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6.3A: ATP: Adenosine Triphosphate - Biology

6.3A: ATP: Adenosine Triphosphate - Biology



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Cells couple the exergonic reaction of ATP hydrolysis with endergonic reactions to harness the energy within the bonds of ATP.

Learning Objectives

  • Explain the role of ATP as the currency of cellular energy

Key Points

  • Adenosine triphosphate is composed of the nitrogenous base adenine, the five-carbon sugar ribose, and three phosphate groups.
  • ATP is hydrolyzed to ADP in the reaction ATP+H2O→ADP+Pi+ free energy; the calculated ∆G for the hydrolysis of 1 mole of ATP is -57 kJ/mol.
  • ADP is combined with a phosphate to form ATP in the reaction ADP+Pi+free energy→ATP+H2O.
  • The energy released from the hydrolysis of ATP into ADP is used to perform cellular work, usually by coupling the exergonic reaction of ATP hydrolysis with endergonic reactions.
  • Sodium-potassium pumps use the energy derived from exergonic ATP hydrolysis to pump sodium and potassium ions across the cell membrane while phosphorylation drives the endergonic reaction.

Key Terms

  • energy coupling: Energy coupling occurs when the energy produced by one reaction or system is used to drive another reaction or system.
  • endergonic: Describing a reaction that absorbs (heat) energy from its environment.
  • exergonic: Describing a reaction that releases energy (heat) into its environment.
  • free energy: Gibbs free energy is a thermodynamic potential that measures the useful or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure (isothermal, isobaric).
  • hydrolysis: A chemical process of decomposition involving the splitting of a bond by the addition of water.

ATP: Adenosine Triphosphate

Adenosine triphosphate (ATP) is the energy currency for cellular processes. ATP provides the energy for both energy-consuming endergonic reactions and energy-releasing exergonic reactions, which require a small input of activation energy. When the chemical bonds within ATP are broken, energy is released and can be harnessed for cellular work. The more bonds in a molecule, the more potential energy it contains. Because the bond in ATP is so easily broken and reformed, ATP is like a rechargeable battery that powers cellular process ranging from DNA replication to protein synthesis.

Molecular Structure

Adenosine triphosphate (ATP) is comprised of the molecule adenosine bound to three phosphate groups. Adenosine is a nucleoside consisting of the nitrogenous base adenine and the five-carbon sugar ribose. The three phosphate groups, in order of closest to furthest from the ribose sugar, are labeled alpha, beta, and gamma. Together, these chemical groups constitute an energy powerhouse. The two bonds between the phosphates are equal high-energy bonds (phosphoanhydride bonds) that, when broken, release sufficient energy to power a variety of cellular reactions and processes. The bond between the beta and gamma phosphate is considered “high-energy” because when the bond breaks, the products [adenosine diphosphate (ADP) and one inorganic phosphate group (Pi)] have a lower free energy than the reactants (ATP and a water molecule). ATP breakdown into ADP and Pi is called hydrolysis because it consumes a water molecule (hydro-, meaning “water”, and lysis, meaning “separation”).

ATP Hydrolysis and Synthesis

ATP is hydrolyzed into ADP in the following reaction:

ATP+H2O→ADP+Pi+free energy

Like most chemical reactions, the hydrolysis of ATP to ADP is reversible. The reverse reaction combines ADP + Pi to regenerate ATP from ADP. Since ATP hydrolysis releases energy, ATP synthesis must require an input of free energy.

ADP is combined with a phosphate to form ATP in the following reaction:

ADP+Pi+free energy→ATP+H2O

ATP and Energy Coupling

Exactly how much free energy (∆G) is released with the hydrolysis of ATP, and how is that free energy used to do cellular work? The calculated ∆G for the hydrolysis of one mole of ATP into ADP and Pi is −7.3 kcal/mole (−30.5 kJ/mol). However, this is only true under standard conditions, and the ∆G for the hydrolysis of one mole of ATP in a living cell is almost double the value at standard conditions: 14 kcal/mol (−57 kJ/mol).

ATP is a highly unstable molecule. Unless quickly used to perform work, ATP spontaneously dissociates into ADP + Pi, and the free energy released during this process is lost as heat. To harness the energy within the bonds of ATP, cells use a strategy called energy coupling.

Energy Coupling in Sodium-Potassium Pumps

Cells couple the exergonic reaction of ATP hydrolysis with the endergonic reactions of cellular processes. For example, transmembrane ion pumps in nerve cells use the energy from ATP to pump ions across the cell membrane and generate an action potential. The sodium-potassium pump (Na+/K+pump) drives sodium out of the cell and potassium into the cell. When ATP is hydrolyzed, it transfers its gamma phosphate to the pump protein in a process called phosphorylation. The Na+/K+ pump gains the free energy and undergoes a conformational change, allowing it to release three Na+ to the outside of the cell. Two extracellular K+ ions bind to the protein, causing the protein to change shape again and discharge the phosphate. By donating free energy to the Na+/K+ pump, phosphorylation drives the endergonic reaction.

Energy Coupling in Metabolism

During cellular metabolic reactions, or the synthesis and breakdown of nutrients, certain molecules must be altered slightly in their conformation to become substrates for the next step in the reaction series. In the very first steps of cellular respiration, glucose is broken down through the process of glycolysis. ATP is required for the phosphorylation of glucose, creating a high-energy but unstable intermediate. This phosphorylation reaction causes a conformational change that allows enzymes to convert the phosphorylated glucose molecule to the phosphorylated sugar fructose. Fructose is a necessary intermediate for glycolysis to move forward. In this example, the exergonic reaction of ATP hydrolysis is coupled with the endergonic reaction of converting glucose for use in the metabolic pathway.


ATP Adenosine Triphosphate

Adenosine Trisphosphate, also known as the ‘currency of energy’ allows us to sprint, jump, walk, run, and think.

It’s ATP’s role to supply energy throughout the whole body, where it’s used for hundreds of different bodily functions.

In short, ATP captures energy from foods we eat, converting them into energy with the help of the mitochondria.

Therefore, the more ATP we have available, or the more efficiently ATP can be created will allow us to increase our performance.


Cellular

ATP is an excellent energy storage molecule to use as "currency" due to the phosphate groups that link through phosphodiester bonds. These bonds are high energy because of the associated electronegative charges exerting a repelling force between the phosphate groups. A significant quantity of energy remains stored within the phosphate-phosphate bonds. Through metabolic processes, ATP becomes hydrolyzed into ADP, or further to AMP, and free inorganic phosphate groups. The process of ATP hydrolysis to ADP is energetically favorable, yielding Gibbs-free energy of -7.3 cal/mol.[1]ਊTP must continuously undergo replenishment to fuel the ever-working cell. The routine intracellular concentration of ATP is 1 to 10 uM.[2] Many feedback mechanisms are in place to ensure the maintenance of a consistent ATP level in the cell. The enhancement or inhibition of ATP synthase is a common regulatory mechanism. For example, ATP inhibits phosphofructokinase-1 (PFK1) and pyruvate kinase, two key enzymes in glycolysis, effectively acting as a negative feedback loop to inhibit glucose breakdown when there is sufficient cellular ATP.

Conversely, ADP and AMP can activate PFK1 and pyruvate kinase, serving to promote ATP synthesis in times of high-energy demand. Other systems regulate ATP, such as in the regulatory mechanisms involved in regulating ATP synthesis in the heart. Novel experiments have demonstrated that ten-second bursts called mitochondrial flashes can disrupt ATP production in the heart. During these mitochondrial flashes, the mitochondria release reactive oxygen species and effectively pause ATP synthesis. ATP production inhibition occurs during mitochondrial flashes. During low demand for energy, when heart muscle cells received sufficient building blocks needed to produce ATP, mitochondrial flashes were observed more frequently. Alternatively, when energy demand is high during rapid heart contraction, mitochondrial flashes occurred less often. These results suggested that during times when substantial amounts of ATP are needed, mitochondrial flashes occur less frequently to allow for continued ATP production. Conversely, during times of low energy output, mitochondrial flashes occurred more regularly and inhibited ATP production.[3]


20 ATP: Adenosine Triphosphate

By the end of this section, you will be able to do the following:

  • Explain ATP’s role as the cellular energy currency
  • Describe how energy releases through ATP hydrolysis

Even exergonic, energy-releasing reactions require a small amount of activation energy in order to proceed. However, consider endergonic reactions, which require much more energy input, because their products have more free energy than their reactants. Within the cell, from where does energy to power such reactions come? The answer lies with an energy-supplying molecule scientists call adenosine triphosphate , or ATP . This is a small, relatively simple molecule ((Figure)), but within some of its bonds, it contains the potential for a quick burst of energy that can be harnessed to perform cellular work. Think of this molecule as the cells’ primary energy currency in much the same way that money is the currency that people exchange for things they need. ATP powers the majority of energy-requiring cellular reactions.

As its name suggests, adenosine triphosphate is comprised of adenosine bound to three phosphate groups ((Figure)). Adenosine is a nucleoside consisting of the nitrogenous base adenine and a five-carbon sugar, ribose. The three phosphate groups, in order of closest to furthest from the ribose sugar, are alpha, beta, and gamma. Together, these chemical groups constitute an energy powerhouse. However, not all bonds within this molecule exist in a particularly high-energy state. Both bonds that link the phosphates are equally high-energy bonds ( phosphoanhydride bonds ) that, when broken, release sufficient energy to power a variety of cellular reactions and processes. These high-energy bonds are the bonds between the second and third (or beta and gamma) phosphate groups and between the first and second phosphate groups. These bonds are “high-energy” because the products of such bond breaking—adenosine diphosphate (ADP) and one inorganic phosphate group (Pi)—have considerably lower free energy than the reactants: ATP and a water molecule. Because this reaction takes place using a water molecule, it is a hydrolysis reaction. In other words, ATP hydrolyzes into ADP in the following reaction:

Like most chemical reactions, ATP to ADP hydrolysis is reversible. The reverse reaction regenerates ATP from ADP + Pi. Cells rely on ATP regeneration just as people rely on regenerating spent money through some sort of income. Since ATP hydrolysis releases energy, ATP regeneration must require an input of free energy. This equation expresses ATP formation:

Two prominent questions remain with regard to using ATP as an energy source. Exactly how much free energy releases with ATP hydrolysis, and how does that free energy do cellular work? The calculated ∆G for the hydrolysis of one ATP mole into ADP and Pi is −7.3 kcal/mole (−30.5 kJ/mol). Since this calculation is true under standard conditions, one would expect a different value exists under cellular conditions. In fact, the ∆G for one ATP mole’s hydrolysis in a living cell is almost double the value at standard conditions: –14 kcal/mol (−57 kJ/mol).

ATP is a highly unstable molecule. Unless quickly used to perform work, ATP spontaneously dissociates into ADP + Pi, and the free energy released during this process is lost as heat. The second question we posed above discusses how ATP hydrolysis energy release performs work inside the cell. This depends on a strategy scientists call energy coupling. Cells couple the ATP hydrolysis’ exergonic reaction allowing them to proceed. One example of energy coupling using ATP involves a transmembrane ion pump that is extremely important for cellular function. This sodium-potassium pump (Na + /K + pump) drives sodium out of the cell and potassium into the cell ((Figure)). A large percentage of a cell’s ATP powers this pump, because cellular processes bring considerable sodium into the cell and potassium out of it. The pump works constantly to stabilize cellular concentrations of sodium and potassium. In order for the pump to turn one cycle (exporting three Na+ ions and importing two K + ions), one ATP molecule must hydrolyze. When ATP hydrolyzes, its gamma phosphate does not simply float away, but it actually transfers onto the pump protein. Scientists call this process of a phosphate group binding to a molecule phosphorylation. As with most ATP hydrolysis cases, a phosphate from ATP transfers onto another molecule. In a phosphorylated state, the Na + /K + pump has more free energy and is triggered to undergo a conformational change. This change allows it to release Na + to the cell’s outside. It then binds extracellular K + , which, through another conformational change, causes the phosphate to detach from the pump. This phosphate release triggers the K + to release to the cell’s inside. Essentially, the energy released from the ATP hydrolysis couples with the energy required to power the pump and transport Na + and K + ions. ATP performs cellular work using this basic form of energy coupling through phosphorylation.

One ATP molecule’s hydrolysis releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1 kcal/mol of energy), how many sodium ions could one ATP molecule’s hydrolysis move?

Often during cellular metabolic reactions, such as nutrient synthesis and breakdown, certain molecules must alter slightly in their conformation to become substrates for the next step in the reaction series. One example is during the very first steps of cellular respiration, when a sugar glucose molecule breaks down in the process of glycolysis. In the first step, ATP is required to phosphorylze glucose, creating a high-energy but unstable intermediate. This phosphorylation reaction powers a conformational change that allows the phosphorylated glucose molecule to convert to the phosphorylated sugar fructose. Fructose is a necessary intermediate for glycolysis to move forward. Here, ATP hydrolysis’ exergonic reaction couples with the endergonic reaction of converting glucose into a phosphorylated intermediate in the pathway. Once again, the energy released by breaking a phosphate bond within ATP was used for phosphorylyzing another molecule, creating an unstable intermediate and powering an important conformational change.

See an interactive animation of the ATP-producing glycolysis process at this site.

Section Summary

ATP is the primary energy-supplying molecule for living cells. ATP is comprised of a nucleotide, a five-carbon sugar, and three phosphate groups. The bonds that connect the phosphates (phosphoanhydride bonds) have high-energy content. The energy released from ATP hydrolysis into ADP + Pi performs cellular work. Cells use ATP to perform work by coupling ATP hydrolysis’ exergonic reaction with endergonic reactions. ATP donates its phosphate group to another molecule via phosphorylation. The phosphorylated molecule is at a higher-energy state and is less stable than its unphosphorylated form, and this added energy from phosphate allows the molecule to undergo its endergonic reaction.

Art Connections

(Figure) The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1 kcal/mol of energy), how many sodium ions could be moved by the hydrolysis of one ATP molecule?

(Figure) Three sodium ions could be moved by the hydrolysis of one ATP molecule. The ∆G of the coupled reaction must be negative. Movement of three sodium ions across the membrane will take 6.3 kcal of energy (2.1 kcal × 3 Na + ions = 6.3 kcal). Hydrolysis of ATP provides 7.3 kcal of energy, more than enough to power this reaction. Movement of four sodium ions across the membrane, however, would require 8.4 kcal of energy, more than one ATP molecule can provide.

Review Questions

The energy released by the hydrolysis of ATP is____

  1. primarily stored between the alpha and beta phosphates
  2. equal to −57 kcal/mol
  3. harnessed as heat energy by the cell to perform work
  4. providing energy to coupled reactions

Which of the following molecules is likely to have the most potential energy?

Free Response

Do you think that the EA for ATP hydrolysis is relatively low or high? Explain your reasoning.

The activation energy for hydrolysis is very low. Not only is ATP hydrolysis an exergonic process with a large −∆G, but ATP is also a very unstable molecule that rapidly breaks down into ADP + Pi if not utilized quickly. This suggests a very low EA since it hydrolyzes so quickly.

Glossary


Product description

PEAK ATP is a clinically validated and patented form of Adenosine 5’- Triphosphate (ATP) Disodium shown to improve body composition and athletic performance by increasing muscular excitability, blood flow and recovery.*

How does PEAK ATP work?

PEAK ATP helps to optimize athletic performance through three distinct mechanisms of action: 1) ATP increases muscular excitability resulting in significant gains in strength and power, 2) ATP increases blood flow, resulting in improved oxygen and nutrient delivery to the muscle and 3) ATP is involved in anabolic signaling, resulting in increased lean body mass and muscle thickness.*

What is Muscular Excitability?

Muscular excitability refers to the ability to activate muscle, thereby causing it to contract. The greater the excitability of the muscle the greater its force, velocity, and endurance properties will be. Muscle is excited by the release of calcium into the cell. Calcium serves as the trigger for contraction. Peak ATP works by increasing and sustaining the amount of calcium available to the muscle, which boosts muscular excitability. The result is the athlete will lift greater weights and produce a greater number of repetitions per set.

How does PEAK ATP Improve Blood Flow?

Red blood cells release ATP into the blood when muscles are fatigued, causing vasodilation to occur. PEAK ATP supplementation increases the amount of ATP available in red blood cells. As a result of more ATP being available, significant increases in blood flow, oxygen delivery and clearance of metabolic waste products such as lactate are obtained.


Other triphosphates

There are other nucleotide triphosphates, some containing ribose, and some containing deoxyribose.

Ribonucleotides can act as substrates for the synthesis of RNA (and DNA).

Deoxyribonucleotide triphosphates are very similar compounds containing deoxyribose rather than ribose, so they have a prefix d.
These are used as substrates of DNA polymerase in the synthesis (or replication) of DNA, where they give up PPi (pyrophosphate- a double phosphate) and provide energy, ending up being incorporated in DNA up as monophosphates.
Examples:

Deoxyadenosine triphosphate (dATP) is the deoxyribonucleotide version of (ordinary) ATP - the subject of this topic.

GTP (guanosine triphosphate) This molecule is sometimes formed as a result of substrate level phosphorylation which then produces ATP from ADP. It is also used as an energy source in several important processes e.g. protein synthesis and in stabilising tubulin proteins in microtubule formation within cells. dGTP is the deoxyribonucleotide equivalent.

CTP (cytidine triphosphate) - dCTP is the deoxyribonucleotide equivalent.

dTTP (thymidine triphosphate) does not have a ribonucleotide equivalent - see UTP below.

UTP (uridine triphosphate) - only a ribonucleotide. Its main role is as substrate for the synthesis of RNA during transcription but it also functions like ATP as a source of energy or an activator of substrates in certain metabolic reactions, e.g. glycogen synthesis.

Other related topics on this site

(also accessible from the drop-down menu above)

Interactive 3-D molecular graphic models on this site

(also accessible from the drop-down menu above)

Web references

High-energy phosphate From Wikipedia, the free encyclopedia

ATP/ADP from the LibreTexts libraries

Bioluminescence From Wikipedia, the free encyclopedia

Luminescent Determination of ATP Concentrations Using the Clarity Luminescence Microplate Reader


Adenosine triphosphate

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Adenosine triphosphate (ATP), energy-carrying molecule found in the cells of all living things. ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.

Cells require chemical energy for three general types of tasks: to drive metabolic reactions that would not occur automatically to transport needed substances across membranes and to do mechanical work, such as moving muscles. ATP is not a storage molecule for chemical energy that is the job of carbohydrates, such as glycogen, and fats. When energy is needed by the cell, it is converted from storage molecules into ATP. ATP then serves as a shuttle, delivering energy to places within the cell where energy-consuming activities are taking place.

ATP is a nucleotide that consists of three main structures: the nitrogenous base, adenine the sugar, ribose and a chain of three phosphate groups bound to ribose. The phosphate tail of ATP is the actual power source which the cell taps. Available energy is contained in the bonds between the phosphates and is released when they are broken, which occurs through the addition of a water molecule (a process called hydrolysis). Usually only the outer phosphate is removed from ATP to yield energy when this occurs ATP is converted to adenosine diphosphate (ADP), the form of the nucleotide having only two phosphates.

ATP is able to power cellular processes by transferring a phosphate group to another molecule (a process called phosphorylation). This transfer is carried out by special enzymes that couple the release of energy from ATP to cellular activities that require energy.

Although cells continuously break down ATP to obtain energy, ATP also is constantly being synthesized from ADP and phosphate through the processes of cellular respiration. Most of the ATP in cells is produced by the enzyme ATP synthase, which converts ADP and phosphate to ATP. ATP synthase is located in the membrane of cellular structures called mitochondria in plant cells, the enzyme also is found in chloroplasts. The central role of ATP in energy metabolism was discovered by Fritz Albert Lipmann and Herman Kalckar in 1941.


How is Adenosine Triphosphate Produced?

The primary source of ATP in animals is cellular respiration, which occurs in the cytosol and mitochondria of the cell, beginning with glycolysis, followed by aerobic respiration (the Krebs&rsquo Cycle and the electron transport chain). These three steps will create a total of 36 ATP. 2 ATP are produced in glycolysis and another 2 come from the Krebs&rsquo cycle, while a whopping 32 ATP are produced through the electron transport chain.

In the mitochondrial membrane, there are large protein complexes called ATP synthase. Due to the proton gradient that is maintained between the interior and exterior of the mitochondria, as the protons flow into the mitochondria, ATP can be produced from ADP (by attaching another phosphate group). When ATP is converted into ADP, it occurs through a process known as hydrolysis.

In plants, ATP is produced through photosynthesis. When a plant has ready access to carbon dioxide, water and energy from sunlight, it can undergo the light and dark reactions of photosynthesis. In the light reactions, the energy from the sun is converted into chemical energy (ATP) through the phosphorylation of ADP, which gains a phosphate group and becomes ATP. In the dark reactions of photosynthesis (the Calvin Cycle), that same ATP can be used to synthesize glucose, the food that plants need to survive.


Art Connection

The sodium-potassium pump is an example of energy coupling. The energy derived from exergonic ATP hydrolysis pumps sodium and potassium ions across the cell membrane.

One ATP molecule's hydrolysis releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1 kcal/mol of energy), how many sodium ions could one ATP molecule's hydrolysis move?

Often during cellular metabolic reactions, such as nutrient synthesis and breakdown, certain molecules must alter slightly in their conformation to become substrates for the next step in the reaction series. One example is during the very first steps of cellular respiration, when a sugar glucose molecule breaks down in the process of glycolysis. In the first step, ATP is required to phosphorylze glucose, creating a high-energy but unstable intermediate. This phosphorylation reaction powers a conformational change that allows the phosphorylated glucose molecule to convert to the phosphorylated sugar fructose. Fructose is a necessary intermediate for glycolysis to move forward. Here, ATP hydrolysis' exergonic reaction couples with the endergonic reaction of converting glucose into a phosphorylated intermediate in the pathway. Once again, the energy released by breaking a phosphate bond within ATP was used for phosphorylyzing another molecule, creating an unstable intermediate and powering an important conformational change.


ATP is the primary energy-supplying molecule for living cells. ATP is made up of a nucleotide, a five-carbon sugar, and three phosphate groups. The bonds that connect the phosphates (phosphoanhydride bonds) have high-energy content. The energy released from the hydrolysis of ATP into ADP + Pi is used to perform cellular work. Cells use ATP to perform work by coupling the exergonic reaction of ATP hydrolysis with endergonic reactions. ATP donates its phosphate group to another molecule via a process known as phosphorylation. The phosphorylated molecule is at a higher-energy state and is less stable than its unphosphorylated form, and this added energy from the addition of the phosphate allows the molecule to undergo its endergonic reaction.

Figure The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy). If it takes 2.1 kcal/mol of energy to move one Na + across the membrane (∆G = +2.1 kcal/mol of energy), how many sodium ions could be moved by the hydrolysis of one ATP molecule?

Figure Three sodium ions could be moved by the hydrolysis of one ATP molecule. The ∆G of the coupled reaction must be negative. Movement of three sodium ions across the membrane will take 6.3 kcal of energy (2.1 kcal × 3 Na + ions = 6.3 kcal). Hydrolysis of ATP provides 7.3 kcal of energy, more than enough to power this reaction. Movement of four sodium ions across the membrane, however, would require 8.4 kcal of energy, more than one ATP molecule can provide.