Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, not consumed in the catalyzed reaction and can continue to act repeatedly. Because of this, only small amounts of catalyst are required to alter the reaction rate in principle. In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst reacts to form a temporary intermediate, which regenerates the original catalyst in a cyclic process. A substance which provides a mechanism with a higher activation energy does not decrease the rate because the reaction can still occur by the non-catalyzed route. An added substance which does reduce the reaction rate is not considered a catalyst but a reaction inhibitor. Catalysts may be classified as either heterogeneous. A homogeneous catalyst is one whose molecules are dispersed in the same phase as the reactant's molecules.
A heterogeneous catalyst is one whose molecules are not in the same phase as the reactant's, which are gases or liquids that are adsorbed onto the surface of the solid catalyst. Enzymes and other biocatalysts are considered as a third category. In the presence of a catalyst, less free energy is required to reach the transition state, but the total free energy from reactants to products does not change. A catalyst may participate in multiple chemical transformations; the effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons or promoters. Catalyzed reactions have a lower activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature and for the same reactant concentrations. However, the detailed mechanics of catalysis is complex. Catalysts may bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to reactive forms, such as chemisorbed hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions are typical chemical reactions. The catalyst participates in this slowest step, rates are limited by amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A nanomaterial-based catalyst is an example of a heterogeneous catalyst. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts. Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated, or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid–liquid system or sublimate in a solid–gas system; the production of most industrially important chemicals involves catalysis. Most biochemically significant processes are catalysed.
Research into catalysis is a major field in applied science and involves many areas of chemistry, notably organometallic chemistry and materials science. Catalysis is relevant to many aspects of environmental science, e.g. the catalytic converter in automobiles and the dynamics of the ozone hole. Catalytic reactions are preferred in environmentally friendly green chemistry due to the reduced amount of waste generated, as opposed to stoichiometric reactions in which all reactants are consumed and more side products are formed. Many transition metals and transition metal complexes are used in catalysis as well. Catalysts called. A catalyst works by providing an alternative reaction pathway to the reaction product; the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst. The disproportionation of hydrogen peroxide creates oxygen, as shown below. 2 H2O2 → 2 H2O + O2This reaction is preferable in the sense that the reaction products are more stable than the starting material, though the uncatalysed reaction is slow.
In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available. This reaction is affected by catalysts such as manganese dioxide, or the enzyme peroxidase in organisms. Upon the addition of a small amount of manganese dioxide, the hydrogen peroxide reacts rapidly; this effect is seen by the effervescence of oxygen. The manganese dioxide is not consumed in the reaction, thus may be recovered unchanged, re-used indefinitely. Accordingly, manganese dioxide catalyses this reaction. Catalytic activity is denoted by the symbol z and measured in mol/s, a unit, called katal and defined the SI unit for catalytic activity since 1999. Catalytic activity is not a kind of reaction rate, but a property of the catalyst under certain conditions, in relation to a specific chemical reaction. Catalytic activity of one katal of a catalyst means one mole of that catalyst will catalyse 1 mole of the reactant to product in one second. A catalyst may and will have different catalytic activity for di
Demethylases are enzymes that remove methyl groups from nucleic acids and other molecules. Demethylase enzymes are important in epigenetic modification mechanisms; the demethylase proteins alter transcriptional regulation of the genome by controlling the methylation levels that occur on DNA and histones and, in turn, regulate the chromatin state at specific gene loci within organisms. For many years histone methylation was thought to be irreversible, due to the fact that the half-life of the histone methylation was equal to the half-life of histones themselves. In 2004, Shi et al. published their discovery of the histone demethylase LSD1, a nuclear amine oxidase homolog. Since many more histone demethylases have been found. Defined by their mechanisms, two main classes of histone demethylases exist: a flavin adenine dinucleotide -dependent amine oxidase, an Fe and α-ketoglutarate-dependent hydroxylase. Both operate followed by dissociation of formaldehyde. Demethylation has implications for epigenetics.
Hydroxylation: R2NCH3 + → R2NCH2OH loss of formaldehyde: R2NCH2OH → R2NH + CH2OHistone demethylase proteins have a variety of domains that serve different functions. These functions include binding to the histone, recognizing the correct methylated amino acid substrate and catalyzing the reaction, binding cofactors. Cofactors include: alpha-keto glutarate, CoREST, FAD, Fe or NOG. Domains include: SWIRM1: Proposed anchor site for histone molecules. A code has been developed to indicate the substrate for a histone demethylase; the substrate is first specified by the histone subunit and the one letter designation and number of the amino acid, methylated. Lastly, the level of methylation is sometimes noted by the addition of "me#", with the numbers being 1, 2, 3 for monomethylated and trimethylated substrates, respectively. For example, H3K9me2 is histone H3 with a dimethylated lysine in the ninth position. KDM1 The KDM1 family includes KDM1A and KDM1B. KDM1A can act on mono- and dimethylated H3K4 and H3K9, KDM1B acts only on mono- and dimethylated H3K4.
These enzymes can have roles critical in embryogenesis and tissue-specific differentiation, as well as oocyte growth. KDM1A was the first demethylase to be discovered and thus it has been studied most extensively. Deletion of the gene for KDM1A can have effects on the growth and differentiation of embryonic stem cells and can lead to embryonic lethality in knockout mice, who do not produce the KDM1A gene product. KDM1A is thought to play a role in cancer, as poorer outcomes can be correlated with higher expression of this gene. Therefore, the inhibition of KDM1A may be a possible treatment for cancer. KDM1A has many different binding partners. KDM1B, however, is involved in oocyte development. Deletion of this gene leads to maternal effect lethality in mice. Orthologs of KDM1 in D. melanogaster and C. elegans appear to function to KDM1B rather than KDM1A. KDM2 The KDM2 family includes KDM2A and KDM2B. KDM2A can act on mono- and dimethylated H3K36 and trimethylated H3K4. KDM2B acts only on mono- and dimethylated H3K36.
KDM2A has roles in either promoting or inhibiting tumor function, KDM2B has roles in oncogenesis. In many eukaryotes, the KDM2A protein contains a CXXC zinc finger domain capable of binding unmethylated CpG islands, it is thought that KDM2A proteins may bind to many gene regulatory elements without the aid of sequence specific transcription factors. Although the role of KDM2 in eukaryotic developmental differentiation is still a mystery, both KDM2A and KDM2B have been shown to play roles in tumor growth and suppression. KDM2B has been shown to be over-expressed in human adenocarcinomas. Additionally, KDM2B has been shown to prevent senescence in some cells through ectopic expression further indicating its potential as an oncogene. KDM3 The KDM3 family includes KDM3A, KDM3B and JMJD1C. KDM3A can act on mono- and dimethylated H3K9; the substrates for KDM3B and JMJD1C are not known. The KDM3A has roles in metabolic functions. Knockdown studies of KDM3A in mice, where the mouse produces reduced levels of KDM3A, resulted in male infertility and adult onset-obesity.
Additional studies have indicated that KDM3A may play a role in regulation of androgen receptor-dependent genes as well as genes involved in pluripotency, indicating a potential
Saponification is a process that involves conversion of fat or oil into soap and alcohol by the action of heat in the presence of aqueous alkali. Soaps are salts of fatty acids whereas fatty acids are saturated monocarboxylic acids that have long carbon chains e.g. CH314COOH. Vegetable oils and animal fats are the traditional materials; these greasy materials, triesters called triglycerides, are mixtures derived from diverse fatty acids. Triglycerides can be converted to soap in either a one- or a two-step process. In the traditional one-step process, the triglyceride is treated with a strong base, which cleaves to the ester bond, releasing fatty acid salts and glycerol; this process is the main industrial method for producing glycerol. In some soap-making, the glycerol is left in the soap. If necessary, soaps may be precipitated by salting it out with sodium chloride. Fat in a corpse converts into adipocere called "grave wax"; this process is more common where the amount of fatty tissue is high and the agents of decomposition are absent or only minutely present.
The saponification value is the amount of base required to saponify a fat sample. Soap makers formulate their recipes with a small deficit of lye to account for the unknown deviation of saponification value between their oil batch and laboratory averages; the hydroxide anion of the salt reacts with the carbonyl group of the ester. The immediate product is called an orthoester. Expulsion of the alkoxide generates a carboxylic acid: The alkoxide ion is a strong base so that the proton is transferred from the carboxylic acid to the alkoxide ion creating an alcohol: In a classic laboratory procedure, the triglyceride trimyristin is obtained by extracting it from nutmeg with diethyl ether. Saponification to the sodium soap of myristic acid takes place using NaOH in water; the acid itself can be obtained by adding dilute hydrochloric acid. The reaction of fatty acids with base is the other main method of saponification. In this case, the reaction involves neutralization of the carboxylic acid; the neutralization method is used to produce industrial soaps such as those derived from magnesium, the transition metals, aluminium.
This method is ideal for producing soaps that are derived from a single fatty acid, which leads to soaps with predictable physical properties, as required by many engineering applications. Depending on the nature of the alkali used in their production, soaps have distinct properties. Sodium hydroxide gives "hard soap". By contrast, potassium soaps, are soft soap; the fatty acid source affects the soap's melting point. Most early hard soaps were KOH extracted from wood ash. However, the majority of modern soaps are manufactured from polyunsaturated triglycerides such as vegetable oils; as in the triglycerides they are formed from the salts of these acids have weaker inter-molecular forces and thus lower melting points. Lithium derivatives of 12-hydroxystearate and other fatty acids are important constituents of lubricating greases. In lithium-based greases, lithium carboxylates are thickeners. "Complex soaps" are common, these being combinations of metallic soaps, such as lithium and calcium soaps.
Fires involving cooking fats and oils burn hotter than most flammable liquids, rendering a standard class B extinguisher ineffective. Flammable liquids have flash points under 37 degrees Celsius. Cooking oil is a combustible liquid; such fires should be extinguished with a wet chemical extinguisher. Extinguishers of this type are designed to extinguish cooking oils through saponification; the extinguishing agent converts the burning substance to a non-combustible soap. This process is endothermic, meaning that it absorbs thermal energy from its surroundings, which decreases the temperature of the surroundings, further inhibiting the fire. Saponification can occur in oil paintings over time, causing visible deformation. Oil paints are composed of pigment molecules suspended in an oil binding medium. Heavy metal salts are used as pigment molecules, such as in lead white, red lead, zinc white. If those heavy metal salts react with free fatty acids in the oil medium, metal soaps may form in a paint layer that can migrate outward to the painting's surface.
Saponification in oil paintings was described as early as 1912. It is believed to be widespread, having been observed in many works dating from the fifteenth through the twentieth centuries. Chemical analysis may reveal saponification occurring in a painting’s deeper layers before any signs are visible on the surface in paintings centuries old; the saponified regions may deform the painting's surface through the formation of visible lumps or protrusions that can scatter light. These soap lumps may be prominent only on certain regions of the painting rather than throughout. In John Singer Sargent's famous Portrait of Madame X, for example, the lumps only appear on the blackest areas, which may be because of the artist’s use of more medium in those areas to compensate for the tendency of black pigments to soak it up; the process can form chalky white deposits on a painting's surface, a deformation described as "blooming" or "efflorescence", may contribute to the increased transparency of certain paint layers within an oil painting over time.
Saponification does not occur in all oil paintings and
Alpha-ketoglutarate-dependent hydroxylases are non-heme, iron-containing enzymes that consume oxygen and alpha-ketoglutarate as co-substrates. They catalyse a wide range of oxygenation reactions; these include hydroxylation reactions, ring expansions, ring closures and desaturations. Functionally, the αKG-dependent hydroxylases are comparable to cytochrome P450 enzymes, which use oxygen and reducing equivalents to oxygenate substrates concomitant with formation of water. ΑKG-dependent hydroxylases have diverse roles. In microorganisms such as bacteria, αKG-dependent dioxygenases are involved in many biosynthetic pathways. In plants, αKG-dependent dioxygenases are involved in many different reactions in plant metabolism; these include flavonoid biosynthesis, ethylene biosyntheses. In mammals and humans, αKG-dependent dioxygenase have functional roles in biosyntheses, post-translational modifications, epigenetic regulations, as well as sensors of energy metabolism. Many αKG-dependent dioxygenase catalyse uncoupled turnover, in which oxidative decarboxylation of αKG into succinate and carbon dioxide proceeds in the absence of substrate.
The catalytic activity of many αKG-dependent dioxygenases are dependent on reducing agents although the exact roles are not understood. ΑKG-dependent dioxygenases catalyse oxidation reactions by incorporating a single oxygen atom from molecular oxygen into their substrates. This conversion is coupled with the oxidation of the cosubstrate αKG into succinate and carbon dioxide. With labeled O2 as substrate, the one label appears in the succinate and one in the hydroxylated substrate: R3CH + O2 + −O2CCCH2CH2CO2− → R3COH + CO2 + −OOCCH2CH2CO2−The first step involves the binding of αKG and substrate to the active site. ΑKG coordinates as a bidentate ligand to Fe, while the substrate is held by noncovalent forces in close proximity. Subsequently, molecular oxygen binds end-on to Fe cis to the two donors of the αKG; the uncoordinated end of the superoxide ligand attacks the keto carbon, inducing release of CO2 and forming an Fe-oxo intermediate. This Fe=O center oxygenates the substrate by an oxygen rebound mechanism.
Alternative mechanisms have failed to gain support. All αKG-dependent dioxygenases contain a conserved double-stranded β-helix fold, formed with two β-sheets; the active site contains a conserved 2-His-1-carboxylate amino acid residue triad motif, in which the catalytically-essential Fe is held by two histidine residues and one aspartic acid/glutamic acid residue. The N2O triad binds to one face of the Fe center, leaving three labile sites available on the octahedron for binding αKG and O2. A similar facial Fe-binding motif, but featuring his-his-his array, is found in cysteine dioxygenase; the binding of αKG and substrate has been analyzed by X-ray crystallography, molecular dynamics calculations, NMR spectroscopy. The binding of the ketoglutarate has been observed using enzyme inhibitors; some αKG-dependent dioxygenases bind their substrate through an induced fit mechanism. For example, significant protein structural changes have been observed upon substrate binding for human prolyl hydroxylase isoform 2, a αKG-dependent dioxygenase, involved in oxygen sensing, isopenicillin N synthase, a microbial αKG-dependent dioxygenase.
Given the important biological roles that αKG-dependent dioxygenase play, many αKG-dependent dioxygenase inhibitors were developed. The inhibitors that were used to target αKG-dependent dioxygenase include N-oxalylglycine, pyridine-2,4-dicarboxylic acid, 5-carboxy-8-hydroxyquinoline, FG-2216 and FG-4592, which were all designed mimic the co-substrate αKG and compete against the binding of αKG at the enzyme active site Fe. Although they are potent inhibitors of αKG-dependent dioxygenase, they lack selectivity and hence sometimes being referred to as so-called'broad spectrum' inhibitors. Inhibitors that compete against the substrate were developed, such as peptidyl-based inhibitors that target human prolyl hydroxylase domain 2 and Mildronate, a drug molecule, used in Russia and Eastern Europe that target gamma-butyrobetaine dioxygenase. Many assays were developed to study αKG-dependent dioxygenases so that information such as enzyme kinetics, enzyme inhibition and ligand binding can be obtained.
Nuclear magnetic resonance spectroscopy is applied to study αKG-dependent dioxygenases. For example, assays were developed to study ligand binding, enzyme kinetics, modes of inhibition as well as protein conformational change. Mass spectrometry is widely applied, it can be used to characterise enzyme kinetics, to guide enzyme inhibitor development, study ligand and metal binding as well as analyse protein conformational change. Assays using spectrophotometry were used, for example those that measure 2OG oxidation, co-product succinate formation or product formation. Other biophysical techniques including isothermal titration calorimetry and electron paramagnetic resonance were applied. Radioactive assays that uses 14C labelled substrates were developed and used. Given αKG-dependent dioxygenases require oxygen for their catalytic activity, oxygen consumption assay was applied. Martinez, Salette. "Catalytic Mechanisms of Fe- and 2-Oxoglutarate-dependent Oxygenases". The Journal of Biological Chemistry.
290: 20702–20711. Doi:10.1074/jbc. R115.648691. ISSN 0021-9258. PMC 4543632. PMID 26152721. Hegg EL, Que L Jr. "The 2-His-1-
Cytochromes P450 are proteins of the superfamily containing heme as a cofactor and, are hemeproteins. CYPs use a variety of large molecules as substrates in enzymatic reactions, they are, in general, the terminal oxidase enzymes in electron transfer chains, broadly categorized as P450-containing systems. The term "P450" is derived from the spectrophotometric peak at the wavelength of the absorption maximum of the enzyme when it is in the reduced state and complexed with carbon monoxide. CYP enzymes have been identified in all kingdoms of life: animals, fungi, bacteria, in viruses. However, they are not omnipresent. More than 50,000 distinct CYP proteins are known. Most CYPs require a protein partner to deliver one or more electrons to reduce the iron. Based on the nature of the electron transfer proteins, CYPs can be classified into several groups: Microsomal P450 systems, in which electrons are transferred from NADPH via cytochrome P450 reductase. Cytochrome b5 can contribute reducing power to this system after being reduced by cytochrome b5 reductase.
Mitochondrial P450 systems, which employ adrenodoxin reductase and adrenodoxin to transfer electrons from NADPH to P450. Bacterial P450 systems, which employ a ferredoxin reductase and a ferredoxin to transfer electrons to P450. CYB5R/cyb5/P450 systems, in which both electrons required by the CYP come from cytochrome b5. FMN/Fd/P450 systems found in Rhodococcus species, in which a FMN-domain-containing reductase is fused to the CYP. P450 only systems, which do not require external reducing power. Notable ones include thromboxane synthase, prostacyclin synthase, CYP74A; the most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction, e.g. insertion of one atom of oxygen into the aliphatic position of an organic substrate while the other oxygen atom is reduced to water: RH + O2 + NADPH + H+ → ROH + H2O + NADP+ Many hydroxylation reactions use CYP enzymes. Genes encoding CYP enzymes, the enzymes themselves, are designated with the root symbol CYP for the superfamily, followed by a number indicating the gene family, a capital letter indicating the subfamily, another numeral for the individual gene.
The convention is to italicise the name. For example, CYP2E1 is the gene that encodes the enzyme CYP2E1—one of the enzymes involved in paracetamol metabolism; the CYP nomenclature is the official naming convention, although CYP450 or CYP450 is used synonymously. However, some gene or enzyme names for CYPs may differ from this nomenclature, denoting the catalytic activity and the name of the compound used as substrate. Examples include CYP5A1, thromboxane A2 synthase, abbreviated to TBXAS1, CYP51A1, lanosterol 14-α-demethylase, sometimes unofficially abbreviated to LDM according to its substrate and activity; the current nomenclature guidelines suggest that members of new CYP families share at least 40% amino acid identity, while members of subfamilies must share at least 55% amino acid identity. There are nomenclature committees that track both base gene names and allele names; the active site of cytochrome P450 contains a heme-iron center. The iron is tethered to the protein via a cysteine thiolate ligand.
This cysteine and several flanking residues are conserved in known CYPs and have the formal PROSITE signature consensus pattern - - x - - - - - C - -. Because of the vast variety of reactions catalyzed by CYPs, the activities and properties of the many CYPs differ in many aspects. In general, the P450 catalytic cycle proceeds as follows: Substrate binds in proximity to the heme group, on the side opposite to the axial thiolate. Substrate binding induces a change in the conformation of the active site displacing a water molecule from the distal axial coordination position of the heme iron, changing the state of the heme iron from low-spin to high-spin. Substrate binding induces electron transfer from NADH via cytochrome P450 reductase or another associated reductase. Molecular oxygen binds to the resulting ferrous heme center at the distal axial coordination position giving a dioxygen adduct not unlike oxy-myoglobin. A second electron is transferred, from either cytochrome P450 reductase, ferredoxins, or cytochrome b5, reducing the Fe-O2 adduct to give a short-lived peroxo state.
The peroxo group formed in step 4 is protonated twice, releasing one molecule of water and forming the reactive species referred to as P450 Compound 1. This reactive intermediate was isolated in 2010, P450 Compound 1 is an iron oxo species with an additional oxidizing equivalent delocalized over the porphyrin and thiolate ligands. Evidence for the alternative perferryl iron-oxo is lacking. Depending on the substrate and enzyme involved, P450 enzymes can catalyze any of a wide variety of reactions. A hypothetical hydroxylation is shown in this illustration. After the product has been released from the active site, the enzyme returns to its original state, with a water molecule returning to occupy the distal coordination position of the iron nucleus. An alternative route for mono-oxygenation is via the "peroxide shunt"; this pathway entails oxidation of the ferric-substrate complex with oxygen-atom donors such as peroxides and hypochlorites. A hypothetical peroxide "XOOH" is shown in the di
A biomolecule or biological molecule is a loosely used term for molecules and ions that are present in organisms, essential to some biological process such as cell division, morphogenesis, or development. Biomolecules include large macromolecules such as proteins, carbohydrates and nucleic acids, as well as small molecules such as primary metabolites, secondary metabolites, natural products. A more general name for this class of material is biological materials. Biomolecules are endogenous but may be exogenous. For example, pharmaceutical drugs may be natural products or semisynthetic or they may be synthetic. Biology and its subsets of biochemistry and molecular biology study biomolecules and their reactions. Most biomolecules are organic compounds, just four elements—oxygen, carbon and nitrogen—make up 96% of the human body's mass, but many other elements, such as the various biometals, are present in small amounts. The uniformity of specific types of molecules and of some metabolic pathways as invariant features between the diversity of life forms is called "biochemical universals" or "theory of material unity of the living beings", a unifying concept in biology, along with cell theory and evolution theory.
A diverse range of biomolecules exist, including: Small molecules: Lipids, fatty acids, sterols, monosaccharides Vitamins Hormones, neurotransmitters Metabolites Monomers and polymers: Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. Examples of these include cytidine, adenosine and thymidine. Nucleosides can be phosphorylated by specific kinases in producing nucleotides. Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, T, while RNA uses the ribonucleotides C, G, A, U. Modified bases are common, as found in ribosomal RNA or transfer RNAs or for discriminating the new from old strands of DNA after replication; each nucleotide is made of a pentose and one to three phosphate groups. They contain carbon, oxygen and phosphorus, they serve as sources of chemical energy, participate in cellular signaling, are incorporated into important cofactors of enzymatic reactions.
DNA structure is dominated by the well-known double helix formed by Watson-Crick base-pairing of C with G and A with T. This is known as B-form DNA, is overwhelmingly the most favorable and common state of DNA. DNA can sometimes occur as single strands or as A-form or Z-form helices, in more complex 3D structures such as the crossover at Holliday junctions during DNA replication. RNA, in contrast, forms large and complex 3D tertiary structures reminiscent of proteins, as well as the loose single strands with locally folded regions that constitute messenger RNA molecules; those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops and junctions. Examples are tRNA, ribosomes and riboswitches; these complex structures are facilitated by the fact that RNA backbone has less local flexibility than DNA but a large set of distinct conformations because of both positive and negative interactions of the extra OH on the ribose. Structured RNA molecules can do specific binding of other molecules and can themselves be recognized specifically.
Monosaccharides are the simplest form of carbohydrates with only one simple sugar. They contain an aldehyde or ketone group in their structure; the presence of an aldehyde group in a monosaccharide is indicated by the prefix aldo-. A ketone group is denoted by the prefix keto-. Examples of monosaccharides are the hexoses, fructose, Tetroses, galactose, pentoses and deoxyribose. Consumed fructose and glucose have different rates of gastric emptying, are differentially absorbed and have different metabolic fates, providing multiple opportunities for 2 different saccharides to differentially affect food intake. Most saccharides provide fuel for cellular respiration. Disaccharides are formed when two monosaccharides, or two single simple sugars, form a bond with removal of water, they can be hydrolyzed to yield their saccharin building blocks by boiling with dilute acid or reacting them with appropriate enzymes. Examples of disaccharides include sucrose and lactose. Polysaccharides are polymerized complex carbohydrates.
They have multiple simple sugars. Examples are starch and glycogen, they are large and have a complex branched connectivity. Because of their size, polysaccharides are not water-soluble, but their many hydroxy groups become hydrated individually when exposed to water, some polysaccharides form thick colloidal dispersions when heated in water. Shorter polysaccharides, with 3 - 10 monomers, are called oligosaccharides. A fluorescent indicato