What is ATP in Biology?

Core Concepts

In this tutorial, we answer the question “What is ATP in Biology?” Here, you will learn about what is ATP in biology along with its structure and production cycle. You will also learn about how ATP releases energy.

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What is ATP in Biology?

ATP in biology is a molecule that carries energy within cells. Otherwise known as adenosine triphosphate, biochemists commonly refer to ATP to as the “energy currency” of a cell, as it serves as the main cellular energy unit. Many metabolic processes involve ATP, which you can find listed below:

  • Aerobic respiration
  • Fermentation
  • Cellular division
  • Photophosphorylation
  • Motility
  • Endocytosis and exocytosis
  • Photosynthesis
  • Protein synthesis

In addition to these metabolic functions, ATP serves in signal transduction pathways involving cell communication and incorporates into DNA during DNA synthesis.

Why is ATP Important in Metabolic Processes?

ATP is the only source of energy in our body that we are able to directly use. Any form of nutrition intake in the body converts to ATP before it can be utilized for other functions. ATP is not only an energy source as it is responsible for carrying out many other vital functions, like transporting macromolecules in and out of the cell and being an extracellular or intracellular signaling molecule.

How is ATP Biologically Produced?

There are many processes which can produce ATP in the body. The production of ATP can occur in the presence of oxygen or in anaerobic conditions. We will go over the two main process responsible for producing ATP, cellular respiration and anaerobic respiration.

Cellular Respiration

Cellular respiration is the process where glucose is converted into ATP. The glucose becomes catabolized into acetyl-CoA which produces electron carriers that become oxidized during oxidative phosphorylation.

atp production
Cellular Respiration Pathway with Products

During glycolysis, the breakdown of glucose produces two ATP through substrate phosphorylation. However, the cell produces ATP at many other steps of cellular respiration. For instance, ATP forms during the citric acid cycle which yields one equivalent of ATP. The mitochondria produces the most ATP later in cellular respiration, from protons moving across the electrochemical gradient to power ATP synthase. The overall quantity of ATP varies depends on the electron carriers. One NADH molecule produces two and a half ATP, while one FADH2 molecule produces one and a half ATP.

Anaerobic Respiration

Anaerobic respiration occurs when oxygen is unavailable during cellular respiration. This process only yields two molecules of ATP per molecule of glucose. This is because the lack of oxygen causes cellular respiration to undergo lactic acid fermentation, where the NADH molecules are oxidized to keep the reaction going.

atp production
Anaerobic Respiration Pathways with Products

ATP Structure

An ATP molecule in biology is made of adenosine and three phosphate groups. To explain further, adenosine involves a purine base and ribose sugar. The purine base attaches to the 1′ carbon atom of ribose while the three phosphate groups attach to the 5′ carbon atom of ribose. The molecule below depicts the structure of adenosine triphosphate.

ATP structure
Structure of ATP (blue-phosphate groups, green-ribose sugar, yellow-purine base)

Due to its adenosine triphosphate’s structure, it is soluble in water and has a high energy content due to two phosphoanhydride bonds connecting the three phosphate groups.

How is Energy Released in ATP?

ATP can be referred to as “energy currency” of the cell because it provides a releasable energy in the bond between the second and third phosphate groups causing an exothermic reaction.

adenosine triphosphate energy bond
The red circle depicts the bond in ATP that is broken to release energy

These bonds between phosphate groups are high energy because their electronegative charges repel one another. Through the metabolic processes, the loss of a phosphate group hydrolyzes ATP to ADP. Feedback mechanisms control these reactions to maintain a consistent ATP level within the cell.

What is ATP Energy?

Biochemists call the energy produced in cells by adenosine triphosphate “ATP energy”. This energy is essential for many processes in biology, such as muscle contraction and nerve impulses. In biology, ATP generates energy from breaking down high energy foods within cells as well as through converting from ATP to ADP.

ATP Cycle

Due to two outer phosphates of ATP having high-energy phosphoanhydride bonds, their bonds are readily transferrable. Since the terminal phosphate can hydrolyze to form ATP to ADP, this creates the ATP cycle. In turn, enzymes can phosphorylate ADP to produce ATP.

Adenosine triphosphate cycle
ATP Cycle

Functions of ATP in Biology

The hydrolysis of ATP is what provides energy needed for many processes in organisms and cells. Some functions include intracellular signaling, DNA and RNA synthesis (including molecular cloning and PCR) , synaptic signaling, active transport, and muscle contraction.

ATP in Intracellular Signaling

Any form of signal transduction relies on ATP. ATP serves as a substrate for kinases (ATP-binding proteins). Magnesium ions found in a complex with ATP in the cell regulate these kinases. The magnesium binds to the phosphate oxygen centers. In addition to assisting in regulating kinase activity, ATP functions as a trigger of intracellular messenger release. These messengers include hormones, enzymes, and neurotransmitters to name a few.

ATP in DNA and RNA Synthesis

DNA and RNA synthesis require ATP to occur. ATP is one of the four nucleotide-triphosphate monomers needed in RNA synthesis. In DNA synthesis requires a similar mechanism, except ATP must first lose an oxygen atom from the sugar to produce a deoxyribonucleotide, dATP.

ATP in Neurotransmission

The brain consumes the most ATP of anywhere else in the body, due to a large amount of energy needed to maintain ion concentrations for neuronal signaling and synaptic transmission. At the presynaptic terminal, the neuron requires ATP to establish ion gradients to put neurotransmitters into vesicles. This is important because neuronal signaling depends on action potentials being able to reach the presynaptic terminal to signal the release of loaded vesicles. This process depends on ATP restoring the ion concentration in the axon after an action potential to allow another signal to occur. During the process, one molecule of ATP hydrolyzes, three sodium ions exit the cell, and two potassium ions enter the cell.

ATP in Muscle Contraction

Muscle contractions are necessary for everyday life and would be unable to occur without ATP. There are three primary roles that ATP performs in muscle contractions. First, ATP generates force against the adjoining actin filaments by moving the myosin cross-bridges. Secondly, ATP pumps calcium ions from the myoplasm across the sarcoplasmic reticulum by using active transport to move calcium against its concentration gradient. Lastly, ATP participates in the active transport of sodium and potassium ions across the sarcolemma in order to release calcium ions when an action potential occurs.

Further Reading