Prokaryote versus eukaryote

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The phylogenetic tree of life shows three distinct group of organisms: prokaryotes (bacteria and archaea) versus eukaryotes.
The phylogenetic tree of life shows three distinct group of organisms: prokaryotes (bacteria and archaea) versus eukaryotes.

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 domainsBacteria 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
Domain Bacteria Archaea Eukarya
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
Movement Flagellum Cytoskeleton
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
Membrane-enclosed organelles Absent Present
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
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