What is activation energy and how does it relate to cell metabolism?
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Every living cell performs continuously thousands of different chemical reactions. Taken nutrients are transformed into a multitude of cell specific components. In this way, sugars, amino acids and their precursors, organic acids, nucleotides, lipids and other substances are produced. The totality of these reactions is summarized as the cell metabolism. In every chemical reaction, a bond is either formed or broken. This process does generally consume energy, consequently, the cell's metabolism and its energy balance to have be regarded as interdependent parameters. Every covalent bond of a molecule contains energy that is set free upon breaking down and that can subsequently be used for other purposes. It could, for example, be used for the formation of a new bond or it could be transformed into another form of energy like movement, warmth, light or electrical energy. Most chemical bonds and nearly all that occur within a cell are stable under physiological conditions. Hence, activation energy is needed for the break-down of a molecule. In chemical laboratories, high temperatures, high pressures or certain inorganic or organic catalysts are normally used. \n\nThe term activation energy refers to the minimum amount of energy required for a chemical reaction to occur. Most reactions require that atoms and molecules crash into each other with a great deal of force. These violent collisions must occur with enough energy to cause the chemical bonds within the molecules to be weakened or broken. When this occurs, the reactant molecules form an activated complex from which the product molecules are formed. Depending on the strength of the bonds within the reactant molecules the activation energy can be quite large, making the activated complex difficult to form.
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You are probably referring to metabolism.  Metabolism is a collection of chemical reactions that takes place in the body's cells to convert the fuel in the food we eat into the energy needed to power everything we do, from moving to thinking to growing. Specific proteins in the body control the chemical reactions of metabolism, and each chemical reaction is coordinated with other body functions. In fact, thousands of metabolic reactions happen at the same time - all regulated by the body - to keep our cells healthy and working.
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All body processes require energy to run properly. When the body is expending more energy than it is taking in (e.g. when exercising), body cells rely on internally stored energy sources, like complex carbohydrates and fats, for energy. The first source the body turns to is glycogen, which is a complex carbohydrate created by the body. When that source is nearly depleted, the body begins lipolysis, the metabolism of fat for energy. In this process, fats, obtained from fat cells, are broken down into glycerol and fatty acids, which can be used to make energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.\n\nFats are also secreted by the sebaceous glands (in the skin).
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Chemical energy is the amount of heat released from a chemical reaction to do work.  Since not all heat will be utilized, you will have a loss of heat which will lower the efficiency of the process. \n\nIn closer detail to a chemical reaction, studies are made on different reactions to determine the amount of energy released.  One of the best tools to determine this is to look at an Energy vs. time graph.  The barrier to overcome for a chemical reaction to come to completion would be the activation energy (slope to peak); this is the amount needed for a chemical reaction to proceed.  Once the requirements are met, the release of energy (negative slope of the same curve from apex), the difference between starting energy (baseline from beginning before additional energy was applied) and ending energy (the bottom of the slope where m = dE/dt = 0).  If the difference of energy is positive, the reaction is endothermic.  If negative, the reaction is said to be exothermic.  Exothermic reactions are used in many applications to power devices such as steam engines, and gasoline motors which are about 20-30% efficient at most.  Rockets, on the other hand are really inefficient yet they are our main means of propelling stuff into space.\n\nOn the other hand, more subtle means of chemical energy exists in fuel cells and batteries; they power devices through the transfer of electrons and a porous media of some sort connecting the two cells.  Although it is an alternative that to mixing two substances and sparking an explosion.\n\nIf a material spontaneously combusts, it is said that the requirements of meeting the activation energy has been met; look at the reaction of Na(s) with O2(g).  Sodium most readily gives up an electron which the oxygen will take.  Oxygen is more electronegative (It loves electrons more than Sodium).  Oxygen will prefer to take electrons from Sodium as opposed from it's own because Sodium would feel more satisfied with having one less electron.  Oxygen - Oxygen bonding on the other hand would mean that oxygen would have to share 4 electrons to feel satisfied (remember, octet rule - higher stability with complete s, p, d, orbitals filled).  So what does this mean?\n\nChemical energy is due to the release of energy due to trying to BEST satisfy the conditions of the electron-nucleus relationship.  If the nucleus requires 10 electrons, they are going to be nearby but in a highly defined probable region where they will linger to make the nucleus feel happy.  If another buddy (compound) comes along and offers the POTENTIAL for a better and more STABLE life, the substance will jump on it, thus reducing the potential energy of the whole substance.\n\nAlthough, look at this you would think chemical energy would even come from nuclear power plants.  But, don't let it fool you.  Nuclear power is a different beast itself.  It does not arise from chemical reactions but from decay of nucleus to produce energy.
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Cellular respiration is the process of oxidizing food molecules, like glucose, to carbon dioxide and water. The energy released is trapped in the form of ATP for use by all the energy-consuming activities of the cell.\nThe process occurs in two phases:glycolysis, the breakdown of glucose to pyruvic acid; the complete oxidation of pyruvic acid to carbon dioxide and water.\n\nIn eukaryotes, glycolysis occurs in the cytosol. The remaining processes take place in mitochondria. \n\nsee link.
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Kinetic Energy\nKinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another). To keep matters simple, we will focus upon translational kinetic energy. The amount of translational kinetic energy (from here on, the phrase kinetic energy will refer to translational kinetic energy) which an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object. The following equation is used to represent the kinetic energy (KE) of an object.\n                     \nke=1/2*m*v^2\n\nwhere m = mass of object\n\nv = speed of object
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Wow... that's a question that could be answered on many different levels, and you're optimistic as hell to think you can get a "real" answer here. Basically, an enzyme provides a micro-enviroment that is very conducive to the formation of an intermediate form that leads from the substrate to the product. Another way of saying this is that an enzyme, like any other catalyst, lowers the activation energy of a reaction.\n\nBut seriously, dude. You're asking for a course in biochemistry here. Try Stryer, or any other classic biochem textbook, for a more thorough answer.
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Metabolism is a measure of how quickly chemical reactions take place in the body. (Since these require energy it is often referred to syonmously as energy use). \n\nDifferent people have different metabolic rates, mostly based on the proportion of their body weight that is made up of lean muscle mass which one of the most metabolically active in the  body (the nervous system and the liver are more active but make up smaller percentages of the body so their effect is neglegable by comparison).\n\nWhen energy is generated from food storage (glocose or fatty acid chains), a couple of different "metabolic" pathways can be taken. First gluclose can be converted anerobically into pyruvate and two high-energy ATP andeosene-tri-phospate molecules. Then it may be further processed in a mitochondria in a process called the Krebs cycle into ATP, CO2, and water. Fatty acid chains, unfortunately, can only be processed aerobically. After some pre-processing they can also enter the Krebs cycle.
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The contraction phenomenon in muscular cells are mostly due to interaction of two elements, ie, Actin and Myosin. Their interaction are powered by some molecules called ATP. The ATP is produced in some cellular structures called mitochondria. The role of food for human is to produce energy. Energy is produced by hydrolyzing of ATP.
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From respiration: Here, glucose molecules in the cell are broken down; the molecules have strong bond between them and so when they are broken, energy is provided(by mitochondria) and when new molecules are formed, energy is released, which the cell uses for various processes.\n\nFrom protein synthesis: It occurs on the ribosomes in the cytoplasm, and aminoacids are combined to form proteins and this releases energy.\n\nFrom ATP(adenosine tri-phosphate): The ATP molecule is a packet of energy which stores the energy released during any process going on in the cell and then releases the energy as and when required by the cell.
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both are needed for cellular respiration\n\noxygen + glucose(food)--> carbon dioxide + water+ energy
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That really depends on what kind of chemical reactions you are talking about.  If you want to know where metabolism takes place (breaking down sugars into energy), that would be in the mitochondria.  Synthesis of proteins occurs on the ribosomes.  Degradation of proteins occurs in the lysosomes.  Synthesis of DNA and RNA occurs in the nucleus.  Each part of the cell is involved in very important chemical reactions.
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the minimum amount of energy required to start a reaction
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Enzymes accelerate the rate of the reaction. When the enzymes are heated, they reach their optimum point. They are activated and thus produce a faster rate of reaction.
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This is basic biochemistry.  All cells (really, all bacteria, all fungi, all plants, all animals) use glucose or other simple sugars as a main source of fuel for energy generation.  (Some will argue that plants actually produce glucose, they both produce and consume it).  The process of glucose breakdown is glycolysis, and it generates energy in the form of ATP, and converts molecules such as NADH to NAD+.  This electron loss gets passed through the electron transport chain  in the mitocondria to generate more ATP.  \n\nCarbohydrates include complex and simple sugars.  Simple sugars can be broken down directly in cells, there are specific receptors that bring in the sugar.  Complex carbs such sucrose (a disaccryide, or a molecule containing two simple sugars) just contain more than one simple sugar in a chain.  They are broken down in the gut by specific enzymes that break the chain and release simple sugars.  Starch is a form of a carbohydrate, but not digestable to mammals, because we lack the enzyme to break it down.  Some bacteria don't though, and they live inside the gut of some mammals such as cows, and when cows eat grass, the starch is broken down by the bacteria and some of it is released into the gut.  So thats why mammalian herbavours exist.  \n\nFat metabolism.  Fats are long carbon chain connected at one end, usually three are connected to glycerol, this is called a triglyceride, and is a perferred form of storage.  Fats are broken down by chopping the carbon chain and generating energy.  Fat burning is slow and fat is a backup fuel source; the primary being simple sugars. \n\nProtein metabolism.  Proteins are digested by proteases in the gut, and the free amino acids are absorbed into the blood stream, where they can enter cells.  Cells can utilize amino acids for energy, but it's not that efficient.  Instead cells utilized amino acids for building new proteins; including the 'essential' amino acids, those that can't be generated by mammalian cells (we lack the enzymes).  So some amino acids are absolutely critical for our well-being.  \n\nLow carb diets simply don't have much carbs, and force the body to switch to fat to burn (in theory).  In reality it doesn't work too well.  During initial exercise, muscles use glycogen, a stored form of glucose, for energy. Also fat is utilized, and a bit of protein.  After 2 hours of exercise (or so, depending on the person), muscle glycogen is depleted, and body must use fat and glucose and protein.  If you do not intake glucose during this exertion, your performance will rapidly drop off; you can only burn so much fat at a time.  So the best advice for fat burning is exercise (at 60-70% max heart rate) for an hour or two, 3, 4x a week, and keep hydrated with water or gatoraid.  \n\nHigh carb diets make it easier for long term exercise by increasing the amount of muscle glycogen.
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The cells takes up glucose that you eat.  Glucose enters Glycolysis and the Krebs Cycle.  These are both reactions that convert glucose to ATP.  ATP has three phosphate bonds.  Bonds hold atoms together and they require energy.  Our bodies then break the third phosphate bond (it holds the most energy).  When this energy is released from the bond, we can use it for energy.
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The sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material.\n\nMy Adice to you: You seem to be doing a researh of some scientific sort. I recommend you take advantage of the internet which could help you in this regard. Try accessing an online Encyclopedia.\n\nGood Luck!