Mitochondria could now be found in most multi-cellular eukaryotes. In animals, the cells which require the most energy have the most mitochondria. For example, heart muscle cells have a lot of mitochondria as our hearts need a constant supply of energy to keep pumping.
Sperm cells also have a lot of mitochondria as they need a lot of energy to be able to swim towards an egg cell for fertilisation. Tel: Email: info centreofthecell. Necessary cookies are absolutely essential for the website to function properly.
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Support us Find out more. Receive our newsletter. Mitochondria are thought to have originated from an ancient symbiosis that resulted when a nucleated cell engulfed an aerobic prokaryote. The engulfed cell came to rely on the protective environment of the host cell, and, conversely, the host cell came to rely on the engulfed prokaryote for energy production.
Over time, the descendants of the engulfed prokaryote developed into mitochondria, and the work of these organelles — using oxygen to create energy — became critical to eukaryotic evolution Figure 1. Modern mitochondria have striking similarities to some modern prokaryotes, even though they have diverged significantly since the ancient symbiotic event. For example, the inner mitochondrial membrane contains electron transport proteins like the plasma membrane of prokaryotes, and mitochondria also have their own prokaryote-like circular genome.
One difference is that these organelles are thought to have lost most of the genes once carried by their prokaryotic ancestor. Although present-day mitochondria do synthesize a few of their own proteins, the vast majority of the proteins they require are now encoded in the nuclear genome.
As previously mentioned, mitochondria contain two major membranes. The outer mitochondrial membrane fully surrounds the inner membrane, with a small intermembrane space in between. The outer membrane has many protein-based pores that are big enough to allow the passage of ions and molecules as large as a small protein. In contrast, the inner membrane has much more restricted permeability, much like the plasma membrane of a cell. The inner membrane is also loaded with proteins involved in electron transport and ATP synthesis.
This membrane surrounds the mitochondrial matrix , where the citric acid cycle produces the electrons that travel from one protein complex to the next in the inner membrane. At the end of this electron transport chain, the final electron acceptor is oxygen, and this ultimately forms water H At the same time, the electron transport chain produces ATP. This is why the the process is called oxidative phosphorylation.
During electron transport, the participating protein complexes push protons from the matrix out to the intermembrane space. 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 -. Generally, mitochondria, and therefore mitochondrial DNA, are inherited only from the mother. Mitochondria are membrane-bound organelles, but they're membrane-bound with two different membranes. And that's quite unusual for an intercellular organelle. Those membranes function in the purpose of mitochondria, which is essentially to produce energy.
That energy is produced by having chemicals within the cell go through pathways, in other words, be converted. And the process of that conversion produces energy in the form of ATP, because the phosphate is a high-energy bond and provides energy for other reactions within the cell.
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