Energy and Metabolism

Energy and Metabolism
Energy releasing processes, ones that "generate" energy, are termed exergonic reactions. Reactions that require energy to initiate the reaction are known as endergonic reactions. All natural processes tend to proceed in such a direction that the disorder or randomness of the universe increases. The fact that energy expenditure is related to body weight and even more closely to fat-free mass is well recognized. Evidence also supports the independent contribution of fat mass to the variance in energy expenditure. Therefore, it is not surprising that changes in body weight and composition induce proportional changes in energy expenditure. Despite this, it is now becoming apparent that factors other than body composition can influence the changes in energy expenditure that occur in response to weight loss.
Skeletal muscle is important in the regulation of energy expenditure and constitutes an important site for the utilization of both carbohydrates and lipids. Because the synthesis and re-synthesis of ATP within skeletal muscle is the result of five energy-generating pathways, and because there are rate-limiting enzymes in each of these pathways, it could be speculated that these enzymes influence energy expenditure. Doucet et al. hypothesized that inter-individual differences in the decrease in key enzymes involved in energy expenditure might be partly responsible for the changes in energy metabolism that occur in response to weight loss. This current study performed by some Canadian researchers investigated the relation between skeletal muscle enzymes and 24-hour energy metabolism in obese persons before and after weight loss.
Potential energy is stored energy, whereas kinetic energy is energy of motion: laws of thermodynamics govern movement of energy; according to the first law of thermodynamics, energy cannot be created or destroyed, although it can be transferred or changed from one form to another; total energy in universe has remained constant, but it is continuously becoming more diffuse through the universe.
The second law of thermodynamics states that when energy is converted from one form to another, some usable energy, some is degraded into a less usable form, i.e. heat.
It should be mentioned that entropy is a measure of disorder or randomness, it is organized, usable energy has low entropy, whereas disorganized entropy such as heat has high entropy. All energy conversions have efficiencies <100%. Compare the efficiency of gas-powered internal combustion engines (20-30%) with aerobic respiration (67%).
Enthalpy is the total potential energy of a system include bond energy is amount of energy required to break a chemical bond and total bond energy is equivalent to the total potential energy of the system, a quantity known as enthalpy. Free energy is energy that is available to do cellular work. It means that free energy is the amount of energy available to do work under the conditions of a biochemical reaction. Entropy and free energy are related inversely. Usually free energy increases during an endergonic reaction. It must occur in such a way that energy can be supplied from the surroundings. In cells, exergonic reactions are often coupled to endergonic reactions in order to provide the energy to drive them.
Another type of reaction is ATP which means the energy currency of the cell. It includes the coupling of a phosphate group to a molecule which is called phosphorylation, and it links exergonic and endergonic reactions. In any chemicals reaction bonds are either formed or broken. Since bonds are a form of energy all reactions result in either the absorption or release of energy. Exergonic reactions are ones that release energy; these reactions will usually occur spontaneously since they do not require energy to occur. On the other hand, endergonic reactions absorb energy to form bonds, so they do not occur spontaneously. Instead, they occur only if energy is available to be used in the reaction.
Some exergonic reactions do not occur spontaneously. Instead, they require a small input of energy from some outside source to cause the reaction. This outside energy is called the activation energy of the reaction. Exergonic reactions also have an activation energy
which is considerably higher than the activation energy for most exergonic reactions. Many reactions in cells are endergonic, so cells require a method of storing energy until it is needed in a chemical reaction.
Enzymes allow many chemical reactions to occur within the homeostasis constraints of a living system. Enzymes function as organic catalysts. A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst.
Enzymes can act rapidly, as in the case of carbonic anhydrase (enzymes typically end in the -ase suffix), which causes the chemicals to react 107 times faster than without the enzyme present. Carbonic anhydrase speeds up the transfer of carbon dioxide from cells to the blood. There are over 2000 known enzymes, each of which is involved with one specific chemical reaction. Enzymes are substrate specific. The enzyme peptidase (which breaks peptide bonds in proteins) will not work on starch (which is broken down by human-produced amylase in the mouth).
The principal energy laws that govern every organization are derived from two famous laws of thermodynamics. The first law of thermodynamics is often called the Law of Conservation of Energy. It states that in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy. The second law, known as Carnot's principle, is controlled by the concept of entropy. The third law of thermodynamics states that if all the thermal motion of moleculars could be removed, a state called absolute zero would occur.
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