Bifidobacterium is a genus of gram-positive, nonmotile branched anaerobic bacteria. They are ubiquitous inhabitants of the gastrointestinal tract and mouth of mammals, including humans. Bifidobacteria are one of the major genera of bacteria that make up the gastrointestinal tract microbiota in mammals; some bifidobacteria are used as probiotics. Before the 1960s, Bifidobacterium species were collectively referred to as "Lactobacillus bifidus". In 1899, Henri Tissier, a French pediatrician at the Pasteur Institute in Paris, isolated a bacterium characterised by a Y-shaped morphology in the intestinal microbiota of breast-fed infants and named it "bifidus". In 1907, Élie Metchnikoff, deputy director at the Pasteur Institute, propounded the theory that lactic acid bacteria are beneficial to human health. Metchnikoff observed that the longevity of Bulgarian peasants was the result of their consumption of fermented milk products. Elie Metchnikoff suggested that “oral administration of cultures of fermentative bacteria would implant the beneficial bacteria in the intestinal tract”.
The genus Bifidobacterium possesses a unique fructose-6-phosphate phosphoketolase pathway employed to ferment carbohydrates. Much metabolic research on bifidobacteria has focused on oligosaccharide metabolism, as these carbohydrates are available in their otherwise nutrient-limited habitats. Infant-associated bifidobacterial phylotypes appear to have evolved the ability to ferment milk oligosaccharides, whereas adult-associated species use plant oligosaccharides, consistent with what they encounter in their respective environments; as breast-fed infants harbor bifidobacteria-dominated gut consortia, numerous applications attempt to mimic the bifidogenic properties of milk oligosaccharides. These are broadly classified as plant-derived fructooligosaccharides or dairy-derived galactooligosaccharides, which are differentially metabolized and distinct from milk oligosaccharide catabolism; the sensitivity of members of the genus Bifidobacterium to O2 limits probiotic activity to anaerobic habitats.
Recent research has reported. Low concentrations of O2 and CO2 can have a stimulatory effect on the growth of these Bifidobacterium strains. Based on the growth profiles under different O2 concentrations, the Bifidobacterium species were classified into four classes: O2-hypersensitive, O2-sensitive, O2-tolerant, microaerophilic; the primary factor responsible for aerobic growth inhibition is proposed to be the production of hydrogen peroxide in the growth medium. A H2O2-forming NADH oxidase was purified from O2-sensitive Bifidobacterium bifidum and was identified as a b-type dihydroorotate dehydrogenase; the kinetic parameters suggested that the enzyme could be involved in H2O2 production in aerated environments. Members of the genus Bifidobacterium have genome sizes ranging from 1.73 to 3.25 Mb, corresponding to 1,352 and 2,557 predicted protein-encoding open reading frames, respectively. Functional classification of Bifidobacterium genes, including the pan-genome of this genus, revealed that 13.7% of the identified bifidobacterial genes encode enzymes involved in carbohydrate metabolism.
Adding bifidobacterium as a probiotic to conventional treatment of ulcerative colitis has been shown to be associated with improved rates of remission and improved maintenance of remission. Some Bifidobacterium strains are used in the food industry. Different species and/or strains of bifidobacteria may exert a range of beneficial health effects, including the regulation of intestinal microbial homeostasis, the inhibition of pathogens and harmful bacteria that colonize and/or infect the gut mucosa, the modulation of local and systemic immune responses, the repression of procarcinogenic enzymatic activities within the microbiota, the production of vitamins, the bioconversion of a number of dietary compounds into bioactive molecules. Bifidobacteria improve the gut mucosal barrier and lower levels of lipopolysaccharide in the intestine. Occurring Bifidobacterium spp. may discourage the growth of Gram-negative pathogens in infants. Mother's milk contains lower quantities of phosphate. Therefore, when mother's milk is fermented by lactic acid bacteria in the infant's gastrointestinal tract, the pH may be reduced, making it more difficult for Gram-negative bacteria to grow.
The human infant gut is sterile up until birth, where it takes up bacteria from its surrounding environment and its mother/ The microbiota that makes up the infant gut differs from the adult gut. An infant reaches the adult stage of their microbiome at around 3 years of age, when their microbiome diversity increases and the infant switches over to solid foods; when breast-fed, infants are colonized earlier by Bifidobacterium when compared to babies that are formula-fed. Bifidobacterium is the most common bacteria in the infant gut microbiome. There is more variability in genotypes over time in infants, making them less stable compared to the adult Bifidobacterium. Infants and children under 3 years old show low diversity in microbiome bacteria, but more diversity between individuals when compared to adults. Reduction of Bifidobacterium and increase in diversity of the infant gut microbiome occurs with less breast-milk intake and increase of solid food intake. Mammalian milk all contain oligosaccharides showing natural selection.
Human milk oligosaccharides are not digested by enzymes and remain whole through the digestive tract before being broken down in the colon by microbiota. Bifidobacterium species genomes of B. long
Glycolaldehyde is the organic compound with the formula HOCH2-CHO. It is the smallest possible molecule that contains both a hydroxyl group, it is a reactive molecule that occurs both in the biosphere and in the interstellar medium. It is supplied as a white solid. Although it conforms to the general formula for carbohydrates, Cnn, it is not considered to be a saccharide. Glycolaldehyde exists; as a solid and molten liquid, it exists as a dimer. In aqueous solution, it exists as a mixture of at least four species, which interconvert, it is the only possible diose, a 2-carbon monosaccharide, although a diose is not a saccharide. While not a true sugar, it is the simplest sugar-related molecule, it is reported to taste sweet. Glycolaldehyde is the second most abundant compound formed. Glycolaldehyde can be synthesized by the oxidation of ethylene glycol using hydrogen peroxide in the presence of Iron sulphate, it can form by action of ketolase on fructose 1,6-bisphosphate in an alternate glycolysis pathway.
This compound is transferred by thiamine pyrophosphate during the pentose phosphate shunt. In purine catabolism, xanthine is first converted to urate; this is converted to 5-hydroxyisourate, which decarboxylates to allantoic acid. After hydrolyzing one urea, this leaves glycolureate. After hydrolyzing the second urea, glycolaldehyde is left. Two glycolaldehydes condense to form erythrose 4-phosphate, which goes to the pentose phosphate shunt again. Glycolaldehyde is an intermediate in the formose reaction. In the formose reaction, two formaldehyde molecules condense to make glycolaldehyde. Glycolaldehyde is converted to glyceraldehyde; the presence of this glycolaldehyde in this reaction demonstrates how it might play an important role in the formation of the chemical building blocks of life. Nucleotides, for example, rely on the formose reaction to attain its sugar unit. Nucleotides are essential for life, because they compose the genetic information and coding for life, it is invoked in theories of abiogenesis.
In the laboratory, it can be converted to amino acids and short dipeptides may have facilitated the formation of complex sugars. For example, L-valyl-L-valine was used as a catalyst to form tetroses from glycolaldehyde. Theoretical calculations have additionally shown the feasibility of dipeptide-catalyzed synthesis of pentoses; this formation showed stereospecific, catalytic synthesis of D-ribose, the only occurring enantiomer of ribose. Since the detection of this organic compound, many theories have been developed related various chemical routes to explain its formation in stellar systems, it was found that UV-irradiation of methanol ices containing CO yielded organic compounds such as glycolaldehyde and methyl formate, the more abundant isomer of glycolaldehyde. The abundances of the products disagree with the observed values found in IRAS 16293-2422, but this can be accounted for by temperature changes. Ethylene Glycol and glycolaldehyde require temperatures above 30 K; the general consensus among the astrochemistry research community is in favor of the grain surface reaction hypothesis.
However, some scientists believe the reaction occurs within colder parts of the core. The dense core will not allow for irradiation; this change will alter the reaction forming glycolaldehyde. The different conditions studied indicate how problematic it could be to study chemical systems that are light-years away; the conditions for the formation of glycolaldehyde are still unclear. At this time, the most consistent formation reactions seems to be on the surface of ice in cosmic dust. Glycolaldehyde has been identified in gas and dust near the center of the Milky Way galaxy, in a star-forming region 26000 light-years from Earth, around a protostellar binary star, IRAS 16293-2422, 400 light years from Earth. Observation of in-falling glycolaldehyde spectra 60 AU from IRAS 16293-2422 suggests that complex organic molecules may form in stellar systems prior to the formation of planets arriving on young planets early in their formation; the interior region of a dust cloud is known to be cold. With temperatures as cold as 4 Kelvin the gases within the cloud will freeze and fasten themselves to the dust, which provides the reaction conditions conducive for the formation of complex molecules such as glycolaldehyde.
When a star has formed from the dust cloud, the temperature within the core will increase. This will cause the molecules on the dust to be released; the molecule will emit radio waves that can be analyzed. The Atacama Large Millimeter/submilliter Array first detected glycolaldehyde. ALMA consists of 66 antennas. On October 23, 2015, researchers at the Paris Observatory announced the discovery of glycolaldehyde and ethyl alcohol on Comet Lovejoy, the first such identification of these substances in a comet. "Cold Sugar in Space Provides Clue to the Molecular Origin of Life". National Radio Astronomy Observatory. September 20, 2004. Retrieved December 20, 2006
Degree of polymerization
The degree of polymerization, or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule. For a homopolymer, there is only one type of monomeric unit and the number-average degree of polymerization is given by D P n ≡ X n = M n M 0, where Mn is the number-average molecular weight and M0 is the molecular weight of the monomer unit. For most industrial purposes, degrees of polymerization in the thousands or tens of thousands are desired; this number does not reflect the variation in molecule size of the polymer that occurs, it only represents the mean number of monomeric units. Some authors, define DP as the number of repeat units, where for copolymers the repeat unit may not be identical to the monomeric unit. For example, in nylon-6,6, the repeat unit contains the two monomeric units —NH6NH— and —OC4CO—, so that a chain of 1000 monomeric units corresponds to 500 repeat units; the degree of polymerization or chain length is 1000 by the first definition, but 500 by the second.
In step-growth polymerization, in order to achieve a high degree of polymerization, Xn, a high fractional monomer conversion, p, is required, according to Carothers' equation X ¯ n = 1 1 − p For example, a monomer conversion of p = 99% would be required to achieve Xn = 100. For chain-growth free radical polymerization, Carothers' equation does not apply. Instead long chains are formed from the beginning of the reaction. Long reaction times increase the polymer yield, but have little effect on the average molecular weight; the degree of polymerization is related to the kinetic chain length, the average number of monomer molecules polymerized per chain initiated. However it differs from the kinetic chain length for several reasons: chain termination may occur wholly or by recombination of two chain radicals, which doubles the degree of polymerization chain transfer to monomer starts a new macromolecule for the same kinetic chain, corresponding to a decrease of the degree of polymerization chain transfer to solvent or to another solute (a modifier or regulator decreases the degree of polymerization Polymers with identical composition but different molecular weights may exhibit different physical properties.
In general, increasing degree of polymerization correlates with higher melting temperature and higher mechanical strength. Synthetic polymers invariably consist of a mixture of macromolecular species with different degrees of polymerization and therefore of different molecular weights. There are different types of average polymer molecular weight, which can be measured in different experiments; the two most important are the weight average. The number-average degree of polymerization is a weighted mean of the degrees of polymerization of polymer species, weighted by the mole fractions of the species, it is determined by measurements of the osmotic pressure of the polymer. The weight-average degree of polymerization is a weighted mean of the degrees of polymerization, weighted by the weight fractions of the species, it is determined by measurements of Rayleigh light scattering by the polymer. Anhydroglucose unit
Gut flora, or gut microbiota, or gastrointestinal microbiota, is the complex community of microorganisms that live in the digestive tracts of humans and animals, including insects. The gut metagenome is the aggregate of all the genomes of gut microbiota; the gut is one niche. In humans, the gut microbiota has the largest numbers of bacteria and the greatest number of species compared to other areas of the body. In humans, the gut flora is established at one to two years after birth, by which time the intestinal epithelium and the intestinal mucosal barrier that it secretes have co-developed in a way, tolerant to, supportive of, the gut flora and that provides a barrier to pathogenic organisms; the relationship between some gut flora and humans is not commensal, but rather a mutualistic relationship. Some human gut microorganisms benefit the host by fermenting dietary fiber into short-chain fatty acids, such as acetic acid and butyric acid, which are absorbed by the host. Intestinal bacteria play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids and xenobiotics.
The systemic importance of the SCFAs and other compounds they produce are like hormones and the gut flora itself appears to function like an endocrine organ, dysregulation of the gut flora has been correlated with a host of inflammatory and autoimmune conditions. The composition of human gut microbiota changes over time, when the diet changes, as overall health changes. A systematic review from 2016 examined the preclinical and small human trials that have been conducted with certain commercially available strains of probiotic bacteria and identified those that had the most potential to be useful for certain central nervous system disorders; the microbial composition of the gut microbiota varies across the digestive tract. In the stomach and small intestine few species of bacteria are present; the colon, in contrast, contains a densely-populated microbial ecosystem with up to 1012 cells per gram of intestinal content. These bacteria represent between 1000 different species. However, 99 % of the bacteria come from about 40 species.
As a consequence of their abundance in the intestine, bacteria make up to 60% of the dry mass of feces. Fungi, protists and viruses are present in the gut flora, but less is known about their activities. Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities, it is estimated that these gut flora have around a hundred times as many genes in total as there are in the human genome. Many species in the gut have not been studied outside of their hosts because most cannot be cultured. While there are a small number of core species of microbes shared by most individuals, populations of microbes can vary among different individuals. Within an individual, microbe populations stay constant over time though some alterations may occur with changes in lifestyle and age; the Human Microbiome Project has set out to better describe the microflora of the human gut and other body locations. The four dominant bacterial phyla in the human gut are Firmicutes, Bacteroidetes and Proteobacteria.
Most bacteria belong to the genera Bacteroides, Faecalibacterium, Ruminococcus, Peptostreptococcus, Bifidobacterium. Other genera, such as Escherichia and Lactobacillus, are present to a lesser extent. Species from the genus Bacteroides alone constitute about 30% of all bacteria in the gut, suggesting that this genus is important in the functioning of the host. Fungal genera that have been detected in the gut include Candida, Aspergillus, Rhodotorula, Pleospora, Sclerotinia and Galactomyces, among others. Rhodotorula is most found in individuals with inflammatory bowel disease while Candida is most found in individuals with hepatitis B cirrhosis and chronic hepatitis B. Archaea constitute another large class of gut flora which are important in the metabolism of the bacterial products of fermentation. Industralization is associated with changes in the microbiota and the reduction of diversity could drive certain species to extinction. An enterotype is a classification of living organisms based on its bacteriological ecosystem in the human gut microbiome not dictated by age, body weight, or national divisions.
There are indications. Three human enterotypes have been proposed. Due to the high acidity of the stomach, most microorganisms cannot survive there; the main bacterial inhabitants of the stomach include: Streptococcus, Lactobacillus, Peptostreptococcus, types of yeast. Helicobacter pylori is a gram-negative spiral bacterium that establishes on gastric mucosa causing chronic gastritis and peptic ulcer disease and is a carcinogen for gastric cancer; the small intestine contains a trace amount of microorganisms due to the proximity and influence of the stomach. Gram-positive cocci and rod-shaped bacteria are the predominant microorganisms found in the small intestine. However, in the distal portion of the small intestine alkaline conditions support gram-negative bacteria of the Enterobacteriaceae; the bacterial flora of the small intestine aid in a wide range of intestinal functions. The bacterial flora provide regulatory signals that enable the utility of the gut. Overgrowth of bacteria in the small intestine can lead to intestinal failure.
In addition the large intestine contains the largest bacterial ecosystem in the human bod
Enzymes are macromolecular biological catalysts. Enzymes accelerate chemical reactions; the molecules upon which enzymes may act are called substrates and the enzyme converts the substrates into different molecules known as products. All metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps; the study of enzymes is called enzymology and a new field of pseudoenzyme analysis has grown up, recognising that during evolution, some enzymes have lost the ability to carry out biological catalysis, reflected in their amino acid sequences and unusual'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Most enzymes are proteins; the latter are called ribozymes. Enzymes' specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the reaction rate by lowering its activation energy; some enzymes can make their conversion of substrate to product occur many millions of times faster.
An extreme example is orotidine 5'-phosphate decarboxylase, which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, activators are molecules that increase activity. Many therapeutic drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH, many enzymes are denatured when exposed to excessive heat, losing their structure and catalytic properties; some enzymes are used commercially, in the synthesis of antibiotics. Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein, starch or fat stains on clothes, enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew.
By the late 17th and early 18th centuries, the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were known but the mechanisms by which these occurred had not been identified. French chemist Anselme Payen was the first to discover an enzyme, diastase, in 1833. A few decades when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was caused by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms, he wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."In 1877, German physiologist Wilhelm Kühne first used the term enzyme, which comes from Greek ἔνζυμον, "leavened" or "in yeast", to describe this process. The word enzyme was used to refer to nonliving substances such as pepsin, the word ferment was used to refer to chemical activity produced by living organisms.
Eduard Buchner submitted his first paper on the study of yeast extracts in 1897. In a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts when there were no living yeast cells in the mixture, he named the enzyme that brought about the fermentation of sucrose "zymase". In 1907, he received the Nobel Prize in Chemistry for "his discovery of cell-free fermentation". Following Buchner's example, enzymes are named according to the reaction they carry out: the suffix -ase is combined with the name of the substrate or to the type of reaction; the biochemical identity of enzymes was still unknown in the early 1900s. Many scientists observed that enzymatic activity was associated with proteins, but others argued that proteins were carriers for the true enzymes and that proteins per se were incapable of catalysis. In 1926, James B. Sumner crystallized it; the conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley, who worked on the digestive enzymes pepsin and chymotrypsin.
These three scientists were awarded the 1946 Nobel Prize in Chemistry. The discovery that enzymes could be crystallized allowed their structures to be solved by x-ray crystallography; this was first done for lysozyme, an enzyme found in tears and egg whites that digests the coating of some bacteria. This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail. An enzyme's name is derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase. Examples are alcohol dehydrogenase and DNA polymerase. Different enzymes that catalyze the same chemical reaction are called isozymes; the International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers. The first number broadly classifies the enzyme based on its mechanism; the top-level classification is: EC 1, Oxidoreductases: catalyze oxidation/reducti
A cyclohexane conformation is any of several three-dimensional shapes that a cyclohexane molecule can assume while maintaining the integrity of its chemical bonds. The internal angles of a flat regular hexagon are 120°, while the preferred angle between successive bonds in a carbon chain is about 109.5°, the tetrahedral angle. Therefore, the cyclohexane ring tends to assume certain non-planar conformations, which have all angles closer to 109.5° and therefore a lower strain energy than the flat hexagonal shape. The most important shapes are called chair, half-chair and twist-boat; the molecule can switch between these conformations, only two of them—chair and twist-boat—can be isolated in pure form. Cyclohexane conformations have been extensively studied in organic chemistry because they are the classical example of conformational isomerism and have noticeable influence on the physical and chemical properties of cyclohexane. In 1890, Hermann Sachse, a 28-year-old assistant in Berlin, published instructions for folding a piece of paper to represent two forms of cyclohexane he called symmetrical and unsymmetrical.
He understood that these forms had two positions for the hydrogen atoms, that two chairs would interconvert, how certain substituents might favor one of the chair forms. Because he expressed all this in mathematical language, few chemists of the time understood his arguments, he had several attempts at publishing these ideas, but none succeeded in capturing the imagination of chemists. His death in 1893 at the age of 31 meant, it was only in 1918 when Ernst Mohr, based on the molecular structure of diamond, solved using the very new technique of x-ray crystallography, was able to argue that Sachse's chair was the pivotal motif. Derek Barton and Odd Hassel shared the 1969 Nobel Prize for work on the conformations of cyclohexane and various other molecules; the carbon-carbon bonds along the cyclohexane ring are sp³ hybrid orbitals, which have tetrahedral symmetry. Therefore, the angles between bonds of a tetravalent carbon atom have a preferred value θ ≈ 109.5°. The bonds have a fixed bond length λ.
On the other hand, adjacent carbon atoms are free to rotate about the axis of the bond. Therefore, a ring, warped so that the bond lengths and angles are close to those ideal values will have less strain energy than a flat ring with 120° angles. For each particular conformation of the carbon ring, the directions of the 12 carbon-hydrogen bonds are fixed. There are eight warped polygons with six distinguished corners that have all internal angles equal to θ and all sides equal to λ, they comprise two ideal chair conformations, where the carbons alternately lie above and below the mean ring plane. In theory, a molecule with any of those ring conformations would be free of angle strain. However, due to interactions between the hydrogen atoms, the angles and bond lengths of the actual chair forms are different from the nominal values. For the same reasons, the actual boat forms have higher energy than the chair forms. Indeed, the boat forms are unstable, deform spontaneously to twist-boat conformations that are local minima of the total energy, therefore stable.
Each of the stable ring conformations can be transformed into any other without breaking the ring. However, such transformations must go through other states with stressed rings. In particular, they must go through unstable states where four successive carbon atoms lie on the same plane; these shapes are called half-chair conformations. In 2011, Donna Nelson and Christopher Brammer surveyed comprehensive undergraduate organic chemistry textbooks in use at that time, in order to determine consistency among the textbooks and with research literature; the two chair conformations have the lowest total energy, are therefore the most stable, have D3d symmetry. In the basic chair conformation, the carbons C1 through C6 alternate between two parallel planes, one with C1, C3 and C5, the other with C2, C4, C6; the molecule has a symmetry axis perpendicular to these two planes, is congruent to itself after a rotation of 120° about that axis. The two chair conformations have the same shape; the perpendicular projection of the ring onto its mean plane is a regular hexagon.
All C-C bonds are tilted relative to the mean plane. As a consequence of the ring warping, six of the 12 carbon-hydrogen bonds end up perpendicular to the mean plane and parallel to the symmetry axis, with alternating directions, are said to be axial; the other six C-H bonds lie parallel to the mean plane, are said to be equatorial. The precise angles are such that the two C-H bonds in each carbon, one axial and one equatorial, point in opposite senses relative to the symmetry axis. Thus, in a chair conformation, there are three C-H bonds of each kind — axial "up", axial "down", equatorial "up", equatorial "down"; the hydrogens in successive carbons are thus staggered. This geometry is preserved when the hydrogen atoms are replaced by halogens or other simple
A carbohydrate is a biomolecule consisting of carbon and oxygen atoms with a hydrogen–oxygen atom ratio of 2:1 and thus with the empirical formula Cmn. This formula holds true for monosaccharides; some exceptions exist. The carbohydrates are technically hydrates of carbon; the term is most common in biochemistry, where it is a synonym of saccharide, a group that includes sugars and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides and polysaccharides. Monosaccharides and disaccharides, the smallest carbohydrates, are referred to as sugars; the word saccharide comes from the Greek word σάκχαρον, meaning "sugar". While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides often end in the suffix -ose, as in the monosaccharides fructose and glucose and the disaccharides sucrose and lactose. Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as structural components; the 5-carbon monosaccharide ribose is an important component of coenzymes and the backbone of the genetic molecule known as RNA.
The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, preventing pathogenesis, blood clotting, development, they are found in a wide variety of processed foods. Starch is a polysaccharide, it is abundant in cereals and processed food based on cereal flour, such as bread, pizza or pasta. Sugars appear in human diet as table sugar, lactose and fructose, both of which occur in honey, many fruits, some vegetables. Table sugar, milk, or honey are added to drinks and many prepared foods such as jam and cakes. Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible, insoluble dietary fiber helps to maintain a healthy digestive system by easing defecation. Other polysaccharides contained in dietary fiber include resistant starch and inulin, which feed some bacteria in the microbiota of the large intestine, are metabolized by these bacteria to yield short-chain fatty acids.
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar", "saccharide", "ose", "glucide", "hydrate of carbon" or "polyhydroxy compounds with aldehyde or ketone". Some of these terms, specially "carbohydrate" and "sugar", are used with other meanings. In food science and in many informal contexts, the term "carbohydrate" means any food, rich in the complex carbohydrate starch or simple carbohydrates, such as sugar. In lists of nutritional information, such as the USDA National Nutrient Database, the term "carbohydrate" is used for everything other than water, fat and ethanol; this includes chemical compounds such as acetic or lactic acid, which are not considered carbohydrates. It includes dietary fiber, a carbohydrate but which does not contribute much in the way of food energy though it is included in the calculation of total food energy just as though it were a sugar. In the strict sense, "sugar" is applied for sweet, soluble carbohydrates, many of which are used in food.
The name "carbohydrate" was used in chemistry for any compound with the formula Cm n. Following this definition, some chemists considered formaldehyde to be the simplest carbohydrate, while others claimed that title for glycolaldehyde. Today, the term is understood in the biochemistry sense, which excludes compounds with only one or two carbons and includes many biological carbohydrates which deviate from this formula. For example, while the above representative formulas would seem to capture the known carbohydrates and abundant carbohydrates deviate from this. For example, carbohydrates display chemical groups such as: N-acetyl, carboxylic acid and deoxy modifications. Natural saccharides are built of simple carbohydrates called monosaccharides with general formula n where n is three or more. A typical monosaccharide has the structure H–x–y–H, that is, an aldehyde or ketone with many hydroxyl groups added one on each carbon atom, not part of the aldehyde or ketone functional group. Examples of monosaccharides are glucose and glyceraldehydes.
However, some biological substances called "monosaccharides" do not conform to this formula and there are many chemicals that do conform to this formula but are not considered to be monosaccharides. The open-chain form of a monosaccharide coexists with a closed ring form where the aldehyde/ketone carbonyl group carbon and hydroxyl group react forming a hemiacetal with a new C–O–C bridge. Monosaccharides can be linked togeth