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AMOUD
UNIVERSITY
SCHOOL OF DENTISTRY
1ST YEAR STUDENTS
Course Title: DNS 6111
Course Code: Cytology
Lecturer: Harun Ismail Warsame(BSc/MPH)

3. Learning Objectives
1. Define cell division.
2. Explain the cell cycle.
3. Distinguish between mitosis and
meiosis.
4. Describe the stages of mitosis.
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Chapter 7: The cell division and Cell Cycle

4. Cell division
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20 µm
Cell division: is the process by which one
cell produces two or more daughter cells.
200 µm
(a) An amoeba,
a single-celled eukaryote, is
dividing into two cell
(b) Growth and development.
This embryo shortly after
the fertilized egg divided, forming
two cells
(c) Tissue renewal. These
dividing bone marrow cells will
give rise to new blood cells

5. Cell Cycle
The cell cycle is a repeated
pattern of growth and
division that occurs in
eukaryotic cells.
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7. Phases of cell cycle
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 Cell cycle consist of
two phase
 interphase phase
 mitosis phase

8. Interphase
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 G1 - Cells undergo
majority of growth
 S - Each chromosome
replicates
(Synthesizes)
 G2 - Chromosomes
condense - Assemble
machinery for division
such as centrioles

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 Almost 90% of the cycle is taken up with Interphase
 during which DNA in the nucleus is replicated
 Mitosis and cytokinesis only take up 10% of cycle

10. The cell cycle has four main stages.
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 The cell cycle is a regular pattern of growth, DNA
replication, and cell division.

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 The main stages of the cell cycle are gap 1, synthesis,
gap 2, and mitosis.
– Gap 1 (G1): cell growth and
normal functions
• Mitosis occurs only if the cell is large enough and the DNA
undamaged.
– DNA synthesis (S): copies
DNA
– Gap 2 (G2): additional growth
(chromatids become replicated
chromosomes)
– Mitosis (M): includes division
of the cell nucleus (mitosis)
and division of the cell
cytoplasm (cytokinesis)

12. Mitosis
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 haploid and 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.

13. Condensed, duplicated chromosome
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 DNA plus proteins is called chromatin.
• One half of a duplicated chromosome
is a chromatid.
• Sister chromatids are held together at
the centromere.
• Telomeres protect DNA and do not
include genes.
Condensed, duplicated chromosome
chromatid
telomere
centromere
telomere

15. Mitosis
•The purpose of mitosis is cell division: making two
cells out of one.
• Each cell has to have its own cytoplasm and DNA.
•The DNA is replicated in interphase when two
chromosome strands became four strands (two strands
per chromatid).
•In mitosis the four strands (two sister chromatid) have
to break apart so that each new cell only has one
double-stranded chromosome.
•Two sister chromatids together make a chromosome
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16. Mitosis
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 Interphase
 Prophase I P M A T
 Metaphase
 Anaphase
 Telophase

17. Interphase
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1. Cell preparing to divide
2. Genetic material doubles

18. Prophase
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1. Chromosomes thicken
and shorten
-become visible
-2 chromatids joined
by a centromere
2. Centrioles move to
the opposite sides of
the nucleus
3. Nucleolus disappears
4. Nuclear membrane
disintegrate

19. Metaphase
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 Chromosomes
meet in the
middle!
1. Chromosomes
arrange at
equator of cell
2. Become attached
to spindle fibres
by centromeres

20. Anaphase
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 Chromosomes get pulled apart
1. Spindle fibres contract pulling chromatids
to the opposite poles of the cell

21. Telophase
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 Now there are
two!
1. Chromosomes
uncoil
2. Spindle fibres
disintegrate
3. Centrioles
replicate
4. Nucleur membrane
forms
5. Cell divides

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25. Cells divide at different rates.
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 The rate of cell division varies with the need for those
types of cells.

26. Class Activity
Do the following Questions
1. During what phase of mitosis
do centromeres divide and the
chromosomes move toward
their respective poles?
2. What is the phase where
chromatin condenses to form
chromosomes? 6/1/2023
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27. 3. What is the name
of the structure that
connects the two
chromatids?
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