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Energy, Diet and Aging: The Roles of Photosynthesis and Bioenergetics in Energy

By: Peter T. Pugliese, MD
Posted: September 10, 2009, from the October 2009 issue of Skin Inc. magazine.

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What about the hydrogen ions? They pass out of the thylakoid space through special channels in the membrane, and the movement of these ions through the channels provides the energy to make ATP synthetase enzymes, where ATP molecules are made. A steady flow of electrons from the water, through the membrane and finally to NADPH produces an electric current that provides the energy for the making of ATP and NADPH. It is the energy in ATP and NADH that is used for the making of carbohydrates in stage two of photosynthesis, the carbon cycle.

The second stage of photosynthesis is sometimes referred to as the carbon-fixing process because carbon from carbon dioxide is fixed into the beginnings of simple sugar, also called carbohydrate molecules. In the stroma, different enzymes use the carbon dioxide molecules and hydrogen ions made during the light dependent phase to assemble sugar fragments that are only half of a glucose molecule (just three carbon atoms, instead of the six carbons in a complete glucose molecule). This is really the end of photosynthesis, but a sugar molecule has not yet been created. The three-carbon half-glucose molecule is pushed out of the chloroplast into the waiting arms of an eager enzyme that joins these little fragments into real six-carbon glucose molecules. The glucose molecules serve as building blocks for other carbohydrates, such as sucrose, lactose, ribose, cellulose and starch. Then when the leaf gets eaten, the glucose goes into animal cells where it can be used to make fats, oils, amino acids and proteins.

Bioenergetics and ATP

ATP is part of a more comprehensive topic called bioenergetics. When a student is first introduced the subject, it is either love or hate at first sight. In my case, initially I didn’t like it at all; perhaps it took me more than 30 years to love it. Keep in mind that every biochemical reaction in the body relates in some manner to the topic of bioenergetics. Energy is not an easy term to define since the only thing seen or felt is the transfer of energy. Wikipedia has a very good explanation for energy: “In physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law. Eight different forms of energy exist to explain all known natural phenomena. These forms include (but are not limited to) kinetic, potential, thermal, gravitational, sound, light, elastic and electromagnetic energy. The forms of energy are often named after a related force.”

A key concept to remember is that any form of energy can be transformed into another form. For example, light can be transformed to electricity, and heat to kinetic energy, or motion, as in driving a car. In order to measure heat, a unit must be used, just as pounds or grams are used when measuring the weight of an object. In energy, the term “joule” is used. The definition of a joule is the work done to produce the power of one watt continuously for one second; or one watt second. First, one watt as the rate at which work is done is defined when an object is moved at a speed of one meter per second against a force of one newton. A newton is the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second per second. Hang on a bit, and it will all be put together.

Let’s change now from basic terms to the real world of bioenergy. As learned earlier in the article, all energy comes from the sun, then into plants and made into sugars. Sugar can be taken and made into a sweet drink. For example, you drink an orange soda that contains 100 g of glucose, actually sucrose. The glucose is metabolized by the body, and the energy derived is converted to ATP. How much energy as ATP are you going to get from that amount of glucose? A little math will show you a surprising answer.