BIO1MGC - Archaeans essay PDF

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Topic A: Archaeans Kaewphada Kaewsuriyathumrong

Prokaryotes and eukaryotes are commonly known to be two types of distinguished cells which enables the classification of organisms due to the eminent features present within the cells. The two living groups can be further divided to accurately classify living organisms. Eukaryotes can be divided into plants, animals, Protista and fungi, whereas prokaryotes can be divided into two groups which includes eubacteria and archaeans. Recently, it is claimed that archaeans are more closely related to eukaryotes. However, others argued that archaeans are prokaryotes. Scientists struggle to arrive to a conclusion whether they are indeed more related to eukaryotes or prokaryotes. This essay explores the similarities and differences in the characteristics of the two groups of living organisms and provides evidence that can concludes whether archaeans are more closely related to eukaryotes or prokaryotes.

Prokaryotes are unicellular organisms that do not contain a nucleus and membrane-enclosed organelles. Eukaryotes are known to be a multicellular organism with membrane bound organelles (Reece et al., 2017). Living organisms can be divided into prokaryotes and eukaryotes from certain characteristics. Firstly, Prokaryotes lack the presence of membrane bound organelles. This can include the nucleus, ribosomes, endoplasmic reticulum, the Golgi apparatus, and the mitochondria which are commonly found in eukaryotic cells. (Reece et al., 2017). The reason for this is that the cell does not require a cytoskeleton, an internal membrane system and a copious amount of energy produced. Eukaryotes requires membrane bound organelles as they store of genetic information, increases efficiency in function and the synthesis of energy (Reece et al., 2017). Secondly, the prokaryotic cell lacks the nucleus, whereas eukaryotes posseses a ‘true’ nucleus. The prokaryotic cell lacks the nucleus but has a nucleoid region in the cytoplasm, which encompass a circular DNA that contains the genetic code. On the other hand, the eukaryotic cell consists of a nucleus which is comprised of the cell’s DNA and the nucleolus, which includes the RNA and is responsible for ribosome biogenesis (Olson & Dundr, 2015). Lastly, the prokaryotic cell replicates by binary fission, whereas the eukaryotic cell replicates by mitosis and meiosis. Binary fission is asexual reproduction where the parent cell split into two identical daughter cells after the replication of the genetic material. In comparison, mitosis involves six steps which includes interphase, prophase, metaphase, anaphase, telophase and cytokinesis. Meiosis is sexual reproduction which involves twelve steps which includes the process of mitosis being repeated which results in two haploid gametes (d'Erfurth et al., 2009).

Eubacteria are prokaryotic cells which are mainly known to be ‘true bacteria.’ Archaeans are single celled extremophiles which share the characteristics of both prokaryotes and eukaryotes (Esko, Doering & Raetz, 2009). Both the eubacteria and archaeans share similar features such as lacking membrane bound organelles, containing a circular DNA and not having a ‘true’ nucleus. (Reece et al., 2017). However, there are key characteristics that distinguishes both living organisms from one another. Firstly, eubacteria can be found almost everywhere especially on or in humans. Eubacteria is known to kill thousands of humans every year but, they can assist human bodies by producing key nutrients, being food digesters, antibiotics and being involved in weight gain and brain development (Esko, Doering & Raetz, 2009). In comparison, archaeans survive in extreme temperatures over 100 degrees Celsius. They can be found oil wells, geysers and hydrothermal vents (Kletzin, 2007). Secondly, eubacteria consist of a peptidoglycan cell wall, whereas archaeans lack peptidoglycan in their cell wall. Peptidoglycan consists of a sugar and amino acid chain. It is present in almost all bacteria ( Rogers et al., 1980). This prevents mutation, preserve cell integrity and supporting its size and shape when it is exposed to the changing chemical and osmotic environments of the cell (Chattaway, 1982). In addition to this, eubacteria contain lipopolysaccharide and S-layer proteins which are protective coats that contributes to surface recognition and adhesion in bacteria (Sleytr, Schuster, Egelseer & Pum, 2014). On the other hand, the cell wall of archaeans contain polysaccharides and the S-layer protein external to the plasma membrane. The S-layers determine the cell shape and division in archaeans (Sleytr, Schuster, Egelseer & Pum, 2014). Lastly, both the eubacteria and archaeans have different rRNA. Eubacteria consist of the 16S rRNA gene which exists in all bacteria. In contrast, the rRNA in archaeans consists of features such as ‘lobes’ and ‘bills’ which are found in Eukaryotes (Londei, 2010). In addition, the primary sequences of rRNA are similar to eukaryotes than to prokaryotes.

There are several evidences that supports the claim that archaeans are more closely related to eukaryotes. The first evidence that proves this is the phylogenetic tree. According to the tree, it suggests that there is a divergent evolution between prokaryotes and eukaryotes, which the eukaryotes later diverged into archaeans. Even though the archaea may be visually similar to bacteria, the archaea contain genes and metabolic pathways that are more similar to eukaryotes. Examples of this is that archaeans generates ATP through chemiosmosis which is the same process that occurs in in the mitochondria in eukaryotic cells, also archaeans uses the same DNA polymerases as eukaryotes to undergo chromosome replication and it contains the same enzymes that is involved in transcription and translation (Woese, Kandler & Wheelis, 1990). The second evidence is the Lokiarchaeota which is a phylum of archaeans. It has similar functions to eukaryotes which includes cell membrane deformation, cell shape formation and contains a protein cytoskeleton. The microorganism also contains actin which is a protein essential for phagocytosis in

eukaryotes. This means that it may contain the mitochondria or chloroplasts which are present in eukaryotes (Jørgensen, Thorseth, Pedersen, Baumberger & Schleper, 2013).

Ultimately, there are two groups of living organisms which includes prokaryotes and eukaryotes which classifies living organisms from their cellular anatomy which can involve the absence or presence of features needed for an internal membrane system and having different processes for cell functionality. Both the eubacteria and the archaeans are visually similar, but has distinguished characteristics and survives in different environments. In addition to this, the features and functions of the archaeans are similar to eukaryotes. This claim was supported by the phylogenetic tree and the Lokiarchaeota. Despite the archaean being classified as a prokaryote, the evidences clearly support the close relationship between archaeans and eukaryotes.

References: Reece, J., Urry, L., Meyers, N., Cain, M., Wasserman, S., & Minorsky, P. (2017). Campbell Biology: Australian and New Zealand Version (11th ed.). Frenchs Forest, NSW: Pearson Education Australia. Tindall, B., Busse, H., Ludwig, W., Rosselló-Móra, R., & Kämpfer, P. (2010). Notes on the characterization of prokaryote strains for taxonomic purposes. International Journal Of Systematic And Evolutionary Microbiology, 60(1), 249-266. doi: 10.1099/ijs.0.016949-0 Vellai, T., & Vida, G. (1999). The origin of eukaryotes: the difference between prokaryotic and eukaryotic cells. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1690172/pdf/10467746.pdf Mayr, E. (1998). Two empires or three?. Proceedings Of The National Academy Of Sciences, 95(17), 9720-9723. doi: 10.1073/pnas.95.17.9720 Kletzin, A. (2007). Chapter 2 : General Characteristics and Important Model Organisms. Archaea, 14-92. doi: 10.1128/9781555815516.ch2 Esko, J., Doering, T., & Raetz, C. (2009). Eubacteria and Archaea. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK1945/?report=reader#!po=2.77778 Woese, C., Kandler, O., & Wheelis, M. (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. doi: 10.1073/pnas.87.12.4576 Olson MO, Dundr M (16 February 2015). "Nucleolus: Structure and Function". Encyclopedia of Life Sciences (eLS). doi:10.1002/9780470015902.a0005975.pub3. ISBN 978-0-470-01617-6. d'Erfurth, I., Jolivet, S., Froger, N., Catrice, O., Novatchkova, M., & Mercier, R. (2009). Turning Meiosis into Mitosis. Plos Biology, 7(6), e1000124. doi: 10.1371/journal.pbio.1000124 Vollmer, W., Blanot, D., & De Pedro, M. (2008). Peptidoglycan structure and architecture. FEMS Microbiology Reviews, 32(2), 149-167. doi: 10.1111/j.1574-6976.2007.00094.x Chattaway, F. (1982). Microbial Cell Walls and Membranes. Biochemical Education, 10(1), 33. doi: 10.1016/0307-4412(82)90023-1 Sleytr, U., Schuster, B., Egelseer, E., & Pum, D. (2014). S-layers: principles and applications. FEMS Microbiology Reviews, 38(5), 823-864. doi: 10.1111/1574-6976.12063 Londei, P. (2010). Archaeal Ribosomes. Encyclopedia Of Life Sciences. doi: 10.1002/9780470015902.a0000293.pub2 Jørgensen, S., Thorseth, I., Pedersen, R., Baumberger, T., & Schleper, C. (2013). Quantitative and phylogenetic study of the Deep Sea Archaeal Group in sediments of the Arctic mid-ocean spreading ridge. Frontiers In Microbiology, 4. doi: 10.3389/fmicb.2013.00299...