Cell Division
علي عبد الزهره عماره
Aصباحي
Overview
• Cell division is a fundamental process in biology that allows
organisms to grow, develop, and repair tissues. It plays a
crucial role in maintaining a constant cell population. Cell
division is a highly regulated and precisely controlled
process.
The Cell Cycle
• The cell cycle is a series of events that cells go through as
they grow and divide. It consists of three main phases:
Interphase, Mitosis, and Cytokinesis. Each phase has
specific tasks and contributes to the overall process of cell
division.
Interphase
• Interphase is the longest phase of the cell cycle. It can be
divided into three sub-phases: G1, S, and G2. During G1,
the cell grows, carries out its normal functions, and
prepares for DNA replication. In the S phase, DNA
replication occurs, resulting in the duplication of
chromosomes. G2 is a phase of further growth and
preparation for mitosis.
Mitosis
• Mitosis is the process of dividing the nucleus into two
identical daughter nuclei. It consists of four main stages:
Prophase, Metaphase, Anaphase, and Telophase. Each
stage has distinct events that ensure accurate separation
of genetic material.
Prophase
• In prophase, the chromatin condenses, and the
chromosomes become visible. The nuclear membrane
disintegrates, allowing the chromosomes to move freely
in the cell. The spindle apparatus forms, consisting of
microtubules that will aid in chromosome movement.
Metaphase
• During metaphase, the chromosomes align at the
equatorial plate (center) of the cell. The spindle fibers
attach to the centromeres of each chromosome, ensuring
proper alignment.
Anaphase
• Anaphase is characterized by the separation of sister
chromatids. The microtubules shorten and pull the
chromatids towards opposite poles of the cell. Once
separated, each chromatid is considered an individual
chromosome.
Telophase
• Telophase marks the end of nuclear division. The nuclear
membranes reform around the separated chromosomes.
Chromosomes decondense, and the spindle apparatus
disassembles.
Cytokinesis
• Cytokinesis is the division of the cytoplasm and organelles.
In animal cells, a cleavage furrow forms, pinching the cell
into two daughter cells. In plant cells, a cell plate forms,
eventually becoming the cell wall that separates the
daughter cells.
Regulation of Cell Division
• Cell division is tightly regulated to maintain proper growth
and prevent abnormalities. Checkpoints within the cell
cycle control system ensure that each phase is completed
accurately. These checkpoints monitor DNA integrity, cell
size, and other factors before allowing progression.
Importance of Cell Division
• Cell division is essential for growth, development, and
tissue repair in organisms. Abnormalities in cell division
can lead to diseases like cancer. Understanding the
mechanisms of cell division provides insights into various
biological processes.
Mitosis vs. Meiosis
• Mitosis and meiosis are two types of cell division with
distinct purposes and outcomes. Mitosis is a form of cell
division involved in growth, tissue repair, and asexual
reproduction. Meiosis is a specialized cell division that
produces gametes (sperm and egg cells) for sexual
reproduction.
Main Differences:
• Mitosis produces two diploid daughter cells with the same
number of chromosomes as the parent cell. Meiosis
involves two rounds of cell division, resulting in four
haploid daughter cells with half the number of
chromosomes. Mitosis is responsible for the growth and
maintenance of multicellular organisms. Meiosis
contributes to genetic diversity and the formation of
offspring.
Non-Dividing Cells: Nerve Cells
(Neurons)
• Nerve cells, or neurons, are a specialized type of cell that
typically do not undergo cell division. One of the main
reasons neurons do not divide is the absence of a
centrosome, a critical structure involved in cell division.
Centrosomes play a crucial role in organizing the mitotic
spindle during cell division. Neurons are post-mitotic cells,
meaning they have exited the cell cycle and entered a
non-dividing state. Instead of dividing, neurons have other
mechanisms for growth and development, such as
dendritic branching and synapse formation.
Conclusion
• Cell division is a fundamental process that ensures the
growth and development of organisms. The cell cycle,
mitosis, and cytokinesis work together to achieve
accurate cell division. Studying cell division enhances our
understanding of biology and has implications in various
fields.
References
• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., &
Walter, P. (2002). Molecular Biology of the Cell (4th ed.).
Garland Science. Chapter 17: The Cell Cycle Lodish, H.,
Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., &
Darnell, J. (2000). Molecular Cell Biology (4th ed.). W. H.
Freeman and Company. Chapter 18: The Cell Cycle and
Cell Division Cooper, G. M., & Hausman, R. E. (2009). The
Cell: A Molecular Approach (5th ed.). Sinauer Associates.
Chapter 12: The Cell Cycle
