2. Introduction :
• Mitochondria is a double membrane bound organelle found eukaryotic cells.
• Mitochondria : mitos = thread + Chondrion = granule
• Mitochondria, first discovered in 1857 by physiologist Albert von Kolliker.
• The term was first used by Benda in 1897
• First observed by Richard Altman
• mitochondria produces, stored and supplies biological energy, hence called as
“power houses of cells.”
Benda Richard Altman
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4. Morphology
• Shape : Granular , club shaped ,vesicular or rod shaped.
• Size : diameter 0.2 μ to 1 μ
Length 3-10 μ
• Number : Depends on type, size and functional state of cell.
e.g : in the cell of rat liver 500 ,1000 and sometime 2500
mitochondria per cell have been reported.
• Composition : Protein 70% , Lipids 25-30 %, RNA 1 % , DNA <1 %
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6. Structure:
Mitochondria consist of three main parts, viz.,
(1) Membrane
(2) Cristae
(3) Matrix
1) Membrane : Each mitochondria is enclosed by two concentric unit
membranes, The Outer membrane and The Inner membrane.
Each of the two unit membrane is 60 Å thick.
The Outer membrane is a in width and filled with watery fluid. It is
smooth and continuous, permeable to small molecules or solute.
Outer membrane posses porion or minute pores or protein lined
channels for passage of low molecular weight substances. They make
outer membrane more permeable.
The outer membrane contains about 50% proteins and 50% lipids.
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7. The Inner membrane is rough, selectively permeable and infolded in to
number of finger like projections called Cristae or crests. They increase
surface area of inner membrane for enzymatic activity.
Inner membrane has 75% proteins and 25 % lipids.
The side of inner membrane facing the matrix is called M-side (inner matrix)
while the side facing outer chamber is C- side. (Cytostol).
The space between two membrane is known as outer chamber.
2) Cristae : The inner membrane has a series of inside folds known as cristae.
Cristae project into the inner chamber.
3) Matrix : Inner membrane is filled with colourless, granular matrix of
protein and lipid.
The space between cristae into the inner chamber is called matrix.
The matrix contains 70s types of ribosomes called mitoribosomes, 2-6
circular, naked DNA molecules, RNAs.
The matrix also consist of insoluble salts like Mg++ and Ca++.
The DNA is either present in the matrix or is attached to the inner membrane.
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8. Elementary particles : on the M-face of inner membrane, number of
stalk particles are present called Elementary particles /F1 particles/
Oxysomes/Electron transport particles/respiratory assemblies/inner
membrane spheres/ fo – f1 particles/subunits of Fernandze Moran.
Each f1 particle consist of three parts, 1)base, 2)stalk and 3)head.
1) Base piece (Fo subunit)- It is embedded in inner mitochondrial
membrane. It is rectangular. It functions as proton channel or tunnel.
2) Stalk (F5-F6 subunit)- It is about 50Å in length, spherical head is
connected to base piece by cylindrical short stalk.
3) Head piece (F1- subunit)- It is spherical. It contains the enzymes like,
ATP synthase or ATP ase which controls ATP synthesis, hence, they are
called as ATP particles.They projects into matrix and contain electron
acceptors, enzymes, co-enzymes, required for ATP synthesis during
ETS.
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10. Chemical composition:
The chemical composition of the mitochondria varies in different
animal and plant cells.
They are found to contain 65 to 75 % protein, 25 to 30% lipid,
0.5% RNA and small amount of DNA.
The lipid part of mitochondria is composed of 90%
phospholipids, 5% or less cholesterol and 5% free fatty acids
and triglycerides.
Small amount of Sulphur, iron, copper and some vitamins are
present. There are more than 70 enzymes and coenzymes in
mitochondria.
The inner membrane is rich in the phospholipid, called cardiolipin
that makes the membrane impermeable to various ions and small
molecules.
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11. The enzyme composition of mitochondrial compartments and membranens
are given below:
Enzymes of outer membrane:- Mono amine oxidase, kynurenine hydroxylase,
fatty acid Co ligase etc. These are involved in mitochondrial lipid synthesis &
in the conversion of lipid substrate into forms that are subsequently
metabolized in the matrix.
Enzymes of inter-membrane space:- It contains several enzymes that use ATP
passing out of the matrix to phosphorylate other nucleotides. The main
enzymes are adenylate kinase & nucleoside diphosphokinase
Enzymes of inner membrane:- Enzymes of inner membrane are the enzymes of
electron transport pathways – nicotinamide adenine dinucleotide (NAD), flavin
adenine dinucleotide (FAD), diphosphopyridine nucleotide dehydrogenase,
ATP synthetase, succinate dehydrogenase etc.
Enzymes of mitochondrial matrix:- Malate dehydrogenase, isocitrate
dehydrogenase, citrate synthetase, beta oxidation enzymes.
(Source :https://www.notesonzoology.com/cytology/mitochondria-meaning-
morphology-and-function-cytology/2138)
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12. Origin of Mitochondria :
Two mains views about the origin of mitochondria.
1. Mitochondria have a self replication capacity, and the new
mitochondria are formed from the fission of pre-existing
mitochondria.
2. They originate from nuclear envelope.
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13. Theory of origin of mitochondria
• Mitochondria evolved from engulfed prokaryotes that once lived as
independent organisms.
• A eukaryotic cell engulfed an aerobic prokaryote, which then formed
an endosymbiotic relationship with the host eukaryote, gradually
developing into a mitochondrion.
• Theory of endosymbiosis first proposed by Lynn Margulis in 1960.
• Much evidence to support eukaryotic cellular respiration originated
via endosymbiosis of aerobic purple bacteria( alphaproteobacteria)
which ultimately became mitochondria.
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15. Evidence of The theory
Many lines of evidence support this idea. Most important are the many striking
similarities between prokaryotes (like bacteria) and mitochondria and
chloroplasts. Margulis suggested that mitochondria descended from aerobic
bacteria, while the chloroplast descended from photosynthetic blue-green
bacteria.
Aerobic bacteria have the ability to convert food into energy at a very efficient
speed.
1. Membranes — Mitochondria have their own cell membranes, just like a prokaryotic
cell does.
2. DNA — Each mitochondrion has its own circular DNA genome, like a bacteria's
genome, but much smaller. This DNA of the mitochondrion DNA is very similar to the
aerobic bacteria.
3. Reproduction — Mitochondria reproduce by pinching in half (binary fission) — the
same process used by bacteria. Every new mitochondria must be produced from a
parent mitochondria in this way; if a cell’s mitochondria are removed, it can’t build
new ones from scratch.
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16. Mitochondrial DNA
Mitochondrial DNA or mtDNA or mDNA.
The mitochondria has a small amount of DNA of their own. In human genome
the mtDNA contains 37 genes. All these genes are essential for normal function
of the mitochondria.
These DNA help the mitochondria divide independently from the cell.
The mtDNA in most multicellular organisms is circular, covalently closed,
double-stranded DNA.
The mtDNA of animals is smaller then the plant.
mtDNA is smaller than cpDNA.
The genomes of human and most other animal mitochondria are only about 16
kb, but substantially larger mitochondrial genomes are found in yeasts
(approximately 80 kb) and plants (more than 200 kb).
Mitochondrial DNA (mtDNA) encodes for proteins that are involved in electron
transport and oxidative phosphorylation, which occur in cellular respiration.
Proteins synthesized from mtDNA also encode for the production of the RNA
molecules: transfer RNA and ribosomal RNA.
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18. Functions :
They are the sites of cell respiration. The oxidation of carbohydrates,
lipids and proteins occurs in the mitochondria.
They supply energy to various processes of cell in the form of ATP.
Mitochondria contain some amount of DNA and thus are associated
with cytoplasmic inheritance.
Mitochondria produce ATP through process of cellular respiration—
specifically, aerobic respiration, which requires oxygen. The citric
acid cycle, or Krebs cycle, takes place in the mitochondria. This cycle
involves the oxidation of pyruvate, which comes from glucose, to
form the molecule acetyl-CoA. Acetyl-CoA is in turn oxidized and
ATP is produced.
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19. The citric acid cycle reduces nicotinamide adenine dinucleotide
(NAD+) to NADH. NADH is then used in the process of oxidative
phosphorylation, which also takes place in the mitochondria.
Electrons from NADH travel through protein complexes that are
embedded in the inner membrane of the mitochondria. This set of
proteins is called an electron transport chain. Energy from the electron
transport chain is then used to transport proteins back across the
membrane, which power ATP synthase to form ATP.
Mitochondria have many other functions as well. They can store
calcium, which maintains homeostasis of calcium levels in the cell.
They also regulate the cell’s metabolism and have roles in
apoptosis (controlled cell death), Cell signaling, and thermogenesis
(heat production).
(SOURCE: https://biologydictionary.net/mitochondria/)
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Engineering Mitochondrial Genome For
Crop Improvement
• Mitochondria are often described as "power house of cell"
because they generate most of the cell's supply of adenosine
triphosphate (ATP), used as a source of chemical energy.
• Although most of a cell's DNA is contained in the nucleus,
the mitochondrion has its own independent genome and its
DNA shows substantial similarity to bacterial genomes.
• Among these genomes, nuclear genes are inherited by both
the parents whereas chloroplast and mitochondrial genes are
inherited maternally, therefore chloroplast and mitochondrial
genomes could act as a useful candidates for transgene
containment which is a crucial concern in genetically
modified crops, where transgene esacpe is a major concern
(Siddra Ijaz 2010).
CASE STUDY - 1 Dr. Kiran B. Gaikwad
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Methods of mitochondrial transformation:
•Protoplast fusion
•Particle bombardment of cell culture
•Agrobacterium mediated gene transfer
•Microinjection method
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Plant mitochondrial manipulation:
• Genetic manipulations of mitochondria have been attempted
in many organisms but it is mostly successful to yeast and C.
reinhardtii. Sequencing of mitochondrial genomes in most of
the plant species has been done. Plant mitochondria offer
great advantages in its manipulation because of following
reasons.
1. Maternal inheritance
2. No pleiotropic effect
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Conclusion:
• Many economically important crop species are devoid of
CMS system due to unavailability of cytoplasmic genetic
male sterility. In such species mitochondrial manipulation
could provide a novel means to develop CMS lines as non-
GMO/ transgenic materials
• Once the mitochondrion is transformed with "gene of
interest", their maternal inheritances will confind the gene
through successive generations thus reducing the risk of
transgene escape.
• Use of mitochondrial plasmid as a vector for transgene
would be more compatible than the bacterial plasmid being
its origin from the plant genome itself.
