Biochemistry Terms Starting With O
Biochemistry Glossary: O
Jump to Biochemistry Term
Oligosaccharide
/ ol-ih-GO-sak-uh-ryde / · Greek oligos meaning few and sakcharon meaning sugar
Oligosaccharides are carbohydrates composed of 3 to 10 monosaccharide units linked together by glycosidic bonds.
Human milk contains over 200 structurally distinct oligosaccharides that reach concentrations of 5 to 15 grams per liter, making them the third most abundant solid component after lactose and fat. Raffinose, a trisaccharide found in beans and legumes, consists of galactose, glucose, and fructose units joined by alpha-glycosidic bonds. Because humans lack the enzyme alpha-galactosidase needed to cleave certain oligosaccharides like raffinose and stachyose, these compounds pass undigested into the colon where resident bacteria ferment them, producing carbon dioxide and hydrogen gas.
Certain oligosaccharides called fructooligosaccharides are now added to commercial infant formulas to mimic the prebiotic effects of human breast milk, and clinical trials have measured a 20 to 30 percent reduction in pathogenic gut bacteria in formula-fed infants receiving these supplements.
Building Blocks of Carbohydrates →All carbohydrates provide energy to the body. Many oligosaccharides, including those in beans, pass through the human digestive system undigested and yield calories only after bacterial fermentation in the colon, a process that also generates gas as a byproduct.
Fermentation Biology →Oligosaccharides attached to glycoproteins on the surface of human red blood cells determine ABO blood type, with type A cells carrying N-acetylgalactosamine at the terminal position and type B cells carrying galactose instead. These sugar chains extend roughly 10 nanometers above the cell membrane surface.
Omega-3 Fatty Acid
/ oh-MAY-guh THREE FA-tee A-sid / · Greek omega (last letter of the alphabet) + 3 (position of first double bond from methyl end) + Latin acidus (sour)
Omega-3 fatty acid is a polyunsaturated fatty acid containing a carbon-carbon double bond at the third position from the methyl end of its hydrocarbon chain.
Cold-water fish like Atlantic salmon (Salmo salar) accumulate high concentrations of EPA and DHA, two omega-3 fatty acids with 20 and 22 carbons respectively. These molecules incorporate into cell membranes throughout the body, particularly in neural tissue where DHA comprises approximately 40 percent of brain polyunsaturated fatty acids. Flaxseeds provide alpha-linolenic acid, an 18-carbon omega-3 that humans must convert enzymatically to EPA and DHA, though this conversion operates at only 5 to 10 percent efficiency in most individuals, making direct marine sources far more effective at raising tissue DHA levels.
The Inuit population of Greenland traditionally consumed over 10 grams of omega-3 fatty acids daily from marine sources, yet exhibited remarkably low rates of cardiovascular disease despite a high-fat diet, an observation that prompted Danish researchers Bang and Dyerberg to begin systematic studies of omega-3 biochemistry in the 1970s.
Building Blocks of Lipids →All fish oils deliver the same omega-3 benefits. EPA to DHA ratios vary dramatically by species: sardines typically provide about 1.5 parts EPA for every part DHA, while tuna offers roughly equal amounts of both, and these differences matter because EPA and DHA have distinct physiological effects on inflammation and neural function.
Biochemistry News in 2017 →Krill (Euphausia superba) in Antarctic waters obtain omega-3 fatty acids by grazing on marine algae, then concentrate these molecules in their bodies where omega-3s comprise roughly 30 percent of total lipid content. A single Antarctic krill swarm can cover 450 square kilometers and represent a biomass exceeding 2 million metric tons, making krill collectively one of the largest reservoirs of marine omega-3 fatty acids on Earth.
Oxidation
/ ok-si-DAY-shun / · From French oxygène (oxygen) + -ation, literally meaning the process of combining with oxygen
Oxidation is a chemical reaction in which a molecule, atom, or ion loses electrons, often accompanied by the loss of hydrogen atoms or the gain of oxygen atoms.
During cellular respiration in mitochondria, glucose undergoes oxidation through a series of enzyme-catalyzed reactions that strip away electrons and hydrogen atoms in a controlled sequence. Complete oxidation of one glucose molecule yields approximately 30 to 32 ATP molecules, providing energy for cellular processes in organisms from baker’s yeast (Saccharomyces cerevisiae) to humans. Iron atoms in hemoglobin can undergo oxidation from the ferrous state (Fe2+) to the ferric state (Fe3+), producing methemoglobin, which cannot bind oxygen and reduces blood oxygen-carrying capacity.
The browning of a sliced apple results from the oxidation of polyphenol compounds by the enzyme polyphenol oxidase, which catalyzes these reactions at a rate roughly 10 million times faster than uncatalyzed oxidation would proceed.
Are Enzymes Proteins? →Oxidation always requires oxygen. Oxidation refers to the loss of electrons and proceeds without any oxygen present, as when sodium metal loses an electron to chlorine gas and becomes Na+ during the formation of table salt.
Pseudomonas bacteria oxidize ammonia to nitrite in soil ecosystems, converting NH3 to NO2- while harvesting the released electrons to generate ATP. This reaction proceeds at measurable rates even in waterlogged soils where oxygen concentrations drop below 1 percent, demonstrating that biological oxidation can couple to electron acceptors other than molecular oxygen.
Oxidative Phosphorylation
/ OK-sih-day-tiv fos-for-ih-LAY-shun / · Latin oxidare meaning to combine with oxygen + Greek phosphoros meaning light-bearing + Latin -ation meaning process
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate through the electron transport chain and chemiosmosis in mitochondria.
During oxidative phosphorylation, electrons from NADH and FADH2 pass through four protein complexes embedded in the inner mitochondrial membrane, creating a proton gradient that drives ATP synthase to rotate and synthesize ATP. A single glucose molecule can yield approximately 32 to 34 ATP molecules through this pathway, making it far more efficient than glycolysis alone, which produces only 2 ATP per glucose. Brown adipose tissue in hibernating mammals like ground squirrels (Spermophilus lateralis) redirects this process by expressing uncoupling protein 1, which dissipates the proton gradient as heat rather than driving ATP synthesis, allowing the animal to generate body warmth without shivering.
Cyanide is lethal because it binds to cytochrome c oxidase in Complex IV with a dissociation constant near 0.2 micromolar, blocking the final step of the electron transport chain and halting ATP production within minutes even at nanomolar blood concentrations.
Oxidative phosphorylation does not happen in the mitochondrial matrix. The electron transport chain complexes are embedded in the inner mitochondrial membrane, and ATP synthase spans that membrane, using the proton gradient across it rather than any reaction occurring in the matrix fluid.
Do Prokaryotes Have Mitochondria? →The flight muscles of hummingbirds contain exceptionally high mitochondrial densities, with mitochondria occupying up to 35 percent of muscle cell volume, to support the oxidative phosphorylation rates that power wing beats exceeding 80 times per second during hovering flight.
Oxidizing Agent
/ OX-i-dy-zing AY-jent / · From Greek oxys (sharp, acid) + gen (producer); Latin agens (acting)
Oxidizing Agent oxidizing agent is a chemical species that accepts electrons from another substance during a redox reaction, becoming reduced itself while causing the oxidation of the donor substance.
In cellular respiration, oxygen is the terminal oxidizing agent in the electron transport chain, accepting electrons from NADH and FADH2 to form water. The human body consumes approximately 550 liters of oxygen daily, oxidizing glucose and other nutrients to produce ATP. Hydrogen peroxide also oxidizes cellular components, which is why the enzyme catalase degrades it at roughly 40 million molecules per second to prevent tissue damage.
Beyond biology, industrial oxidizing agents such as chlorine gas disinfect municipal water supplies by oxidizing the cell membranes of bacteria.
Potassium permanganate, a powerful oxidizing agent used in water treatment, can oxidize organic compounds so rapidly that it generates enough heat to ignite paper on contact.
Oxidizing agents lose electrons during reactions. They gain electrons while causing other substances to be oxidized and lose their electrons.
NAD+ accepts electrons from glyceraldehyde-3-phosphate during glycolysis in yeast cells, making it the oxidizing agent in that reaction and becoming NADH in the process.
Translation Biology →Oxidoreductase
/ ok-si-doh-ree-DUK-tays / · Latin: oxidare (to oxidize) + reducere (to reduce) + -ase (enzyme suffix)
Oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule to another through oxidation-reduction reactions.
These enzymes form the first and largest class in the Enzyme Commission classification system, designated EC 1, and include hundreds of distinct members across all domains of life. The human mitochondrial enzyme cytochrome c oxidase transfers approximately 1 billion electrons per second during cellular respiration, ranking it among the most active oxidoreductases in metabolism. Lactate dehydrogenase in muscle cells converts pyruvate to lactate during anaerobic exercise, regenerating NAD+ so glycolysis can continue.
Alcohol dehydrogenase in brewer’s yeast (Saccharomyces cerevisiae) performs the analogous reduction of acetaldehyde to ethanol during fermentation.
The enzyme catalase, an oxidoreductase found in nearly all living organisms, can decompose up to 40 million molecules of hydrogen peroxide per second, making it one of the fastest enzymes known to science.
Oxidation requires oxygen. Oxidoreductases catalyze electron transfer reactions that proceed without any oxygen present, as when NADH dehydrogenase passes electrons to ubiquinone in the electron transport chain.
Glucose-6-phosphate dehydrogenase in human red blood cells oxidizes glucose-6-phosphate while reducing NADP+ to NADPH, providing the reducing power that protects cells from oxidative damage.