Hydrogenosome Research Paper

When life arose on Earth about 4 billion years ago, the first types of cells to evolve were prokaryotic cells. For approximately 2 billion years, prokaryotic-type cells were the only form of life on Earth. The oldest known sedimentary rocks found in Greenland are about 3.8 billion years old. The oldest known fossils are prokaryotic cells, 3.5 billion years in age, found in Western Australia and South Africa. The nature of these fossils, and the chemical composition of the rocks in which they are found, indicates that these first cells made use of simple chemical reactions to produce energy for their metabolism and growth. Eukaryotic cells evolved into being between 1.5 and 2 billion years ago. Eukaryotic cells appear to have arisen from prokaryotic cells, specifically out of the archaea. Indeed, there are many similarities in molecular biology of contemporary archaea and eukaryotes. However, the origin of the eukaryotic organelles, specifically chloroplasts and mitochondria, is explained by evolutionary associations between primitive nucleated cells and certain respiratory and photosynthetic bacteria, which led to the development of these organelles and the associated explosion of eukaryotic diversity. Today Prokaryotes

According to Margulis, the pre-eukaryotic cell engulfed an aerobic bacterium, but rather than digest and kill the bacterium, a symbiotic relationship was born. This relationship, the aerobic bacterium provided energy through ATP and the eukaryotic cell provided an environment to live while protecting the new symbiont from harm in environmental factors such as oxygen. Because almost all living eukaryotes have a mitochondria, it is safe to assume that this event happened before plants and animals split in the evolutionary lineage.After this first evolutionary leap came a

Mitochondria and chloroplasts have two membranes that surround them. The inner membrane is probably from the engulfed bacterium and this is supported by that the enzymes and proteins are most like their counterparts in prokaryotes. The outer membrane is formed from the plasma membrane or endoplasmic reticulum of the host cell. The electron transport enzymes and the H+ ATPase are only found in the mitochondria and chloroplasts of the eukaryotic cell. (2)

Mitochondria are small organelles found in eukaryotic cells which respire aerobically. They are responsible for generating energy from food to ‘power the cell’. They contain their own DNA, reproducing by dividing in 2. As they closely resemble bacteria, it gave the idea that they were derived from bacteria (which were engulfed by ancestors of the eukaryotes we know today). This idea has since been confirmed from further investigations, and it is now widely accepted. (Alberts et al., 2010a)

7. The theory of endosymbiosis says that mitochondria and plastids used to be small prokaryotes living within larger cells. The prokaryotic ancestors of mitochondria and plastids were bacteria engulfed by a larger cell. Because they both benefited from this situation, the bacteria living inside the cell was passed down from generation to generation. The evidence is that mitochondria reproduce and move independently within the cell.

Mitochondria, dubbed the ‘powerhouse of the cell’, are a type of organelle present in most human cells. Their primary function is to generate Adenosine Triphosphate (ATP), the cell’s principal source of chemical energy. Unlike most other organelles, mitochondria store their own set of genetic material, distinct from the DNA situated in a cell’s nucleus. Although this ‘mitochondrial genome’ represents only 0.1% of a cell’s genetic information, it often plays a significant role in development.

This results in increased energy expenditure, fuel mobilization and oxidation for energy extraction, oxygen consumption, respiratory rate, and heat production and release (Dauncey.,1990). The stimulation of the respiratory rate would intuitively lead to greater ROS production but, the relation between these two variables is not linear. Instead, ROS production depends largely on the mitochondria. Mitochondria are the primary intracellular site of oxygen consumption and the major source of reactive oxygen species (ROS), most of them originating from the mitochondrial respiratory chain(Armstong &Jones.,2002). Although THs do not directly determine the respiratory state of the mitochondria (Katyare and Raian.,2005), stimulation by THs by augmenting ATP breakdown by different energy-consuming mechanisms in the cell (Dauncey.,1990) and thus increasing ADP availability. This would be expected to decrease ROS production. However, THs also promote a reduction state in the cell by increasing fuel availability and extramitochondrial production of ATP and NADH, which in turn promote reduction of the components of the mitochondrial respiratory chain

The second important endosymbiotic event occurred as a result, in the acquisition of mitochondria by the earliest eukaryotes (Avissar et al., 2016). Mitochondria are responsible for aerobic cellular respiration in eukaryotic cells, and for a long time it was believed that they were simply organelles. But much like plastids in photoreactive eukaryotes, the evidence points to mitochondria having been absorbed by early eukaryotes, forming a symbiotic relationship in which the larger cell protected the smaller and provided a ready source of nutrients, and in turn the mitochondria allowed the larger cells to process all of the new molecular oxygen as an energy source to promote glycolysis (Cooper, 2000).

While there are many different hypotheses to the evolution of eukaryotic organisms, two in particular have very plausible yet different approaches to this complex question. The Margulis hypothesis of the evolution of eukaryotic organisms focuses on the idea of endosymbiosis, which is the close interaction or association between different species with one of those species being inhabited within the other. Margulis hypothesized that free-living bacteria that were capable of energy production and photosynthesis where engulfed by a free-living cell. The cell and the bacteria now inside of it formed a mutualistic and symbiotic relationship with the bacteria providing the cell with the energy and food it needs while remaining protected inside the cell. Through evolutionary time this symbiotic relationship would grow so strong that the two individuals would not be able to function alone and thus the eukaryote would arise. The idea was supported by the fact that mitochondria and chloroplasts both have unique genomes that resemble the single circular chromosomes found within bacteria.

The mitochondrion has a double membrane surrounding its ellipse shape. Some of the reactions of aerobic respiration (the process living things go through to use food energy) occur in the mitochondrion and they are the ‘powerhouses’ of the cell. They produce energy in the form of ATP.

Both chloroplasts and mitochondria contain circular DNA knowns as chloroplast DNA and mitochondrial DNA respectively, signifying that both organelles have prokaryotic origins. The presence of mitochondria in eukaryotes allows for ATP synthesis through the electron transport chain and oxidative phosphorylation (Chinney et al, 2003), thus enabling eukaryotes to satisfy their high metabolic requirements, particularly in animals. The production of large amounts of ATP energy allows for the sustenance of life in a wide variety of environmental conditions as they are able to produce the energy required. The unique double membrane of the mitochondria suggest that it was formed as a result of primary symbiosis, and are homologous to plastids. Similarly chloroplasts enable eukaryotes to take advantage of sunlight as a natural resource, which allows the process of photosynthesis, where the reaction of carbon dioxide and water is converted to glucose and oxygen gas (Cogdell, 2013), using light energy produced by the sun with the aid of chlorophyll. This conversion of light energy into chemical energy forms the primary source of all energy accessible by the animal consumers on land, through the producers - the plants. At the cellular level, protists are the most simple examples of endosymbiosis. In the amoeba Paulinella chromatophora it contains two chromatophores, derived from once free living cyanobacteria (Wernegreen,

Per this theory, GpII invaded the eukaryotic lineage in its genesis via the mitochondrial endosymbiosis and have been inserting themselves into coding genes continuously since; a mechanism consistent with the high levels of GpII in some α-proteobacteria (Robart & Zimmerly, 2005) and the ability of yeast mitochondrial GpII to insert themselves into double stranded genomic DNA (Zimmerly et al., 1996). Symbiosis-related selection pressure upon the α-proteobacteria coupled with its bacterial nature of jettisoning unwanted genes caused the exchange of GpII and cognate maturases (Schmitz-Linneweber et al., 2015) between the proto-mitochondrion and the host cell which lacked the necessary control mechanisms to restrict their spread. Hence, the proportion of introns in the LECA genome is considerably greater than in contemporary eukaryotic lineages, excluding some vertebrates (Figure.1). Comparison of nuclear-encoded cytoplasmic ribosomal proteins and mitochondrial ribosomal proteins showed that intron positions were conserved (Yoshihama et al., 2006), suggestive of common descent between all eukaryotes. However, the presence of introns presents significant problems to the host. Principally, random and aggressive insertion of foreign gene elements is likely to disrupt essential coding sequences within the host genome; hence, only neutral intron-insertions could persist. Additionally, splicing reactions require the energetically expensive and complex machinery of the spliceosome, comprised of over 150 proteins and 5 snRNA units (Wahl et al., 2009), any fault in which would cause broad harm to the cell (Chorev & Carmel,

With surely convincing evidence researchers have been able to compile in support of the endosymbiosis theory, it becomes hard for one to deny the possibility that cilia, mitochondria and chloroplasts once existed as bacterial organisms (later to be taken up by host cells by endosymbiosis).

However, amplification efficiency of a short fragment is independent on mtDNA damage. We found higher mtDNA damage (Fig. 10A) and lower mitochondria amount (Fig. 10B) in emphysema in comparison with controls. We also wanted to analyze changes in mitochondrial amount in A549 cells treated with H2O2 for 0.5h, 1h, 1.5h and 2h. We used Tom20 as a marker of mitochondria and live cell confocal microscopy (Zeiss LSM 510). We found time-dependent decreased mitochondrial amount after 2h treatment (Fig. 11).

The Serial Endosymbiotic Theory (SET) was a hypothesized process by which prokaryotes give rise to the first eukaryotic (an organism which contains a nucleus and organelles enclosed within a membrane ). Was pioneered in the 1960’s by the seminal work of Lynn Margulis. This theory attempts to explain the origins of eukaryotic cell organelles, specifically the mitochondria (providing the cells ATP (used for the cells metabolism) supply used by the cell as chemical energy ). With the theory suggesting that the mitochondria and plastids within a eukaryotic cell were once independent prokaryotic cells (a single celled organism, which contains a nucleus and other organelles that are absent of a membrane ), having been obtained by another organism through endosymbiosis, to become endosymbiot around 1.5 billion years ago. Where the eukaryotes several key organelles originated through a process called symbiosis, with this occurring between separate single celled organisms (prokaryotic cells). Through research and locating molecular and biochemical evidence, it suggests that the mitochondrion developed from proteobacteria, and chloroplast from cyanobacteria.