Pre-Test and Lecture in Cell Division

1. Pre-test
1. What is a cell?
2. Do cells reproduce? Yes or No? If yes, how?
3. What do you think is meant by Rodulf Virchow’s cell
theory, “Cells come from pre-existing cells.”?
4. What is your idea about cell division?
5. A skin tissue is damaged, skin cells then divide to
renew the damaged skin tissue. What do you call that
type of cell division? (Mitosis, Meiosis)
6. Individuals need to maintain the production of egg
cells and sperm cells. What type of cell division do
you think is involved? (Mitosis, Meiosis)

4. CELL DIVISION

5. Cell Division
Cell Division — process by which
a cell divides into 2 new cells
• Why do cells need to divide?
1.Living things grow by
producing more cells, NOT
because each cell increases in
size
2.Repair of damaged tissue

6. • The original cell is called the parent cell; 2 new cells are
called daughter cells
• Before cell division occurs , the cell replicates (copies) all
of its DNA, so each daughter cell gets complete set of
genetic information from parent cell
• Each daughter cell is exactly like the parent cell – same
kind and number of chromosomes as the original cell
Parent Cell
2
Daughter
Cells

7. •Many organisms, especially unicellular
organisms, reproduce by means of cell division –
called asexual reproduction – Ex: bacteria

8. The Animal Cell

9. Organelles involved in Cell Division
1. NUCLEUS
• The control center of the cell and is bound by
a nuclear membrane.
• It contains the genetic material DNA that is
replicated prior to cell division.

12. o 2 identical “sister”
chromatids attached at
an area in the middle
called a centromere
o When cells divide,
“sister” chromatids
separate and 1 goes to
each new cell

13. Chromatin
Duplicates
itself
Coils up into
chromosomes
•Chromatin to chromosomes illustration:
Why does DNA need to change
from chromatin to chromosome?
More efficient division

14. Chromosome number
•Every organism has its own specific number of
chromosomes
Examples: Human = 46 chromosomes or 23 pairs
Dog = 78 chromosomes or 39 pairs
Goldfish = 94 chromosomes or 47 pairs
Lettuce = 18 chromosomes or 9 pairs

15. • All somatic (body) cells in an organism have the same
kind and number of chromosomes
Examples: Human = 46 chromosomes
Human skin cell = 46 chromosomes
Human heart cell = 46 chromosomes
Human muscle cell = 46 chromosomes
Fruit fly = 8 chromosomes
Fruit fly skin cell = 8 chromosomes
Fruit fly heart cell = 8 chromosomes
Fruit fly muscle cell = 8 chromosomes

16. Organelles involved in Cell Division
2. CENTRIOLES
• It is a minute cylindrical organelle arranged
near the nucleus in animal cells. They are
found in pairs and move towards the poles of
the nucleus when it is time for cell division.
• They are also involved in the development of
spindle fibers in cell division.

18. 2 types of Cell Division
Mitosis
• When body cells undergo a cell division.
• Somatic cells
Meiosis
• When sex cells undergo a cell division.
• Gametes (egg, sperm)

19. Cell Cycle -- series of events cells go through as
they grow and divide
•Cell grows, prepares for division, then divides to
form 2 daughter cells – each of which then begins
the cycle again

20. The Cell Cycle

22. MITOSIS
Prophase
– phase of chromosome condensation
Metaphase
– phase of alignment
Anaphase
– phase of separation
Telophase
– phase of nuclear formation

23. PROPHASE
• Nuclear envelope breaks down
• Nucleolus disappears
• Duplicated centrioles begin to move in
opposite poles and form spindle fibers
between them.
• Chromatin fibers become visible as they
condense, coil, and become shorter and
thicker.

24. PROPHASE

25. METAPHASE
• Chromosomes migrate randomly and line up
toward the equator.

26. METAPHASE (continued)
• Another checkpoint occurs at this stage
• When a chromosome is not properly aligned
at the mitotic spindle, mitosis will be arrested.
• As a result, of this checkpoint, sister
chromatids do not separate until a complete
set of chromosomes will be distributed to
each new individual.

27. ANAPHASE
• Sister chromatids separate and move towards
the opposite ends.

28. TELOPHASE
• Nuclei forms in both poles as new nuclear
membrane forms around the new nucleus.
• Nucleus reappears and spindle fibers begin to
disappear.
• Division of cytoplasm (Cytokinesis) begins and
is completed when the cell contents have
been divided equally to the two daughter cells
produced.

29. TELOPHASE (continued)

34. QUIZ
1. A phase that is composed of three stages and is mostly
involved in preparing the cell for cell division.
2. A phase where DNA is replicated.
3. A phase that re-checks all the necessary materials
before it proceeds mitotic phase.
4. A mitotic phase wherein chromosomes condensed and
nuclear membrane breaks.