Key Pointers

  • Mitochondria is the powerhouse of the cell and NAD+ is essential for its functioning.
  • Mitochondria produce a major part of cellular energy.
  • Mitochondria is a self-sustainable organelle.
  • Mitochondria is the storehouse of Ca+2.
  • Mitochondria regulate important enzymes in stressful situations.

A cell is composed of many organelles which perform all its functions. Through organelles, the cell performs its function under the law “Division of labor”.

Organelles include:

  • Nucleus
  • Mitochondria
  • Endoplasmic reticulum
  • Ribosomes
  • Golgi apparatus
  • Lysosomes

Our main focus will be on:


Mitochondria is the powerhouse of the cell. All the energy used by the cell for the various functions is generated by mitochondria. The optimal ratio of NAD/NADH is essential for the proper functioning of the mitochondria. The biosynthesis of NAD+ in the mitochondria is modified in response to the environmental stimulus. Even upon tremendous insufficiency of NAD+, mitochondrial NAD+ levels can be conserved at least 24hours or even up to 3 days. It shows that mitochondria continue to produce ATP and supply energy until their membrane is breached.

Structure of Mitochondria

Mitochondria is a double membrane structure and can vary in shape in different cells and organisms.

The inner and outer layer of the membrane is a form of phospholipid and protein.

There are five structures present in mitochondria:

  • The outer layer of the membrane of Mitochondria
  • The inter-membrane space b/w inner and outer layer of Mitochondria
  • The inner layer of the membrane 
  • Cristae infoldings of the inner layer of the membrane
  • The matrix inner space, where most of the chemical reactions take place.

The outer layer of the membrane maintains the structure of Mitochondria intact and contains pores for protein and other chemical exchange into inner space for energy production.

Inter-membrane space is the mitochondrial space where the proton is being pumped, and this produces an energy gradient between the inner layer and this space.

The inner layer of the membrane contains three types of protein.

  • Those that perform Electron transport chain reaction.
  • ATP synthase generates ATP in the matrix.
  • Special transport protein. It regulates metabolic pathways.

Inner membrane structure contains cristae which increase the surface area of the membrane. Matrix is 2/3 of total mitochondria and contains ATP SYNTHASE and Ribosomes, DNA, and RNA.

The function of Mitochondria

As mitochondria are a powerhouse of the cell, the most prominent function of Mitochondria is the production of energy currency ATP.

Following are the functions of Mitochondria:

  • ATP production
  • Energy conversion
  • Heat production
  • Pyruvate and citric acid synthesis
  • NADH/ FADH2 Electron transport chain reaction.
  • Ca+² storage 
  • Cell proliferation regulator

Age-related changes in Mitochondria occur as a decline in the function of mitochondria. With the advancement in age, mitochondria 

DNA volume, integrity, and function are lost due to the accumulation of mutation and oxidative damage due to reactive oxygen species (ROS). Mitochondria play an important role in mediating and amplifying the oxidative stress that drives the aging process.

Mitochondrial function lost in stress and 

  • production of ROS increased which accelerate the Aging process.
  • ROS scavenging enzymes decline with aging.
  • Mutation of DNA occurs during aging.
  • A vicious cycle starts and increases the production of ROS.
  • Mitochondria are involved in programmed cell death.

During stress conditions, Ca+² ions accumulate in the cell pour out of mitochondria. Excess Ca+²cause stimulation of various enzymes. These enzymes the cell's main components protein, nucleic acid, etc. 


Mitochondria is a powerhouse of the cell which generates energy for maximum function. Energy is in the form of energy currency, ATP. Mitochondria also regulate numerous functions like heat production, oxidative phosphorylation, and ions. Mitochondria plays important role in the aging process through the signaling pathway. It produces ROS in stressful situations. Reactive oxygen species produce free radicals. Free radicals cause mutations in DNA, neoplasm formation, and the aging process.


  1. Harman D. Aging: a theory based on free radical and radiation chemistry. J Gerontol. 1956;11(3):298–300.
  2. Müftüoglu M, et al. Mitochondrial complex I and IV activities in leukocytes from patients with parkin mutations. Mov Disord. 2004;19(5):544–548.
  3. Herbener G. A morphometric study of age-dependent changes in mitochondrial populations of mouse liver and heart. J Gerontol. 1976;31(1):8–12
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