A brief account of Mitochondria and their functions

1. MITOCHONDRIA
Dr. Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry

2. MITOCHONDRIA
Mitochondria (Gr. Mito = thread , chondrion =
granule ; Singular : Mitochondrion) are granular
or filamentous organelles present in the
cytoplasm of all eukaryotic cells.
• First observed by Kolliker (1880)
• Altman (1894) gave the name ‘Bioblasts’.
• The name ‘Mitochondrion’ was given by
Benda(1897).
• The shape is variable – filamentous or granular
• Morphology varies from one cell to another, but
is more or less constant in cells of a similar type
or in those performing the same function.

3. Size :
• Variable
• Generally 0.5 µm in diameter.
• Length – up to 7 µm.
Number :
• Varies from cell to cell.
• Green plants contain fewer Mitochondria
than animal cells.
• Growing, dividing and actively synthesizing
cells contain more Mitochondria than other
cells – 1000 to 1600 in Liver cell; 3,00,000 in
some oocytes.

4. Distribution :
• Related to their function as suppliers of energy.
• Generally they are uniformly distributed
through out the cytoplasm
• In some cases, they accumulate preferentially
around the nucleus.
• Peripheral cytoplasm.

5. MITOCHONDRIA - ULTRASTRUCTURE
• Rod – shaped or filamentous
• Double membrane bound – both the
membranes have a trilaminar (unit
membrane ) structure – 60 to 70 A° thickness
• Space between the two membranes –
perimitochondrial space.
• Outer membrane smooth.

6. • Inner membrane form a number of infoldings
into the cavity of the mitochondrion- Cristae
( Cristae chondrialis or mitochondrial crests) –
do not interrupt the continuity of the inner
chamber.
• In some cases, Cristae may fuse with those
of opposite side dividing the mitochondrion
into compartments.

7. • Cristae may be simple, branched, straight or
zig zag, lamellar or tubular.
• The number of Cristae per unit volume is also
variable – related to the oxidative activity of
the Mitochondrion.
• Cristae greatly increase the inner surface area
of the Mitochondrion.

8. MITOCHONDRIA - Ultrastructure

9. MITOCHONDRIA - Ultrastructure

10. • Inner membrane divides the Mitochondrion
into two chambers or compartments – The
outer chamber is contained between the two
membranes and in the core of crests and the
inner chamber is filled with a relatively dense
proteinaceous material – mitochondrial
matrix – generally homogeneous – contains
the enzymes for Kreb’s cycle (Respiratory
enzymes) – Also contains 70 S Ribosomes
(Mitoribosomes), DNA, RNA etc.

11. • Inner membrane of
Cristae bears minute,
regularly placed
particles – Oxysomes
(Inner membrane sub
units or Elementary
particles or F1 particles
or F0 – F1 particles ).
Image:https://www.embibe.com

12. Oxysomes - Three parts –
a rounded head piece
or F1 sub unit , joined
by a short stalk to a
base piece or F0 sub
unit, located in the
inner membrane.
• Correspond to a special
ATPase or ATP
synthetase enzyme -
concerned with ATP
formation.

13. • Mitochondria are semiautonomous
organelles – capable of self- duplication
(Replication). For replication they have
i. Genetic information (DNA)
ii. Protein synthesizing machinery
(Ribosomes).
iii. Energy – producing mechanism (Respiratory
enzymes).

14. MITOCHONDRIA - FUNCTIONS
1. Mitochondria function as energy - transducing
organelles (Transducer – transmit energy from
one system to another) – main seat of cell
respiration – bring about step wise oxidation of
food stuffs and the energy released is used to
synthesize energy rich compound ATP – the
immediate source of energy in a cell –
‘Universal energy currency’.
Since Mitochondria are concerned with the
synthesis, storage and release of energy rich
ATP molecules, they are called as ‘Power houses
‘ or ‘Storage batteries’ or ‘ATP mills’ .

15. 2. Mitochondria provide intermediates for the
synthesis of chlorophyll, cytochromes,
steroids etc.
3. Some amino acids are also formed in
Mitochondria.
4. It regulates the Calcium ion concentration in
the cell by storing and releasing Ca ions as
needed.

16. THANK YOU