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What Is the Nucleotide
Adenosine Triphosphate (ATP)?
CLASS NOTES from Science Prof Online
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 we do. Essentially all metabolic functions of living cells require energy for operation and obtain it directly from stored ATP.
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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Page last updated: 5/2013
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
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 their 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 molecules and sunlight energy. Living things that can do this neat trick accomplish it by using photosynthetic pigments to capture 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 Made?
ATP is produced by autotrophs during photosynthesis, as described above, and is also produced by both autotrophs and heterotrophs during a process known as cellular respiration.
In cellular respiration food molecules are catabolized (broken down) and the released energy is transformed into ATP. Carbohydrates, most commonly glucose, are the food source typically used to make ATP. Carbs can be catabolized through the processes of cellular respiration or 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, water and ATP energy. Through these catabolic pathways, up to 38 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 and 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 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 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.
- ATP and Energy Storage interactive animation from Dr. Saul's Biology In Motion
- What ATP Is and How It Works video by Leslie Samuel TV
- ATP: Adenosine Triphosphate lecture from Kahnacademy
- Organic Chemistry Lecture Main Page from the Virtual Cell Biology Classroom
- Aerobic Respiration Lecture Main Page from the Virtual Cell Biology Classroom
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Portions of this article originally appeared on Suite101 online magazine.
