Atp - an Exemplary Essay

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ATP and its Role in Living Organisms
An exemplary biology essay

ATP (adenosine triphosphate) is vital to living organisms. It acts as a short-term store of energy in a cell, carrying it from where it is synthesised (e.g. the mitochondria) to where it is needed for biological processes. It is well suited to this job for the following reasons: it is small and soluble (and so can be easily transported around a cell); it is easily broken down to release energy; it can transfer energy to other molecules; and it cannot leave the cell. All of these facts mean that ATP is always available to the cell as an immediate source of energy.

ATP consists of adenine, ribose (adenosine) and a chain of three phosphates. The phosphates are joined to
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The first occurs during the light dependent reaction of photosynthesis, when light energy absorbed by photosynthetic pigments in the thylakoids is used to excite electrons, which then move along an electron transport chain. The energy the electrons lose as they travel down this electron transport chain is used to transport H+ ions the thylakoid membrane to form a proton gradient across it. As the protons diffuse back across the membrane, the energy from this movement combines ADP and Pi to make ATP.

The second two processes occur during aerobic respiration. Oxidative phosphorylation, like photo-phosphorylation, relies on an electron transport chain to provide energy for the generation of a proton gradient across a membrane (this time a mitochondrial membrane). Again, energy from the movement of the H+ ions back across the membrane combines ADP and Pi. An example of substrate-level phosphorylation is the oxidation of triose phosphate during glycolysis, which provides the energy required to phosphorylate two molecules of ADP.

ATP acts as an energy source for many biological processes, among them metabolism (i.e. the creation of macromolecules from smaller molecules), active transport, the maintenance, repair and division of cells and organelles, the production of substances used within organisms, and muscle contraction. For example, during muscle contraction, ATP is required to move the globular heads on myosin filaments, which pull the actin

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