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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