Mitochondria Introduction Structure and Functions

Mitochondria: –

  • Mitochondria word  from greek word  Mitos – thread; Chondrion – granule.
  • First seen by kolliker in striated muscles of insects.
  • Term mitochondria was given by Benda.
  • Fleming gave them name filla.
  • Altman considered them cell organelle and called them bioplast.
  • It is called power house of cell.
  • It is maternal inheritance or cytoplasmic inheritance.


  • Cells with more metabolic activity have more number of mitochondria.
  • Generally their number is 1000-1600 in a cell.
  • In ova, number of mitochondria increase in order to increase.
  • Prokaryotic cell, anaerobic cells and old mammalian RBCs lack
  • Microsterias green alga and sporozoite have one mitochondria.
  • Chaos Chaos amoeba and pleomyxa have 5 lac mitochondria.
  • Animal cell have more mitochondria than plant cell.

Typically it is sausage-shaped or cylindrical or rod like or filamentous having a diameter of 0.2-1.0µm and length 1.0-4.1µm.
Mitochondria is a double membrane structure having following components –
(A) Outer membrane:-

  • Outer membrane of mitochondria transfer very large molecules about 6000 kD.
  •  It has more Phosphatidyl choline.
  • It enclose entire organelle made up of protein and phospholipid in ratio 1:1 by weight.
  • It consists of large number of integral proteins called porins. So more permeable than inner membrane.
  • It can associate with E.R. it is 60-70 Å thick.
  • It has stalk less particles on outer surface known as subunits of parson.

(B) Perimitochondrial space: –

  •  It is of 80-100Å size.

(C) Inner membrane: –

  • These perform redox reactions of oxidative phosphorylation.
  • ATP synthesis.
  • Transport protein.
  • Protein import machinery.

–> Outer surface of inner membrane is known by as C-face while inner surface is called M-face.
(D) Cristae:

  •  Inner membrane possess many projection called cristae.
  • Cristae contains with small round bodies called F2 particles or oxysomes or inner membrane subunit.
  • At the base of F2 particle, factor F0 is present which helps in attachment of F1 particle with inner membrane and called as OSCP (oligomycin sensitivity conferring protein).
  • Distance between two oxysomes is 100Å.
  • Oxysomes are made up of ATPase enzyme and are related with oxidative phosphorylation.
  • It is a space enclosed by inner membrane. It contain about 2/3 of the total protein a mitochondrion.

(E) Inner chamber: –

  • It contains fluid knows as matrix.
  • It consists of mixture of large number of Krebs cycle enzyme, special mitochondrial ribosomes, t-RNA and several copies of the mitochondrial DNA genome.

(F) Mitochondrial DNA: – .

    • It constitute 1% of total DNA of cell.
    • Size of mt-DNA is greater in plant than animals.
    • In mitochondria genome size is small but gene no is very high.
    • Mitochondrial genome size in human is 16kD and yeast 200kD
  • Mutation in mt-DNA produce Labour Optic Neuropathy. In this neuron connected with optic nerve get damaged.
  •  DNA is double stranded, naked granular, circular, molecule with higher G-C ratio.
  • Mt-DNA is used for the study of Phylogenetic relationships.
  • It have 70s type Ribosomes.
  • It is called semi-autonomous bodies because of presence of mitochondrial DNA (m-DNA) in them


  1. Cellular respiration and ATP production.
  2. ATP storage and transport
  3. Vitellogenesis – mitochondrial kinase makes yolk dense and insoluble. Mitochondria are also called yolk nuclei in egg.
  4. It found in neurons where they help to from neurohormone. Rg. Acetylcholine.

Mitochondria is similar to rickettsia bacteria
Mitoplast- if outer membrane of mitochondria is removed then it called mitoplast. After it mitochondria can work.
Similarities between plastids and mitochondria: –   

  1. Both exhibit similar growth and origin.
  2. Both are able to synthesize their own required protein.
  3. It is believed that both are evolved from endosymbiotic bacteria.

Programmed Cell Death: –
When mobile electron carrier (Cyt-c) comes  into the cytoplasm it is a signal of programmed cell death. In cytoplasm Cyt-c bind to APAF by procaspases and cell undergo to death.

References and source:-
BSER Books
Molecular Biology of the Cell-Alberts
Cell and Molecular Biology Concepts and Experiments.Geraldkarp
Cell Biology, Genetics, Molecular Biology, Evolution and Ecology by Verma, Agarwal

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