The Mitotic Phase: The Process of Eukaryotic Cell Division
Written by: Andrew Simonson
Cover image: biology-pictures.blogspot.com
Audience
This paper has been written for the benefit of those with a general knowledge of biology. As such,
the following is a basic level explanation of cellular division through the process of mitosis. This
paper will give readers an understanding of one of the most important processes in the biological
world that is similar to that offered in a general biology course.
Scope
This paper discusses cellular division in eukaryotes, particularly animal cells, only. In order to aid the
reader in gaining a general understanding of mitosis and cytokinesis, no other stages of cell life are
covered in depth in this document. Instead, each stage of the mitotic process is individually
introduced, explained and illustrated. In addition, definitions are provided along the right side of the
page as important terms or concepts are discussed to assist readers who are unfamiliar to the
subject or particular terminology.
Why Does Cell Division Occur?
Ordinary cellular division of eukaryotic cells occurs for a
variety of reasons. In unicellular organisms, such as
amoebas and certain algae, mitosis and cytokinesis is the
process through which they reproduce asexually. In
multicellular organisms, such as humans, it assists in the
growth, repair and replacement of tissues. For example, cell
division is responsible for the rapid increase in cell count
from embryo to full sized human, healing bone tissue after
sustaining a fracture and replacing dead skin cells. These
phenomena are possible as a result of mitosis and
cytokinesis increasing the total number cells.
Eukaryotic Cell – Cell which
contains functional
organelles, including a
membrane bound nucleus.
Organelle – A specialized
structure in a cell.
Nucleus – An organelle
containing all genetic
material for the cell that is
bound by a membrane.
Mitosis – Division of the nucleus
and chromosomes into two.
Cytokinesis – Division of
cytoplasm into two
genetically identical
daughter cells.
Asexual Reproduction –
Production of offspring
from a single parent.
All cell images: www.edupic.net
Mitosis and Cytokinesis
After the cell has grown and replicated its chromosomes
during interphase, the cell moves into the M-stage of its life.
This is commonly referred to as simply mitosis, although
this is a misnomer. During the M-stage, the cell undergoes
six stages: prophase, prometaphase, metaphase, anaphase,
telophase and cytokinesis, each of which is explained in
detail below. Over the course of the division, the parent
condenses and divides chromosomes such that each
daughter cell gets a complete set after splitting.
Chromosome – Thread of DNA
containing genes, or
functional genetic material.
Interphase – The stage in which a
cell spends the majority of its
life. Growth and gene
replication occur during this
stage.
A cell in interphase, right before
mitosis begins.
Prophase
Prophase is the first, and longest, stage of mitosis. In this
stage, genetic material, which is stored as long thin strands
during cell growth, condenses and becomes tightly bundled.
The chromosomes can now be seen under a microscope
and appear in an X-shape. This is because each
chromosome contains identical sister chromatids which are
joined at the centromere. In the figure below, the
chromosome pairs are represented by the red and blue
figures in the center of the cell. As this is occurring, the
nuclear envelope, or membrane, begins to degrade. This is a
key step is producing identical offspring as it exposes the
genetic material of the cell and allows for distribution to
both daughter cells. Also in prophase, centrioles begin to
migrate towards opposite poles, and mitotic spindles form
in the cytoplasm of the cell. The nuclear envelope is
completely degraded by the end of prophase.
A cell in prophase.
All cell images: www.edupic.net
Sister Chromatid – Identical
copies of a duplicated
chromosome.
Centromere – Condensed section
of the chromosome joining
two chromatids.
Centriole – Cylindrical organelle
composed of condensed
microtubules.
Mitotic Spindle – Protein-based,
tube-like structures formed
by the centriole.
Cytoplasm – Gel, organelles and
molecular structures within
the cell, excluding the
nucleus.
Prometaphase
Prometaphase is the stage of mitosis in which the mitotic
spindles connect to centromeres. Structures called
kinetochores have been formed on the centromeres to
facilitate this connection.
Kinetochore – Protein structure
on centromeres that allow
attachment to spindle fibers.
A cell in prometaphase.
Metaphase
Metaphase, the shortest stage of mitosis, occurs after the
centrioles reach opposite poles of the cell and the spindles
have been fully developed. This allows the condensed
chromosomes to migrate to the metaphase plate. During
this movement, sister chromatids are aligned parallel to the
plate so that each is facing a centriole.
Metaphase Plate – Equatorial
plane where chromosomes
align themselves during
metaphase.
A cell in metaphase.
Anaphase
Anaphase, the fourth stage of mitosis, begins with the separation of sister chromatids. This allows
the centriole to pull one chromatid from each pair away from the metaphase plate. This “pulling”
action comes from the decomposing of the fibers that make up the mitotic spindle on the end
attached to the kinetochore. This means the chromosomes move along the fibers rather than the
apparent pull that is observed. Due to a centralized centromere, the chromosomes assume a Vshape while migrating. The end of anaphase is indicated by the gathering of a complete set of
chromosomes at the pole.
All cell images: www.edupic.net
A cell in anaphase.
Telophase
During telophase, the chromosomes unravel and return to the fibrous appearance associated with
interphase. At the same time, a nuclear envelope begins to form around each set of chromosomes.
Meanwhile, the mitotic spindles completely degrade and disappear. At this point, each with a
complete set of chromosomes, the daughter cells begin assuming the appearance of full grown cells.
A cell undergoing telophase
and early stages of cytokinesis.
Cytokinesis
Cytokinesis is the final step in cell division. While it is
considered to be after telophase, it often begins while
telophase is still occurring. This stage is the division of
cytoplasm. This is typically achieved by a cleavage furrow
formed by a ring of intracellular proteins and fibers. Once
cytokinesis is complete, the membrane is pinched closed
and two daughter cells that are identical to the parent have
been produced.
Cleavage furrow – An indentation
in the cellular membrane at
the equator of the cell
formed by a contractile ring.
Identical daughter cells after
the completion of mitosis.
Summary
The mitotic (M) stage is the process through which cells produce offspring with identical genetic
coding to a single parent. Through this process, the cell goes through the five stages of mitosis
(prophase, prometaphase, metaphase, anaphase and telophase), the division of the nucleus and
All cell images: www.edupic.net
genetic material, and cytokinesis, the division of cytoplasm. In short, the cell’s replicated
chromosomes condense while the nuclear envelope degrades. Then, mitotic spindles connect with
the chromosomal centromeres and the chromosomes line up along the equatorial plane, or the
metaphase plate. After this is complete, the sister chromatids break apart and migrate to their
respective poles where the nuclear envelope reforms. This is then succeeded by cytokinesis and the
formation of two, genetically identical daughter cells.
The M stage of cell life is important for organism survival in so many ways. While these are laid out
at the beginning of this piece, hopefully this description helped improve knowledge and
understanding of the mitotic process, in addition to raising interest levels in the field of biological
sciences.
All cell images: www.edupic.net