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Mitochondria

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Mitochondria is a double membrane organelle present in the cytoplasm of all eukaryotic cells. Mitochondria generates the ATP i.e., the energy molecule of a cell because of which mitochondria is known as the powerhouse of the cell. They also store calcium in them which helps with the proper functioning of a cell. It also regulates the death of the cell. 

What are Mitochondria?

It is also known as the mitochondrion. Found in most eukaryotic cells have a double membrane present in the cytoplasm of the cell. One of its popular names is the powerhouse of the cell. It is named so because its main function is to produce ATP for the cell so that cell can perform metabolic activities. ATP (Adenosine Triphosphate) which is used by the cell as chemical energy is produced by aerobic production.

Mitochondria are taken from Geek language (mitos and chondrion) which means thread and granules like. Mitochondria play a significant role in producing energy by breaking carbohydrates. Many important biochemical reactions occurred in the mitochondria. 1857 it was the first time discovered by Albert von Kolliker. In 1898 Carl Benda was the first person to name it the mitochondrion. Control of cell growth, cell cycle, cell death, signaling, and differentiation is also performed by mitochondria besides the production of ATP in a cell. 

Mitochondria Diagram

The diagram illustrating the structural feature of mitochondria:

Mitochondria Diagram

 

Structure of Mitochondria

Different shapes of mitochondria can be seen in different species of plants and animals. Proteins and phospholipids bilayers form the outer and inner membranes of mitochondria. Different functions are assigned to two different membranes. ATP production increases in mitochondria because of the folding in it. Microplasts are the peeled-off outer membrane of mitochondria. They have five distinct parts due to double membrane organization. 

Outer Membrane

The outer membrane is thick i.e., 60-75 angstroms. A similar ratio of phospholipids to proteins is seen in mitochondria as in cell membranes. The size of the mitochondria is 0.5 to 1.0 mm. Porins are the integral membrane proteins that are present in their outer membrane. Between cytosol and the intermembrane, the proteins, ions, and metabolites are transported with the help of an anion channel called VDAC (Voltage-dependent Anion Channel). Cell death can be caused when the proteins get leaked into cytosol due to disruption in the outer membrane.

Intermembrane Space

The outer membrane and inner membrane have some space in them that space is known as intermembrane space. Perimitochondrial space is also the name given to intermembrane space. The concentration of ions, small molecules, and sugar in this space is the same as in cytosol because the outer membrane is permeable to all these molecules. If we talk about large proteins then the ratio differs because large molecules are transported in the outer membrane by certain transporters. Cytochrome c is a protein that is brought into this space by transporters.

Inner membrane

The ratio of protein in the inner membrane is very high i.e., one-fifth of proteins. Cardiolipin is a phospholipid that is present abundantly in mitochondria. Porins are not present in the inner membrane. It is not permeable to all molecules like the outer membrane. The inner membrane is helpful in the electron transport chain as it has enzymes present which are helpful in ETC. Inner membrane protein OPA1 mediates the fusion of the inner membrane.

Cristae

Cristae are the folds in the inner membrane which form compartments in mitochondria. Due to these folds, the surface area of mitochondria increases which is helpful in more production of ATP. The folds of the inner membrane are five times more than the outer membrane in the cells where the need for ATP is more like in liver cells. The inner mitochondrial membrane is selectively permeable to oxygen and ATP. The cells which have more need for energy will have a greater number of cristae in them. Oxysomes or F1 particles are the small circled bodies attached to cristae.

Mitochondrial Matrix

Space in the inner membrane having the fluid in it is known as a mitochondrial matrix. It also contains a huge number of proteins in it i.e., two third part of proteins. ATP synthase is present in the inner membrane so the inner membrane is very important for the production of ATP. Many copies of the mitochondrial genome, mitochondrial ribosomes, tRNA, and many enzymes are present in the matrix. Fatty acid oxidation, citric acid cycle, and oxidation of pyruvate are the main functions performed by the inner membrane.

Also Read: Difference between Mitochondria and Plastid

Functions of Mitochondria

The primary function of the mitochondria is to generate ATP via oxidative phosphorylation. Other functions of mitochondria are:

  1. Helps in ammonia detoxification in liver cells.
  2. Regulation of metabolic activity.
  3. Helps in cell growth and multiplication.
  4. Apoptosis which is a cell death program is also performed by mitochondria.
  5. Through the specialized somatic junctions status of microglia is controlled by neuronal mitochondria.
  6. Membrane potential and cellular metabolism are maintained by mitochondria.
  7. It also contributes to heme synthesis reactions and also in steroid synthesis.
  8. It is helpful in immune signaling and also in hormonal signaling.

Mitochondrial Disease

If mitochondria are not working properly it will directly affect the human. Symptoms of mitochondrial effect disease vary from person to person. In some cases ineffective mitochondrial lead to organ failure in severe cases. Examples of Mitochondrial disease are:

  • Alpers Disease
  • Barth Syndrome
  • Alzheimer’s Disease
  • Muscular Dystrophy
  • Diabetes

FAQs on Mitochondria

Question 1: Why are mitochondria called the powerhouse of the cell?

Answer:

In the inner membrane, ATP synthases are embedded which help in generating ATP. That’s why mitochondria are known as the power house of the cell.

Question 2: Do mitochondria have DNA?

Answer:

Yes, mitochondria carried DNA and because of this there are known as semiautonomous organelles.

Question 3: Where are the mitochondria found?

Answer: 

Mitochondria is a double membrane organelle that is found in every cell cytoplasm. Their number varies according to the type of cells.

Question 4: What is the structure of mitochondria?

Answer:

Mainly mitochondria have five parts in which it is structurally divided. 

  • The outer membrane is thicker and it contains many enzymes which provide protection to mitochondria but if it gets disrupted the proteins can leak from it and can cause cell death. 
  • Inner membrane space is the space between the outer and inner membranes containing proteins that are to be transported into the inner membrane. 
  • The inner membrane is not permeable to all molecules like the outer membrane. Here for the entry and exit of every molecule, there are some transporters that help the molecules to move in and out of the inner membrane. 
  • The folds or compartments in the inner membrane are called cristae and the fluid in it is called matrix.
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Last Updated : 16 Mar, 2023
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