Mitochondria - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x Mitochondria (singular: mitochondrion) are double membrane-bound cell organelles with a typical size of 0.75-3 μm². They are found in most mammalian cells, with notable exceptions including mature erythrocytes. Classically referred to as the ‘powerhouse of the cell’, they are the site of the majority of ATP synthesis and are therefore exceptionally important to function both microscopically and macroscopically. In this article we will look at the structure and function of mitochondria, and consider some clinical relevance. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Structure Mitochondria have an inner and outer membrane, with an inter-membrane space between them. The outer membrane contains proteins known as porins, which allow movement of ions into and out of the mitochondrion. Enzymes involved in the elongation of fatty acids and the oxidation of adrenaline can also be found on the outer membrane. The space within the inner membrane of the mitochondrion is known as the matrix, which contains the enzymes of the Krebs (TCA) and fatty acid cycles, alongside DNA, RNA, ribosomes and calcium granules. The inner membrane contains a variety of enzymes. It contains ATP synthase which generates ATP in the matrix, and transport proteins that regulate the movement of metabolites into and out of the matrix. The inner membrane is arranged into cristae in order to increase the surface area available for energy production via oxidative phosphorylation. By Rice University [CC BY 4.0], via openstax CNX Fig 1Electron micrograph of a mitochondrion Function The mitochondrion is the site of ATP synthesis for the cell. The number of mitochondria found in a cell are therefore a good indicator of the cell’s rate of metabolic activity; cells which are very metabolically active, such as hepatocytes, will have more mitochondria. Mitochondria also have a role to help maintain the intracellular environment. They: Store caspases responsible for triggering apoptosis. Are able to transiently store calcium contributing to calcium homeostasis. Kelvinsong; modified by Sowlos, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia CommonsFig 2A mitochondrion with its main features In brown adipose tissue, mitochondria have an alternative function of heat production using the electron transport chain. DNA and Inheritance Mitochondria replicate their DNA by a process called binary fission and can use this to make multiple copies in one mitochondrion. Their DNA has maternal lineage which means their DNA is passed from mother to child with little change. Clinical Relevance Leber’s Hereditary Optic Neuropathy As a result of how crucial mitochondria are to the survival of the cell, mitochondrial disorders are rare. Some general features of mitochondrial disease include exercise intolerance, myopathy and muscle weakness. The most common mitochondrial disease is Leber’s Hereditary Optic Neuropathy (LHON) which affects the optic nerve causing blurring of central vision and loss of colour vision and carries a risk of developing blindness. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Mitochondria Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What are mitochondria and what is their primary function? Mitochondria are double membrane-bound organelles that serve as the primary site for ATP synthesis in cells, earning them the title 'powerhouse of the cell'. They are crucial for cellular energy production and overall metabolic activity. How do the structures of mitochondria support their function? Mitochondria consist of an inner and outer membrane, with the inner membrane folded into cristae to increase surface area for energy production. The matrix contains enzymes for the Krebs cycle and ATP synthase, essential for ATP generation. What role do mitochondria play in calcium homeostasis? Mitochondria contribute to calcium homeostasis by transiently storing calcium ions, which helps regulate intracellular calcium levels. This function is vital for various cellular processes and maintaining cellular health. How is mitochondrial DNA inherited? Mitochondrial DNA is inherited maternally, meaning it is passed from mother to child with minimal changes. This unique inheritance pattern allows for the study of lineage and genetic disorders related to mitochondria. What is Leber's Hereditary Optic Neuropathy and its clinical significance? Leber's Hereditary Optic Neuropathy (LHON) is the most common mitochondrial disease, affecting the optic nerve and leading to vision impairment. Its clinical features include blurring of central vision and a risk of blindness, highlighting the critical role of mitochondria in neuronal health. Rate This Article