Prokaryote versus eukaryote
It is believed that a single, common universal ancestor of all life was a prokaryotic cell. Prokaryotes were the only life-forms for billions of years. As a consequence of evolution in different environments the prokaryotes have evolved to become more genetically and physically diverse, adapted to different styles of life. Prokaryotes consist of two domains – Bacteria and Archaea.
Eukaryotes are more complex than prokaryotes and are (hypothetically) created when prokaryotes fuse (endosymbiosis). Prokaryotes have evolved a multitude of metabolic strategies and are found in a wide range of habitats, including conditions where most other organisms (Eukaryotes) fail to survive.
In contrast to most eukaryotes, prokaryotes reproduce asexually. While sexual reproduction in eukaryotes results in offspring with genetic material which is a mixture of the parents’ genome, a prokaryote will reproduce clones of itself. During reproduction, eukaryotes generate genetic variation by sexual recombination. Genetic variation mechanisms of prokaryotes are not tied to reproduction. One extremely rare genetic variation mechanism among eukaryotes is horizontal gene transfer.
Prokaryotes are generally smaller than eukaryotes. The smallness has, among other things, consequences for growth rates and generation times. Diffusion limitation generally restricts the maximal size of prokaryotic cells. Because of the asexual reproduction and short generation time relative to larger organisms, prokaryotes pass the genome rapidly on to subsequent generations. Therefore genetically changed genomes are also rapidly transferred. And therefore prokaryotes swiftly adapt and colonize new niches and a wide range of habitats.
Prokaryotes are one-celled and often live in clusters or colonies. Prokaryote species live among and interact with other species in communities and consortia. The microenvironment and the interactions hold important selection pressures which affect the evolution of the prokaryotes.
|Prokaryotic cell||Eukaryotic cell|
|Diversity||Prokaryotes are more diverse than eukaryotes|
|Complexity||Prokaryotes are less complex than eukaryotes|
|Genetic variation mechanisms||Asexual. Produce clones. May transfer genetic material horizontally.||Sexual recombination|
|Organisation||Uni-cellular||Uni-cellular or multicellular|
|Diameter (micrometer)|| The smallest 0,1 |
The largest >50
|Typically between 2-200|
|Cell division||Binary fission||Mitotic spindle|
|Electron acceptor||Oxygen or other compounds||Oxygen|
|Major structures||Nucleoid , cell wall, cytoplasmic membrane, ribosomes, inclusions||Organelles, nucleus. Otherwise the same basic elements of a prokaryote|
|Peptidoglycan in cell wall||Present||Absent|
|Antibiotic sensitivity||Growth inhibited by streptomycin & chloramphenicol||Not inhibited by these antibiotics|
|Membrane lipids||Unbranched hydrocarbons||Some branched hybrocarbons||Unbranched hybrocarbons|
|Species that survive above 65°C||Yes||No|
|Genetic material||Often only one, circular chromosome and small amounts of extrachromosomal DNA arranged in (usually circular) plasmids||Several, linear chromosomes|
(noncoding parts of genes)
|Absent||Present in some genes||Present|
|Typical number of gene copies||Haploid → Genotype reflects phenotype.||Diploid or multiploid → Recessive genes are not expressed and hence “hidden” from selection pressure.|
|Location of chromosomes||Cytoplasma||Nucleus|
|Location of RNA synthesis||Cytoplasma||Nucleus|
|Location of protein synthesis||Cytoplasma|
|RNA polymerase||One kind||Several kinds|
|Initiator amino-acid for start of protein synthesis||Formyl-methionine||Methionine|