Cellular Biology

Difference between Prokaryotes and Eukaryotes



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Cells are the basic units of life, and although there are many different forms of specialized cells, there are only two true types of cells — prokaryotes and eukaryotes.The differences between these two cell types include the following.

* Cell Walls – Although most prokaryotes, and some eukaryotes, have a cell wall — cell-supporting structures located outside the plasma membrane, cell walls are composed of different materials, based on the type of organism. Bacteria (prokaryotes of the domain Eubactera) have cell walls that contain the molecule peptidoglycan. No other type of organism has a cell wall containing this molecule. Prokaryotes in the domain Archea have cell walls, but they are made of materials other than peptidoglycan. Eukaytotic animal cells do not have cell walls. Eukaryotic plants and fungi have cells walls, made of cellulose and chitin, respectively.

* Centriomes and Centrostomes (some Eukaryotes) – Animal and some fungal cells possess these structures, whereas plants, algae, fungi and prokaryotes do not have them. Centrioles (two together make a centrosome) are involved in cytoskeleton production and cell division of animal cells.

* Energy-related Organelles (Eukaryotes) – Mitochondria and chloroplasts are membrane-bound organelles, so are not found in prokaryotes. Mitochondia are found in nearly all eukaryotic cells (other than a few oddball parasites) and chloroplasts are found only in eukaryotes that photosynthesize (capture sunlight energy and turn it into food). These two energy-related organelles have their own DNA and are believed to have originally been independent prokaryotes that formed a symbiotic (mutualistic) relationship with another cell. This is called the endosymbiotic theory.

* Endomembrane System (all Eukaryotes) – Although both prokaryotes and eukaryotes have a plasma membrane, a phospholipid bilayer that separates the inside from the outside of the cell, only eukaryotes have additional membrane-bound organelles within the cell, including the nuclear membrane, endoplasmic reticulum, Golgi apparatus, lysosomes and vesicles.

* Evolution – Eukaryotic cells are more evolutionarily advanced, having arisen from prokaryote-like predecessors.

* Location of Genome – The genome (chromosomes) of a eukaryote resides within the nucleus, a membrane bound structure which encloses the genetic material within the nuclear membrane. Prokaryotes don’t have a nucleus. Their genetic material (called a nucleoid) floats freely within the cytoplasm.

* Type of Genome – Although the genomes of all living organisms are composed of deoxyribonucleic acid (DNA), eukaryotes can have their DNA present in few to many linear chromosomes (humans have 46 chromosomes). Prokaryotes typically have a single, circular chromosome.

* Plasmids (Bacterial Prokaryotes) – A plasmid is an extra piece of ‘bonus’ genetic material that is separate from the genome and not use for day to day functions of the cell. This small piece of DNA typically confers some advantage to the bacteria, such as antibiotic resistance, virulence factors or augmenting conjugation.

* Size – Nearly all prokaryotes are much smaller in size that a eukaryotic cell. Prokaryotes usually range between 1 – 10 micrometers, whereas eukaryotic cells range from 10 micrometer – 1 millimeter.

Sources:

Bauman, R. (2004). Microbiology. Pearson Benjamin Cummings.

Campbell, N. and Reece J. (2002). Biology, Sixth Edition. Benjamin Cummings.

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