Mitochondria [Singular – Mitochondrion] [Gr. Mitos = thread; Chondrion – granule]
They were first seen by Kolliker (1880) in the striated muscles of the insects. Fleming (1882) named them as “Fila”. Altmann (1890) called mitochondria as “Bioplast”. Term “mitochondria” was coined by C. Benda (1897-98). F. Meves (190) made the first recorded observation of mitochondria in plant cells (white water lilly).
Number:
They are found in all types of cells except the prokaryotic cells. They are round or rod-like or filamentous. The average length is 5 to 8 micron and the diameter is 0.5 to 1 micron. Their number varies from species to species and it is 50 to 5000. However, Microsterias green alga & sporozoite (a stage of Plasmoduim), its number is one. There are about 5 lakh mitochondria in Pelomyxa.
Structure:
They are bounded by two unit membranes viz. – Outer and inner membranes which are made up of proteins & phospholipids. The inner membrane forms numerous finger like processes into the cavity called Cristae. The cristae may be tubular (branched or unbranched) or vesicular. There is a perimitochondrial space between the outer and inner membranes which contains respiratory enzymes to perform oxidative phosphorylation. The central cavity of the mitochondria is full of matrix which consists of 70S ribosome, mDNA (mitochondrial DNA), all types of RNA, Redox enzymes and ATP.
The inner surface of inner membrane of cristae are attached with small granules which are called as elementary particles or respiratory granules or oxysomes. Every oxyosome consists of head, stalk and base. The diameter of head is about 86A°. These oxysomes remain equally spaced by 100A°. The oxysomes contain ATP synthetase enzyme which performs oxidative phosphorylation.
The mitochondrial DNA is circular and has more C-G combinations. The mitochondria shows auto reproduction ie. they divide to form new mitochondria. Therefore, they are also called as semiautonomous orgenelles. Chemically, they consists of proteins (65-70%), phospholipids (25%), RNA (0.5%); DNA & ATP etc.
