Metabolism:

Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism uses energy to construct components of cells such as proteins and nucleic acids.
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Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism


The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release energy. As enzymes act as catalysts they allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells.

Taken fron: http://en.wikipedia.org/wiki/Metabolism

Metabolism Basics

Our bodies get the energy they need from food through metabolism, the chemical reactions in the body's cells that convert the fuel from food into the energy needed to do everything 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.
Metabolism is a constant process that begins when we're conceived and ends when we die. It is a vital process for all life forms — not just humans. If metabolism stops, a living thing dies.
Here's an example of how the process of metabolism works in humans — and it begins with plants. First, a green plant takes in energy from sunlight. The plant uses this energy and the molecule cholorophyll (which gives plants their green color) to build sugars from water and carbon dioxide in a process known as photosynthesis.
When people and animals eat the plants (or, if they're carnivores, when they eat animals that have eaten the plants), they take in this energy (in the form of sugar), along with other vital cell-building chemicals. The body's next step is to break the sugar down so that the energy released can be distributed to, and used as fuel by, the body's cells.
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taken from
http://kidshealth.org/parent/general/body_basics/metabolism.html




.What is metabolism?
Metabolism is a set of chemical reactions that occur in cells of the body. The transformation of energy metabolism in the foods we eat into the fuel we need to everything we do, from moving to think or grow. Specific proteins in the body control the chemical reactions of metabolism, and all these chemical reactions are coordinated with other body functions. In fact, our bodies take place simultaneously thousands of metabolic reactions, all of which are regulated by the body, which enable our cells are healthy and functioning properly.
. Every time you bite into a sandwich or sip a fruit smoothie, your body has to work hard to process the nutrients you have consumed. Long after you leave the bowl clean as a whistle and digieras food you've ingested nutrients will become the basic components and fuel your body needs to function and grow. Your body gets the energy it needs from food through a process called metabolism.
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taken from.http://kidshealth.org/teen/en_espanol/cuerpo/metabolism_esp.html

coenzymes
Metabolism involves a vast array of chemical reactions, but most fall under a few basic types of reactions that involve the transfer of functional groups. This common chemistry allows cells to use a small set of metabolic intermediates to carry chemical groups between different reactions. These group-transfer intermediates are called coenzymes. Each class of group-transfer reaction is carried out by a particular coenzyme, which is the substrate for a set of enzymes that produce it, and a set of enzymes that consume it. These coenzymes are therefore continuously being made, consumed and then recycled.
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Coenzymes are small organic molecules that transport chemical groups from one enzyme to another.

what is metabolism?

Your metabolism, experts say, involves a complex network of hormones and enzymes that not only convert food into fuel but also affect how efficiently you burn that fuel.
"The process of metabolism establishes the rate at which we burn our calories and, ultimately, how quickly we gain weight or how easily we lose it," says Robert Yanagisawa, MD, director of the Medically Supervised Weight Management Program at Mount Sinai Medical Center in New York.
Of course, not everyone burns calories at the same rate.
Your metabolism is influenced by your age (metabolism naturally slows about 5% per decade after age 40); your sex (men generally burn more calories at rest than women); and proportion of lean body mass (the more muscle you have, the higher your metabolic rate tends to be).
And yes, heredity makes a difference.
"Some people just burn calories at a slower rate than others," says Barrie Wolfe-Radbill, RD, a nutritionist specializing in weight loss at New York University Medical Center.
Occasionally, Yanagisawa says, a defect in the thyroid gland can slow metabolism, though this problem is relatively rare.
And here's a fact that may surprise you: the more weight you carry, the faster your metabolism is likely running.
"The simple fact is that the extra weight causes your body to work harder just to sustain itself at rest, so in most instances, the metabolism is always running a bit faster," says Molly Kimball, RD, sports and lifestyle nutritionist at the Oscher's Clinic's Elmwood Fitness Center.
That's one reason it's almost always easiest to lose weight at the start of a diet, and harder later on, Kimball says: "When you are very overweight your metabolism is already running so high that any small cut in calories will result in an immediate loss."
Then, when you lose significant amounts of body fat and muscle, your body needs fewer calories to sustain itself, she says. That helps explain why it's so easy to regain weight after you've worked to lose it.
"If two people both weigh 250 pounds, and one got there by dieting down from 350 and the other one was always at 250, the one who got there by cutting calories is going to have a slower metabolism," says Yanagisawa. "That means they will require fewer calories to maintain their weight than the person who never went beyond 250 pounds."​

taken from: http://www.webmd.com/fitness-exercise/guide/make-most-your-metabolism

What Is Metabolism?
Metabolism (pronounced: muh-tah-buh-lih-zum) is a collection of chemical reactions that takes place in the body's cells. Metabolism converts 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.
Metabolism is a constant process that begins when we're conceived and ends when we die. It is a vital process for all life forms — not just humans. If metabolism stops, living things die.
Here's an example of how the process of metabolism works in humans — and it begins with plants. First, a green plant takes in energy from sunlight. The plant uses this energy and a molecule called cholorophyll (which gives plants their green color) to build sugars from water and carbon dioxide. This process is called photosynthesis, and you probably learned about it in biology class.
When people and animals eat the plants (or, if they're carnivores, they eat animals that have eaten the plants), they take in this energy (in the form of sugar), along with other vital cell-building chemicals. The body's next step is to break the sugar down so that the energy released can be distributed to, and used as fuel by, the body's cells.
After food is eaten, molecules in the digestive system called enzymes break proteins down into amino acids, fats into fatty acids, and carbohydrates into simple sugars (e.g., glucose). In addition to sugar, both amino acids and fatty acids can be used as energy sources by the body when needed. These compounds are absorbed into the blood, which transports them to the cells. After they enter the cells, other enzymes act to speed up or regulate the chemical reactions involved with "metabolizing" these compounds. During these processes, the energy from these compounds can be released for use by the body or stored in body tissues, especially the liver, muscles, and body fat.
http://kidshealth.org/teen/nutrition/general/metabolism.html