Adenosine triphosphate

Adenosine triphosphate (ATP) is a special molecule that all living things use to get energy for their activities. You can think of it like a rechargeable battery for cells. Each ATP molecule is built from three main parts: a base called adenine, a sugar called ribose, and three phosphate groups linked in a row. The bonds between the phosphate groups store a lot of energy, and when one of these bonds is broken, the cell can use the released energy to do work.

The molecular structure of ATP.

Your body is constantly making and using ATP because it cannot store much of it at once. In fact, an average person only has about 250 grams of ATP in their body at a given moment, but it gets recycled more than 1,000 times per day to keep up with energy needs. Cells make ATP in different ways. Most ATP comes from mitochondria, often called the “powerhouses” of the cell, through a process called cellular respiration. Plants and algae make ATP in their chloroplasts using sunlight in a process called photosynthesis. Some ATP is also made directly in the fluid part of the cell, the cytoplasm, during glycolysis.

When ATP is used, it usually loses one phosphate group and becomes ADP (adenosine diphosphate), or sometimes loses two to become AMP (adenosine monophosphate). This release of energy powers important jobs in the body. For example, ATP helps muscles contract so you can move, it drives pumps in cell membranes that move ions in and out to keep cells alive. It fuels the building of proteins, DNA, and RNA. ATP is not just about energy, it also helps control how cells work. It can turn certain enzymes on or off to keep metabolism balanced, like a traffic light controlling when to go or stop. One key system that senses energy levels is called AMPK, which acts like a fuel gauge for the cell. Outside of cells, ATP can even act as a signal, sending messages between nerve cells, helping with senses like taste, and controlling blood flow.

Even though ATP has a lot of potential energy, it is stable enough that it does not fall apart in water. Special enzymes are needed to release its energy at the right time, preventing waste. Different organisms have found unique ways to make ATP. For example, some bacteria make it without oxygen by fermentation, while others use unusual processes like methanogenesis. Because ATP levels inside cells must stay steady, a sudden drop in ATP can be deadly since the pumps that keep cells alive would stop working almost instantly.

ATP was first discovered in 1929 by a scientist named Karl Lohmann, but its importance was not fully understood until the 1940s when Fritz Lipmann showed that it was the universal energy carrier. Today we know that ATP is not for long-term energy storage like fats or sugars. Instead, it is the quick, ready-to-use “cash” of cellular energy, always being earned, spent, and recycled to keep every living thing alive.

Use

The ATP molecule is very versatile: it is used for many chemical reactions in the body. Energy is stored in its chemical bonds.

The energy that is stored can be used later. When ATP breaks a bond with a phosphate group and becomes ADP, energy is released. This is an exothermic reaction.

The ATP phosphate exchange is a nearly never-ending cycle, stopping only when the cell dies.

Functions in cells

ATP is the main energy source for most cellular functions. This includes the synthesis of macromolecules. It is used in DNA and RNA. ATP also helps macromolecules get across cell membranes.

DNA and RNA synthesis

In all known organisms, DNA is made by the action of ribonucleotide reductase (RNR) enzymes.^[1] These enzymes reduce the sugar residue from ribose to deoxyribose by removing oxygen.^[1]

ATP is one of the four nucleotides put into RNA molecules by RNA polymerases. The energy driving this polymerization comes from cutting off two phosphate groups.^[2] The process is similar in DNA biosynthesis.

History

• ATP was discovered in 1929 by Karl Lohmann and Jendrassik and, independently, by Cyrus Fiske and Yellapragada Subba Rao of Harvard Medical School. Both teams were competing against each other to find an assay (way of measuring) for phosphorus.
• ATP was proposed to be the intermediary between energy-yielding and energy-requiring reactions in cells by Fritz Albert Lipmann in 1941.
• ATP was first synthesized (created) in the laboratory by Alexander Todd in 1948.
• The Nobel Prize in Chemistry 1997 was split, one half given to both Paul D. Boyer and John E. Walker for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP) and the other half to Jens C. Skou for the first discovery of an ion-transporting enzyme, Na+, K+ -ATPase.