How is ATP production, what is adenosine triphosphate (ATP)

In 1997 the Nobel Prize for Chemistry was awarded to 3 biochemists for the study of an important biological molecule, adenosine triphosphate. The chemical substance that functions as the energy currency in cells is adenosine triphosphate (ATP). ATP is called a currency because it can be "used" to make chemical reactions occur. The more energy needed for a chemical reaction, the more ATP molecules must be expelled.

All living things, plants and animals, need a continuous supply of energy in order to function. Energy is used for all continuous processes of living organisms. Some of these processes occur continuously, such as food metabolism, large synthesis, biologically important molecules, for example proteins and DNA, and transport of molecules and ions throughout the organism.

Other processes only occur at certain times, such as muscle contractions and other cellular movements. Animals obtain energy through food oxidation, plants do it by trapping sunlight using chlorophyll. However, before energy can be used, it is first converted into a form that organisms can handle easily. The special energy carriers are the adenosine triphosphate molecule, or ATP.

Nearly all forms of life use ATP, an almost universal molecule to transfer energy. The energy released during the catabolic reaction is stored in ATP molecules. In addition, energy trapped in anabolic reactions (such as photosynthesis) is trapped in ATP molecules.

An ATP molecule consists of three parts. One part is a double ring of carbon and nitrogen atoms called adenine. Attached to the adenine molecule is a small five-carbon carbohydrate called ribose. Attached to the ribose molecule are three phosphate units bound together by covalent bonds.

A covalent bond that holds the phosphate unit together in ATP is a high energy bond. When the ATP molecule is broken down by enzymes, the third (terminal) phosphate unit is released as a phosphate group, which is an ion. When this happens, about 7.3 kilocalories of energy are released. (Kilocalories equals 1,000 calories.) This energy is made available to do cell work.

The enzyme Adenosine Triphosphatase completes the breakdown of the ATP molecule. The breakdown product is ATP adenosine diphosphate (ADP) and phosphate ions. Adenosine diphosphate and phosphate ions can be dissolved to form ATP, as batteries can be recharged. To achieve this, synthesis energy must be available. This energy can be made available in cells through two very important processes: photosynthesis and cellular respiration.

ATP production

ATP is produced from ADP and phosphate ions by a series of complex processes that occur in cells. This process depends on the activities of special groups called coenzyme cofactors. Three important coenzymes are: adenine dinucleotide nicotinamide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), and flavin adenine dinucleotide (FAD).

Both NAD and NADP are structurally similar to ATP. Both molecules have a ring containing nitrogen called nicotinic acid, which is the chemically active part of coenzymes. In FAD, the chemically active part is the flavin group. Riboflavin is used in the body to produce this group of flavins.

All coenzymes do essentially the same job. During metabolic chemical reactions, coenzymes receive electrons and pass them on to other coenzymes or other molecules. The removal of electrons or protons from coenzymes is the addition of oxidation. In electrons to molecules is a reduction. Therefore, chemical reactions carried out by coenzymes are called oxidation-reduction reactions.

Oxidation-reduction reactions carried out by coenzymes and other molecules are very important for cellular energy metabolism. Other molecules involved in this energy reaction are called cytochromes. Together with coenzymes, cytochromes accept and release electrons in a system called the electron transport system. The energy-rich portion of electrons between cytochrome and coenzymes drains energy from electrons to form ATP from ADP and phosphate ions.

The actual formation of ATP molecules requires a complex process called aschemiosmosis. Chemiosmosis involves the creation of a steep gradient proton (hydrogen ion). This gradient occurs between the membrane compartment of the mitochondria of all cells and the chloroplasts of plant cells. Gradients form when large numbers of protons (hydrogen ions) are pumped into membrane-bound compartments from the mitochondria. Protons build dramatically in compartments, eventually reaching large numbers. The energy released from electrons during proton electron transport system pumps.

After a large number of protons have gathered inside the mitochondrial and chloroplast compartments, they suddenly reverse their direction and escape back across the membrane and out of the compartment. Protons come out releasing their energy in this movement. This energy is used by enzymes to fuse ADP with phosphate ions to form ATP. The energy is trapped in the high-energy ATP bond by this process, and the ATP molecule is made available to do cell work. Proton movement is chemiosmosis because it is a chemical movement (in this case protons) across a semipermeable membrane. Because chemiosmosis occurs in mitochondria and chloroplasts, these organelles play an important role in cellular energy metabolism.

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