Mitochondrial crest

Mitochondria structure:
1) Internal membrane
2) External membrane
3) Cresta
4) Matrix.

The mitochondrial cristae are the internal folds of the inner membrane of a mitochondrion, which somewhat define compartments within the mitochondrial matrix. They contain embedded numerous proteins, including ATP synthase and various varieties of cytochromes. This geometric arrangement ensures a large surface area available for chemical reactions to occur within the mitochondria. This enables cellular respiration to take place (aerobic respiration since the mitochondria need oxygen).

Crest Electron Transport Chain

NADH is oxidized by an enzyme producing the ions NAD+, H⁺, and electrons. FADH2 is also oxidized to produce H⁺ ions, electrons, and FAD. As these electrons travel down the electron transport chain in the inner membrane, energy is gradually released and used to pump hydrogen ions from the NADH and FADH₂ fragments into the zone between them. the inner membrane and the outer membrane (called the intermembrane space), creating an electrochemical gradient. This electrochemical gradient creates potential energy in the inner mitochondrial membrane, which is called the proton motor force. The result is that chemiosmosis occurs, generating ATP from ADP and the phosphate group when ATP synthase takes up the potential energy of the concentration gradient formed by H⁺ ions. H⁺ ions pass passively through the mitochondrial matrix by ATP synthase, and subsequently help reform H₂O.

The electron transport chain requires a constant supply of electrons in order to function properly and generate ATP. However, the electrons that have entered the electron transport chain, if there were no appropriate mechanism, would stack up at the end, for which the electrons are finally accepted by oxygen (O₂), which combines with some of the hydrogen ions from the mitochondrial matrix via ATP synthase and the electrons that have traveled through the electron transport chain. The result is that two water molecules (H₂O) are formed for every oxygen molecule. By accepting the electrons, oxygen allows the electron transport chain to continue to function.

The electrons of each NADH molecule can form a total of 3 ATPs from ADPs and phosphate groups via the electron transport chain, while each FADH₂ molecule can produce in total 2 ATPs. Thus the 10 NADH molecules (from glycolysis 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 together with the Krebs cycle and glycolysis, the efficiency of the electron transport chain is approximately 65%, compared to the 3.5% efficiency of glycolosis alone.

Types of ridges

Image of a selected mitochondria, showing the variety of structures found in mitochondrial ridges. This model is based on images obtained for mitochondria of rat liver.

By studying the fine structure of the mitochondria of the different species of the kingdoms Protista, Plantae and Animalia, the following types and shapes of mitochondrial cristae have been found:

• Flat crestas. This is the most common guy. They are made up of flat sheets coming from the inner membrane of the mitochondria, usually connected with it. Sometimes they look isolated, but this may be an artifact because of the section of the mitochondra that is visible under the microscope. The number of crests varies considerably, but is generally dependent on the metabolic activity of the cell. They can be subdivided into four morphological subtypes: foil, ribbon, lump and rounded (discoidal and dish).

• Tubular crestas. In cross section they are seen as circulars, while in longitudinal section they may appear as isolated short tubes, long irregular winding tubes or long tubes attached to the inner membrane of the mitochondria by one end of the tube or by the two.

• Vesicular creams. They appear as isolated spheres or connected to the inner membrane of mitochondria. They can be divided into the morphological subtypes bubble, blistering and sac.

The three types of mitochondrial cristae have been observed among the different representatives of the three kingdoms, Protista, Plantae and Animalia. Most cells of higher plants and higher animals have flat mitochondrial cristae, but sometimes some tissues have cells with tubular or vesicle-like mitochondria.

The type of mitochondrial crista can help classify protists. A few protist phyla have only one type of crest, such as Ciliophora, with only tubular crests, and Cryptophyta, with only flat crests. In most of the phyla a certain type of crest dominates, but then there are some species with different type, for example, in Euglenophyta, Chlorophyta, Chrysophyta, Myxomycota, etc. Finally, in other phyla two or three types of crests may appear even among species of the same genus, for example, Ascetosporea.

Additionally you can find other types of crests:

• Concentric crestas. Formed by concentric circles or by spirals.

• Crestas en zig-zag. Lines that regularly change direction to one side and to the other.

• Phenate Crestas. With discontinuities.

• Longitudinal creams. Usually the ridges of the mitochontria are transversal, but in this type they are longitudinal, that is, they cross the mitochondria on the longest side.

• Prismatic creams. Prismatic volumes that in section present the triangular or rhombic form.

• Reticulated creams. From the plates form a undulating and reticulated pattern.