Mitochondria(Gk.Mito=threa; chondrion=granule) are semi autonomous having hollow sac like structures present in all eukaryotes except mature RBCs of mammals and sieve tubes of phloem.Mesosomes of prokaryotes(bacteria) is analogous to mitochondrion in eukarkyotes.
Mitochondria are also called chondriosome,chondrioplast ,plasmosome,plastosomes and plastochondrione.
1.These were first observed in striated muscles(Voluntary) of insects as granules by Kolliker(1850),he called them "sarcosomes".
2.Flemming (1882) called them "fila" for thread like structure.
3.Altman(1890) called them "bioplast".
4.C.Benda(1897) gave the term mitochondria.
5.F.Meves(1904) observed mitochondria in plant(Nymphaea).
6.Michaelis(1898) demonstrated that mitochondria play a significant role in respiration.
7. Bensley and Hoerr(1934) isolated mitochondria from liver cells.
8. Seekvitz called them "Power house of the cell".
9.Nass and Afzelius(1965) observed first DNA in mitochondria.
Number of mitochondria:
Presence of mitochondria depends upon the metobolic activity,higher is the number e.g.,in germinating seeds.
Minimum number of mitochondria is one in Microasterias, Trypanosoma,Chlorella, Chlamydomonas(green alga) and Micromonas.Maximum numbers are found(upto 500000) in flight muscles cells,(upto 50000) in giant Amoeba called Chaos-Chaos.
There are 25 in human sperm,300-400 in kidney cells and 1000-1600 in liver cells.
Mitochondria of a cell are collectively called chondriome.
Size of mitochondria:
Average size is 0.5-1.00 micrometer.Smallest sized mitochondria in yeast cells(1um 3) and largest sized are found in oocytes of Rana pipiens and are 20-40 um(micrometer).
Ultrastructure of mitochondria:
Mitochondria is bounded by two unit membranes separated by perimitochondrial space(6-10nm wide).The outer membrane is specially permeable because of presence of integral proteins called porins.The inner membrane is selective permeable.The inner membrane is folded or convulated to form mitochondrial crests.In animals these are called cristae and in plants these folding are called tubuli or microvili.
The matrix facing face is called 'M' face and face towards perimitochondrial space is called 'C' face.The 'M' face have some small stalked particles called oxysomes or F1 particle or elementary particle or Rackers particle or Fernandez-Moran particles(104-105 per mitochondria).Each particle is made up of base ,stalk and head and is about 10nm in length.
Oxysomes have ATPase enzyme molecule(packer,1967) and therefore, responsible for ATP synthesis.The reaction of ATP formation is endergonic.These elementary particles are also called F0-F1 particles.The F1 particle is made up of five types of subunits.F0 particles synthesize all the enzymes required to operate Kreb's cycle.