A brief discussion on Mitochondria and Chloroplast

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CHLOROPLAST & MITOCHONDRIA
A Brief on
Mitochondria and Chloroplast

Mitochondrion
Mitochondria & Chloroplast

Mitochondrion
Definition: The mitochondrion (plural mitochondria) is a membrane-
bound organelle found in most eukaryotic cells (the cells that make up
plants, animals, fungi, and many other forms of life).
Mitochondria range from 0.5 to 1.0 micrometer (μm) in diameter.
These structures are sometimes described as "cellular power plants"
because they generate most of the cell's supply of adenosine
triphosphate (ATP), used as a source of chemical energy.

Origin & History
 When life first began on our planet, single celled organisms
produced energy in a way that was highly inefficient (anaerobic
respiration, meaning without oxygen) compared to what most
multi-cellular organisms use today (aerobic respiration, using
oxygen).
 Through evolutionary time, plants came about and were able to
produce oxygen in the atmosphere giving rise to aerobic respiration
which produced energy in a highly efficient manner.

Origin & History
 The theory of endosymbiosis suggests that mitochondria were once
free living organisms on their own that used aerobic respiration.
Larger anaerobic cells simply engulfed these aerobic mitochondria
to use their energy, giving rise to complex cells we find today such
as those in our bodies.
 The first observations of intracellular structures that probably
represent mitochondria were published in the 1840s.

Structure
 A mitochondrion contains outer and inner membranes composed
of phospholipid bilayers and proteins. The two membranes have
different properties. Because of this double-membraned
organization, there are five distinct parts to a mitochondrion.

Structure
Five distinct parts to a mitochondrion are:
 the outer mitochondrial membrane
 the intermembrane space (the space between the
outer and inner membranes)
 the inner mitochondrial membrane
 the cristae space (formed by infoldings of the inner membrane)
 the matrix (space within the inner membrane)
Mitochondria stripped of their outer membrane are called mitoplasts.

Organization and distribution
 Mitochondria are found in nearly all eukaryotes.
 They vary in number and location according to cell type.
 A single mitochondrion is often found in unicellular organisms.
 Conversely, numerous mitochondria are found in human liver cells,
with about 1000–2000 mitochondria per cell, making up 1/5 of the
cell volume.

Function
 Energy conversion
• Pyruvate and the citric acid cycle
• NADH and FADH2: the electron transport chain
• Heat production
 Storage of calcium ions
 Additional functions
• Signaling through mitochondrial reactive oxygen species
• Regulation of the membrane potential
• Calcium signaling
• Steroid synthesis.

Genome
 The human mitochondrial genome is a circular DNA molecule of
about 16 kilobases.
 It encodes 37 genes: 13 for subunits of respiratory complexes I, III,
IV and V, 22 for mitochondrial tRNA (for the 20 standard amino
acids, plus an extra gene for leucine and serine), and 2 for rRNA.
 One mitochondrion can contain two to ten copies of its DNA.

Replication and Inheritance
 Mitochondria divide by binary fission, similar to bacterial cell division
 Mitochondria must be duplicated during cell cycle and segregated to the daughter cell
 Replication of mtDna maybe stochastic

Replication and Inheritance
 Energy high-mitochondria grow and divide
 Energy low-mitochondria destroyed and inactive
 Most cases inherited only from mother which is
known as maternal inheritance
 Paternal inheritance may happen in some coniferous
plants, some species and some insects.
When is replication not normal?

Mitochondrial Disease
 Result from failures of the mitochondria
 Less energy is generated within the cell. Cell injury
and even cell death follow.
 Genocopies of Mitochondrial Disease &Phenocopies
of Mitochondrial Disease

Mitochondrial Disease
 Primarily affects children but adult onset is
becoming more common.
 Damage to cells of the brain, heart, liver, skeletal
muscles, kidney and the endocrine and
respiratory systems.

Treatment
 To alleviate symptoms and slow down the
progression of the disease
 Treatment may be beneficial and noted
immediately in some disorders.
 Sometimes, the benefits of treatment may take a
few months to notice.

Therapy
 Dietary Therapy
 Supportive Therapies
 Avoidance of Toxins
 Vitamins and Supplements That May Be Helpful
 Medication, Minerals, Vitamins and Substrates
That May Be Helpful
 Avoidance of Physiologic "Stress"

Possible Relationship to Aging
 A number of changes can occur to mitochondria
during the aging process
 Tissues from elderly patients show a decrease in
enzymatic activity of the proteins of the respiratory
chain.
 Mutated mtDNA can only be found in about 0.2% of
very old cells.

Possible Relationship to Aging
 Large deletions have been hypothesized to lead high
levels of oxidative stress and neuronal death in
Parkinson's disease.
 Mitochondrial changes are causes of aging or merely
characteristics of aging.

Chloroplast

Chloroplast
 Chloroplasts are organelles found in plant cells and
eukaryotic algae that conduct photosynthesis.
 Cyanobacteria are considered the ancestors of
chloroplasts.

Primary endosymbiosis
 A eukaryote with mitochondria engulfed
acyanobacterium in an event of serial primary
endosymbiosis, creating a lineage of cells with both
organelles. The cyanobacterial endosymbiont
already had a double membrane— thephagosomal
vacuole-derived membrane was lost.

 Many other organisms obtained chloroplasts from
the primary chloroplast lineages through secondary
endosymbiosis.
Chromatophores
 Being in the early stages of endosymbiosis, Paulinella
chromatophora can offer some insights into how
chloroplasts evolved.
Secondary and tertiary endosymbiosis

 In some groups of mixotrophic protists, chloroplasts are separated from a
captured alga or diatom and used temporarily. These klepto chloroplasts may
only have a lifetime of a few days and are then replaced.
Chloroplast DNA
 Chloroplasts have their own DNA. Its also known as the Plastome. Its existence was
1st proved in 1962.
Kleptoplastidy

 Most chloroplasts have their entire chloroplast genome combined into a single large
ring.
Inverted repeats: Chloroplast DNA contain 2 inverted repeats.
1. Long single copy section (LSC)
2. Short single copy section (SSC)
Many nucleoids can be found in each chloroplast.
Protein synthesis
 Protein synthesis within chloroplasts relies on two RNA polymerases.
Molecular structure

 The movement of so many chloroplast genes to the nucleus
means that lots of chloroplast proteins that were supposed to be
translated in the chloroplast are now synthesized in the
cytoplasm.
 In most, but not all cases, nuclear-encoded chloroplast proteins
are translated with a cleavable transit peptide that's added to
the N-terminus of the protein precursor.
Protein targeting & import

 Outer chloroplast membrane
 Inter-membrane space
 Inner chloroplast membrane
 Stroma
 Pyrenoids
 Thylakoid system
Structure

 Lipid composition
 Phospholipids(48%)
 Galactolipid(46%)
 Sulfolipid(6%)
 Semi-porous membrane
 Sometimes forms Stromule
Outer chloroplast membrane
Inter-membrane space
 10-20 nanometers thick
 Exists between outer & inner wall

 Lipid composition
• Phospholipids(16%)
• Galactolipids(79%)
• Sulfolipids(5%)
 Regulates passage of materials
 Fatty acids, lipids, carotenoids are synthesized
Inner chloroplast membrane

 Colorless fluid surrounding grana
 Protein rich
 Location of chloroplast DNA & ribosomes
 Calvin cycle takes place
Stroma

 Membrane bound compartment
 Site of light-dependent reactions
 Forms stack of disks(Grana)
 Grana are connected by inter-grana thylakoids
Thylakoid system

 Chloroplasts use Rubisco
 Trouble distinguishing oxygen & carbon dioxide
 C4 plants evolved a solution
 Separating light reactions & Calvin cycle
Specialized chloroplast in c4 plants

 Distribution in plants
 Cellular location
Location
Distribution in a plant
 All green parts contain chloroplast
 Usually parenchyma cells
 Can be found in collenchyma tissue
 Known as Chlorenchyma cell
 Concentrated in leaves

 Can change orientation
 Low light condition
• Spread out in a sheet
 Intense light
• Aligns in vertical columns
 Reduces exposure
 Protects from photo-oxidative damage
Cellular location

 Plant innate immunity
 Hypersensitive response
 Systemic Acquired Resistance
 Photosynthesis:
 Light reactions
 Photophosphorylation
 Dark reactions
 pH level
Function and chemistry

 Plastid interconversion
 Chloroplast division
 Chloroplast Inheritance
Differentiation, replication and inheritance

References
 http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.html
 http://ccdb.ucsd.edu/sand/main?stype=lite&keyword=chloroplast&Submit=Go&e
vent=display&start=1
 http://www.mitodb.com/
 http://www.uni-mainz.de/FB/Medizin/Anatomie/workshop/EM/EMMitoE.html
 http://www.cytochemistry.net/Cell-biology/mitoch1.htm

A brief discussion on Mitochondria and Chloroplast

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