Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP) is a vital energy-carrying molecule found in the cells of all living organisms, serving as a fundamental fuel source necessary for life. It captures and releases energy derived from the breakdown of food, enabling essential cellular functions. Structurally, ATP is a nucleotide composed of adenine, ribose sugar, and three phosphate groups. The energy stored in ATP is concentrated in the bonds between these phosphate groups, particularly between the second and third phosphates, which allows for efficient energy release during hydrolysis. When ATP is broken down, it transforms into adenosine diphosphate (ADP), which can be regenerated back into ATP through the oxidation of carbohydrates and fats during cellular respiration. This continuous cycle of ATP breakdown and regeneration is crucial, as organisms require a consistent supply of energy for various activities, including muscle movement, substance transport across membranes, and metabolic reactions. Remarkably, the human body can turnover its ATP supply multiple times per minute, highlighting its importance in daily physiological functions.
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Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP) is an energy-carrying molecule that exists within the cells of all living organisms. By capturing and releasing the chemical energy that results from the breakdown of food, ATP provides the essential fuel that makes life possible at the most basic level. The energy supplied by ATP is one of the fundamental building blocks of life. Without it, no living organisms could exist.
Historical Background
Although ATP has existed since life first appeared on Earth, human awareness and understanding of the substance is a relatively recent development. The presence of ATP in muscle tissue was first discovered by Alan Drury and Albert Szent-Györgyi in 1929. Together, Drury and Szent-Györgyi studied the newfound substance and determined its effect on the heart and blood vessels. More than ten years later, in 1941, German-born American biochemist Fritz A. Lipmann published the first detailed explanation of ATP's primary function of storing and distributing energy on the cellular level. This achievement was so important that Lipmann was eventually awarded the Nobel Prize in physiology or medicine for his work. Since that time, ATP has consistently remained a popular subject of study for scientists around the world.
Form and Function
ATP is a type of molecule known as a nucleotide. Each ATP nucleotide is made of a combination of carbon, hydrogen, nitrogen, oxygen, and phosphorus atoms. Together, these atoms form a structure consisting of a molecule of a base called adenine, a molecule of ribose sugar, and three phosphorus atoms. Each phosphorus atom lies at the center of a larger group of atoms called a phosphate. These three phosphates are attached to the ribose and linked to one another by a chemical bond called a phosphate bond. It is within these bonds that the energy of ATP is held. Each of the three phosphate bonds in an ATP molecule holds a different amount of energy. The bond between the ribose and the first phosphate contains the least amount of energy, while the bond between the first and second phosphates contains a moderate amount of energy, and the bond between the second and third phosphate contains the most energy. The amount of energy depends on the strength of the bond itself. Simply put, the stronger the bond, the greater the amount of energy released when it is broken. As it happens, the strength of the bond between the second and third phosphate in an ATP molecule is an ideal source of energy—it is strong enough to store a considerable amount of energy but weak enough to be broken with relative ease.
The energy given off by ATP is released through a process called hydrolysis. When a cell requires energy, a molecule of water is allowed to come into contact with the ATP molecule, causing the outermost phosphate to separate from the rest. This separation results in the release of energy in the form of heat. Once released, the energy is transferred by special enzymes to the parts of the cell where it is needed.
In addition to facilitating the release of energy from ATP, the process of hydrolysis also yields a new substance: adenosine diphosphate (ADP). ADP is the remnant of the original ATP molecule, which is left with only two of its phosphates after hydrolysis. In order for more cellular energy to be produced, ADP must be converted back into ATP—a process that depends upon the ingestion of food for completion. Specifically, ingested carbohydrates and fats are broken down through a process of oxidation called cellular respiration. The occurrence of this type of oxidation subsequently sets off a series of chemical reactions that allow ADP to acquire a new third phosphate and ultimately regenerate into ATP.
The breakdown and regeneration of ATP is an ongoing process within all living things. This is largely because most organisms are in constant need of energy and actually possess relatively few ATP molecules. In fact, the typical person generally possesses only a few hundred grams of ATP at any one time. As a result, to meet a person's demand for energy, the body must turn over its supply of ATP at a very rapid rate. For example, a woman working out at a gym can run through her entire bodily supply of ATP two times per minute. On a day when she does little more than lounge on the sofa watching television, she can still turn over all her ATP more than one hundred times in just twenty-four hours.
The body turns over its supply of ATP at an incredible rate because ATP energy serves a number of important purposes that are constantly or near-constantly ongoing. ATP energy provides fuel for mechanical work. By providing the energy needed to use muscles, ATP energy powers every motion living organisms make, from a simple blink to the complex movements involved in walking. ATP energy is also used on the cellular level to move various substances across cellular membranes. Lastly, ATP energy also powers important metabolic reactions that could not occur without its support. Taking all this into consideration, it is clear why ATP is such a critical component of organic life.
Bibliography
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