The document discusses the mechanism of cell division in eukaryotic cells. It describes the four main phases of the cell cycle - growth, DNA synthesis, nuclear division through mitosis, and cytokinesis. The S phase involves DNA replication, while the M phase comprises mitosis and cytokinesis. Mitosis is further broken down into the prophase, metaphase, anaphase and telophase stages. Cytokinesis then divides the cytoplasm, resulting in two daughter cells each with identical DNA to the original parent cell. The cell cycle is tightly regulated by control proteins to ensure proper division.

1. UNIVERSITY FOR DEVELOPMENT STUDIES
FACULTY OF BIOSCIENCES
BTC 503: PRINCIPLES OF CELLAND MOLECULAR BIOLOGY
BY
ISSAH ABDUL-HANAN GIRASU
(M. PHIL BIOTECHNOLOGY)
EMAIL: abdul-hanan.issah14@uds.edu.gh

2. MECHANISM OF CELL DIVISION
• Overview
• Cell cycle
• Mitosis
• Cytokinesis
• Meiosis
• Control of the Cell Cycle
Principles of Cell and Molecular Biology (Cell Division)

3. OVERVIEW
• Cells passes through an ordered series of events in which the cell duplicates its contents and
divide into two through a mechanism known as the cell cycle.
• In unicellular organism such as bacteria and yeast, each cell division produces a complete
new organism.
• However in multicellular organisms, long and complex sequences of cell division are
required to produce a functioning organism
• The cell cycle varies from organism to organism though certain characteristics are universal
for the ultimate aim of passing genetic information to the next generation.
Principles of Cell and Molecular Biology (Cell Division)

4. WHY CELLS DIVIDE
• For growth
• For repair and
• For reproduction (sexual /asexual)
Principles of Cell and Molecular Biology (Cell Division)

5. THE EUKARYOTIC CELL CYCLE
This process of cell division in multicellular organisms is highly ordered and tightly regulated and
has been divided into 4 phases; growth, synthesis, nuclear division and cytokinesis.
There are two major phases of this cycle;
S-phase (“S” for synthesis)
M-phase (“M” for mitosis)
Along with gap phases in between these major
phases (G1 and G2).
Principles of Cell and Molecular Biology (Cell Division)

6. THE EUKARYORTIC CELL CYCLE (Summary)
Principles of Cell and Molecular Biology (Cell Division)

7. S-PHASE
• In the S-phase, there is duplication of DNA chromosomes and segregation
into two identical daughter cells
• The end of the S-phase entails of the duplication of chromosomes which is
immediately followed by the M-phase (characterized by mitosis)
• This requires 10-12 hours and occupies about half of the cell cycle time in
mammals.
Principles of Cell and Molecular Biology (Cell Division)

8. M-PHASE
Comprises 2 major events; nuclear division (mitosis) and cytoplasmic division
(cytokinesis)
Most cells require a great amount of time to grow and for chromosome
multiplication and so have extra gap phases.
G1-phase (between M and S-phases)
G2-phase (between S and M-phases)
Principles of Cell and Molecular Biology (Cell Division)

9. MITOSIS
There are 4 main phases of mitosis;
Prophase
Metaphase
Anaphase and
Telophase
Principles of Cell and Molecular Biology (Cell Division)

10. PROPHASE
In this phase,
 DNA molecules gradually condense into pair of rigid and compact rods
called sister chromatids
The nuclear envelope also breaks up, exposing the chromosomes
spindle fibres begin to form from centrioles
Principles of Cell and Molecular Biology (Cell Division)

11. METAPHASE
In this phase,
Chromosomes align at the equator with the help of spindle fibres
ANAPHASE
Characterized by the dissociation of sister chromatids
Principles of Cell and Molecular Biology (Cell Division)

12. TELOPHASE
Nuclear membrane begins to form around the separate chromosomes
Chromosomes begin to unravel into their loose form
Spindle fibres begin to dissemble
Principles of Cell and Molecular Biology (Cell Division)

13. Principles of Cell and Molecular Biology (Cell Division)

14. CYTOKINESIS
This is when the cytoplasm divides into 2
Principles of Cell and Molecular Biology (Cell Division)

15. Principles of Cell and Molecular Biology (Cell Division)

16. MEIOSIS I
Principles of Cell and Molecular Biology (Cell Division)

17. MIEOSIS I
Principles of Cell and Molecular Biology (Cell Division)

18. MIEOSIS II
Principles of Cell and Molecular Biology (Cell Division)

19. Principles of Cell and Molecular Biology (Cell Division)

20. THE CELL CYCLE CONTROL SYSTEM
• There are some key proteins that make up the control system which are
distinct from the proteins that performs the processes of replication and
chromosome segregation.
Principles of Cell and Molecular Biology (Cell Division)

21. THANK YOU
Principles of Cell and Molecular Biology (Cell Division)