
◦ G1 - primary growth
◦ S - genome replicated
◦ G2 - secondary growth
 M - mitosis
 C - cytokinesis

10. 10
Mitosis
 Some haploid & diploid cells divide by mitosis.
 Each new cell receives one copy of every
chromosome that was present in the original cell.
 Produces 2 new cells that are both genetically
identical to the original cell.
DNA duplication
during interphase
Mitosis
Diploid Cell

11. 11
Mitotic Division of an Animal Cell
G2 OF INTERPHASE PROPHASE PROMETAPHASE
Centrosomes
(with centriole pairs) Chromatin
(duplicated)
Early mitotic
spindle
Aster
Centromere
Fragments
of nuclear
envelope
Kinetochore
Nucleolus Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Kinetochore
microtubule
Nonkinetochore
microtubules

12. 12
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
Spindle
Metaphase
plate Nucleolus
forming
Cleavage
furrow
Nuclear
envelope
formingCentrosome at
one spindle pole
Daughter
chromosomes
Mitotic Division of an Animal Cell

13. 13
Mitosis in a plant cell
1 Prophase.
The chromatin
is condensing.
The nucleolus is
beginning to
disappear.
Although not
yet visible
in the micrograph,
the mitotic spindle is
staring to from.
Prometaphase.
We now see discrete
chromosomes; each
consists of two
identical sister
chromatids. Later
in prometaphase, the
nuclear envelop will
fragment.
Metaphase. The
spindle is complete,
and the chromosomes,
attached to microtubules
at their kinetochores,
are all at the metaphase
plate.
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends
of cell as their
kinetochore
microtubles shorten.
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will
divided the cytoplasm
in two, is growing
toward the perimeter
of the parent cell.
2 3 4 5
Nucleus
Nucleolus
ChromosomeChromatine
condensing

14. 14

15. 15
Meiosis
 Reduces the chromosome number such
that each daughter
 Cell has a haploid set of chromosomes
 Ensures that the next generation will
have:
◦ Diploid number of chromosome
◦ Exchange of genetic information
(combination of traits
◦ that differs from that of either
parent)
 Only diploid cells can divide by meiosis.
 Prior to meiosis I, DNA replication
occurs.
 During meiosis, there will be two
nuclear divisions, and the result will be
four haploid nuclei.
 No replication of DNA occurs between
meiosis I and meiosis II.
Interphase
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids Diploid cell with
replicated
chromosomes
1
2
Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Sister chromatids
separate
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II

16. 16
Meiosis Phases
 Meiosis involves the same four phases seen in mitosis
 prophase
 metaphase
 anaphase
 telophase
 They are repeated during both meiosis I and meiosis II.
 The period of time between meiosis I and meiosis II is
called interkinesis.
 No replication of DNA occurs during interkinesis because
the DNA is already duplicated.
Prophase I
of meiosis
Tetrad
Nonsister
chromatids
Chiasma,
site of
crossing
over

17. 17
Sister
chromatids
Chiasmata
Spindle
Centromere
(with kinetochore)
Metaphase
plate
Homologous
chromosomes
separate
Sister chromatids
remain attached
Microtubule
attached to
kinetochore
Tetrad
PROPHASE I METAPHASE I ANAPHASE I
Homologous chromosomes
(red and blue) pair and
exchange segments; 2n = 6
in this example
Pairs of homologous
chromosomes split up
Tetrads line up
Meiosis I is very important to variation
(crossing over)

18. 18
 Meiosis II is very similar to mitosis
Cleavage
furrow
PROPHASE II METAPHASE II ANAPHASE II
TELOPHASE I AND
CYTOKINESIS
TELOPHASE II AND
CYTOKINESIS
Sister chromatids
separate
Haploid daughter cells
forming

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A Comparison of Mitosis and Meiosis
 Mitosis conserves the number of chromosome sets,
producing cells that are genetically identical to the parent
cell
 Meiosis reduces the number of chromosomes sets from two
(diploid) to one (haploid), producing cells that differ
genetically from each other and from the parent cell
 The mechanism for separating sister chromatids is virtually
identical in meiosis II and mitosis

20. 20
MITOSIS MEIOSIS
Prophase
Duplicated chromosome
(two sister chromatids)
Chromosome
replication
Chromosome
replication
Parent cell
(before chromosome replication)
Chiasma (site of
crossing over)
MEIOSIS I
Prophase I
Tetrad formed by
synapsis of homologous
chromosomes
Metaphase
Chromosomes
positioned at the
metaphase plate
Tetrads
positioned at the
metaphase plate
Metaphase I
Anaphase I
Telophase I
Haploid
n = 3
MEIOSIS II
Daughter
cells of
meiosis I
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Daughter cells of meiosis II
n n n n
Sister chromatids separate during anaphase II
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n 2n
Daughter cells
of mitosis
2n = 6
A Comparison Of Mitosis And Meiosis

21. 21
Assignment:
 Worksheet
 Pages 7-9
◦ 1.1, 1.2 and 1.3
Sent me back
in this class !!!