Key characteristics that divide organisms into prokaryotes and eukaryotes

All living organisms are classified as either prokaryotic or eukaryotic. Prokaryotes and eukaryotes are categorized based on the characteristics of their cells. Some of the main characteristics that divide the organisms into prokaryotes and eukaryotes include;

Cell structure

Even though the cells of both prokaryotes and eukaryotes have some similar basic features like the cytoplasm and the plasma membrane, the prokaryote’s cells are simpler in comparison to the cells of eukaryotes. This is mainly because eukaryotic cells contain many internal cellular organelles that prokaryotic cells lack. Eukaryotic cells have the nucleus which mainly consists of deoxyribonucleic acid (DNA) and proteins. Some of the examples of eukaryotes include animals, plants, fungi, and protists. On the other hand, prokaryotic cells lack the nucleus. Examples of organisms with prokaryotic cells include archaeans and bacteria. Eukaryotic cells are more often multi-cellular and have cytoskeleton while prokaryotic cells are always unicellular with no cytoskeleton (De Duve, 2007).

Cell division

This is the process where a parent cell divides into two new cells known as daughter cells. In prokaryotic cells, the division process is simpler than in eukaryotic cells. Prokaryotic cells mostly divide through the process of binary fission. Binary fission consists of a series of continuous steps which include DNA replication, chromosome segregation, and separation. In eukaryotic cells, cell division takes place through the process of mitosis or meiosis. Before the division, the DNA multiple chromosomes replicate and the organelles are also duplicated. The division then takes place in two major steps i.e. mitosis and cytokinesis.

Reproduction

In prokaryotes, reproduction is always asexual i.e. there is no union of gametes. These organisms are able to reproduce without a mate. Eukaryotes, on the other hand, can reproduce both asexually and sexually. Sexual reproduction is a mode of reproduction where male and female gametes fuse to form a zygote which eventually develops into an offspring.

Key characteristics that divide prokaryotes into eubacteria and archaeans

While both eubacteria and archaeans are classified as prokaryotes, they are different evolutionarily. There exist two types of eubacteria i.e. Gram-positive and gram-negative while there are three types of archaeans which include halophiles, thermophiles, and methanogens. Examples of eubacteria are Bacillus, Mycobacteria, Clostridium, and Anaerobacter among others. Archaeans include Lokiarchaeum, Ferroplasma, Halobacterium, Thermoplasma etc. Some of the key characteristics which divide eubacteria and archaeans include;

Cellular structure

The cell wall of eubacteria is made of peptidoglycan which consists of lipopolysaccharide or muramic acid. They also have ester-linked lipids arranged in shape of a straight chain. On the other hand, archaeans have a cell wall which is said to be pseudo-peptidoglycan and also have ester-linked lipids which are in the shape of branched chains.

 

Reproduction

Eubacteria reproduce asexually but some are able to produce spores which enable them to be dormant during harsh or unfavorable conditions. Archaeans, on the other hand, reproduce asexually through binary fission, budding or by fragmentation process. Binary fission is where the organisms divide itself into two parts and its genetic material is also copied to both the two bodies during the process (DeLong, 2010).

Metabolic pathways

In breaking down the glucose, eubacteria follow the glycolysis pathway and the Kreb’s cycle. Kreb’s cycle is a series of reactions through which living cells produce energy. Archaeans, on the other hand, do not follow Kreb’s cycle or glycolysis. They are however able to extract nutrition and energy from different sources which include sunlight, sugars, metal ions and hydrogen.

Composition of RNA polymerase

The core architecture of eubacteria consists of four sub-units while that of archaeans consist of ten sub-units. Considering also their pathogenicity, some species of eubacteria are pathogenic while archaeans are non-pathogenic (Esko and Jeffrey, 2017).

The evidence that archaeans and eukaryotes are more closely related than eubacteria

Multiple biochemical and genetic lines

Biologists argue that since the discovery of archaeans, it has been demonstrated that they have some evolutionary links with eukaryotes. Particularly, the informational systems of the archaeans demonstrate a higher similarity sequence with their eukaryotic homologues as compared to their bacterial homologues, on several occasions these are not found in bacteria. For instance, thirty ribosomal proteins are particularly found in both the eukaryotes and the archaeans but are absent in bacteria, and most of the translation factors of archaeans demonstrate some similarities to their counterparts (eukaryotes) (McDonald, et.al 2012).

In terms of their structure and subunit composition, the RNA polymerases of both archaeans and eukaryotes are closely related and they also use the same promoters as well as basal transcription factors during initiation.

The four major activities which take place during DNA replication i.e. initiation, fragments priming, new strands synthesis and unwinding of the DNA are facilitated by enzymes which are shared by both the eukaryotes and the archaeans but are not homologous to bacteria.

Various operational systems that are membrane-based such as secretion pathways, vacuolar ATPases of archaeans and eukaryotes also seem to be related (Wang et.al 2007). An evolutionary link in metabolic systems may also be harbored between the archaeans and eukaryotes, for example between arginine biosynthesis pathway and carbamoylphosphate synthetase in the pyrimidine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

De Duve, C. (2007). The origin of eukaryotes: a reappraisal. Nature Reviews Genetics, 8(5), 395.

DeLong, J. P., Okie, J. G., Moses, M. E., Sibly, R. M., & Brown, J. H. (2010). Shifts in metabolic scaling, production, and efficiency across major evolutionary transitions of life. Proceedings of the National Academy of Sciences, 107(29), 12941-12945.

Esko, Jeffrey D. “Eubacteria and Archaea.” Essentials of Glycobiology. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 18 Apr. 2017.

McDonald, D., Price, M. N., Goodrich, J., Nawrocki, E. P., DeSantis, T. Z., Probst, A., … & Hugenholtz, P. (2012). An improved Greengenes taxonomy with explicit ranks for ecological and evolutionary analyses of bacteria and archaea. The ISME Journal, 6(3), 610.

Wang, Q., Garrity, G. M., Tiedje, J. M., & Cole, J. R. (2007). Naive Bayesian classifier for rapid assignment of rRNA sequences into the new bacterial taxonomy. Applied and environmental microbiology, 73(16), 5261-5267.

Woese, C. R., Kandler, O., & Wheelis, M. L. (1990). Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya. Proceedings of the National Academy of Sciences, 87(12), 4576-4579