Mitochondria and Chloroplasts Descended from Free-living Bacterial Ancestors

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)

Until recent years, the mitochondrial genome, located in the mitochondrion, and the genetic information encoded by it have been given little attention. However, recently it became apparent that the mitochondrial genome, despite its small size, is crucial for the study of human evolution and disease, as mtDNA mutations lead to some serious diseases.

Mitochondria are the powerhouses of every cell in our bodies. According to the United Mitochondrial Disease Foundation, the mitochondrial produce most of the energy for the body (United Mitochondrial Disease Foundation). When this process is interrupted or does not take place then cellular damage begins to occur (United Mitochondrial Disease Foundation). Rolf Luft, Lars Ernster, and Bjorn Afzelius are credited with the first diagnosis of mitochondrial disease via muscle biopsy in 1962 (DiMauro, 2011). Succinctly, it is a “defect in the respiratory chain (DiMauro, 2011)”. Since mitochondria are in every cell in the body, and cells are specialized to the organ system to which they belong, the disease will manifest different symptoms in different individuals based on the organ system(s) affected (United Mitochondrial Disease Foundation). Symptoms can be present from every organ system, however, depending upon the actual genetic encoding affecting the mitochondrial can determine which disease classification a patient may fall within (DiMauro, 2011), (United Mitochondrial Disease Foundation).

The mitochondrion is known as the powerhouse of the cell. It is similar to the engine in a car. This organelle is known for giving the cell energy to function properly. The mitochondrion is the place where cellular respiration and many other processes, including protein translation, autophagy and oxidative phosphorylation occur. The damage of this vital organ would be distressing to the body. When the mitochondrion fails to produce enough energy or ATP (andesine triphosphate) to support the cell’s functions, this phenomenon is known as mitochondrial disease. Due to failure of critical physiological processes, a person inflicted with mitochondrial disease will have loose muscles, coordination issues, involuntary movement of the eyes, and the inability to exercise. Additionally, the individual will have poor growth and even neurological problems. Though quite rare, the disease is extremely dangerous.

The role of DNA in cells is to store genetic information for extended periods of time. DNA are long strands that contain genetic code, or instructions, for the development and functions of living things. DNA tells cells what to do and how to function, they are found in the nucleus of a cell. The role of mitochondria in cells is to produce and supply the cell with energy, so it can complete its function. They can be found floating around in the cytoplasm of the cell. Mitochondria are able to duplicate or reproduce themselves without interfering with the replication of the cell and vise versa. The value of mitochondrial DNA (mtDNA) is to supply cells with energy by absorbing the sugars that were broken down from food. Mitochondrial DNA contains

The body contains trillions of cells, and within one of those cells are thousands of miniscule organelles. They provide a eukaryote with the ability of cellular respiration. Cellular respiration is defined as: "…a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products". Basically these organelles produce energy, and that is what allows us to live. They are called "mitochondria", and their processes involve very complex biomolecular procedures, all happening on the scale of a few atoms. They can be difficult to understand but I hope to clear that up.

Mitochondria convert energy from food for example glucose to usable energy for a cell: ATP. The mitochondria have a small amount of their own DNA this is inherited from your mother only. It is rarer for the mutation to be caused in a genetically unaffected individual. Some examples of mitochondrial diseases are listed below.

Mitochondrial diseases arise from inherited defects in mitochondrial genes of either genome, although the bulk of the clinical research has been focused on defects in the mitochondrial genome. In any case, the problem is conveniently divided into categories of dysfunction: primary or secondary. The primary category is characterized by mutations in genes encoded by mtDNA or a NEMP, while the secondary category encompasses dysfunction due to mitochondrial toxins or to less specific processes such as infections or sterile inflammation. The five most common inherited mitochondrial disorders, Friedreich's ataxia (FA), Leber’s hereditary optic neuropathy or LHON, mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes or MELAS,

FOR THE REGULATION of mitochondria biogenesis the nuclear and mitochondrial communication is needed to ensure a correct assemble and activity of the complexes form the electron transport chain (NAderson : Sequence and organization of the human mitochondrial genome)

Mitochondria are double membrane bound organelles that are essential for producing 95% of our cells energy in the form of ATP1. We have around a hundred to a thousand of these organelles present in each of our cells and they are unique to other organelles in that they contain their own DNA1. But why is this? And how has this benefited the cell in evolutionary terms? Mitochondria are most commonly thought of as the ‘power house’ of the cell due to ATP production being their main function however they have also evolved with many other abilities. I plan to focus how the mitochondria came about and how its structure and function have changed. As mitochondria have many functions I will be looking specifically into mitochondria’s roles in ATP production

Mitochondria are double membraned cell organelle that plays central role in cellular energy provision . These organelles have their own genome which is small in size and are transmitted exclusively through female germ line. The human mitochondrial DNA (mtDNA) is a double-stranded, circular and has 16 569 bp which contains 37 genes coding for two rRNAs, 22 tRNAs and 13 polypeptides which are required in oxidative phosphorylation.

The mitochondrion is an organelle which originated from the endosymbiosis of eubacteria and, as a result, contains its own genome which encodes for essential mitochondrial transcriptional machinery proteins and subunits of electron transport chain (ETC) complexes [1, 2]. However, the vast majority of mitochondrial proteins are encoded for by the nucleus [3]. As a result, these two organelles must be able to communicate in order to coordinate protein synthesis and maintain mitochondrial homeostasis [4]. This communication is also particularly important in the cells response to stress. Mitochondria are deemed ‘endogenous stress detectors’ as they can sense stresses induced by high reactive oxygen species (ROS) levels and oxidative stress, membrane depolarisation, cellular energy levels, and an accumulation of unfolded proteins [5]. Therefore, in response to stress, this mitochondrial-to-nuclear communication is essential to bring about a change in nuclear gene expression, which will relieve the stress and protect the cell from damage. This commonly occurs through the activation of specific retrograde stress response pathways from mitochondria to the nucleus, which combat the stress and allow mitochondria to regain homeostasis [6, 7].

After the unanticipated discovery of a separate mitochondrial genome, there have been new insights into its inheritance and mutation. There is enough evidence to bolster the fact that fusion between a-proteobacteria and archaebacteria is an integral event in evolution of eukaryotic cells. However, it has also been conjectured that eukaryotic cell may have originated from prokaryotes. As a part of this evolution, many mitochondrial ancestral genes were lost. These are the genes that were no longer required in their new host cell environment. All eukaryotes contain genes of mitochondrial origin in their nuclear genome. However, this is only true for a few genes. Studies indicate that humans and mice have only 35% of mitochondrial gene products that are similar to bacteria Rickettsia. Remaining mitochondrial proteins are derived from either non-mitochondrial nuclear genes or as a result of horizontal gene transfer events. Mitochondria have developed different states during the evolution of eukaryotic cell. Aerobic mitochondria retain a small mtDNA while anaerobic mitochondria and hydrogen-producing mitochondria alter the function of respiratory chain and also maintain mtDNA.

In order to prevent cell damage and eventual cell death, elimination of dysfunctional mitochondria, defined as an impairment in the ability to produce ATP, is necessary and this is done through mitophagy.