Mitochondria

Introduction

Mitochondria is the powerhouse of the cell, which produces energy. It is a membrane-bound organelle, present in the cytoplasm of the cell of Eukaryotic organisms which synthesizes energy molecules in the form of ATP, which is used by the cell. Hypothetically mitochondria are believed to have originated as prokaryotic cells like bacteria. They were capable of oxidative mechanisms. Over the course of evolution, they started living as endosymbionts inside the cell of prokaryotes.

Mitochondria has fragments of the genetic information in the form of DNA and can multiply on their own by division. 

What is a Mitochondrion?

A mitochondrion is a double membrane-bound organelle, which is found in the cytoplasm of most of the cells of most Eukaryotic organisms. This little center for energy generation digests the nutrients and releases chemical energy in the cell in the form of ATP- Adenosine Triphosphate. Apart from generating ATP molecules, the mitochondria also regulate cell growth and cell death, it signals the cells and generates heat. It plays a major role in cellular respiration. Anaerobic fermentation is another process by which ATP is generated in the body but anaerobic fermentation does not take place in mitochondria. Mitochondria necessarily need oxygen and glucose to generate ATP. The energy generated through this process is more in than the energy generated by anaerobic fermentation.

Structure of Mitochondria

Mitochondria in animals is round or oval in shape and is bound by a double membrane. These membranes are composed of phospholipid bilayers and proteins. The different parts of mitochondria in animal cell are:

a) Outer membrane- The outer membrane keeps the inner organelles intact and in place. It is made up of protein and phospholipid bilayer. The outer membrane contains the enzymes involved in various activities. This layer is also permeable to macromolecules so that ions, ATP, ADP, etc. can easily pass through this membrane.

c) Inter membrane space- The space between the outer membrane and inner membrane is the intermembrane space. This space also consists of small molecules like ions and sugars, as the outer membrane surrounding it is permeable to these molecules.

b) Inner membrane- The inner membrane of the mitochondria is made up of proteins that carry out different functions. It also has enzymes necessary which catalyzes processes necessary in the production of ATP. The inner mitochondrial membrane is permeable to oxygen, carbon dioxide, and water. The inner mitochondrial membrane is the fundamental site of ATP generation. The inner mitochondrial membrane has several folds in it called Cristae, so as to increase the surface area.

d) Cristae- The inner membrane of mitochondria is folded into several folds. These folds are called cristae. The cristae increase the surface area inside the mitochondrial membrane in order to generate ATP molecules efficiently. The larger the surface, the more the space to carry out cell functions. The surface of the cristae has oxysomes attached to it, which aids the osmosis of ions. A lot of chemical reactions occur in the inner membrane on the surface of the cristae.

e) Matrix- The space in the inner membrane apart from the cristae is the Matrix. It is fluidic and contains proteins, ribosomes, enzymes, tRNA, and genomic DNA. Due to the presence of genetic material, the Mitochondrial Matrix can synthesize its own RNA and proteins. The synthesis of ATP would be incomplete without the enzymes of the matrix which aid the most important chemical cycles. 

Functions of Mitochondria

The prime function of mitochondria is to produce energy. It is the power generation plant where the nutrients turn into ATP by a chemical process. The other major roles played by mitochondria are carrying out cellular metabolism. Through cellular metabolism, three major processes are carried.

  1. Conversion of food into energy

  2. Conversion of food into molecules that are essential for the body like proteins, carbohydrates, etc.

  3. Eliminations of the wastes.

Mitochondria is also responsible for cell growth and multiplication. When there’s too much strain on an organ, performing a specific task, mitochondria multiply on its own to carry out its purpose more efficiently.

It also plays a major role in apoptosis or cellular suicide. During apoptosis, a cell does not die of an injury but a series of chemical reactions leading to the elimination of the cell.

It is also responsible for homeostasis by heat production. It happened by the process of mitochondrial uncoupling, wherein the re-entered protons in the matrix are not converted to ATP.

It stores calcium ions thus helping cell signaling. Free calcium regulates a series of chemical reactions in the cell and thus, mitochondria regulate cell signaling.

Apart from these, mitochondria regulate cell differentiation and cell senescence or the cessation of the cell division.

Facts about Mitochondria

Mitochondria are colorless organelles; therefore, they cannot be seen under a microscope unless they are dyed. So, it was Richard Altman who used and dye and observed these organelles under a microscope and explained that these structures are the basic units of cellular activity. In 1898, Carl Benda coined the term ‘Mitochondria’ for these organelles.

Red Blood Cells or RBCs lack mitochondria. As RBC uses none of the oxygen which they transport in the body, they do not possess mitochondria. Instead, they derive energy from a different chemical process called glycolysis.

Mitochondria have a lot of features common with bacteria.

FAQ (Frequently Asked Questions)

1. Why is Mitochondria called the powerhouse of the cell?

Mitochondria generate ATP from various chemical processes that drive the cell to carry out different processes. Hence it is called the powerhouse of the cell.

2. Apart from energy generation, what are the other functions of mitochondria?

Mitochondria are involved in processes like cell signaling, cell growth, apoptosis. Mitochondria has reserves of free calcium, which regulates a series of chemical reactions. It also maintains homeostasis within the cell, by heat production.

3. Why do RBCs lack mitochondria?

One of the many functions of RBCs is to carry oxygen throughout the body. However, while doing this, it does not use up any oxygen on its own. Rather it follows a simple process of generating energy from glucose molecules by a chemical process called glycolysis. Therefore, RBCs neither need mitochondria nor possess them.