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|−|<p>Another Function of Mitochondria is non- shivering thermogenesis which is the production of heat by the body without the muscles shivering. This occurs due to H+ ions moving into the mitochondrial matrix by facilitated diffusion, allowing the exploitation of the energy produced from the movement of the H+ ions down an electrochemical gradient to be used as heat energy. |+|
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also useful because they store Ca2+ ions which can be used in all sorts of other functions such as muscle contraction and blood clotting. Additionally the mitochondria by storing Ca2+ ions they help towards maintaining homeostasis within the cell by acting as a cytosolic buffer. |+|
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Revision as of 07:48, 2 December 2016
Mitochondria (singular- Mitochondrion) are membrane
(double membrane structure), that carry out oxidative phosphorylation
, to produce ATP
. What is more, mitochondria produce the majority of ATP
used by eukaryotic organisms
and are often referred to as the power houses of the cell
. Furthermore, due to the fact that mitochondria are the site ATP synthesis
, there is often a linear relationship between the number of mitochondria in a cell
and the cells ATP
requirements e.g. a muscle
cell uses vast amounts of ATP
and thus often contains many mitochondria to adhere to this requirement and maintain function. A further point that must be brought to attention is that mitochondria contain their own DNA
(mostly circular), referred to as mtDNA
. The size of mitochondrial DNA
and its percentage of total cellular DNA varies between species
. In mammalian cells only about 1% of the total cellular DNA is composed of mitochondrial DNA whereas in other organisms (for example in the egg cells of amphibians) there is a much higher percentage of mitochondrial DNA. Human mitochondrial DNA
consists of 16,569 base
pairs coding for 13 proteins
. In humans, mitochondrial DNA is inherited from the mother because an egg cell has many more mitochondria than a sperm cell
. Mitochondria are semiautonomous organelles
, depending on the host cell for their existence
- Range from 0.5-1μm in diameter (similar to bacteria).
- Contain an inner (folds in) and outer membrane.
- Contain cristae (singular crista) - internal compartments formed by the inner membrane folds.
- Contain a matrix- large overall internal compartment.[[Image:Mitochondira.jpg|thumb|right
In sexual reproduction only the female gamete (ovum) has mitochondria when the gametes eventually fertilise, this is because the male gamete (sperm) draws upon all of its mitochondria for locomotion, to aid its travel to the ovum (egg). Furthermore, mitochondria in relation to the structure of the sperm, is wrapped tightly around the flagellum in the sperm and is fixed in this position, to enable the mitochondria to comply with the sperm's unusually high ATP consumption.
Mitochondrion is the site of the Krebs cycle and the electron transport chain in eukaryotic organisms. It has a variable diameter from 0.5 to 1 micrometre thus can be easily seen under a light microscope. Using time-lapse micro-cinematography, it has been established that mitochondria can alter their shape continuously, and are also able to fuse and separate with other mitochondria. It is surrounded by two phospholipid membranes: the outer and inner membrane. The inner membrane is folded inwards to form cristae and it is the location where electron transport chain occur. On the other hand, the outer membrane is the envelope that holds all the organelles and it is relatively permeable to small molecules.
The internal mitochondrial compartment is called the matrix where the link reaction and Krebs cycle occur. As a result of oxidative phosphorylation, ATP is synthesised in the latter by the activity of ATP synthase on the cristae. The advantage that this has over glycolysis is that it reaps 15 times more ATP for all energy-requiring reactions of the cell, both inside and outside the mitochondria. Moreover, it has its own DNA which is circular and also contains 70S ribosomes. In addition, it is also beneficial in the event of cell damage, as it is the one who signals the process of apoptosis (programmed cell death) by releasing mitochondrial protein into the cytoplasm.
Mitochondria, containing there own DNA (mtDNA), are susceptible to mutations in their own base sequences which can lead to disease (when the mutations are non-silent). These mutations causing gene abnormalities can give rise to a host of diseases, some of which can be fatal, and which can vary in severity from person to person.
A type of Cardiovascular disease which is associated with gene abnormalities in mtDNA and/or nulceur DNA (which encode some of the mitochondrial proteins) is Familial Dilated Cardiomyopathy. This disease is caused as the result of lack of matabolite passage across the inner membrane space, due to a non-silent mutation which results in the transport proteins having a changed genomic sequence.
Another disease, which more recently is being linked to gene abnormalities in mitochondria is Alzheimer's disease (AD). Free radicals are able to accumulate in the brain as a person ages, due to increased oxidative phosphorolation. The free radicals created can damage mtDNA to cause healthy neurones (in neuronal pathways) to become impaired which leads to a reduction in energy in the neurones. This leads to the requirement for more ATP which comes from increased oxidative phosphorolation by unaffected/mutant mitochondria. These mitochondria with increased oxidative phosphorolation then have a selective advantage and accumulate more rapidly to cause the death of healthy neurones. This cascade of events continues and can eventually lead to the progression of AD.
- ↑ Berg J.M, Tymoczko J.L., Stryer L (2001) Biochemistry, 5th edition, New York: WH Freeman. p492
- ↑ Molecular Biology of THE CELL, Fifth Edition, Alberts, Johnson, Lewis, Raff, Roberts, Watter (2008), Chapter 1 Cells and Genomes, Figure 1-33 A mitiochondrion, Page 28
- ↑ Bruce Alberts (et al)-2007: pg815
- ↑ Alberts, Johnson, Lewis, Raff, Roberts, Walter (2008) Molecular Biology of the cell, Fifth edition, p815
- ↑ Berg J.M, Tymoczko J.L, Stryer (2012) Biochemistry, seventh Edition, New York: WH Freema.. pg 543
- ↑ Alberts, Johnson, Lewis, Raff, Roberts, Walter (2008) Molecular Biology of the cell, Fifth edition, pg 815
- ↑ The Muscular Dystrophy Association (MDA). Mitochondrial Myopathies (MM). 2016 [cited 18/11/16]; Available from: https://mda.org/disease/mitochondrial-myopathies/causes-inheritance
- ↑ U.S National Library of Medicine Genetics Home Reference. Familial Dilated Cardiomyopathy. 2016 [cited 14/11/16]; Available from: https://ghr.nih.gov/condition/familial-dilated-cardiomyopathy#genes
- ↑ Marin-Garcia J, Goldenthal MJ. Mitochondria and the Heart. New York: Springer. 2005
- ↑ Resell P. A new understanding of Alzheimer's. Harvard Gazette. 2015 February 25th.