Cellular Respiration and CoQ10 - Part 1
When nutrients are broken down by the body into simpler components, they can then either be stored, or metabolized for energy. For example, carbohydrates are broken down into individual sugar molecules, called monosaccharides. For energy production, they are then passed through a series of metabolic pathways, which are in total referred to as cellular respiration. These reactions eventually produce adenosine triphosphate (ATP), which is the body’s main source of readily available energy.
This process consists of 3 steps, each of which is a series of reactions. Following along with the image at the bottom of this page may be helpful when reading about these steps. The first step is called Glycolysis, in which sugar molecules are broken down into intermediate products, which can then by passed to the next step. The second step is called the Krebs Cycle, or the Citric Acid Cycle. This step is referred to as a cycle, because the series of reactions forms a loop. This step is used to generate high energy molecules, which then can be passed to the third and final step.
The final step, called oxidative phosphorylation (also referred to as the electron transport chain), is where the vast majority of ATP is generated. This is also where CoQ10 plays a vital role. The first two steps were used to generate energetic intermediates, along with a small amount of ATP. This third step is where those high energy products (e.g. NADH and FADH2) are now used to generate large amounts of ATP. For reference, the typically cited ATP production for each step is as follows – 2 ATP from glycolysis, 2 ATP (or GTP) from the Krebs Cycle, and 32 ATP from oxidative phosphorylation. In order to better follow along with the description of the electron transport chain’s processes, it may be helpful to view the image provided in Part 2 of this article.
The electron transport chain consists of a series of proteins embedded in the inner membrane of the mitochondria. These proteins are grouped into a series of 4 complexes, along with the protein actually used to generate ATP, called ATP Synthase. The purpose of the 4 complexes is to take high energy electrons produced by the previous steps, and pass them along, extracting energy along the way. Complexes 1 and 2 accept electrons from the intermediates that were generated and pass them to Complex 3, and finally the electrons are then passed to Complex 4.
CoQ10 is vital to this process. It functions to accept electrons from Complexes 1 and 2, and carries them to Complex 3. Cytochrome C serves a similar role to CoQ10, as it carries electrons from Complex 3 to Complex 4. Oxygen is the final acceptor of the electrons that have passed through these complexes, and Complex 4 facilitates this reaction. Complex 4 passes the electrons to the O2 that you breathe, ultimately generating water. This is why we need oxygen to live!
We have examined how electrons move through the electron transport chain, but how does this actually produce ATP? Why did we pass electrons through the chain in the first place? The reason is because these protein complexes can utilize the energy in the electrons in order to pump hydrogen ions (H+) across the inner mitochondrial membrane, forming a large concentration gradient across the membrane. This is the main goal of the electron transport chain to this point – to form the H+ gradient across the membrane.
To continue reading, please view Part 2 of this article, also listed under the Blogs section.
Image source: https://old-ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled/aerobic-overview.html