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Glycolysis is the metabolic pathway that converts glucose into pyruvate, and in most organisms, occurs in the liquid part of cells, the cytosol. The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH). Glycolysis is a sequence of ten reactions catalyzed by enzymes.
Pyruvic acid (IUPAC name: 2-oxopropanoic acid, also called acetoic acid) (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. The ability to exhibit aerobic respiration may yield benefits to the aerobic organism, as aerobic respiration yields more energy than anaerobic respiration. Energy production of the cell involves the synthesis of ATP by an enzyme called ATP synthase. In aerobic respiration, ATP synthase is coupled with an electron transport chain in which oxygen acts as a terminal electron acceptor. In July 2020, marine biologists reported that aerobic microorganisms (mainly), in "quasi-suspended animation", were found in organically poor sediments, up to 101.5 million years old, 250 feet below the seafloor in the South Pacific Gyre (SPG), and could be the longest-living life forms ever found.
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenated environment. Anaerobes may be unicellular or multicellular. Most fungi are obligate aerobes, requiring oxygen to survive. However, some species, such as the Chytridiomycota that reside in the rumen of cattle, are obligate anaerobes; for these species, anaerobic respiration is used because oxygen will disrupt their metabolism or kill them. Deep waters of the ocean are a common anoxic environment.
Cellular respiration is the process by which biological fuels are oxidized in the presence of an inorganic electron acceptor, such as oxygen, to drive the bulk production of adenosine triphosphate (ATP), which contains energy. Cellular respiration may be described as a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from nutrients into ATP, and then release waste products.
Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O2) are available. Anaerobic glycolysis is an effective means of energy production only during short, intense exercise, providing energy for a period ranging from 10 seconds to 2 minutes. This is much faster than aerobic metabolism. The anaerobic glycolysis (lactic acid) system is dominant from about 10–30 seconds during a maximal effort. It replenishes very quickly over this period and produces 2 ATP molecules per glucose molecule, or about 5% of glucose's energy potential (38 ATP molecules). The speed at which ATP is produced is about 100 times that of oxidative phosphorylation.
Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.
Digestion is the breakdown of carbohydrates to yield an energy-rich compound called ATP. The production of ATP is achieved through the oxidation of glucose molecules. In oxidation, the electrons are stripped from a glucose molecule to reduce NAD+ and FAD. NAD+ and FAD possess a high energy potential to drive the production of ATP in the electron transport chain. ATP production occurs in the mitochondria of the cell. There are two methods of producing ATP: aerobic and anaerobic. In aerobic respiration, oxygen is required. Using oxygen increases ATP production from 4 ATP molecules to about 30 ATP molecules. In anaerobic respiration, oxygen is not required. When oxygen is absent, the generation of ATP continues through fermentation. There are two types of fermentation: alcohol fermentation and lactic acid fermentation.
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environments with an oxygen concentration greater than 0.5%.
Ethanol fermentation, also called alcoholic fermentation, is a biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. Because yeasts perform this conversion in the absence of oxygen, alcoholic fermentation is considered an anaerobic process. It also takes place in some species of fish where it provides energy when oxygen is scarce.
The Cori cycle, named after its discoverers, Carl Ferdinand Cori and Gerty Cori, is a metabolic pathway in which lactate, produced by anaerobic glycolysis in muscles, is transported to the liver and converted to glucose, which then returns to the muscles and is cyclically metabolized back to lactate.
In oncology, the Warburg effect is the observation that most cancer cells release energy predominantly not through the 'usual' citric acid cycle and oxidative phosphorylation in the mitochondria as observed in normal cells, but through a less efficient process of 'aerobic glycolysis' consisting of a high level of glucose uptake and glycolysis followed by lactic acid fermentation taking place in the cytosol, not the mitochondria, even in the presence of abundant oxygen. This observation was first published by Otto Heinrich Warburg, who was awarded the 1931 Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme". The precise mechanism and therapeutic implications of the Warburg effect, however, remain unclear.
In biochemistry, mixed acid fermentation is the metabolic process by which a six-carbon sugar is converted into a complex and variable mixture of acids. It is an anaerobic (non-oxygen-requiring) fermentation reaction that is common in bacteria. It is characteristic for members of the Enterobacteriaceae, a large family of Gram-negative bacteria that includes E. coli.
Fermentation is a metabolic process that produces chemical changes in organic substances through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food production, it may more broadly refer to any process in which the activity of microorganisms brings about a desirable change to a foodstuff or beverage. The science of fermentation is known as zymology.
The Crabtree effect, named after the English biochemist Herbert Grace Crabtree, describes the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol (alcohol) in aerobic conditions at high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle, the usual process occurring aerobically in most yeasts e.g. Kluyveromyces spp. This phenomenon is observed in most species of the Saccharomyces, Schizosaccharomyces, Debaryomyces, Brettanomyces, Torulopsis, Nematospora, and Nadsonia genera. Increasing concentrations of glucose accelerates glycolysis which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption. The phenomenon is believed to have evolved as a competition mechanism around the time when the first fruits on Earth fell from the trees. The Crabtree effect works by repressing respiration by the fermentation pathway, dependent on the substrate.
Bioenergetic systems are metabolic processes that relate to the flow of energy in living organisms. Those processes convert energy into adenosine triphosphate (ATP), which is the form suitable for muscular activity. There are two main forms of synthesis of ATP: aerobic, which uses oxygen from the bloodstream, and anaerobic, which does not. Bioenergetics is the field of biology that studies bioenergetic systems.
Cellular waste products are formed as a by-product of cellular respiration, a series of processes and reactions that generate energy for the cell, in the form of ATP. One example of cellular respiration creating cellular waste products are aerobic respiration and anaerobic respiration.
Aerobic fermentation or aerobic glycolysis is a metabolic process by which cells metabolize sugars via fermentation in the presence of oxygen and occurs through the repression of normal respiratory metabolism. Preference of aerobic fermentation over aerobic respiration is referred to as the Crabtree effect in yeast, and is part of the Warburg effect in tumor cells. While aerobic fermentation does not produce adenosine triphosphate (ATP) in high yield, it allows proliferating cells to convert nutrients such as glucose and glutamine more efficiently into biomass by avoiding unnecessary catabolic oxidation of such nutrients into carbon dioxide, preserving carbon-carbon bonds and promoting anabolism.
References
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- ↑ "Pasteur effect". The Free Dictionary by Farlex.
- ↑ Dang, Chi Van; Kim, Jung-Whan (2018). "Convergence of Cancer Metabolism and Immunity: An Overview". Biomolecules & Therapeutics. 26 (1): 4–9. doi:10.4062/biomolther.2017.194. PMC 5746032 . PMID 29212301.
- ↑ Pasteur L (1857). "Mémoire sur la fermentation applée lactique" [Dissertation on apple lactic fermentation]. Comptes rendus de l'Académie des Sciences (in French). 45 (913–916): 1032–1036.
Pasteur, L. (1995). "Mémoire sur la fermentation appelée lactique (Extrait par l'auteur)". Molecular Medicine. 1 (6): 599–601. PMC 2229983 .
Brock, Thomas D. (1995). "Report on the Lactic Acid Fermentation (Author's abstract)". Molecular Medicine. 1 (6): 601–602. doi: 10.1007/BF03401600 . S2CID 92130442. - ↑ Vadlakonda L, Dash A, Pasupuleti M, Anil Kumar K, Reddanna P (2013). "Did we get Pasteur, Warburg, and Crabtree on a right note?". Frontiers in Oncology. 3: 186. doi: 10.3389/fonc.2013.00186 . PMC 3710993 . PMID 23875175.
- ↑ McDonnell G, Russell AD (January 1999). "Antiseptics and disinfectants: activity, action, and resistance". Clinical Microbiology Reviews. 12 (1): 147–179. doi:10.1128/CMR.12.1.147. PMC 88911 . PMID 9880479.
- ↑ Beckner M, Ivey ML, Phister TG (October 2011). "Microbial contamination of fuel ethanol fermentations". Letters in Applied Microbiology. 53 (4): 387–394. doi:10.1111/j.1472-765X.2011.03124.x. PMID 21770989. S2CID 6941273.
