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Adenosine
Triphosphate
What You Need To Know About Adenosine
Triphosphate or ATP
By Anne Marie Helmenstine, Ph.D.
Adenosine triphosphate or ATP
is often called the energy currency of the cell because this molecule plays a
key role in metabolism, particularly in energy transfer within cells.
The molecule acts to couple
the energy of exergonic and endergonic processes, making
energetically unfavorable chemical reactions able to proceed.
Metabolic Reactions Involving ATP
Adenosine triphosphate is used
to transport chemical energy in many important processes, including:
·
aerobic
respiration (glycolysis and the citric acid cycle)
· fermentation
· cellular division
· photophosphorylation
·
motility
(e.g., shortening of myosin and actin filament cross-bridges as well as cytoskeleton construction)
· exocytosis and
endocytosis
· photosynthesis
· protein synthesis
In addition to metabolic
functions, ATP is involved in signal transduction. It is believed to be the
neurotransmitter responsible for the sensation of taste.
The human central
and peripheral nervous system, in particular, relies on ATP signaling. ATP
is also added to nucleic acids during transcription.
ATP is continuously recycled,
rather than expended. It's converted back into precursor molecules, so it can
be used again and again.
In human beings, for example,
the amount of ATP recycled daily is about the same as body weight, even though
the average human being only has about 250 grams of ATP.
Another way to look at it is
that a single molecule of ATP gets recycled 500-700 times every day.
At any moment in time, the
amount of ATP plus ADP is fairly constant. This is important since ATP is not a
molecule that can be stored for later use.
ATP may be produced from
simple and complex sugars as well as from lipids via redox reactions. For this
to occur, the carbohydrates must first be broken down into simple sugars, while
the lipids must be broken into fatty acids and glycerol.
However, ATP production is
highly regulated. Its production is controlled via substrate concentration,
feedback mechanisms, and allosteric hindrance.
ATP Structure
As indicated by the molecular
name, adenosine triphosphate consists of three phosphate groups (tri- prefix
before phosphate) connected to adenosine.
Adenosine is made by attaching
the 9' nitrogen atom of the purine base adenine to the 1' carbon of
the pentose sugar ribose.
The phosphate groups are
attached connecting and oxygen from a phosphate to the 5' carbon of the ribose.
Starting with the group
closest to the ribose sugar, the phosphate groups are named alpha (α), beta
(β), and gamma (γ).
Removing a phosphate group
results in adenosine diphosphate (ADP) and removing two groups produces
adenosine monophosphate (AMP).
How ATP Produces Energy
The key to energy production
lies with the phosphate groups. Breaking the phosphate bond is
an exothermic reaction.
So, when ATP loses one or two
phosphate groups, energy is released. More energy is released breaking the
first phosphate bond than the second.
ATP + H2O → ADP + Pi + Energy (Δ G = -30.5 kJ.mol-1)
ATP + H2O → AMP + PPi + Energy (Δ G = -45.6 kJ.mol-1)
ATP + H2O → AMP + PPi + Energy (Δ G = -45.6 kJ.mol-1)
The energy that is released is
coupled to an endothermic (thermodynamically unfavorable) reaction in order to
give it the activation energy needed to proceed.
ATP Facts
ATP was discovered in 1929 by
two independent sets of researchers: Karl Lohmann and also Cyrus
Fiske/Yellapragada Subbarow.
Alexander Todd first
synthesized the molecule in 1948.
Empirical Formula
|
C10H16N5O13P3
|
Chemical Formula
|
C10H8N4O2NH2(OH2)(PO3H)3H
|
Molecular Mass
|
507.18 g.mol-1
|
What Is ATP an Important
Molecule in Metabolism?
There are essentially two
reasons ATP is so important:
1. It's the only chemical in the
body that can be directly used as energy.
2. Other forms of chemical energy
need to be converted into ATP before they can be used.
Another important point is
that ATP is recyclable. If the molecule was used up after each reaction, it
wouldn't be practical for metabolism.
ATP Trivia
· Want to impress your friends?
Learn the IUPAC name for adenosine triphosphate.
It's [(2''R'',3''S'',4''R'',5''R'')-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methyl(hydroxyphosphonooxyphosphoryl)hydrogen
phosphate.
· While most students study ATP
as it relates to animal metabolism, the molecule is also the key form
of chemical energy in plants.
·
The
density of pure ATP is comparable to that of water. It's 1.04 grams per cubic
centimeter.
· The melting point of pure
ATP is 368.6°F (187°C).
Anne Marie Helmenstine, Ph.D.
Chemistry Expert
Education
Ph.D., Biomedical Sciences, University of
Tennessee at Knoxville
B.A., Physics and Mathematics, Hastings
College
Introduction
Ph.D. in biomedical sciences from the
University of Tennessee at Knoxville - Oak Ridge National Laboratory.
Science educator with experience
teaching chemistry, biology, astronomy, and physics at the high school,
college, and graduate levels.
ThoughtCo and About Education chemistry
expert since 2001.
Widely-published graphic artist, responsible
for printable periodic tables and other illustrations used in science.
Experience
Anne Helmenstine, Ph.D. has covered
chemistry for ThoughtCo and About Education since 2001, and other sciences
since 2013. She taught chemistry, biology, astronomy, and physics at the high
school, college, and graduate levels. She has worked as a research
scientist and also abstracting and indexing diverse scientific literature for
the Department of Energy.
In addition to her work as a science writer,
Dr. Helmenstine currently serves as a scientific consultant, specializing in
problems requiring an interdisciplinary approach. Previously, she worked
as a research scientist and college professor.
Education
Dr. Helmenstine holds a Ph.D. in biomedical
sciences from the University of Tennessee at Knoxville and a B.A.
in physics and mathematics with a minor in chemistry from Hastings
College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive
chemical detection and medical diagnostic tests.
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