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Bioenergetics
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==Overview== Bioenergetics is the part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the [[molecules]] found in biological [[organism]]s.<ref name="AutoRefA">{{Cite journal |last1=Ferrick |first1=David A. |last2=Neilson |first2=Andy |last3=Beeson |first3=Craig |date=March 2008 |title=Advances in measuring cellular bioenergetics using extracellular flux |url=https://pubmed.ncbi.nlm.nih.gov/18342804/ |journal=Drug Discovery Today |volume=13 |issue=5โ6 |pages=268โ274 |doi=10.1016/j.drudis.2007.12.008 |issn=1359-6446 |pmid=18342804}}</ref> It can also be defined as the study of energy relationships and energy transformations and transductions in living organisms.<ref>Nelson, David L., Cox, Michael M. ''Lehninger: Principles of Biochemistry.'' New York: W.H. Freeman and Company, 2013. Sixth ed., pg. 506.</ref> The ability to harness energy from a variety of metabolic pathways is a property of all living organisms. [[Cell growth|Growth]], [[Developmental biology|development]], [[anabolism]] and [[catabolism]] are some of the central processes in the study of biological organisms, because the role of energy is fundamental to such [[biological process]]es.<ref>Nelson, David L., Cox, Michael M. ''Lehninger: Principles of Biochemistry.'' New York: W.H. Freeman and Company, 2013. Sixth ed., pg. 28. </ref> [[Life]] is dependent on [[energy transformation]]s; living organisms survive because of exchange of energy between living tissues/cells and the outside environment. Some organisms, such as [[autotrophs]], can acquire energy from sunlight (through [[photosynthesis]]) without needing to consume nutrients and break them down.<ref>Nelson, David L., Cox, Michael M. ''Lehninger: Principles of Biochemistry.'' New York: W.H. Freeman and Company, 2013. Sixth ed., pg. 22. </ref> Other organisms, like [[heterotrophs]], must intake nutrients from food to be able to sustain energy by breaking down chemical bonds in nutrients during metabolic processes such as [[glycolysis]] and [[Citric acid cycle|the citric acid cycle]]. Importantly, as a direct consequence of the [[first law of thermodynamics]], autotrophs and heterotrophs participate in a universal metabolic networkโby eating autotrophs (plants), heterotrophs harness energy that was initially transformed by the plants during [[photosynthesis]].<ref>Nelson, David L., Cox, Michael M. ''Lehninger: Principles of Biochemistry.'' New York: W.H. Freeman and Company, 2013. Sixth ed., pgs. 22, 506. </ref> In a living organism, [[chemical bond]]s are broken and made as part of the exchange and transformation of energy. Energy is available for work (such as mechanical work) or for other processes (such as chemical synthesis and [[anabolism|anabolic]] processes in growth), when weak bonds are broken and stronger bonds are made. The production of stronger bonds allows release of usable energy. Adenosine triphosphate ([[Adenosine triphosphate|ATP]]) is the main "energy currency" for organisms; the goal of metabolic and catabolic processes are to synthesize ATP from available starting materials (from the environment), and to break- down ATP (into adenosine diphosphate ([[Adenosine diphosphate|ADP]]) and inorganic phosphate) by utilizing it in biological processes.<ref name="AutoRefC" /> In a cell, the ratio of ATP to ADP concentrations is known as the "[[energy charge]]" of the cell. A cell can use this energy charge to relay information about cellular needs; if there is more ATP than ADP available, the cell can use ATP to do work, but if there is more ADP than ATP available, the cell must synthesize ATP via oxidative phosphorylation.<ref name="AutoRefA" /> Living organisms produce ATP from energy sources via [[oxidative phosphorylation]]. The terminal phosphate bonds of ATP are relatively weak compared with the stronger bonds formed when ATP is [[Hydrolysis|hydrolyzed]] (broken down by water) to adenosine diphosphate and inorganic phosphate. Here it is the thermodynamically favorable free energy of hydrolysis that results in energy release; the phosphoanhydride bond between the terminal phosphate group and the rest of the ATP molecule does not itself contain this energy.<ref> Nelson, David L., Cox, Michael M. ''Lehninger: Principles of Biochemistry.'' New York: W.H. Freeman and Company, 2013. Sixth ed., pg. 522- 523. </ref> An organism's stockpile of ATP is used as a battery to store energy in cells.<ref>{{Cite journal |last1=Hardie |first1=D. Grahame |last2=Ross |first2=Fiona A. |last3=Hawley |first3=Simon A. |date=April 2012 |title=AMPK: a nutrient and energy sensor that maintains energy homeostasis |journal=Nature Reviews Molecular Cell Biology |language=en |volume=13 |issue=4 |pages=251โ262 |doi=10.1038/nrm3311 |pmid=22436748 |issn=1471-0080|pmc=5726489 }}</ref> Utilization of chemical energy from such molecular bond rearrangement powers biological processes in every biological organism. Living organisms obtain energy from organic and inorganic materials; i.e. ATP can be synthesized from a variety of biochemical precursors. For example, [[lithotroph]]s can oxidize minerals such as [[nitrate]]s or forms of [[sulfur]], such as elemental sulfur, [[sulfite]]s, and [[hydrogen sulfide]] to produce ATP. In [[photosynthesis]], [[autotroph]]s produce ATP using light energy, whereas [[heterotroph]]s must consume organic compounds, mostly including [[carbohydrate]]s, [[fat]]s, and [[protein]]s. The amount of energy actually obtained by the organism is lower than the [[Food energy|amount present in the food]]; there are losses in digestion, metabolism, and [[thermogenesis]].<ref>{{Cite web|url=https://www.fao.org/3/Y5022E/y5022e04.htm|title=CHAPTER 3: CALCULATION OF THE ENERGY CONTENT OF FOODS - ENERGY CONVERSION FACTORS|website=www.fao.org|access-date=2023-05-08|archive-date=2023-03-21|archive-url=https://web.archive.org/web/20230321035607/https://www.fao.org/3/Y5022E/y5022e04.htm|url-status=live}}</ref> Environmental materials that an organism intakes are generally combined with [[oxygen]] to release energy, although some nutrients can also be oxidized anaerobically by various organisms. The utilization of these materials is a form of slow [[combustion]] because the nutrients are reacted with oxygen (the materials are oxidized slowly enough that the organisms do not produce fire). The oxidation releases energy, which may evolve as heat or be used by the organism for other purposes, such as breaking chemical bonds.
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