Anaerobic microorganisms, those that evolved and live without oxygen, can produce all the energy they need from anaerobic glycolysis or other fermentations with no net change in oxidative state. However, aerobic organisms, such as animals, require another major step called the citric acid cycle. The citric acid cycle increases energy production by complete oxidation of the glycolytic endproducts lactic acid and pyruvate. The reduced electron carriers created from the citric acid cycle enter the redox chain of cellular respiration that then generates energy-rich ATP from oxidative phosphorylation and chemiosomotic coupling.
In contrast, plants and photosynthetic microbes drive energy conversion through capture of radiant fuels or light in the visible spectrum. Photonic energy is passed from light-harvesting antennae to photopigment-containing reaction centers of photosystems. There water is cleaved, oxygen is evolved, and reduced electron carriers are created.
Photophosphorylation during light reactions and chemiosmotic coupling next drive the synthesis of ATP from ADP and inorganic phosphate. Exceptions to these examples exist. But regardless of the organisms involved i. IntechOpen: What amounts of energy can be derived during chemical processes and for what is this energy utilised? I will concentrate on several examples to keep my answer brief. For oxidative metabolism, 36 to 38 molecules of ATP are produced per mole of glucose oxidized, depending on the energy cost of shuttle systems.
Prokaryotes and other cells that employ the glutamate-aspartate shuttle expend no energy when transferring reducing equivalents to mitochondria. However, cells which use the glycerol phosphate shuttle loose 2 total ATP molecules to deliver reducing equivalents to the respiratory chain. ATP hydrolysis releases For two-system photosynthesis, approximately 48 photons must be absorbed to yield 18 ATP molecules via noncyclic photophosphorylation.
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Hydrolysis of these ATP molecules helps fix atmospheric carbon dioxide into carbohydrates during the dark reaction. Cyclic photophosphorylation also yields ATP for biological work. In addition to oxidative phosphorylation and photophosphorylation, a process called substrate-level phosphorylation produces GTP and ATP from super high-energy compounds important to glycolysis and the citric acid cycle.
Well, this is an interesting question because it can be viewed from both micro- and macroscopic levels of physical organization, each reciprocally interacting with the other. When one thinks about bioenergetics imbalances, the imbalances of metabolic diseases probably first come to mind. Metabolic diseases can be inherited or acquired. They oftentimes produce dysfunctional enzymes, abnormally low concentrations of enzymes, or no enzymes essential for proper cell energetics. Imbalances may yield low energy production or transport and harmful levels of bioreactants or bioproducts. These conditions stress cellular function and may cause cell death and, consequently, organism death under extreme perturbation.
Many metabolic disorders exist in humans and animals, such as sugar intolerances e. In addition to cellular and organismic levels of description for bioenergetics imbalances, one can imagine effects at the larger biosphere scale. Remember that all life on Earth exists in delicate interactive states between and within dynamic systems. For example, the oxygen consumption and carbon dioxide emission needed for the metabolism of aerobic organisms dramatically affect photosynthetic organisms.
And the oxygen evolution and carbon dioxide fixation needed for the metabolism of photosynthetic organisms likewise affect aerobic organisms. Cells behave as engines when transforming potential energy into biologically useful energy. Defective cell energetics impairs engine performance. Biospheres also behave as engines, cyclically producing products that maintain life.
If the biosphere becomes irreversibly imbalanced, such as might occur through habitat destruction, pollution, species-specific lethal diseases, and other factors, then the biosphere engine breaks-down. Such imbalance at the biosphere scale could flourish to the point of global life extinction. For instance, the evolved bioenergetics pathways of organisms and cells would be challenged by unfamiliar poor nutrition availability e.
Without the appropriate biological substrate and niche restrictions, even healthy organisms simply cannot adequately perform the bioenergetics processes needed to sustain life. IntechOpen: Also, can bioenergetics and some of its principles be used for treating or curing currently incurable diseases? Of course, there are a number of progressive degenerative metabolic diseases for which an understanding and application of bioenergetics principles are used in attempts to treat patients. A few of those diseases were mentioned in my answer to a previous question. Sometimes early diagnosis through genetic testing or other methods, dietary changes, medication e.
However, many diseases remain incurable, such as Tay-Sachs disease. But strong clinical evidence remains elusive for most cases. Another promising clinical area for bioenergetics applications is cancer therapy.
Cancer cells require high metabolism to live and proliferate. Cancers poorly treated by standard methods can be controlled by selectively disrupting or preventing oxidative phosphorylation or aerobic glycolysis. In particular, experimental work to suppress oncogenes which encode metabolic substrate, to lower metabolic rate via glycolytic enzyme inhibitors, and to alter metabolic cycles via respiratory chain inhibitors, phosphorylation inhibitors, uncoupling agents, transport inhibitors, and Krebs cycle inhibitors may lead to real clinical successes.
IntechOpen: What is the role of bioenergetics in stem cell maintenance and aging? No clear explanation of aging exists. Many biological premises favor evolution- , gene- , and disease-based mechanisms which incorporate aspects of bioenergetics. Some leading explanations that involve cell energetics include programmed cell death, accummulative DNA damage and mutation, faulty cellular metabolic waste disposal, and free radical formation. For example, new research into the cross-kingdom symbiosis and coevolution of organisms has provided insight into adaptive metabolism, apoptosis, transmissible diseases and immunoprotection, and other issues germane to the relationship between bioenergetics, aging, and disease.
Some findings suggest, perhaps unsurprisingly, that organisms evolved over time to become energetically efficient in certain niches of variable climate, food supply, and dietary demands. But as those niches deviate beyond acceptable parameter ranges, the same organisms, such as humans, show increasing vulnerability to cytopathogenesis via oxidative stress and other mechanisms.
What ever the reasons for aging, changes in environmental signals and tissue integrity may induce somatic stem cell proliferation and differentiation to recover or renew tissue function and viability. IntechOpen: Are there any significant research developments currently being explored which are aimed at generating new insights for the field of bioenergetics? My answers to earlier questions partly address this question. Certainly clinical application of bioenergetics to understand and treat diseases and aging have produced significant research findings and insights about bioenergetics processes and the influence bioenergetics has on organism lifespan and health.
Much of this work focuses on the limits of cell efficiency, protection, and repair, on mitochondrial target sites for therapeutics, and on genetic and epigenetic control over the transmission and expression of metabolic states e. Basic research into bioenergetics is also beginning to uncover a wealth of information regarding the molecular biology of , among other topics, cellular energy transport and byproduct disposal, response regulator networks, nucleotide metabolism, mitochondrial upregulation, calcium signaling, and ion channel structure and function.
The self-regulation system of ATP has been described as follows:. The high-energy bonds of ATP are actually rather unstable bonds. Note that ATP is an energy-coupling agent and not a fuel. It is not a storehouse of energy set aside for some future need. Rather it is produced by one set of reactions and is almost immediately consumed by another. ATP is formed as it is needed, primarily by oxidative processes in the mitochondria. Oxygen is not consumed unless ADP and a phosphate molecule are available, and these do not become available until ATP is hydrolyzed by some energy-consuming process.
Energy metabolism is therefore mostly self-regulating Hickman, Roberts, and Larson, , p. ATP is not excessively unstable, but it is designed so that its hydrolysis is slow in the absence of a catalyst. The ATP is used for many cell functions including transport work moving substances across cell membranes. It is also used for mechanical work , supplying the energy needed for muscle contraction. It supplies energy not only to heart muscle for blood circulation and skeletal muscle such as for gross body movement , but also to the chromosomes and flagella to enable them to carry out their many functions.
A major role of ATP is in chemical work , supplying the needed energy to synthesize the multi-thousands of types of macromolecules that the cell needs to exist. ATP is also used as an on-off switch both to control chemical reactions and to send messages. The shape of the protein chains that produce the building blocks and other structures used in life is mostly determined by weak chemical bonds that are easily broken and remade.
These chains can shorten, lengthen, and change shape in response to the input or withdrawal of energy. The changes in the chains alter the shape of the protein and can also alter its function or cause it to become either active or inactive. The ATP molecule can bond to one part of a protein molecule, causing another part of the same molecule to slide or move slightly which causes it to change its conformation, inactivating the molecule.
Subsequent removal of ATP causes the protein to return to its original shape, and thus it is again functional. The cycle can be repeated until the molecule is recycled, effectively serving as an on and off switch Hoagland and Dodson, , p.
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Both adding a phosphorus phosphorylation and removing a phosphorus from a protein dephosphorylation can serve as either an on or an off switch. ATP is manufactured as a result of several cell processes including fermentation, respiration and photosynthesis. Most commonly the cells use ADP as a precursor molecule and then add a phosphorus to it. In eukaryotes this can occur either in the soluble portion of the cytoplasm cytosol or in special energy-producing structures called mitochondria.
This energy comes from the estimated 10, enzyme chains in the membranous sacks on the mitochondrial walls. Most of the food energy for most organisms is produced by the electron transport chain. As the charge builds up, it provides an electrical potential that releases its energy by causing a flow of hydrogen ions across the inner membrane into the inner chamber. Plants can also produce ATP in this manner in their mitochondria but plants can also produce ATP by using the energy of sunlight in chloroplasts as discussed later.
In the case of eukaryotic animals the energy comes from food which is converted to pyruvate and then to acetyl coenzyme A acetyl CoA. How does this potential difference serve to reattach the phosphates on ADP molecules? The more protons there are in an area, the more they repel each other. When the repulsion reaches a certain level, the hydrogens ions are forced out of a revolving-door-like structure mounted on the inner mitochondria membrane called ATP synthase complexes.
The ATP synthase revolving door resembles a molecular water wheel that harnesses the flow of hydrogen ions in order to build ATP molecules. Each revolution of the wheel requires the energy of about nine hydrogen ions returning into the mitochondrial inner chamber Goodsell, , p. Under maximum conditions, the ATP synthase wheel turns at a rate of up to revolutions per second, producing ATPs during that second.
ATP is used in conjunction with enzymes to cause certain molecules to bond together. The correct molecule first docks in the active site of the enzyme along with an ATP molecule. The enzyme then catalyzes the transfer of one of the ATP phosphates to the molecule, thereby transferring to that molecule the energy stored in the ATP molecule. Next a second molecule docks nearby at a second active site on the enzyme. The phosphate is then transferred to it, providing the energy needed to bond the two molecules now attached to the enzyme. Once they are bonded, the new molecule is released. This operation is similar to using a mechanical jig to properly position two pieces of metal which are then welded together.
Once welded, they are released as a unit and the process then can begin again. Although ATP contains the amount of energy necessary for most reactions, at times more energy is required. The solution is for ATP to release two phosphates instead of one, producing an adenosine monophosphate AMP plus a chain of two phosphates called a pyrophosphate. How adenosine monophosphate is built up into ATP again illustrates the precision and the complexity of the cell energy system.
The enzymes used in glycolysis, the citric acid cycle, and the electron transport system, are all so precise that they will replace only a single phosphate. Adenylate kinase is a highly organized but compact enzyme with its active site located deep within the molecule. The deep active site is required because the reactions it catalyzes are sensitive to water. To prevent this, adenylate kinase is designed so that the active site is at the end of a channel deep in the structure which closes around AMP and ATP, shielding the reaction from water. Many other enzymes that use ATP rely on this system to shelter their active site to prevent inappropriate reactions from occurring.
Pyrophosphates and pyrophosphoric acid, both inorganic forms of phosphorus, must also be broken down so they can be recycled.
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This phosphate breakdown is accomplished by the inorganic enzyme pyrophosphatase which splits the pyrophosphate to form two free phosphates that can be used to charge ATP Goodsell, , p. This system is so amazingly efficient that it produces virtually no waste, which is astounding considering its enormously detailed structure. Goodsell , p. The Krebs cycle charges only ADP, but the energy contained in ATP can be transferred to one of the other nucleosides by means of an enzyme called nucleoside diphosphate kinase.
This enzyme transfers the phosphate from a nucleoside triphosphate, commonly ATP, to a nucleoside diphosphate such as guanosine diphosphate GDP to form guanosine triphosphate GTP. The nucleoside diphosphate kinase works by one of its six active sites binding nucleoside triphosphate and releasing the phosphate which is bonded to a histidine.
Scores of other enzymes exist in order for ATP to transfer its energy to the various places where it is needed. Each enzyme must be specifically designed to carry out its unique function, and most of these enzymes are critical for health and life. Also, back-up mechanisms sometimes exist so that the body can achieve the same goals through an alternative biochemical route.
These few simple examples eloquently illustrate the concept of over-design built into the body. They also prove the enormous complexity of the body and its biochemistry. Without ATP, life as we understand it could not exist. It is a perfectly-designed, intricate molecule that serves a critical role in providing the proper size energy packet for scores of thousands of classes of reactions that occur in all forms of life.
Even viruses rely on an ATP molecule identical to that used in humans. The ATP energy system is quick, highly efficient, produces a rapid turnover of ATP, and can rapidly respond to energy demand changes Goodsell, , p. Furthermore, the ATP molecule is so enormously intricate that we are just now beginning to understand how it works. In manufacturing terms, the ATP molecule is a machine with a level of organization on the order of a research microscope or a standard television Darnell, Lodish, and Baltimore, In addition, a potential ATP candidate molecule would not be selected for by evolution until it was functional and life could not exist without ATP or a similar molecule that would have the same function.
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ATP is an example of a molecule that displays irreducible complexity which cannot be simplified and still function Behe, ATP could have been created only as a unit to function immediately in life and the same is true of the other intricate energy molecules used in life such as GTP. Although other energy molecules can be used for certain cell functions, none can even come close to satisfactorily replacing all the many functions of ATP.
Over , other detailed molecules like ATP have also been designed to enable humans to live, and all the same problems related to their origin exist for them all.
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Many macromolecules that have greater detail than ATP exist, as do a few that are less highly organized, and in order for life to exist all of them must work together as a unit. An enormous gap exists between prokaryote bacteria and cyanobacteria cells and eukaryote protists, plants and animals type of cells:.
The organizational complexity of the eukaryotes is so much greater than that of the prokaryotes that it is difficult to visualize how a eukaryote could have arisen from any known prokaryote Hickman et al. Some of the differences are that prokaryotes lack organelles, a cytoskeleton, and most of the other structures present in eukaryotic cells. Consequently, the functions of most organelles and other ultrastructure cell parts must be performed in bacteria by the cell membrane and its infoldings called mesosomes.
A crucial difference between prokaryotes and eukaryotes is the means they use to produce ATP. All life produces ATP by three basic chemical methods only: oxidative phosphorylation, photophosphorylation, and substrate-level phosphorylation Lim, , p. In prokaryotes ATP is produced both in the cell wall and in the cytosol by glycolysis.
In eukaryotes most ATP is produced in chloroplasts for plants , or in mitochondria for both plants and animals. No means of producing ATP exists that is intermediate between these four basic methods and no transitional forms have ever been found that bridge the gap between these four different forms of ATP production. They require cells to manufacture it and viruses have no source of energy apart from cells. The cell membrane must for this reason be compared with the entire eukaryote cell ultrastructure which performs these many functions.
No simple means of producing ATP is known and prokaryotes are not by any means simple. They contain over 5, different kinds of molecules and can use sunlight, organic compounds such as carbohydrates, and inorganic compounds as sources of energy to manufacture ATP. Another example of the cell membrane in prokaryotes assuming a function of the eukaryotic cell ultrastructure is as follows: Their DNA is physically attached to the bacterial cell membrane and DNA replication may be initiated by changes in the membrane.
Further, the mesosome appears to guide the duplicated chromatin bodies into the two daughter cells during cell division Talaro and Talaro, The mitochondria produce ATP in their internal membrane system called the cristae. Since bacteria lack mitochondria, as well as an internal membrane system, they must produce ATP in their cell membrane which they do by two basic steps. The bacterial cell membrane contains a unique structure designed to produce ATP and no comparable structure has been found in any eukaryotic cell Jensen, Wright, and Robinson, In bacteria, the ATPase and the electron transport chain are located inside the cytoplasmic membrane between the hydrophobic tails of the phospholipid membrane inner and outer walls.
Breakdown of sugar and other food causes the positively charged protons on the outside of the membrane to accumulate to a much higher concentration than they are on the membrane inside. This creates an excess positive charge on the outside of the membrane and a relatively negative charge on the inside. This results in a potential energy gradient similar to that produced by charging a flashlight battery. The force the potential energy gradient produces is called a proton motive force that can accomplish a variety of cell tasks including converting ADP into ATP.
In some bacteria such as Halobacterium this system is modified by use of bacteriorhodopsin , a protein similar to the sensory pigment rhodopsin used in the vertebrate retina Lim, , p. Illumination causes the pigment to absorb light energy, temporarily changing rhodopsin from a trans to a cis form. The trans to cis conversion causes deprotonation and the transfer of protons across the plasma membrane to the periplasm.
This modification allows bacteria to live in low oxygen but rich light regions. This anaerobic ATP manufacturing system, which is unique to prokaryotes, uses a chemical compound other than oxygen as a terminal electron acceptor Lim, , p. The location of the ATP producing system is only one of many major contrasts that exist between bacterial cell membranes and mitochondria. Chloroplasts are double membraned ATP-producing organelles found only in plants. Inside their outer membrane is a set of thin membranes organized into flattened sacs stacked up like coins called thylakoids Greek thylac or sack, and oid meaning like.
The chloroplasts first convert the solar energy into ATP stored energy, which is then used to manufacture storage carbohydrates which can be converted back into ATP when energy is needed. The chloroplasts also possess an electron transport system for producing ATP. The electrons that enter the system are taken from water.