Biology

Mitochondria

Mitochondria are organelle present only in eukaryotic animals. It is a double-membrane-bound organelle (tiny organs within the cell).  It contains an inner and outer layer. Moreover, these layers are composed of phospholipids and proteins. These are small 0.7 to 3 mm. However, without staining they are invisible even under a microscope. Mitochondria are the powerhouse of the cell, as certainly it is the place where the production of ATP takes place.

mitochondria

Structure

Certainly, it has 5 distinct regions.

1. Outer Membrane

The outer membrane is about 60 to 70 Ã… (angstroms) thick. Proteins and phospholipids comprise this layer. Molecules of small size can easily pass through this membrane. Moreover, this membrane contains proteins that are prions. These prions help other proteins to cross the membrane.

The outer membrane contains various enzymes for example rotenone, monoamine oxidase, etc. The interchange of information, cations, and metabolites happen through it. It acts as the skin of the organelle. Its ratio of protein to phospholipid is similar to that of the cell membrane.

2. Intermembrane Space

The intermembrane space is the space between the outer membrane and inner membranes of mitochondria. Moreover, per mitochondrial space is another name for intermembrane space. Certainly, the protein, cytochrome is restricted to intermembrane spaces.

3. Inner Membrane

This layer consists of proteins that are responsible for electron transport chains, and the synthesis of ATP. It has a high ratio of protein to phospholipids. Moreover, a phospholipid, cardiolipin is present in a rich amount.

The inner membrane is not permeable for many proteins because it does not have prions. The cardiolipin helps in making the membrane less permeable. In addition, for entering and exit of the membrane, special transporter mediums are used. Most importantly, almost all the ATP production occurs in this membrane.

4. Cristae

The inner membrane comprises many folds of cristae. These folds increase the surface area for ATP synthesis. In other words, the cristae increase the surface area by five times as the outer membrane for reactions to occur.

Cristae consist of F1 particles or oxysomes.

5. Matrix

The space enclosed within the inner membrane is the matrix. The matrix consists of hundreds of enzymes. In addition, it consists of tRNA, mitochondrial ribosomes, and mitochondrial DNA.

Mitochondrial DNA

We know that DNA is mostly present in the nucleus. However, mitochondria have their DNA which resembles bacterial DNA. It is often referred to as mtDNA. The offspring inherits this mtDNA from his maternal side only. However, the normal genetic material is inherited from both parents. It has a high mutation rate.

Functions

The main function is the production of energy in the form of ATP (Adenosine triphosphate). However, there are many other functions that it performs. Some of the functions are-

Production of Energy

The energy production is by the cycle of events i.e. Krebs cycle or citric acid cycle. However, the unit of energy production i.e. ATP is the product of the Krebs cycle. The production of ATP occurs over cristae.

The process by which the chemical energy of food is converted into ATP which a body can use is oxidative phosphorylation. In oxidative phosphorylation, a phosphate group attaches to the ADP (adenosine diphosphate) and forming ATP (adenosine triphosphate).

Storing Calcium Ions

The calcium ions enter the organelle by MCU (mitochondria calcium uniporter). This organelle can store the calcium and releases it whenever in need. Calcium is necessary for many metabolic processes; therefore its storage is quite necessary.

Calcium helps in the synthesis of steroids and releases substances that help in cellular communication.

Death of the Cell

The process of elimination of unwanted damaging cells is apoptosis. In other words, the removal of unwanted cells is very important for a normal healthy lifestyle.

On the release of cytochrome C the caspase, turn on. This enzyme is responsible for the destruction of useless cells. Most importantly, this process plays a very important role in the treatment of cancer.

However, sometimes apoptosis can be due to a lack of nutrients and stress which damages the cell.

Production of Heat

Heat production occurs by the process of proton leak. The diffusion of protons occurs in the matrix. As a result, the potential energy of the protons is released in the form of heat energy. Thermogenin, present in brown adipose tissue, however, is responsible for heat production without shivering of the body.

Disorders

Any dysfunction or disorder in the mitochondria can cause a serious illness. However, the cause of the disorder may be when the organelle is unable to change the food and oxygen into energy completely.

The disorders are often neurological. In addition, it may affect the heart, liver, eyes, or pancreas. Mutation in mtDNA causes Kearns-Sayre syndrome, Leber’s hereditary optic neuropathy, and MELAS syndrome.

The diseases may be genetic; however, female inherits many diseases to the zygote as mtDNA is from the maternal side only. Every 1 person in 5000 can have mitochondrial disorders.

Symptoms

Most importantly, the symptoms vary from person to person. It depends upon the organ affected. Some of the symptoms are-

  • Muscle weakness
  • Autism spectrum disorder
  • Bad growth
  • Risk of other infections
  • Thyroid problems
  • Respiratory disorders

For the diagnosis of the disease, the doctors look for the family history, neurological, and physical examinations. MRI (magnetic resonance imaging), EKG (electrocardiogram), skin, and blood samples help in identifying the disease.

Replication

The replication of mitochondria includes binary fission just like bacteria. Moreover, it divides when there is high demand for energy supply. On the other hand, when there is a lesser need for energy then the organelles become inactive.

 A Source of Research

As the mtDNA is of maternal inheritance only, therefore it provides a great source for the study of human evolution and migration. Moreover, this maternal inheritance plays a great role in discovering the line of ancestors.

In addition, they believe that all humans have one woman ancestor who was about 150,000 to 200,000 years ago. However, the variations in the mtDNA are useful for the scientists in their researches for geographical origins.

FAQs on Mitochondria

Question 1- What are mitochondria?

Answer 1- These are the organelles that are present in the cytoplasm of the cell. They are double-membrane structures. In other words, it consists of an inner membrane and an outer membrane. Moreover, inner membranes have finger-like structures i.e. cristae.

Question 2- Why is mitochondria term as the powerhouse of the cell?

Answer 2- They are known as the powerhouse of the cell as the energy production happens here. Food and oxygen are utilized in the formation of ATP (adenosine triphosphate). ATP is the unit of energy. The process by which ATP formation occurs is oxidative phosphorylation.

In oxidative phosphorylation, a phosphate group attaches to the ADP (adenosine diphosphate) and forms ATP (adenosine triphosphate).

Question 3- What are mitochondrial disorders and symptoms?

Answer 3- The disorders can be genetic or due to the inability of the organelle when it is unable to change the food and oxygen into energy completely. Mutation in mtDNA causes Kearns-Sayre syndrome, Leber’s hereditary optic neuropathy, and MELAS syndrome. Moreover, every 1 person in 5000 can have mitochondrial disorders. Therefore,  the symptoms vary from person to person. Some of them are-

  • Muscle weakness
  • Autism spectrum disorder
  • Bad growth
  • Risk of other infections
  • Thyroid problems
  • Respiratory disorders
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