Mitochondria
The power plants of our body
Functions of the mitochondria
Energy is essential for all processes in our body. It is therefore not surprising that our cells have their own "power plants" to cover the continuous energy demand. These power stations are the mitochondria. In this text, you will find out how mitochondria obtain energy from our food and why their performance decreases with age.
What are mitochondria
Mitochondria are dynamic cell organelles found in all eukaryotic cells, with the exception of red blood cells. They are responsible for energy metabolism and are often referred to as the "powerhouse of the cell", as they convert food energy into energy that can be used by the cell, specifically adenosine triphosphate (ATP). This process is known as cellular respiration.
The number of mitochondria varies depending on the cell's energy requirements. A particularly large number of mitochondria are found in muscle cells, nerve cells, germ cells and liver cells. For example, a single heart muscle cell contains several thousand mitochondria, while a mature egg cell can contain up to 100,000. Research in recent years has shown that mitochondrial activity decreases with age, leading to a decline in our energy levels. One reason for this could be that free radicals accumulate with age, which damage the mitochondrial proteins and DNA, leading to dysfunction. This so-called mitochondrial dysfunction plays an important role in the ageing process and in the development of age-related diseases such as cardiovascular diseases, diabetes and neurodegenerative diseases. However, a healthy lifestyle, regular exercise and a balanced, plant-rich diet can help to support the mitochondria.
Human cell
Structure of a mitochondrion
With a size of only 0.75 to 3 µm, mitochondria are one of the smallest cell organelles. Nevertheless, in certain tissues, such as heart muscle cells, they make up a considerable proportion of the cell volume (up to 36 %). The structure of mitochondria is relatively simple. Their mostly oval body is surrounded by a double membrane consisting of a lipid bilayer and proteins.
The outer membrane surrounds the mitochondrion and forms the intermembrane space, which lies between the outer and inner membrane. It contains various protein channels that enable the transport of small molecules and ions into the cytosol. In addition, the outer membrane can connect to the endoplasmic reticulum (ER) to exchange signals and transfer lipids. Since the outer membrane is permeable to smaller molecules such as sugars or ions, the intermembrane space has a similar concentration of these substances as the cytosol. However, the composition of larger proteins differs, as these can only be transported into the cytosol under certain conditions. Cytochrome C, for example, is concentrated in the mitochondrion and is only released when required.
The inner mitochondrial membrane has invaginations that protrude far into the mitochondrial matrix and significantly increase the surface area. Depending on the type of folding, a distinction is made between different types of mitochondria: Cristae type (chamber-like invaginations), tubule type (tubular invaginations), sacculus type (invaginations with round protrusions) and prism type (triangular invaginations). This increase in surface area is crucial, as the inner membrane contains proteins that are responsible for electron transport in the respiratory chain. This enables the cell to produce more ATP. In addition to the protein complexes for cellular respiration, the inner membrane also contains ATP synthases for ATP formation, transport proteins and proteins involved in the fusion and division of mitochondria. The mitochondrial matrix, which is located behind the inner membrane, contains around 60 % of mitochondrial proteins. Hundreds of enzymes, mitochondrial ribosomes, transfer RNA (tRNA) and several copies of mitochondrial DNA (mtDNA) are found here.
The mitochondrial ribosomes are specialized in converting the genetic code, which they receive via tRNA, into a specific sequence of amino acids and assembling these into proteins.
Mitochondrium
Mitochondria: Tasks and functions
Mitochondria are the powerhouses of our body and produce 10,000 to 50,000 times more energy than the sun compared to their weight. Every day, they produce an amount of adenosine triphosphate (ATP) equivalent to our body weight. In addition to energy production, mitochondria are responsible for cell respiration and control cell metabolism. They also play an important role in programmed cell death (apoptosis) by sending out signals that cause damaged cells to die. In addition, they store calcium ions, which are important for many cellular processes, and are involved in fatty acid metabolism and heat production.
Overall, mitochondria are crucial for life, our health and our well-being.
Energy production in mitochondria
The main task of the mitochondria, as the power plants of the cell, is to convert food energy and ionized oxygen into ATP for cell metabolism. This vital ATP production takes place as part of cellular respiration, which is subdivided into various metabolic pathways. The process of ATP production in mitochondria is as follows:
First, in glycolysis, which takes place in the cytosol, glucose is broken down into pyruvate in several steps and transported into the mitochondrial matrix. During this process, energy is stored in the form of ATP. In the mitochondrion, pyruvate is converted into acetate by oxidative decarboxylation, which is then further processed into acetyl-CoA. The citrate cycle (Krebs cycle) then begins, in which energy is generated from acetyl-CoA in the form of GTP (guanosine triphosphate) or ATP as well as NADH and FADH. Acetyl-CoA can be obtained not only from carbohydrates, but also from lipids and proteins.
In the final step of cellular respiration, the respiratory chain, electrons are transported along the mitochondrial membrane with the help of NADH and FADH. Four protein complexes and electron transporters such as coenzyme Q10 and cytochrome C are involved in this reaction chain. During electron transfer, protons (positively charged particles) are transported, which creates a charge difference on both sides of the membrane. This proton gradient activates the enzyme ATP synthase, which provides energy in the form of ATP (oxidative phosphorylation) for the cell.
Worth knowing
Mitochondria are dependent on a variety of micronutrients for the respiratory chain to function optimally. These include B vitamins such as vitamin B1 and B12 as well as various minerals. Another important role is played by coenzyme Q10, which is needed in the mitochondria to provide the body with sufficient energy. However, the coenzyme Q10 level in the cells decreases with age. It is therefore important to support the mitochondria with a balanced diet. Foods that contain coenzyme Q10 include fatty fish, meat, pulses, seeds, nuts and the vegetable oils obtained from them.
Redox homeostasis
Cellular respiration produces free radicals, which in small quantities are essential for important processes in the body. However, if they occur in excess, they cause oxidative stress, which can damage the cells and their organelles. To counteract this, mitochondria have efficient protective mechanisms, including antioxidants, whose activity is influenced by the production of free radicals.
Mitochondria also have other mechanisms for maintaining the redox balance. They can neutralize excess electrons in the respiratory chain, adjust their activity or specifically break down overactive mitochondria through mitophagy.
Further functions
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Furthermore, mitochondria store calcium
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regulate apoptosis
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support fatty acid oxidation
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involved in cortisol production
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important part of cell communication
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contain inhibitors for hemoglobin
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metabolic regulation
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produce important substances for cell growth
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support the immune system in communication
Mitochondria have their own DNA
Mitochondria have their own DNA, the so-called mitochondrial DNA (mtDNA), which distinguishes them from other organelles. This mtDNA is significantly shorter than the DNA in the cell nucleus, but is present in multiple copies. The ring-shaped mtDNA comprises 37 genes that contain information for 13 proteins of the respiratory chain as well as various rRNAs and tRNAs.
Thanks to their own genome, mitochondria can replicate independently of the cell. Similar to bacteria, they divide by cross-division, whereby the mitochondrial DNA is evenly distributed among the daughter cells. The genetic material is not rearranged, but copied exactly and passed on.