4 min|Dr. Maya Kuczma
Mitochondria (Part 1): More Than Just the PowerhouseWellness, Health, Education
What is Mitochondria?
Anyone who has sat in a biology class has probably heard the line - 'mitochondria are the powerhouses of the cell'. But these tiny rod-shaped organelles are more than just energy-producing factories; they are vital to our health, and our life.
It is hypothesized that mitochondria used to be separate, free-living prokaryotic cells that were engulfed by eukaryotic cells; these separate entities began to function as one, retaining their own DNA, but living symbiotically.(1) Today, this means that our cells have both nuclear DNA, residing inside the nucleus, and mitochondrial DNA, stored within the mitochondria. The number of mitochondria within each cell varies greatly; certain cell types such as neurons, retinal cells (in the eye), heart muscle cells, and hepatocytes (in the liver), contain thousands of mitochondria, due to the high energy demands on those cells.
Mitochondria are encapsulated by an outer membrane, and have an inner, undulating membrane. The area within the inner membrane is known as the matrix. Within the matrix, adenosine triphosphate (ATP), the energy that keeps us alive, is produced. Most of our cells need ATP in order to function; therefore, we require mitochondria in order to stay alive. And we require efficient mitochondria in order thrive. Our mitochondria also play an important role in cellular communication, cellular differentiation, and regulation of cell growth and death. Basically, they are calling the shots, and if we want a healthy mind and body, we have to look to the source: our mitochondria.
How Does It Work?
On a basic level, the most important concept to grasp is that our mitochondria metabolize fatty acids and carbohydrates in order to produce energy, in the form of ATP. Skip ahead if that’s all you want to know; we’re about to deep dive into the science.
In order for carbohydrates to be used by the mitochondria, they first must be broken down into glucose, and put through glycolysis - a metabolic process that converts glucose into pyruvate. Once the conversion is complete, pyruvate is brought into the mitochondria where it will be converted into acetyl-CoA.
Fatty acids go through a process called beta-oxidation, within the mitochondria, to convert them into acetyl-CoA, NADH, and FADH2. The NADH and FADH2 will be used in the electron transport chain (ETC) within the inner membrane of the mitochondria. Acetyl-CoA is the molecule required for the first step of the Krebs cycle (also known as the Citric Acid Cycle). The Krebs cycle produces carbon dioxide (CO2), as well as more NADH and FADH2; these molecules collectively provide carbon and electrons, the building blocks the mitochondria need in order to make ATP via the ETC.
NADH and FADH2 are rich in electrons - negative charges - that will be passed along a chain of proteins within the ETC. These proteins act like a shuttle system, picking up a negatively charge electron and passing it along to the next protein. Within this system there are also positive charges known as protons; the electrons and protons must be ‘paired’ in a sense; as an electron is passed along the shuttle system, from one protein to the next, a little bit of energy is produced, and this energy moves the positively charged proton across the membrane (remember - all of this is occurring along the inner membrane of the mitochondria) and into an area known as the intermembrane space.
The energy harnessed from all of these positively charged protons moves through the ATP synthase complex (an enzyme-rich area of the membrane) and helps to convert adenosine diphosphate (ADP) and phosphate into ATP. Energy has been formed!
In addition to energy production, mitochondria also play a key role in cellular communication by serving as a physical platform for cellular signaling interactions, and via regulating certain intracellular signaling molecules, such as calcium and reactive oxygen species (ROS).(2) Through these methods, mitochondria play an important role in regulating inflammation, cell death, innate immunity, and autophagy.(3,2)
Mitochondria also serve as key sites for steroid hormone production within the adrenals, gonads, placenta, and brain.(4) The mitochondria within renal cells play a role in activating and degrading vitamin D.(5) Via regulation of intracellular calcium, the mitochondria play an important role in hormonal signaling.(6)
Now that we understand how the mitochondria work, we can see how healthy mitochondria benefit us, and we can begin to understand how detrimental it could be if they don’t work optimally. In Part 2, we are going to take a deeper look at how dysfunctional mitochondria affect our health.