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ATP: Biological Transfer of Energy

Diagram of a typical animal cell. Organelles are labelled as follows: Nucleolus Nucleus Ribosomes (dots on rough reticulum walls) Vesicle Rough endoplasmic reticulum Golgi apparatus (or “Golgi body“) Cytoskeleton Smooth endoplasmic reticulum Mitochondrion Vacuole Cytosol Lysosome Centriole Cell membrane. By Kelvinsong – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=22952603


Diagram of a mitochondrion – Source: By Kelvinsong – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=27715320


Electron transport chain in the mitochondrial intermembrane space

Graphic credit: By T-Fork – http://commons.wikimedia.org/wiki/File:ETC_electron_transport_chain.svg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=17593027



Bioenergetics is a field in biochemistry and cell biology that concerns energy flow through living systems. This is an active area of biological research that includes the study of the transformation of energy in living organisms and the study of thousands of different cellular processes such as cellular respiration and the many other metabolic and enzymatic processes that lead to production and utilization of energy in forms such as 1) ___ ___, or ATP molecules. The goal of bioenergetics is to describe how living organisms acquire and transform 2) ___ in order to perform biological work. The study of metabolic pathways is thus essential to bioenergetics.


Energy homeostasis is the homeostatic control of energy 3) ___ – the difference between energy obtained through food consumption and energy expenditure – in living systems. Bioenergetics is the part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the 4) ___ found in biological organisms. It can also be defined as the study of energy relationships and energy transformations and transductions in living organisms. The ability to harness energy from a variety of metabolic pathways is a property of all living 5) ___. Growth, 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 processes. Life is dependent on energy transformations. 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 6) ___ (through photosynthesis) without needing to consume nutrients and break them down. 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 the citric acid cycle. Importantly, as a direct consequence of the First Law of Thermodynamics, autotrophs and heterotrophs participate in a universal metabolic network. By eating autotrophs, or 7) ___, heterotrophs harness energy that was initially transformed by the plants during photosynthesis.


In a living organism, chemical bonds 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 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 (ATP) is the main “energy currency“ for organisms; the goal of metabolic and catabolic processes is to synthesize ATP from available starting materials (from the environment), and to break down ATP (into adenosine diphosphate (ADP) an inorganic phosphate) by utilizing it in biological processes. 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. 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 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. An organism’s stockpile of ATP is used as a battery to store energy in 8) ___. 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, lithotrophs can oxidize minerals such as nitrates or forms of sulfur, such as elemental sulfur, sulfites, and hydrogen sulfide to produce ATP. In photosynthesis, autotrophs produce ATP using light energy, whereas heterotrophs must consume organic compounds, mostly including carbohydrates, fats, and proteins. The amount of energy actually obtained by the organism is lower than the amount present in the food; there are losses in digestion, metabolism, and thermogenesis. Environmental materials that an organism intakes are generally combined with oxygen to release energy, although some can also be oxidized anaerobically by various organisms. The bonds holding the molecules of nutrients together and in particular the bonds holding molecules of free oxygen together are relatively weak compared with the chemical 9) ___ holding carbon dioxide and water together. The utilization of these materials is a form of slow combustion because the nutrients are reacted with 10) ___ (the materials are oxidized slowly enough that the organisms do not actually produce fire). The oxidation releases energy because stronger bonds (bonds within water and carbon dioxide) have been formed. This net energy may evolve as heat, which may be used by the organism for other purposes, such as breaking other bonds to do chemistry required for survival.


ANSWERS: 1) adenosine triphosphate; 2) energy; 3) balance; 4) molecules; 5) organisms; 6) sunlight; 7) plants; 8) cells; 9) bonds; 10) oxygen



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