Question

What is the function of mitochondria in a cell?

Answer 1

The cell is the structural and functional unit of life. The cells are of mainly two types- Prokaryotic and Eukaryotic. The Prokaryotic cells are the primitive types of cells that are common among the microorganisms like the bacteria. These cells lack a well-organized nucleus and the cell organelles like chloroplasts, mitochondria, Golgi bodies, etc.
The Eukaryotic cells are the advanced type of cells that have a membrane-bound nucleus, and cell organelles like Golgi bodies, mitochondria, lysosome, etc.
The mitochondria are double membrane-bound organelles that are found in the eukaryotic cells.

Complete answer:
The mitochondria are the “powerhouse” of the cell.
Energy production in the mitochondria occurs around its inner membrane with the help of a particular chain of complexes that transfer electrons and protons. The mitochondria are the centers for metabolic oxidative reactions to generate the reduced coenzymes ($NADH_2$ and $FADH_2$) which, in turn, are utilized in ETC to liberate energy in the form of ATP.
It is majorly concerned in the cellular respiration processes, which ultimately convert the consumed food into energy. The energy produced is utilized for various activities in the body.
Apart from this, the mitochondria are also responsible for heat production of the body. This is achieved by a phenomenon called mitochondrial uncoupling. The energy production in mitochondria occurs specifically due to two processes: Oxidative phosphorylation and the ETC. This mitochondrial transport of electrons is tightly coupled with oxidative phosphorylation (ATP synthesis). Now, certain agents uncouple these two reactions. The uncouplers actually increase the permeability of the inner mitochondrial membrane to protons. The result is that ATP synthesis stops.
The mitochondria is also believed to help in cellular growth. The mitochondria are self-replicating organelles and can increase their numbers under stressful conditions and help in enhanced energy production. They also play a crucial role during programmed cell death or apoptosis.

Note:
One should be aware of the structure of mitochondria:
1. The mitochondria are a double membrane-bound structure.
2. Under normal microscopic conditions, they cannot be viewed as they are colorless organelles. They are thus stained by a vital stain Janus Green to make them visible for observation.
3. Outer membrane is chemically 40% lipid and 60% proteins and the inner membrane is 80% protein and 20% lipid.
4. The inner membrane is thrown into many finger-like projections that helps to increase the surface area for performing vital metabolic reactions.
5. The matrix contains a single circular dsDNA molecule, a few RNA molecules, and 70S ribosomes.