The distinction between prokaryotes and eukaryotes is considered to be the most important distinction among groups of organisms. Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Differences in cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomal DNA.
Prokaryotes were the only form of life on Earth for millions of years until more complicated eukaryotic cells came into being through the process of evolution.
|Number of chromosomes||More than one||One--but not true chromosome: Plasmids|
|Cell Type||Usually multicellular||Usually unicellular (some cyanobacteria may be multicellular)|
|True Membrane bound Nucleus||Present||Absent|
|Example||Animals and Plants||Bacteria and Archaea|
|Genetic Recombination||Meiosis and fusion of gametes||Partial, undirectional transfers DNA|
|Lysosomes and peroxisomes||Present||Absent|
|Microtubules||Present||Absent or rare|
|Cytoskeleton||Present||May be absent|
|DNA wrapping on proteins.||Eukaryotes wrap their DNA around proteins called histones.||Multiple proteins act together to fold and condense prokaryotic DNA. Folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.|
|Chloroplasts||Present (in plants)||Absent; chlorophyll scattered in the cytoplasm|
|Flagella||Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlets||Submicroscopic in size, composed of only one fiber|
|Permeability of Nuclear Membrane||Selective||not present|
|Plasma membrane with steroid||Yes||Usually no|
|Cell wall||Only in plant cells and fungi (chemically simpler)||Usually chemically complexed|
Definition of eukaryotes and prokaryotes
Prokaryotes (pro-KAR-ee-ot-es) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. -otes; also spelled "procaryotes") are organisms without a cell nucleus (= karyon), or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular.
Eukaryotes (IPA: [juːˈkæɹɪɒt]) are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane bound structure is the nucleus. This feature gives them their name, (also spelled "eucaryote,") which comes from the Greek ευ, meaning good/true, and κάρυον, meaning nut, referring to the nucleus. Animals, plants, fungi, and protists are eukaryotes.
Differences Between Eukaryotic and Prokaryotic Cells
The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms.
- The most fundamental difference is that eukaryotes do have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound.
- In eukaryotes, the mitochondria and chloroplasts perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare.
- The cell walls of prokaryotes are generally formed of a different molecule (peptidoglycan) to those of eukaryotes (many eukaryotes do not have a cell wall at all).
- Prokaryotes are usually much smaller than eukaryotic cells.
- Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organised chromosomes. Although some eukaryotes have satellite DNA structures called plasmids, these are generally regarded as a prokaryote feature and many important genes in prokaryotes are stored on plasmids.
- Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes.
- Prokaryotes also differ from eukaryotes in the structure, packing, density, and arrangement of their genes on the chromosome. Prokaryotes have incredibly compact genomes compared to eukaryotes, mostly because prokaryote genes lack introns and large non-coding regions between each gene.
- Whereas nearly 95% of the human genome does not code for proteins or RNA or includes a gene promoter, nearly all of the prokaryote genome codes or controls something.
- Prokaryote genes are also expressed in groups, known as operons, instead of individually, as in eukaryotes.
- In a prokaryote cell, all genes in an operon(three in the case of the famous lac operon) are transcribed on the same piece of RNA and then made into separate proteins, whereas if these genes were native to eukaryotes, they each would have their own promoter and be transcribed on their own strand of mRNA. This lesser degree of control over gene expression contributes to the simplicity of the prokaryotes as compared to the eukaryotes.