Mitochondria (Mc) are present in all eukaryotic cells and are the major sites of aerobic respiration within cells. they were first seen as granules in muscle cells in 1850. The number of mitochondria per cell varies considerably and depends on the type of organism and nature of the cell.

mitochondria structure

Historical background:

  • 1850 – Kolliker – observed in muscle cells of insects
  • 1882 – Flemming– gave the name as “filia”
  • 1892 – Altmann– gave systematic name observation name as “Bioblast
  • 1897-98 – Benda– gave a name as “Mitochondria”. He stained the mitochondria with “alizarin” and “crystal violet”.
  • 1900 – Michaelis– stained mitochondria with “Janus green”
  • 1934 – Bensley & Hoperr – said mitochondria is the site for the cellular respiration.
  • 1940- Palade and Sjostrand – They worked out the fine structure of mitochondria under the electron microscope.

Other name:

  • Fuchsinophilic granules,
  • Parabasal bodies,
  • Plasmosomes,
  • Fila,
  • Chondriosomes,
  • Vernicules
  • Bioblasts.

Biochemistry and Anatomy of Mitochondria:

Mitochondria (Mc) were first observed by “Altmann” in 1894 who described as “bioblasts”. Benda (1897) called them “mitochondria”. (mitoG =thread; chondrionG=granule). The number of Mc varies with the cell type and functional stages. In eukaryotes, approximately 2000 Mc copies one-fifth of its total cell volume. The Mcs chemical composition is concerned, It consists of 65-70% proteins, 25-30% lipids, 5-7% DNA and 0.5%RNA. The outer membrane of the mitochondria has “porins”, which permits molecules up to 10kd. Matrix is gel like a solution, containing the high concentration of soluble enzymes, substrate, nucleotide cofactors, ions.

The Mc is a subcellular organelle having the outer and inner membranes enclosing the matrix. The inner membrane is highly selective in its permeable characteristics. The inner membrane contains the respiratory chain and translocation systems. The knobs like protrusions represent the ATP synthase system. The inner membrane is folded into a series of internal ridges called “Cristae”, which may be longitudinally or transversely oriented, branched or tabular. Hence, there are two compartments in Mc: the intermembrane space between the outer and inner membranes and the matrix, which is bounded by the inner membrane. Most of the reactions of the TCA cycle and fatty acid oxidation occur in the matrix.

Size: The average length of Mc is 3-4 microns and the average diameter 0.5 to 1.0 micron.

Shape: Mitochondria vary in shape but are generally filamentous or granular. If a filamentous mitochondrion swells at one end, it gives a club shape club-shaped. If the swollen and hollows out then it becomes tennis racket shaped. If there is a central clear zone, the mitochondrion becomes vesicular.

Number: The number of mitochondria varies in different cell types. the number of mitochondria depends upon the metabolic activity of the cell. in a normal liver cell, there are 1000 to 1600 mitochondria while in plant cells their number is very small.

Distribution: Ordinarily, The Mc is evenly distributed in the Cytoplasm. In columnar or prismatic cells, Mc is oriented parallel to the long axis of the cell.

Enzymes localization in Mc:

LOCALISATION OF SOME ENZYMES IN RAT-LIVER MITOCHONDRIA:

Outer membrane EnzymesInner membrane EnzymesMatrixBetween membrane Space
  • Monoamine oxidase
  • Kynurenine-3-monoxygenase
  • NADH dehydrogenase
  • Acyl. CoA Synthetase
  • Phospholipase-A2
  • Nucleoside diphosphate kinase
  • NADPH dehydrogenase
  • Iron-Sulfur Proteins
  • Cyt.b,c,c1and aa3
  • F1 ATPase
  • Succinate dehydrogenase
  • Carnitine acyl transferase
  • TCA Cycle enzymes
  • Fatty acyl-CoA oxidation enzyme
  • Adenylate kinase
  • Creatine Kinase

Functions:

What are the functions For Mitochondria? The Mc are organelles which transfer the chemical energy of the metabolites of the cell (through Krebs cycle and the respiratory chain) into the high-energy phosphate bond of ATP. Thus, mitochondria are the “power house of the cell”, that produce the energy necessary for many vital cellular functions via, motility contraction (muscle contraction), biosynthesis of cell bioluminescence etc.