Eukaryotic cells contain a nucleus, which contains the genetic information of the cell in the
DNA, packed into thread-like structures known as chromosomes. Each chromosome has a
constriction point called the centromere. Eukaryotic cells also contain organelles, specialized
subunits that carry out specific functions within the cell body. Such organelles include the Golgi
complex, mitochondria, endoplasmic reticulum, lysosomes, and ribosomes, etc. The Golgi
complex is used to create glucose, the mitochondria is used to create energy through cellular
respiration, the rough endoplasmic reticulum is used for transport and storage, the smooth
endoplasmic reticulum is used to create lipids and fats, the lysosomes are used for digestion, and
the ribosomes are used for protein synthesis. All eukaryotic cells are membrane-bound
nucleuses. The membrane, called the cytoplasm, protects and organizes the cell, keeping the
things that need to stay inside, inside, and keeping the things that need to stay outside, outside. It
is mostly composed of phospholipids, which cause the membrane to be very fluid. Spindle fibers
in the cell form a protein structure and divide the genetic material of the cell.
The processes of mitosis and meiosis both take place in a eukaryotic cell. The processes
of mitosis and meiosis are as follows:
Mitosis
Stage
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Description
Cell grows, copies its DNA, and prepares for
cell division
Chromosomes coil up and become visible, the
nuclear envelope dissolves, and the spindle
forms
Chromosomes line up along the spindle
equator, spindle fibers link the chromatids (two
thread-like structures into which the
chromosome divides) of each chromosome to
opposite poles
Centromeres divide, the two chromatids (now
chromosomes) move toward opposite poles
while the spindle fibers attach to shorten them
A nuclear envelope forms around the
chromosomes at each pole, the chromosomes
uncoil, and the spindle dissolves as the spindle
fibers dissolve
The cell cytoplasm is split to form two new
cells.
Meiosis
Stage
Interphase
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis I
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis II
Description
The chromosomes condense, the nucleolus
dissolves, spindles form, and the nuclear
envelope dissolves. Through snyapsis,
homologous chromosomes pair up, resulting in
a tetrad consisting of two chromatids from
each chromosome. Crossing-over may occur,
increasing the genetic variation in the gametes,
and four different chromosomes may occur.
Chromosome tetrads line up along the spindle
equator, and spindle fibers attach to the
centromeres of each homologous chromosome.
The chromosome tetrads separate, as replicated
chromosomes are pulled to opposite ends of
the cell. Unlike in mitosis, the centromeres
remain intact, and each chromosome is a
replica containing two sister chromatids.
There is now only one set of chromosomes in
each cell. A nuclear envelope may form, and
some animal cells divide the centrioles.
The cell splits into 2 diploid cells.
If a nuclear envelope was formed by
Telophase I, it dissolves during this phase. The
spindle fibers reform and attach to the
chromosomes, and the centromeres realign
again.
The spindles move the replicated doublestranded chromosomes into the equatorial area
of the spindle apparatus, attaching to opposite
ends of the centromeres.
The centromeres split, and the former
chromatids, now chromosomes, are pulled to
opposite sides of the cell.
The chromosomes drift away from each other,
and a nuclear envelope forms.
Each cell again splits into 2, resulting in 4
haploid gametes.
While these processes are different in many respects, they remain similar in some ways. For
instance, the stages of mitosis and meiosis are very similar; in fact, Prophase II, Metaphase II,
and Telophase II are very similar to the respective stages of mitosis (Prophase, Metaphase, and
Telophase). Indeed, the events of Telophase II are the same as the Telophase of mitosis.
However, mitosis and meiosis, in Prophase I of meiosis, homologous chromosomes pair up in a
process known as synapsis. This does not occur in mitosis. Additionally, during Anaphase in
mitosis, the centromeres split up. In Anaphase I of meiosis, the centromeres remain intact. The
end results of mitosis and meiosis are also different. For instance, mitosis maintains the ploidy of
all cells, while meiosis reduces it by one-half. Mitosis creates cells for growth and repair;
meiosis creates cells for use in sexual reproduction. Mitosis only produces two diploid cells,
while meiosis can produce up to four haploid cells.