Crista
Encyclopedia
Inner mitochondrial membrane
The mitochondrial inner membrane forms internal compartments known as cristae, which allow greater space for the proteins such as cytochromes to function properly and efficiently. The electron transport chain is located on the inner membrane of the mitochondria...
of a mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
. They are studded with proteins, including ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
and a variety of cytochrome
Cytochrome
Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....
s. The maximum surface for chemical reactions to occur is within the mitochondria. This allows cellular respiration
Cellular respiration
Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...
(aerobic respiration since the mitochondrion requires oxygen) to occur.
Electron transport chain of the cristae
NADH is oxidized into NAD+, H+ ions, and electrons by an enzymeEnzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
. FADH2 is also oxidized into H+ ions, electrons, and FAD
FAD
In biochemistry, flavin adenine dinucleotide is a redox cofactor involved in several important reactions in metabolism. FAD can exist in two different redox states, which it converts between by accepting or donating electrons. The molecule consists of a riboflavin moiety bound to the phosphate...
. As those electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s travel further through the electron transport chain
Electron transport chain
An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...
in the inner membrane, energy is gradually released and used to pump the hydrogen ions from the splitting of NADH and FADH2 into the space between the inner membrane and the outer membrane (called the intermembrane space
Intermembrane space
The intermembrane space also known as IMS is the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. The main function of the intermembrane space is oxidative phosphorylation....
), creating an electrochemical gradient
Electrochemical gradient
An electrochemical gradient is a spatial variation of both electrical potential and chemical concentration across a membrane; that is, a combination of the membrane potential and the pH gradient...
. This electrochemical gradient
Electrochemical gradient
An electrochemical gradient is a spatial variation of both electrical potential and chemical concentration across a membrane; that is, a combination of the membrane potential and the pH gradient...
creates potential energy across the inner mitochondrial membrane, known as the proton-motive force. As a result, chemiosmosis
Chemiosmosis
Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration....
occurs, producing ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
from ADP
Adenosine diphosphate
Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....
and a phosphate group when ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
harnesses the potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
from the concentration gradient formed by the amount of H+ ions. H+ ions passively pass into the mitochondrian matrix
Matrix (biology)
In biology, matrix is the material between animal or plant cells, in which more specialized structures are embedded, and a specific part of the mitochondrion that is the site of oxidation of organic molecules. The internal structure of connective tissues is an extracellular matrix...
by the ATP synthase, and later on help to reform H2O.
The electron transport chain
Electron transport chain
An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...
requires a constant supply of electrons in order to properly function and generate ATP. However, the electrons that have entered the electron transport chain would eventually pile up like cars traveling down a one-way dead-end street. Those electrons are finally accepted by oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(O2), which combine with some of the hydrogen ions from the mitochondrian matrix through ATP synthase
ATP synthase
right|thumb|300px|Molecular model of ATP synthase by X-ray diffraction methodATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate . ATP is the most commonly used "energy currency" of cells from most organisms...
and the electrons that had traveled through the electron transport chain. As a result they form two molecules of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
(H2O). By accepting the electrons, oxygen allows the electron transport chain to continue functioning.
The electrons from each NADH molecule can form a total of 3 ATPs from ADPs and phosphate groups through the electron transport chain, while each FADH2 molecule can produce a total of 2 ATPs. As a result, the 10 NADH molecules (from glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
and the Krebs cycle) and the 2 FADH2 molecules can form a total of 34 ATPs from this electron transport chain during aerobic respiration. This means that combined with the Krebs Cycle and glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
, the efficiency for the electron transport chain is about 65%, as compared to only 3.5% efficiency for glycolysis alone.
Usefulness
The cristae greatly increase the surface area on which the above mentioned reactions take place. If they were absent, the inner membrane would (perhaps) be reduced to a single sphericalSphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
shape
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
, and with less reaction surface available, the reaction efficiency would be likewise reduced. Therefore, cristae are a necessity for the mitochondria to function efficiently.
One mathematical modeling study has suggested that the optical properties of the christae in filamentous mitochondria may affect the generation and propagation of light within the tissue.