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Energy, Diet and Aging
By: Peter T. Pugliese, MD
Posted: September 25, 2009, from the October 2009 issue of Skin Inc. magazine.
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Without food, of course, people would die. Energy is needed in the form of adenosine triphosphate (ATP) every second of life. A fundamental physical law states that energy can neither be created nor destroyed, but only changed from one form to another. It is also known that all the energy on the Earth comes from the sun in the form of radiant—or electromagnetic—energy, which includes light at all wavelengths. From the sun, energy is captured by plants and locked into chemical bonds in the form of sugar molecules during the process of photosynthesis. Animals eat the plants and convert the energy into meat. Humans eat the meat produced by animals, releasing the stored energy and capturing it on their ATP molecules to be used to run the thousands of physical and biochemical reactions occurring in their bodies every minute. This process of energy production and utilization is related in a subtle way to the aging process. To get the full picture, see Figure 1 to trace the pathway from the sun to ATP.
Energy and aging
If you are not familiar with mitochondria in the cell, you should be. Mitochondria are rod-shaped organelles that are about one micrometer in length with a double membrane. A cell’s specific function and energy needs determine the number of mitochondria per cell. For example, the number of mitochondria in the liver are about 1,000–2,000 per cell, making up 20% of the cell volume.3 The inner membrane is folded into a form known as cristae that is actually extended into the inner membrane called the matrix, and between the inner and outer membrane is the intermembrane space. Because the mitochondrion has its own circular DNA (mtDNA), there are four to five copies of mtDNA that encode some of the proteins of the electron transport chain (ETC). It is possible that mitochondria were primitive prokaryotic bacteria that were engulfed by an eukaryotic cell, somehow developing a symbiotic relationship.
Mitochondria are the organelles in the cell that make most of a person’s ATP. In Figure 2, the process of making ATP in the cell has been outlined, including the process in the mitochondria. This is the chloroplast stroma where the actual ATP of the leaf is made. This is a complex diagram, so just look at the two sites where the energy of sunlight is needed, and then look at the end of the diagram where ATP is produced in the conversion of hydrogen ions to ATP. This structure is ATP synthase, which is very similar to what humans have in their mitochondria. Notice also that at the first molecule where light is needed, water is being split to oxygen and hydrogen. You will see that all the energy production in the mitochondria requires the presence of oxygen, and with a constant supply of molecular oxygen, you have the potential for free radical damage.
Mitochondria generate the majority of energy from nutrients, but in the process, they generate unstable chemicals that harm both the mitochondrion itself and other components of the cell. This resulting damage is thought to play a important role in aging.
ATP and aerobic respiration
Mitochondria use oxygen to perform aerobic respiration, which generates ATP from nutrient molecules. Three key components of aerobic respiration are glycolysis, the Krebs cycle and the ETC. See Figure 3.