ATP - Energy Currency of the Cell, Structure, Functions, FAQ

What is ATP?

Full form: ATP is a nucleotide and is made up of an adenine base, a ribose sugar and three phosphate groups. This is the reason why it is known as the energy currency of the cell because it plays a central role in energy fulfilment.

Discovery and historical background: ATP was for the first time extracted and characterized as an essential component of cell metabolism by German Chemist Karl Lohmann in the year 1929. Later, Fritz Albert Lipmann in the 1940s determined its role in biology which earned Lipmann the Nobel Prize for the work done on ATP in 1953.

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This Story also Contains

1. What is ATP?
2. Structure of ATP
3. How ATP Works: The Energy Cycle
4. Production of ATP
5. Role of ATP in Cellular Functions
6. Regulation of ATP Production and Utilization
7. Recommended video for ATP - Energy Currency of the Cell

Role of ATP in energy transfer within cells: Thus ATP serves as an energy shuttle that imports and exports energy within the cells. In cellular respiration energy from the nutrients is harnessed and used to produce ATP from ADP (adenosine diphosphate). This highenergy phosphate bond in ATP can then be hydrolyzed to ADP and phosphate, energy is released for cellular activities such as muscle contraction, transport of molecules across cell membranes, and synthesis of proteins and lipids among others.

Structure of ATP

The ATP structure is discussed below:

Molecular structure:

ATP or adenosine triphosphate consists of adenine which is a base, ribose which is a type of sugar and three phosphate radicals. Adenine is one of the nitrogenous organic bases; ribose is a fivecarbon sugar or pentose. All three phosphate groups are bound to the backbone of the ATP molecule and they follow each other in the ribose sugar of ATP.

Explanation of highenergy phosphate bonds:

Concerning the high energy phosphate bonds in ATP, the term phosphate relates to phos which is between phosphate groups, or of the terminal phosphate group. These bonds are described as highenergy bonds primarily due to their inherent nature, and their capability of releasing massive energy once broken. This is more an explanation of instability because of the negative phosphate groups as well as the resonance in ATP molecules.

Diagram of ATP molecule

How ATP Works: The Energy Cycle

The working of ATP is discussed below:

ATP hydrolysis:

ATP hydrolysis looks at the conversion of ATP to ADP (Adenosine Diphosphate and Pi – Inorganic phosphate). This process liberates energy which the cells need to fuel several biochemical reactions and several cellular activities. ATP is hydrolyzed by enzymes called ATPases that help in the transfer of the phosphate group to other molecules usually a substrate in metabolic pathways.

ATP synthesis:

ATP synthesis is a process that operates in contrast to ATP hydrolysis where Adenosine diphosphate (ADP) with the inorganic phosphate (Pi) make ATP. This synthesis is mainly done in cellular respiration whereby in the mitochondria energy from nutrients is used in the synthesis of the phosphate group back to ADP. The enzyme that catalyses this reaction is ATP synthase which proceeds through the use of the proton motive force across the inner mitochondrial membrane to synthesise ATP.

Diagram of the ATP-ADP cycle

Production of ATP

The ATP production is discussed below:

Cellular respiration overview: Another important process that occurs in a cell is called cellular respiration it is a process by which the cell gets energy from glucose molecules to produce ATP.

Glycolysis:

In the cytoplasm, glycolysis works and splits the glucose into pyruvate; it produces a small amount of ATP and NADH.

Krebs cycle (Citric Acid Cycle):

Occurring in the mitochondria, the Krebs cycle oxidises the acetyl CoA formed from pyruvate into ATP, NADH, and FADH2.

Electron Transport Chain:

Located in the inner mitochondrial membrane, the ETC takes electrons from NADH and FADH2, and transfers them to oxygen to produce a huge amount of ATP by oxidative phosphorylation.

Photosynthesis in plants: Photosynthesis is the provider of chemical energy in the form of glucose and this is the process through which plants, algae and certain bacteria convert light energy into chemical energy in the form of glucose through the production of ATP.

Light-dependent Reactions:

Happening in the thylakoid membranes of chloroplasts, photophosphorylation processes involve light energy to bring about cleavage of water molecules to give ATP and NADPH.

Calvin Cycle:

Occurring in the stroma of chloroplasts, this cycle known as the Calvin cycle, makes use of ATP and NADPH products of the lightdependent processes to reduce carbon dioxide into glucose through several enzymecatalyzed steps.

Comparison of ATP yield from different processes (table/chart)

Role of ATP in Cellular Functions

The functions of ATP are discussed below:

Muscle contraction

It has been mentioned that ATP is significant for muscle contraction because it is required to produce tension between actin and myosin filaments of the muscle fibre to enable contraction and, hence, bring about movement.

Active Transport Across Cell Membranes

ATP provides direct energy for transporting substances across the biological membranes by functioning as the direct energy source for membrane proteins such as pumps and carriers that transport ions and molecules from one area to another against a gradient, which could be concentration, electrical or both.

Biosynthesis of Macromolecules

ATP provides the energy needed for the building of other large molecules like proteins, lipids and nucleic acids for the growth, repair and replication of cells.

Signal Transduction Pathways

ATP is directly involved in signal transduction by adding phosphate groups to proteins that alter the activity of enzymes and the genes involved in cell signalling and adaptation to environmental stimuli.

Heat Production (Thermogenesis)

ATP hydrolysis both gets and loses energy. The energy is used to power cellular workings, and control heat and metabolic reactions.

Regulation of ATP Production and Utilization

The regulation of ATP is discussed below:

Enzymes involved in ATP synthesis and breakdown

ATP Synthesis: ATP synthase is a beautiful enzyme which facilitates the process of ATP synthesis through oxidative phosphorylation in mitochondrion and photophosphorylation in chloroplast.

ATP Breakdown: ATPases; ATP synthase; reverse the process by breaking ATP into ADP and phosphate for another cellular process to demand energy.

Role of ATP in metabolic regulation

Energy Currency: ATP is the energy-transporting process that fuels metabolic processes in a cell such as glycolysis, the citric acid cycle, and oxidative phosphorylation.

Activation Energy: Atp reduces the energy that is needed to start up metabolic reactions hence making the metabolic process faster.

Feedback mechanisms

Negative Feedback: ATP also diminishes the ways that produce ATP such as glycolysis and the citric acid cycle, thus conserving energy.

Positive Feedback: ATP depletion activates feedback that can reenergize the cell through other energy-producing pathways.

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