Prokaryotic Cells

There are three main divisions of living organisms: Prokaryotes, eukaryotes and archaea. This essay will outline the division between the prokaryotic and eukaryotic organisms and explore the reasoning behind such differences with regard to general structure, storage of deoxyribonucleic acid and its replication, metabolic processes, protein synthesis and ribonucleic acid processing.

The cell is the most basic unit of life, defined as “The fundamental ... structural and functional unit of all living organisms” (Oed.com, 2013). The prokaryotic cell is typically composed of a plasma membrane and cell wall, containing within it the cytosol and a structure known as the nucleoid. This is a single piece of circular or linear DNA that floats freely in the cytosol of the cell (Thanbichler et al., 2005, pp. 507).

In contrast, eukaryotic organisms typically include (but are not limited to) membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum (E.R.), golgi body, lysosome and peroxisome. The main defining difference between a eukaryote and prokaryote is that the latter does not contain a nucleus or any such organelles. Such a definition, however, can be argued to be a poor discriminator between organisms of Eukarya and Prokarya, because it describes only what prokaryotes are lacking, not what they fundamentally are. This essay aims to detail a more comprehensive definition of why these two kingdoms are so different from each other. A key example of this thinking is that, while prokaryotes are often singly responsible for metabolic processes, reproduction and cell repair, eukaryotes are often highly specialised in order to perform certain functions and rely upon other cells to fulfil different functions. For exa...

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...from double-stranded RNA. This would be a major disadvantage, as its mechanism does not serve as a form of immunity to the organism, were it not for another system unique to prokaryotic cells (and archaea) that utilises “clusters of repetitive chromosomal DNA” (Van Der Oost and Brouns, 2009, pp. 863--865), which allow bacteria to store information from past infections by foreign DNA and hence construct an immune response in the future.

Prokaryotes and eukaryotes are organisms that are divided by their basic biological structure - the presence or lack of membrane-bound organelles. However, they can be defined and discriminated from one another according to certain key cellular functions and their respective differences: the way their DNA is stored and replicated, how they respire or photosynthesise, process their RNA transcripts or respond to foreign nucleic acids.