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What Is the Nucleotide
Adenosine Triphosphate (ATP)?
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Adenosine triphosphate (ATP) is the universal unit of energy used in all living cells. This molecule is produced and broken down in metabolic processes in all living systems.
Known as the ‘energy currency of life,’ ATP can store and transport the energy we need to do just about everything that we do. Essentially all metabolic functions of living cells require energy for operation and obtain it directly from stored ATP.
What is ATP made of?
ATP is a type of organic molecule referred to as a nucleoside or nucleotide. Nucleotides are basically made of three things:
- a pentose sugar
- one or more phosphate groups
- an adenosine base
The portion of the nucleotide molecule that doesn't include the phosphate group is called a nucleoside. So ATP, with three phosphate groups, is considered a nucleotide or nucleoside triphosphate.
Adenosine Phosphates AMP, ADP and ATP
These nucleotides can have different numbers of phosphate groups associated with the molecule, and the specific name of the nucleotide reflects its number of phosphate groups:
- Adenosine monophosphate (AMP) consists of an adenine ring (the base), ribose (the sugar) and one phosphate group.
- Adenosine diphosphate (ADP) has the same base and sugar, but two phosphate groups.
- Adenosine triphosphate (ATP) is composed of the same base and sugar, but three phosphate groups.
Why Are the Phosphate Groups Important?
These molecules can transport energy because phosphate bonds contain a lot of potential energy, which is released when they are broken.
Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy (~ 7 kcal/mole) in the bond between the second and third phosphate groups, known as a pyrophosphate bond.
So Where Does All this Energy Originate?
Autotrophs and Photosynthesis: Every food chain begins with anabolic (molecule building) pathways in organisms that synthesize organic molecules from inorganic carbon dioxide. Most of the living things that can do this neat trick accomplish it by using photosynthetic pigments to capture light energy from the sun. Autotrophs then use the energy that they derive from sunlight to drive the synthesis of carbohydrates from inorganic molecules, CO2 and H2O; a process known as photosynthesis. Autotrophs include plants, some bacteria, and some protists.
Heterotrophs Eat Energy Originally Obtained by Autotrophs: Heterotrophs, like us, are organisms that cannot make organic compounds from inorganic sources. We must obtain organic compounds by consuming other organisms. Heterotrophs include animals, fungi and some Protista and bacteria.
How Is ATP Actually Made?
ATP is produced by autotrophs during photosynthesis, as described above, and is also produced by both autotrophs and heterotrophs during a catabolic process known as cellular respiration.
Cellular Respiration
In cellular respiration food molecules are broken down and the released energy is transformed into ATP. Organisms catabolize (break down) carbohydrates, most commonly glucose, to ultimately make ATP and use if for anabolic cellular reactions. Glucose catabolized by through the processes of aerobic respiration and anaerobic fermentation.
Aerobic cellular respiration utilizes glycolysis, synthesis of acetyl-CoA, Krebs cycle, and electron transport chain; the end result being the complete breakdown of glucose into carbon dioxide and water. Through these catabolic reactions up to 34 molecules of ATP can be made from every molecule of glucose. Oxygen is a vital component of this highly efficient process, hence the name ‘aerobic respiration’
Anaerobic respiration & fermentation are used to derive energy from glucose by organisms that either cannot survive in the presence of oxygen or don’t always have access to oxygen. Fermentation is much less energy efficient than aerobic or anaerobic cellular respiration. Still, even in the absence of oxygen anaerobes can utilize glycolysis to break down glucose and ultimately net a couple ATP.
Where is ATP Made?
In eukaryotic cells, complex cells that possess a nucleus, ATP is synthesized in the tiny energy factories called mitochondria. In more primitive prokaryotes ATP synthesis occurs in the cytoplasm and cytoplasmic membrane.
Sources
- Bauman, R. (2005) Microbiology, Pearson Benjamin Cummings.
- Park Talaro, K. (2008) Foundations in Microbiology.
This article originally appeared on Suite101 online magazine.
Page last updated: 2/7/2012
Article Summary: Adenosine triphosphate is a power-packed nucleotide that the body's cells just can't live without. Here's a summary of what ATP is and how it works.
Adenosine Triphosphate (ATP)
Adenosine triphosphate (ATP)
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