The Birth Of Complex Cells Essay
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Today, all multicellular organism are composed of eukaryotic cells which are larger and
more complex than prokaryotes. These eukaryotic cells consist of organelles, such as
mitochondria and peroxisomes, which were once believed to have been prokaryotes. We
will find that these two organelles, which have triumphed through evolution, serve
important functions within cells.
We will begin with peroxisomes which are believed to have been engulfed by a
larger, eukaryotic, primitive phagocytic cell through a process called endosymbiosis. The
precursors to peroxisomes may have been the first prokaryotes to develop into eukaryotic
organelles. This is believed to be true because long ago there was a toxic oxygen crisis
where anaerobic cells could not handle the high level of oxygen in the atmosphere.
Therefore they implemented peroxisomes which rescued them from the oxygen toxicity.
Peroxisomes convert oxygen to hydrogen peroxide and destroy it with an enzyme called
catalase. They also remove the superoxide ion. It is believed that peroxisomes stem from
primitive aerobic bacteria that were adopted before mitochondria. These primitive oxygen
detoxifiers may have protected their host cells during the period of time before
mitochondria had evolved. Peroxisomes do not contain remnants of an independent gene
system, however it is agreed upon that they have been around for so long that they lost all
their DNA to the nucleus by now through evolution. Hence, this theory gives light to the
implementation of mitochondria.
The precursor of mitochondria proved to be even better at protecting host cells
against oxygen and offered the further ability to generate the energy-rich molecule ATP,
which is a process all living organisms are dependent on. Mitochondria also proved to be
extremely efficient in the detox of oxygen by converting it into water. Like peroxisomes,
mitochondria lost their DNA to the nucleus of the eukaryotic cell, however they still hold
within themselves some of their original genes. This fact about the loss of genes is very
important in support of evolutionary theory. It is theorized that when the larger
eukaryotic cell duplicated, it also replicated the organelles (mitochondria and/or
peroxisomes), since it contained the DNA of the organelle in the nucleus. Also, the fact
that the mitochondria contains some of its own DNA indicates that at one point, the
mitochondria was a free living prokaryotic cell. Further evidence in support of the theory
includes the fact that most prokaryotic cells are about the same size as organelles.Today,...
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