Mitochondria Ultra-Structure & Mitochondria Function

1. SUBMITTED TO: Dr. Reji J. V.
SUMITTED BY: AVANTHIKA.V.G.
1901711085004
3RD BSc. BOTANY

2. • MITOCHONDRIA: INTRODUCTION
• HISTORY
• Distribution Of Mitochondria
• Number Of Mitochondria
• Size And Shape Of Mitochondria
• ULTRASTRUCTURE OF
MITOCHONDRIA
• Mitochondrial Membranes
• Oxysomes
• Mitochondrial Chambers
• MITOCHONDRIA AS
SEMIAUTONOMOUS ORGANELLE
• ACTIVE AND INACTIVE FORMS OF
MITOCHONDRIA
• FUNCTIONS OF MITOCHONDRIA
• [1] RESPIRATION
• Embden- Meyerhof- Parnas
Pathways (EMP Or Glycolysis) ;
• Oxidative Decarboxylation;
• Oxidative Phosphorylation
Including Kreb's Cycle Or
Tricarboxylic Acid (TCA) Cycle
& Respiratory Chain.
• [2] YOLK FORMATION:
• [3] ELONGATION OF FATTY ACIDS

3. MITOCHONDRIA:
AN INTRODUCTION
• In eukaryotes, the utilization of oxygen as a
means of energy extraction takes place in a
specialized organelle, the mitochondria.
• The mitochondria (Gr., mito=thread,
chondrion =granule) are filamentous or
granular cytoplasmic organelles having a
lipoprotein framework which contains
many enzymes and coenzymes required
for energy metabolism.
• These convert the potential energy of
food into kinetic energy and hence are
commonly known as power houses of
the cell. These are essential for aerobic
respiration.
• They also contain a specific DNA for
the cytoplasmic inheritance and
ribosomes for the protein
synthesis.

4. • In 1880, Kolliker for the first time
recognized the structures now known as
mitochondria.
• However, the credit for the discovery of
mitochondria is given to W. Flemming and
R. Altman. While Flemming described
some thread-like structures in 1882,
Altman described granules in 1890.
• These cell inclusions were later called
mitochondria (mitos=thread,
chondrion=granule) by C. Benda in 1897.
These evidences for the presence of
mitochondria were available only in the
animal cells.
• The first evidence for the presence of
mitochondria in plant cells (Nymphaea)
was given by F. Meves in 1904. Since then,
mitochondria have been shown in all kinds
of plant and animal cells.
• However, an important advancement in the
study of mitochondria was made with the
isolation of liver mitochondria for the first
time by Bensley and Hoerr in 1934.
• The mitochondria of a cell are collectively
designated as chondriome.

5. • Distribution of Mitochondria: Mitochondria (sing.
mitochondrion) are absent in prokaryotic cells and anaerobic
eukaryotes and are lost in mature RBCs. These may be
randomly distributed throughout the cytoplasm or
concentrated in regions involved in energy dependent
activities. For example, mitochondria are aggregated at the
base of cilia or flagella, around axial filament, in middle piece
region of sperm and at the light bands of striated muscle
fibres.
• Number of Mitochondria: The number of mitochondria
increases with cellular activity. The number of mitochondria is
much higher in germinating seeds than in dormant seeds.
There is only one mitochondrion in alga, Microsterias and
Chlorella, less than 10 per cell in yeast and several hundreds
or thousands in tissues of vertebrates, about 1,000-1,600 in
the human liver cells and 50,000 in Choas (protozoa) and
about 3, 00,000 in amphibian oocytes. The highest number
occurs in the flight muscles of certain insects (about
5,00,000).
• Size and Shape of Mitochondria: The size of mitochondria
also depends upon the functional stage of cell. The
smallest mitochondrion is found in yeast where it measures
about 1 um or even less. The oocytes of amphibians (Rana
pipens) have mitochondria of about 20-40 um in length.
Normally, these are 1.0-4.1 um in length and 0.2-1.0 um in
diameter.
• Typically, the mitochondria are sausage-shaped, but also
may be granular, filamentous, rod-shaped, spherical or
thread-like.

6. ULTRASTRUCTURE OF MITOCHONDRIA
• Under electron microscope, a mitochondrion appears as a double-walled
structure that consists of an outer & inner membrane and enclosed within
them are two compartments or chambers.
• In most of the cells, mitochondria in electron micrographs show a quite
smooth outer membrane about 6nm thick. Inside and separated from the
outer membrane by a space is present the inner membrane also 6nm thick.
Therefore, a mitochondrion has a double membrane envelope, the two
membranes being separated by a space 6-8nm. Both the mitochondrial
membranes are tri-laminar unit membranes about 60-70 Å thick.
• The fine structure of a mitochondrion can change in different cells of a
tissue, at different stages of development or in different physiological and
pathological conditions. This suggests that mitochondrial membranes are
dynamic structures.
• The mitochondria may be altered due to action of various agents, but most
of these changes are reversible. Only if the change reaches a certain critical
point, it becomes irreversible. Sometimes degenerating mitochondria are
seen at places of autolysis, forming some kind of lysosomes called
cytolysosomes. Mitochondria may also undergo degeneration due to fusion,
forming large bodies called chondriospheres.

7. • The detailed structure of
mitochondrion is shown
in Figure above. As can
be seen, the inner
membrane is convoluted,
the folds consisting of
double membranes and
called cristae (animals).
• These infoldings are
tubular in plants and are
known as tubuli or
microvilli. Frequently in
plants, an intermediate
type of infoldings shown
in Figure below are also
found.

8. MITOCHONDRIAL MEMBRANES
• Outer mitochondrial membrane isolates mitochondrial contents from cytosol.
It is smooth and connected with the membranes of ER. It is permeable to
various small molecules of metabolites which can enter freely in the outer
mitochondrial chamber. It contains enzyme system for oxidizing NADH2 and
cytochrome b5 (e.g. ., NADH, Cyt c reductase, Fatty acid, CoA ligase,
Monoamine oxidase and Kyneurinine hydroxylase). The number of enzymes is
much less as compared to inner membrane. Outer membrane has a protein
porin which permits free movement of metabolites inside. This protein is
similar to that found in Gram negative bacteria. It is rich in lipids but poor in
proteins.
• Inner mitochondrial membrane is highly folded into the matrix forming
incomplete septa, called cristae (sing. crista) or mitochondrial crests. These
increase the surface area of inner membrane and divide the inner
mitochondrial chamber into interconnected compartments. The cristae may be
simple or branched forming a complex network which provides access to the
respiratory enzymes and also provides additional membrane surface.
Inner membrane is selectively permeable and impermeable to most small
ions. It carries large number of enzymes, coupling factors, carrier proteins,
electron carriers and channel proteins for the passage of protons (H+).

9. • Attached to M face (facing
matrix) of inner membrane
are numerous repeated units
of spherical or knob-like
stalked particles called
elementary particles/ inner
membrane subunits or
oxysomes.
• Approximately, there are 104
to 105 oxysomes per
mitochondrion. When the
mitochondrial cristae are
disrupted by sonic vibrations,
oxysomes are obtained and
oxysomesare seen attached on
their outer surface. Oxysomes
are responsible for respiratory
chain phosphorylation. The
oxysomes have been
identified as molecules of
ATPase enzyme (coupling
factor F1) responsible for
catalyzing the terminal step
of ATP synthesis.

10. MITOCHONDRIAL CHAMBERS:
The inner membrane is not smooth and forms mitochondrial crests. This inner
membrane divides the mitochondria into two chambers, namely ;
• Peri-mitochondrial Space/ Outer chamber is the intermembranous or
perichondrial space between the outer and inner membranes of mitochondria
between outer membrane and inner membrane which is continuous into the core
of the crests. It is filled with a fluid which contains certain enzymes like nucleoside
diplophosphokinase and adenylate kinase.
• The Inner Chamber is enclosed within the inner membrane, which is occupied by a
relatively dense homogeneous, gel-like material called the mitochondrial matrix.
The matrix may rarely show finely filamentous or fibrous structures.
• The Matrix contains high concentration of enzymes of Krebs cycle or
tricarboxylic acid (TCA) cycle, some lipids, circular mitochondrial DNA
molecule, 70S ribosomes (mitoribosomes), tRNA and enzymes for functioning
of mitochondrial genes.
Mitochondrial DNA is more stable and has higher density than nuclear DNA
because of higher proportion of guanine-cytosine (G =C) base pairs.

11. • In active state, mitochondria are
condensed. Their outer chamber
is wider but inner chamber or
matrix appears narrow. The
cristae are more randomly
distributed and have narrow
core. These are actively engaged
in electron transfer and ATP
synthesis.
• In inactive or orthodox state,
the outer mitochondrial
chamber is narrow, and matrix is
wide. The cristae are less
prominent and non-functional.
Mitochondria may occur in metabolically active and inactive forms:

12. FUNCTIONS OF MITOCHONDRIA

13. [1] RESPIRATION: Aerobic respiration takes place inside
the mitochondria, during which the metabolic end products
of various foods like glucose, amino acids and fatty acids are
degraded to CO2& H2O with the intervention of oxygen, and
energy is liberated. The energy liberated is locked in an
energy-rich compound, adenosine triphosphate (ATP), and is
utilized whenever needed.
Mitochondria are often referred to as ‘Powerhouse Of
The Cell’, since they produce 95% of ATP molecules in
animal cells (5% ATP is produced during anaerobic
respiration outside the mitochondria), although in plant
cells, ATP is also produced by the chloroplasts.
This energy is produced during the breakdown of food
molecules including carbohydrates, fats and proteins
(catabolic activity) which involves :
A. Embden- Meyerhof- Parnas Pathways (EMP or
Glycolysis) ;
B. Oxidative Decarboxylation;
C. Oxidative Phosphorylation Including
 Kreb's Cycle or Tricarboxylic Acid (TCA)
Cycle
 Respiratory Chain.

14. A. Embden- Meyerhof- Parnas Pathways (EMP
or Glycolysis): Glycolysis (glycos = sugar or
sweet ; lysis = dissolution; also described as
Embden Meyerhof - Parnas or EMP pathway
named after the three discoverers) involves
breakdown of a molecule of glucose anaerobically
into two molecules of pyruvic acid; this process is
also a part of anaerobic respiration or
fermentation and occurs outside the
mitochondria within the cytosol;
B. Oxidative Decarboxylation: Oxidative
decarboxylation involves conversion of pyruvic
acid into acetyl co-enzyme A (acetyl CoA) inside
the mitochondria .The two molecules of pyruvic
acid produced from one molecule of glucose
during glycolysis, enter the mitochondria and
undergo decarboxylation to yield two molecules
of acetyl coenzyme A (acetyl CoA) accompanied
with the liberation of four hydrogen atoms.

15. C. Oxidative Phosphorylation Includes
• Kreb's Cycle or Tricarboxylic Acid
(TCA) Cycle or The Citric acid cycle
is for oxidation of acetyl CoA to
produce NADH and FADH, for the
respiratory chain (occurs in
mitochondrial matrix).
• Respiratory Chain makes use of
FADH, and NADH for oxidation with
molecular O, and consequently
releases enormous energy that is
utilized for the production of ATP
molecules.
Other Functions of Mitochondria Includes:
[2] YOLK FORMATION: Mitochondria help in the
formation of yolk in developing ovum and are
converted into yolk-storing bodies.
[3] ELONGATION OF FATTY ACIDS: Mitochondria
contain enzymes which help in the elongation of
fatty acids by adding acetyl CoA.

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