Mitochondria,the powerhouse of the cell

Found in most eukaryotic cells, mitochondria frequently are called the "powerhouses" of the cell .

 Metabolic processes such as the tricarboxylic acid cycle and the generation of ATP, the major energy cur­ rency of all life forms, take place here.

 When viewed with a transmission electron microscope, many mitochondria are cy­ lindrical structures and measure approximately 0.3 to 1.0 fliD by 5 to 10 11m.

 (In other words, they are about the same size as bacterial cells.)

 Some cells possess 1,000 or more mitochon­  have a single, giant, tubular mitochondrion twisted into a continuous network permeating the cytoplasm.

The mitochondrion is bounded by two membranes: an outer mitochondrial membrane separated from an inner mitochon­ drial membrane by a 6 to 8 nm intermembrane space . 

The outer mitochondrial membrane contains porins and thus is similar to the outer membrane of Gram-negative bacteria.

 The inner membrane has infoldings called cristae (s., crista), which greatly increase its surface area.

 The shape of cristae differs in mitochondria from various species. 

P latelike (laminar) cristae, cristae shaped like disks, tubular cristae, and cristae in the shape of vesicles have all been observed.

 The inner membrane encloses the mitochondrial matrix, a dense material containing ribo­ somes, DNA, and often large calcium phosphate granules.

 In many organisms, mitochondrial DNA is a closed circle, like most bacterial DNA. However, in some protists, mitochondrial DNA is linear.

Each mitochondrial compartment has a characteristic chemical and enzymatic composition. For example, the outer and inner mitochondrial membranes possess different lipids.

 Enzymes and electron carriers involved in electron transport and oxidative phosphorylation are located only in the inner membrane.

 Enzymes of the tricarboxylic acid cycle and those involved with the catabo­ lism (breaking down) of fatty acids are located in the matrix.

The mitochondrion uses its DNA and ribosomes to synthe­ size some of its own proteins.

 In fact, mutations in mitochondrial DNA often lead to serious diseases in humans.

 However, most mitochondrial proteins are manufactured under the direction of the nucleus and must the nucleus and must be transported into the mitochondrion.

 Mitochondria reproduce by binary fission, a reproductive pro- cess  used  by  many   bacteria.