Mitochondria
Origin.
“Mitochondria is ” derives
from two Greek words: “mitos” meaning thread, and “chondros” meaning granule.
History:
Mitochondria, often referred to
as the “powerhouses of the cell”, Mitochondria
were first discovered in 1857 by physiologist Albert von
Kolliker, and later invented “bioblasts” (life germs) by Richard Altman in
1886. After twelve years later, Mitochondria were named by Carl Benda in 1898
from his study of cell internal structure and the first recorded information of
mitochondria in plants in cells was created by Friedrich Meves in 1904.
Defination:
Mitochondria are
membrane-bound cell organelles (mitochondrion, singular) that generate most of
the chemical energy needed to power the cell's biochemical reactions. Chemical
energy produced by the mitochondria is stored in a small molecule called
adenosine triphosphate (ATP).
External
Structure of mitochondria:
Size
of Mitochondria:
Mitochondria
are small, often between 0.75 and 3 micrometers and are not visible under the
microscope unless they are stained. Sometime the size and number of the
mitochondria is depend on the physiological activity of the cell.
Types
of Membrane in Mitochondria:
Mitochondria have two types of membranes. Each membrane has different
functions.
outer membranes:
Small
molecules can pass freely through the outer membrane. This outer portion
includes proteins called porins, which form channels that allow proteins to
cross. The outer membrane has many protein-based
pores that are big enough to allow the passage of ions and molecules as large
as a small protein.The outer membrane also hosts a number of enzymes
with a wide variety of functions.
2.
inner membranes:
Inner membrane holds
proteins that have several roles. Because there are no porins in the inner
membrane, it is impermeable to most molecules. Molecules can only cross the
inner membrane in special membrane transporters. The inner membrane is where
most ATP is created. In, the inner membrane has much more restricted permeability,
much like the plasma membrane of a cell. The inner membrane is also loaded with
proteins involved in electron transport and ATP synthesis. This membrane
surrounds the mitochondrial matrix, where the citric acid cycle
produces the electrons that travel from one protein complex to the next in the
inner membrane.
3.
Inter-membrane
space:
This
is the area between the inner and outer membranes.
Internal
Structure of mitochondria:
Cristae: These are the folds of the inner
membrane. They increase the surface area of the membrane, therefore increasing
the space available for chemical reactions.
F1 Particles: The inner surface of cristae in the
mitochondrial matrix has small knob like structures known as F1 Particles.
Numbers
of mitochondria in cell:
Different cell types have different numbers of mitochondria. For instance, mature red blood cells have none at all, whereas liver cells can have more than 2,000. Cells with a high demand for energy tend to have greater numbers of mitochondria. Around 40 percent of the cytoplasm in heart muscle cells is taken up by mitochondria. . Also, in sperm cells, the mitochondria are spiraled in the mid piece and provide energy for tail motion.
Shape of
mitochondria in cell:
Although
mitochondria are often drawn as oval-shaped organelles, they are constantly
dividing (fission) and bonding together (fusion). So, in reality, these
organelles are linked together in ever-changing networks.
Function of mitochondria:
1. Production
of ATP
2. Calcium
Homeostasis
3. Regulation
of Innate Immunity
4. Programmed
Cell Death
5. Stem Cell Regulation
Mitochondrial DNA(mtDNA):
Although most of our DNA is kept in the nucleus of each cell, mitochondria have their own set of DNA. Interestingly, mitochondrial DNA (mtDNA) is more similar to bacterial DNA. The mtDNA holds the instructions for a number of protein Trusted Sources and other cellular support equipment across 37 genes. The human genome stored in the nuclei of our cells contains around 3.3 billion base pairs, whereas mtDNA consists of less than 17,000 Trusted Source
During reproduction, half of a child’s DNA
comes from their father and half from their mother. However, the child always
receives their mtDNA from their mother. Because of this, mtDNA has proven very
useful for tracing genetic lines.
For instance, mtDNA analyses have concluded
that humans may have originated in Africa relatively recently, around 200,000
years ago, descended from a common ancestor, known as mitochondrial Eve.
Mitochondrial disease:
The DNA within mitochondria is more susceptible to damage than the rest of the genome. This is because free radicals, which can cause damage to DNA, are produced during ATP synthesis. Also, mitochondria lack the same protective mechanisms found in the nucleus of the cell. However, the majority of mitochondrial diseases are due to mutations in nuclear DNA that affect products that end up in the mitochondria. These mutations can either be inherited or spontaneous.
When mitochondria stop functioning, the cell
they are in is starved of energy. So, depending on the type of cell, symptoms
can vary widely. As a general rule, cells that need the largest amounts of
energy, such as heart muscle cells and nerves, are affected the most by faulty
mitochondria.
Diseases that generate different symptoms but
are due to the same mutation are referred to as genocopies.
Conversely, diseases that have the same
symptoms but are caused by mutations in different genes are called phenocopies.
An example of a phenocopy is Leigh Syndrome, which can be caused by several different
mutations.
Although symptoms of a mitochondrial disease
vary greatly, they might include:
- loss
of muscle coordination and weakness
- problems
with vision or hearing
- learning
disabilities
- heart,
liver, or kidney disease
- gastrointestinal
problems
- neurological problems, including dementia
Other conditions that are thought to involve
some level of mitochondrial dysfunction include:
- Parkinson’s
disease
- Alzheimer’s
disease
- bipolar
disorder
- Schizophrenia
- Chronic
fatigue syndrome
- Huntington’s
disease
- Diabetes
- Autism
- Cancer
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