Function of the mitochondria
The mitochondrion is an important organelle of both plants and animals cells. It is one of those organelles in a eukaryotic cell. Usually, the mitochondria are usually referred to as powerhouse to a cell because they produce energy in Adenosine Triphosphate (ATP) form. Usually energy is produced during cellular respiration. Mitochondrion is made of two membranes: inner and outer, where chemical reactions occur and a matrix where some fluid is stored. This mitochondrion takes in nutrients from cells so as to break them down and release energy in turn. This energy in form of ATP is therefore used for carrying out several functions inside a cell.
Different cells contain varied numbers of the mitochondria. This number is determined by the much energy that given cell mainly requires. If a cell needs more energy, it will definitely have more of the mitochondria. The cell is able to produce additional mitochondria if it needs more of them. As well, a cell can combine various mitochondria so as to come up with larger mitochondria.
Mitochondria can be defined as the powerhouse a cell depends on. These are small kind of structures found inside the cell and are composed of a matrix and two membranes. The matrix is responsible for holding some fluid while the membranes allow occurrence of chemical reactions. Mitochondria form part of the eukaryotic cells. Majorly, the mitochondria in a cell are responsible of performing cellular respiration. What this means is that the powerhouse takes nutrients from that cell then breaks those nutrients down so as to produce energy. That energy is all what a cell needs so as to run its normal functions.
Apart from production of energy, other functions of mitochondria include breaking down the harmful waste products to less harmful substances, producing chemicals that the body needs and also the recycling of some waste products. They also help in death of cells. This process is also known as apoptosis. Apoptosis is crucial for both growth and development to take place. The death of some cells ensures that cells do not replicate uncontrollably leading to cancers. This means that mitochondria are targets of the anti-cancer drugs. To convert the food substances to energy, mitochondria require oxygen, in a process called oxidative phosphorylation.
The processes that work together to produce ATP in a mitochondrion are generally referred to as Kreb's cycle or else Citric Acid cycle (TCA). Before citric acid cycle begins, glycolysis happens inside outer membrane. During glycolysis, glucose is broken down into two molecules of pyruvate. Cellular respiration or aerobic respiration in mitochondrion is dependent on oxygen. However, in some cells which mostly lack mitochondria, glycolytic products are usually metabolized in absence of oxygen, a process called anaerobic respiration. Anaerobic respiration produces a low yield of ATP as compared to aerobic respiration.
The two molecules of pyruvate and ATP produced by glycolysis enter inside inner membrane of a mitochondrion. For matrix, pyruvate molecules are either carboxylated to form oxaloacetate, an anaplerotic reaction, or those molecules can be oxidized to form carbon dioxide, acetyl-CoA, and NADH. From acetyl-CoA, various intermediates are produced and they include citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, oxaloacetate and malate. The oxaloacetate then will combine with acetyl-CoA to for citric acid. Numbers of ATPs produced depends on which molecule starts. For instance, The number of ATPs produced by breaking down of glucose is not similar as that produced during fructose breakdown.
TCA cycle oxidizes acetyl-CoA to carbon dioxide and other reduced co-factors which are NADH (three molecules) and FADH2 (one molecule). These reduced cofactors are used in following stage of ATP production in mitochondrion which is called electron transport chain. Electrons transport chain occurs in mitochondrial intermembrane space. The process involves transferring of electrons from donors to acceptors through redox reactions. The electron transfer is followed with transferring of protons across membranes.
NADH and FADH2 are also produced during glycolysis and TCA cycle, but they produce energy during electron transport chain process. Important protein complexes exist inside mitochondrial inner membrane and they include NADH dehydrogenase (ubiquinone), cytochrome c reductase, and cytochrome c oxidase. These complexes are responsible for transfer of electrons and released energy is used to pump H+ protons into mitochondrial intermembrane space.
An electrochemical gradient is created against inner membrane when number of protons increases. The protons then return to matrix and their energy is used to combine Adenosine triphosphate (ADP) and inorganic phosphate to form ATP. Therefore, glycolysis, TCA cycle, and electron transport chain are processes that occur inside mitochondrion to produce energy for cell activities.
