HOW YOUR CELLS GENERATE ENERGY (and harmful waste products too)
The human body needs a constant supply of energy to run smoothly. Your body gathers energy from the food that you eat. The proteins, lipids, and carbohydrates that make up most of the food that you consume are broken down by your digestive system so your cells can use them in a variety of ways. That’s why the quality of food that you put in your body has a tremendous impact on your performance and how you feel throughout the day.
In this post, we will focus on the most important part of the energy production process, the generation of ATP from Glucose. ATP or Adenosine Tri-Phosphate is the energy currency of your cells that makes things happen. Everything from breathing, running, thinking, to winking requires ATP. Once an ATP molecule gives away its energy, it turns into ADP (Adenosine Di-Phosphate). In essence, all of the energy that ATP gives away is stored in a Phosphate-Phosphate bond as shown in the figure below. The third phosphate group is now gone, and the result is two phosphate groups connected to ribose, hence the name Adenosine Di-Phosphate.
The key is to constantly replenish your supply of ATP so you have adequate energy to perform all the tasks of the day. We will now examine the steps that your body takes to produce ATP after you eat food, especially carbohydrates.
THE 4 MAIN STEPS TO ATP PRODUCTION IN THE MITOCHONDRIA
Glucose is the most important energy source and it’s the main fuel in the process that recycles ADP back into ATP. Glucose mainly comes from carbohydrates, which is why it’s the biggest food group in a typical food pyramid. Carbohydrates are easily broken down by your digestive system into glucose molecules, which are then absorbed into the blood. When your body detects a rise in glucose levels in the blood, the hormone insulin is released, which opens up cells to let glucose inside them.
STEP 2: GLUCOSE IS BROKEN DOWN BY A PROCESS CALLED GLYCOLYSIS (GLUCOSE BREAKDOWN). GLYCOLYSIS RESULTS IN 1 GLUCOSE YIELDING 2 NADH MOLECULES AND 2 PYRUVATE MOLECULES
Once glucose molecules enter the cells, they undergo Glycolysis, which breaks down glucose molecules into NADH and Pyruvate. NADH is a transport molecule that takes electrons into the Mitochondria in step 4 for further processing. Pyruvate is a broken down half-piece of glucose that goes into another process to produce more NADH.
STEP 3: PYRUVATE IS SHUTTLED INTO THE MITOCHONDRIA AND ENTERS THE KREBS CYCLE
Pyruvate, which are broken down pieces of glucose, are taken into the Mitochondria to enter the KREBS CYCLE or CITRIC ACID CYCLE. The KREBS CYCLE is a complex cycle of enzymes that rips off electrons from Pyruvate to produce 4 more NADH molecules.
The KREBS CYCLE takes place inside of your Mitochondria. Inside each of the TRILLIONS of cells that make up your body, there are up to THOUSANDS of mitochondria, which means there’s up to a QUADRILLION mitochondria that power your body. (Quadrillion is 1,000,000,000,000,000). A single mitochondria is called a mitochondrion, and each mitochondrion is a tiny little engine that uses glucose and it’s parts as fuel to produce ATP.
While electrons are traveling through the ETC, positive hydrogen ions, also called protons, are pushed into the intermembrane space of the mitochondria. A pressure gradient begins to build up because there are more protons in the intermembrane space than inside the mitochondria. The pressure that builds is like the water pressure that builds on one side of a dam. A dam harnesses the water pressure to push generators. In much the same way, ATP synthase harnesses the pressure gradient of protons to convert ADP into ATP as the protons pass through the ATP Synthase to reach the inside of the mitochondrion.
And that’s it! Although this process seems pretty straight-forward, it’s not a perfect system. Unfortunately, from this seemingly everyday normal production of ATP there are harmful waste products that get generated called FREE RADICALS.
HOW DO FREE RADICALS FORM?
The mitochondrion has an imperfect system. 2-4% of the time, an electron leaks from the ETC and gets taken up by an oxygen molecule, turning the oxygen molecule into a free radical called superoxide. This is where the free radical production begins.
Superoxide by itself is a weak free radical, meaning that it’s not very reactive. It’s usually cleaned up by an antioxidant enzyme called Superoxide Dismutase (SOD). SOD mutates the superoxide into a Hydrogen peroxide, which is also a free radical, but it’s useful because your immune cells use it to kill bacteria. Hydrogen Peroxide is then converted to water by Glutathione Peroxidase.
As you can see there’s a two-step process in completely neutralizing free radicals into water. The problem arises when there’s a buildup of Superoxide and Hydrogen peroxide with not enough SOD and Glutathione Peroxidase (GSH) to eliminate them. When there is too much superoxide and hydrogen peroxide in the cells, there’s a higher chance of them transforming into more dangerous free radicals such as Hydroxyl Radicals. This buildup can happen for two reasons. Either more free radicals are being produced, or there are less antioxidant enzymes available.
Free radicals are like the carbon monoxide pollution that gets produced by a car. Just like how a car engine burns gasoline for fuel and carbon monoxide comes out of the exhaust, in much the same way, free radicals are what gets produced when energy is generated inside your cells.