A crista (; plural cristae) is a fold in the inner membrane of a

mitochondrion A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of

surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...

for chemical reactions to occur on. This aids

aerobic cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

, because the mitochondrion requires oxygen. Cristae are studded with proteins, including

ATP synthase ATP synthase is a protein that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (Pi). It is classified under ligases as it changes ADP by the formation ...

and a variety of cytochromes.

Background

With the discovery of the dual-membrane nature of mitochondria, the pioneers of mitochondrial ultrastructural research proposed different models for the organization of the mitochondrial inner membrane. Three models proposed were: *Baffle model – According to

Palade Palade is a village in Hiiumaa Parish, Hiiu County in northwestern Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from F ...

(1953), the mitochondrial inner membrane is convoluted in a baffle-like manner with broad openings towards the intra-cristal space. This model entered most textbooks and was widely believed for a long time. *Septa model – Sjöstrand (1953) suggested that sheets of inner membrane are spanned like septa (plural of

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

) through the matrix, separating it into several distinct compartments. *Crista junction model – Daems and Wisse (1966) proposed that cristae are connected to the inner boundary membrane via tubular structures characterized by rather small diameters, termed crista junctions (CJs). In the middle of 1990s these structures were rediscovered by EM tomography, leading to the establishment of this currently widely accepted model. More recent research (2019) finds rows of

dimers (formerly known as "elementary particles" or "oxysomes") forming at the cristae. These membrane-curving dimers have a bent shape, and may be the first step to cristae formation. They are situated at the base of the crista. A mitochondrial contact site cristae organizing system (MICOS) protein complex occupies the crista junction. Proteins like

OPA1 Dynamin-like 120 kDa protein, mitochondrial is a protein that in humans is encoded by the ''OPA1'' gene. This protein regulates mitochondrial fusion and cristae structure in the inner mitochondrial membrane (IMM) and contributes to ATP synthesis an ...

are involved in cristae remodeling. Crista are traditionally sorted by shapes into lamellar, tubular, and vesicular cristae. They appear in different cell types. It is debated whether these shapes arise by different pathways.

Electron transport chain of the cristae

NADH is oxidized into NAD⁺, H⁺ ions, and electrons by an enzyme. FADH₂ is also oxidized into H⁺ ions, electrons, and

FAD A fad or trend is any form of collective behavior that develops within a culture, a generation or social group in which a group of people enthusiastically follow an impulse for a short period. Fads are objects or behaviors that achieve short- ...

. As those electrons travel farther through the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

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), creating an electrochemical gradient. This electrochemical gradient creates potential energy (see ') across the inner mitochondrial membrane known as the proton-motive force. As a result, chemiosmosis occurs, and the enzyme

produces

ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals, men's professional tennis governing body * American Technical Publishers, employee-owned publishing company * ', a Danish pension * Armenia Tree Project, non ...

from

ADP Adp or ADP may refer to: Aviation * Aéroports de Paris, airport authority for the Parisian region in France * Aeropuertos del Perú, airport operator for airports in northern Peru * SLAF Anuradhapura, an airport in Sri Lanka * Ampara Air ...

and a phosphate group. This harnesses the

potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...

from the concentration gradient formed by the amount of H⁺ ions. H⁺ ions passively pass into the mitochondrial

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

by the ATP synthase, and later help to re-form H₂O (water). The

requires a varying 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 blocked one-way street. Those electrons are finally accepted by oxygen (O₂). As a result, they form two molecules of water (H₂O). By accepting the electrons, oxygen allows the electron transport chain to continue functioning. The chain is organized in the cristae lumen membrane, i.e. the membrane inside the junction. The electrons from each NADH molecule can form a total of 3 ATP's from ADPs and phosphate groups through the electron transport chain, while each FADH₂ molecule can produce a total of 2 ATPs. As a result, 10 NADH molecules (from

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

and the Krebs cycle), along with 2 FADH₂ molecules, can form a total of 34 ATPs during

aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

(from a single electron transport chain). This means that combined with the Krebs Cycle and

, the efficiency for the electron transport chain is about 65%, as compared to only 3.5% efficiency for glycolysis alone.

Function

The cristae greatly increase the surface area of the inner membrane on which the above-mentioned reactions may take place. A widely accepted hypothesis for the function of the cristae is that the high surface area allows an increased capacity for ATP generation. However, the current model is that active

complexes localize preferentially in dimers to the narrow edges of the cristae. Thus, the surface area of mitochondrial membranes allocated to ATP syntheses is actually quite modest. Mathematical modelling suggested that the optical properties of the cristae in filamentous mitochondria may affect the generation and propagation of light within the tissue.Thar, R.and M. Kühl (2004). "Propagation of electromagnetic radiation in mitochondria?". ''J.Theoretical Biology'', 230(2), 261-270

{{Webarchive, url=https://web.archive.org/web/20130718201720/http://www.mbl.ku.dk/MKuhl/pages/PDF/Thar%26Kuhl2004.pdf , date=2013-07-18

References

Cellular respiration Membrane biology