Process which takes place in mitochondria

The process is called oxidative phosphorylation and it happens inside mitochondria. In the matrix of mitochondria the reactions known as the citric acid or Krebs cycle produce a chemical called NADH. In ATP the energy is stored in the form of chemical bonds.

These bonds can be opened and the energy redeemed. Mitochondrial cells divide using their own circular strand of DNA and as a result there can be many mitochondria in one cell. In cells where there is a high energy demand large numbers of mitochondria are found. The tail of a sperm contains many mitochondria and they run in a spiral like form along the length of the tail.

Mitochondria: determinators Recent research indicates that in addition to converting energy mitochondria play quite a large part in determining when a cell will die by ordinary cell death necrosis or programmed cell death apoptosis.

In apoptosis the mitochondrion releases a chemical, cytochrome c, and this can trigger programmed cell death apoptosis. Mitochondria are also thought to influence, by exercising a veto, which eggs in a woman should be released during ovulation and which should be destroyed by programmed cell death apoptosis. This is part of a process called atresia.

It appears that in this process mitochondria and the nucleus of the cell in which the mitochondria reside, are screened for biochemical compatibility. The pairs that are incompatible are shut down by programmed cell death. Mitochondria: generators of disorders and disease Mitochondria are very important energy converters.

In this process they produce waste products. In mitochondria these are called reactive oxygen species ROSs. These mutations are the source of mitochondrial disease that can affect areas of high energy demand such as brain, muscles, central nervous system and the eye. Mutations caused by ROSs have been suggested as contributing to the ageing process.

Many more mutations in mitochondrial DNA take place in people over 65 than in younger people, but many more factors are involved in this inevitable at present but variable process. The working of mitochondria at a molecular level is also involved in the good or otherwise progress of people in the very early stages of recovery following open heart and transplant surgery.

It appears that the drugs damage mitochondria and block the production of mitochondrial DNA. French and Japanese centenarians appear to have advantageous mutations in their mitochondrial DNA. This is interesting but since we do not know about cause and effect, care needs to be exercised when considering these figures. In the field of sport it is not difficult to reason that athletes with high counts of mitochondria in their heart and other appropriate muscle cells are able to do just that little bit better than others less well endowed.

Mitochondria: providers of genetic history Mitochondria are virtually cells within a cell and each one has its own DNA. Mitochondrial DNA is only inherited through the maternal line. Any mitochondrial DNA contributed by the father is actively destroyed by programmed cell death after a sperm fuses with an egg. This interesting situation has provided geneticists and anthropologists with a very useful analytical and measuring tool.

Over the years maternal mitochondrial DNA has been inherited in a direct line never having been combined or shuffled with DNA from mitochondria of the male line. Some people are sceptical about this idea but strong evidence in support of it is accumulating. Mitochondria: an organelle probably used to boost the success rate of infertility treatment.

The technique called ooplasmic transplantation seeks to correct disorders, possibly associated with the mitochondria, in the egg. The mitochondrial DNA will be incorporated into the cells forming the embryo and for this reason it is the first example of germline gene therapy.

There are concerns about possible long-term side effects, which could be passed on to subsequent generations. What does it look like? This creates a concentration gradient of protons that another protein complex, called ATP synthase , uses to power synthesis of the energy carrier molecule ATP Figure 2. Figure 2: The electrochemical proton gradient and ATP synthase At the inner mitochondrial membrane, a high energy electron is passed along an electron transport chain.

The energy released pumps hydrogen out of the matrix space. The gradient created by this drives hydrogen back through the membrane, through ATP synthase. At the end of the electron transport chain, the two electrons are used for the conversion of oxygen O 2 to water H 2 O.

The build up of transported protons in the intermembrane space causes a gradient that is used by ATP synthase to produce ATP. ATP synthase is depicted as a vase-shaped protein that spans the inner membrane. A piece of the inner and outer mitochondrial membranes is shown. The membranes are depicted as lipid bilayers. The lipids have pink, circular heads and purple tails and are arranged in two rows with their heads facing outward and their tails facing each other.

The outer membrane is shown along the top and side perimeter of the diagram. The inner membrane lies interior to the outer membrane. The space between the two membranes is the intermembrane space, and the space within the inner membrane is the matrix.

Three boxy shapes embedded in the inner membrane — shown in orange, green and pink from left to right — represent the proteins of the electron transport chain. Two electrons are represented by a small, blue sphere, which is labeled 'e -. Mitochondrial genomes are very small and show a great deal of variation as a result of divergent evolution. Mitochondrial genes that have been conserved across evolution include rRNA genes, tRNA genes, and a small number of genes that encode proteins involved in electron transport and ATP synthesis.

The mitochondrial genome retains similarity to its prokaryotic ancestor, as does some of the machinery mitochondria use to synthesize proteins. In addition, some of the codons that mitochondria use to specify amino acids differ from the standard eukaryotic codons. Still, the vast majority of mitochondrial proteins are synthesized from nuclear genes and transported into the mitochondria.

These include the enzymes required for the citric acid cycle, the proteins involved in DNA replication and transcription, and ribosomal proteins. The protein complexes of the respiratory chain are a mixture of proteins encoded by mitochondrial genes and proteins encoded by nuclear genes.

Proteins in both the outer and inner mitochondrial membranes help transport newly synthesized, unfolded proteins from the cytoplasm into the matrix, where folding ensues Figure 3. Figure 3: Protein import into a mitochondrion A signal sequence at the tip of a protein blue recognizes a receptor protein pink on the outer mitochondrial membrane and sticks to it.

This causes diffusion of the tethered protein and its receptor through the membrane to a contact site, where translocator proteins line up green. When at this contact site, the receptor protein hands off the tethered protein to the translocator protein, which then channels the unfolded protein past both the inner and outer mitochondrial membranes.

Figure Detail. Mitochondria cannot be made "from scratch" because they need both mitochondrial and nuclear gene products. These organelles replicate by dividing in two, using a process similar to the simple, asexual form of cell division employed by bacteria. Video microscopy shows that mitochondria are incredibly dynamic.

They are constantly dividing, fusing, and changing shape. Indeed, a single mitochondrion may contain multiple copies of its genome at any given time. This page appears in the following eBook. Aa Aa Aa. Mitochondria are unusual organelles. They act as the power plants of the cell, are surrounded by two membranes, and have their own genome.

They also divide independently of the cell in which they reside, meaning mitochondrial replication is not coupled to cell division.

Some of these features are holdovers from the ancient ancestors of mitochondria, which were likely free-living prokaryotes. What Is the Origin of Mitochondria? Figure 1: A mitochondrion. What Is the Purpose of a Mitochondrial Membranes? Figure 2: The electrochemical proton gradient and ATP synthase. At the inner mitochondrial membrane, a high energy electron is passed along an electron transport chain. Is the Mitochondrial Genome Still Functional? Figure 3: Protein import into a mitochondrion.

A signal sequence at the tip of a protein blue recognizes a receptor protein pink on the outer mitochondrial membrane and sticks to it. Logically, mitochondria multiply when a the energy needs of a cell increase. Therefore, power-hungry cells have more mitochondria than cells with lower energy needs.