Sources of Energy + Energy Carriers

Sources of Energy

Oxidation is a release of energy. Burning wood (in the presence of oxygen) is oxidation because the wood, made mostly of C-H bonds, loses electrons to oxygen from the air, forming the CO₂ molecule (low energy). Note: much of the E is ‘lost’ as heat and light.

There is more available energy in bonds where the electrons are further from the nucleus of the atom. Anytime a molecule has oxygen, the oxygen pulls the electron very close, causing a reduction in available potential energy. This is why fat, which contains no oxygen (has long chains of hydrocarbon) releases more energy through oxidation.

Oxidation occurs through the complete or partial loss of electrons, for our purposes, this mostly happens through the loss of hydrogen atoms, or the addition of oxygen (because oxygen pulls the electrons closer to it). Remember, when one molecule is oxidized, another must be reduced, again, oxygen is often involved as it tends to ‘steal’ the electrons

Burning glucose is the transfer of e^- to oxygen to produce CO₂and water. CO₂and water are fully oxidized and do not contain any more chemical energy.

This could happen quickly (like a fire) but, again, this would result in E ‘lost’ as heat and light.

Instead, we carry out oxidation in a series of enzyme-catalyzed reactions that release small amount of energy that can be transferred to Alternate Energy Carriers.

Alternate Energy Carriers

During metabolic processes, there will be other energy carrier molecules besides ATP. When breaking down food molecules for energy, animals often use enzymes that act as Energy Carriers in redox reactions to facilitate the transfer of energy.

Nicotinamide Adenine Dinucleotide (NAD⁺)

NAD⁺ is a coenzyme: a non-protein, organic molecule that plays an accessory role in enzyme-catalyzed processes often by acting as a donor or acceptor of electrons. NAD⁺plays an important role in Glycolysis, the first step in Aerobic Cellular Respiration, reducing glucose by stealing 2 high energy electrons (hence energy carrier) and two H⁺ ions in the following reaction:

NAD⁺ + 2H⁺ + 2e^- --> NADH + H⁺

The higher energy NADH can then transfer the energy for later use. Besides NAD+, there are other energy carrying molecules, such as FAD and NADP⁺.

Textbook Practice:

p. 151-155#1-5, 7-9

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