A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Due to their broad range of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers, their large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, a tendency to form glasses and semicrystalline structures rather than crystals. The terms polymer and resin are synonymous with plastic; the term "polymer" derives from the Greek word πολύς and μέρος, refers to a molecule whose structure is composed of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant properties. The units composing polymers derive or conceptually, from molecules of low relative molecular mass.
The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, who spent the next decade finding experimental evidence for this hypothesis. Polymers are studied in the fields of biophysics and macromolecular science, polymer science. Products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science. Polyisoprene of latex rubber is an example of a natural/biological polymer, the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts all biological macromolecules—i.e. Proteins, nucleic acids, polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e.g. Isoprenylated/lipid-modified glycoproteins, where small lipidic molecules and oligosaccharide modifications occur on the polyamide backbone of the protein.
The simplest theoretical models for polymers are ideal chains. Polymers are of two types: occurring and synthetic or man made. Natural polymeric materials such as hemp, amber, wool and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, the main constituent of wood and paper; the list of synthetic polymers in order of worldwide demand, includes polyethylene, polystyrene, polyvinyl chloride, synthetic rubber, phenol formaldehyde resin, nylon, polyacrylonitrile, PVB, many more. More than 330 million tons of these polymers are made every year. Most the continuously linked backbone of a polymer used for the preparation of plastics consists of carbon atoms. A simple example is polyethylene. Many other structures do exist. Oxygen is commonly present in polymer backbones, such as those of polyethylene glycol, DNA. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer.
This happens in the polymerization of PET polyester. The monomers are terephthalic acid and ethylene glycol but the repeating unit is —OC—C6H4—COO—CH2—CH2—O—, which corresponds to the combination of the two monomers with the loss of two water molecules; the distinct piece of each monomer, incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization; the essential difference between the two is that in chain growth polymerization, monomers are added to the chain one at a time only, such as in polyethylene, whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester. Newer methods, such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out without a catalyst. Laboratory synthesis of biopolymers of proteins, is an area of intensive research. There are three main classes of biopolymers: polysaccharides and polynucleotides.
In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from the DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids; the protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as rubber, suberin and lignin. Occurring polymers such as cotton and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on the market. Many commercially important polymers are synthesized by chemical modification of occurring polymers. Prominent examples inclu
Clicked peptide polymer
Clicked peptide polymers are poly-triazole-poly-peptide hybrid polymers. They are made of repeating units of an oligopeptide, they can be visualized as an oligopeptide, flanked at both the C-terminus and N-terminus by a triazole molecule. Clicked peptide polymers are prepared by the azide-alkyne Huisgen cycloaddition called the click reaction. Peptide based polymers are produced from a cycloaddition variant of step-growth polymerization; the monomers used in this polymerization are oligopeptides with terminal azide and terminal alkyne groups To prepare and oligopeptide with both a terminal azide and terminal alkyne two modifications must be carried out. The first is the amidation of the oligopeptide's C-terminus by propargylamine; this would done with the C-terminus activated. The second modification required is the addition of an azide to the N-terminus. Unlike the addition of the alkyne this can be done on the whole peptide, or on the N-terminal residue, added to the rest of the oligopeptide by solid-phase peptide synthesis.
The addition of the azide occurs by Cu-catalyzed diazo transfer. The molecules linked to one another by the azide-alkyne Huisgen cycloaddition are connected by an aromatic triazole, stable, can withstand high temperatures and extremes of pH; the oligopeptide units of a clicked peptide polymer are a different story. The triazole bridges do not confer any stability to oligopeptide. Degradation of the polymer occurs at the peptide bonds linking individual amino acids; the amide bonds can be attacked non-specifically by base catalyzed hydrolysis. The polymer's peptide bonds can be attacked by endopeptidases which will cleave at a specific side of a specific peptide bond based upon the residues which make up that bond. For example, if the first residue is a phenylalanine the enzyme chymotrypsin will cleave at site 1, if the third residue of the tripeptide is a lysine trypsin would cleave at the third cleavage site. Biodegradable polymer Peptide nucleic acid Peptide synthesis Peptidomimetic
A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector. The sensitive biological element, e.g. tissue, organelles, cell receptors, antibodies, nucleic acids, etc. is a biologically derived material or biomimetic component that interacts, binds, or recognizes with the analyte under study. The biologically sensitive elements can be created by biological engineering; the transducer or the detector element, which transforms one signal into another one, works in a physicochemical way: optical, electrochemical, electrochemiluminescence etc. resulting from the interaction of the analyte with the biological element, to measure and quantify. The biosensor reader device with the associated electronics or signal processors that are responsible for the display of the results in a user-friendly way; this sometimes accounts for the most expensive part of the sensor device, however it is possible to generate a user friendly display that includes transducer and sensitive element.
The readers are custom-designed and manufactured to suit the different working principles of biosensors. A biosensor consists of a bio-recognition site, biotransducer component, electronic system which includes a signal amplifier and display. Transducers and electronics can be combined; the recognition component called a bioreceptor, uses biomolecules from organisms or receptors modeled after biological systems to interact with the analyte of interest. This interaction is measured by the biotransducer which outputs a measurable signal proportional to the presence of the target analyte in the sample; the general aim of the design of a biosensor is to enable quick, convenient testing at the point of concern or care where the sample was procured. In a biosensor, the bioreceptor is designed to interact with the specific analyte of interest to produce an effect measurable by the transducer. High selectivity for the analyte among a matrix of other chemical or biological components is a key requirement of the bioreceptor.
While the type of biomolecule used can vary biosensors can be classified according to common types of bioreceptor interactions involving: antibody/antigen, enzymes/ligands, nucleic acids/DNA, cellular structures/cells, or biomimetic materials. An immunosensor utilizes the specific binding affinity of antibodies for a specific compound or antigen; the specific nature of the antibody-antigen interaction is analogous to a lock and key fit in that the antigen will only bind to the antibody if it has the correct conformation. Binding events result in a physicochemical change that in combination with a tracer, such as a fluorescent molecules, enzymes, or radioisotopes, can generate a signal. There are limitations with using antibodies in sensors: 1; the antibody binding capacity is dependent on assay conditions and 2. The antibody-antigen interaction is irreversible. However, it has been shown that binding can be disrupted by chaotropic reagents, organic solvents, or ultrasonic radiation; the use of antibodies as the bio-recognition component of biosensors has several drawbacks.
They have high molecular weights and limited stability, contain essential disulfide bonds and are expensive to produce. In one approach to overcome these limitations, recombinant binding fragments or domains of antibodies have been engineered. In another approach, small protein scaffolds with favorable biophysical properties have been engineered to generate artificial families of Antigen Binding Proteins, capable of specific binding to different target proteins while retaining the favorable properties of the parent molecule; the elements of the family that bind to a given target antigen, are selected in vitro by display techniques: phage display, ribosome display, yeast display or mRNA display. The artificial binding proteins are much smaller than antibodies, have a strong stability, lack disulfide bonds and can be expressed in high yield in reducing cellular environments like the bacterial cytoplasm, contrary to antibodies and their derivatives, they are thus suitable to create biosensors.
The specific binding capabilities and catalytic activity of enzymes make them popular bioreceptors. Analyte recognition is enabled through several possible mechanisms: 1) the enzyme converting the analyte into a product, sensor-detectable, 2) detecting enzyme inhibition or activation by the analyte, or 3) monitoring modification of enzyme properties resulting from interaction with the analyte; the main reasons for the common use of enzymes in biosensors are: 1) ability to catalyze a large number of reactions. Notably, since enzymes are not consumed in reactions, the biosensor can be used continuously; the catalytic activity of enzymes allows lower limits of detection compared to common binding techniques. However, the sensor's lifetime is limited by the stability of the enzyme. Antibodies have a high binding constant in excess of 10^8 L/mol, which stands for a nearly irreversible association once the antigen-antibody couple has formed. For certain analyte molecules like glucose affinity binding proteins exist that bind their ligand with a high specificity like an antibody, but with a much smaller binding constant on the order of 10^2 to 10^4 L/mol.
The association between analyte and receptor is of re
Cyanobacteria known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis and are the only photosynthetic prokaryotes able to produce oxygen. The name cyanobacteria comes from the color of the bacteria. Cyanobacteria, which are prokaryotes, are called "blue-green algae", though the term algae in modern usage is restricted to eukaryotes. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes; these are flattened. Phototrophic eukaryotes perform photosynthesis by plastids that may have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis; these endosymbiotic cyanobacteria in eukaryotes may have evolved or differentiated into specialized organelles such as chloroplasts and leucoplasts. By producing and releasing oxygen, cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event and the "rusting of the Earth", which changed the composition of the Earth's life forms and led to the near-extinction of anaerobic organisms.
Cyanobacteria are a group of photosynthetic bacteria, some of which are nitrogen-fixing, that live in a wide variety of moist soils and water either or in a symbiotic relationship with plants or lichen-forming fungi. They include colonial species. Colonies may form filaments, sheets, or hollow spheres; some filamentous species can differentiate into several different cell types: vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions. Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts. Heterocysts may form under the appropriate environmental conditions when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into ammonia, nitrites or nitrates, which can be absorbed by plants and converted to protein and nucleic acids. Free-living cyanobacteria are present in the water of rice paddies, cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, where they may fix nitrogen.
Cyanobacteria such as Anabaena can provide rice plantations with biofertilizer. Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere; the cells in a hormogonium are thinner than in the vegetative state, the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium must tear apart a weaker cell in a filament, called a necridium; each individual cell has a thick, gelatinous cell wall. They lack flagella. Many of the multicellular filamentous. In water columns, some cyanobacteria float by forming gas vesicles, as in archaea; these vesicles are not organelles as such. They are not bounded by a protein sheath. Cyanobacteria can be found in every terrestrial and aquatic habitat—oceans, fresh water, damp soil, temporarily moistened rocks in deserts, bare rock and soil, Antarctic rocks, they can form phototrophic biofilms. They are found in endolithic ecosystem. A few are endosymbionts in lichens, various protists, or sponges and provide energy for the host.
Some live in the fur of sloths. Aquatic cyanobacteria are known for their extensive and visible blooms that can form in both freshwater and marine environments; the blooms can have the appearance of blue-green scum. These blooms can be toxic, lead to the closure of recreational waters when spotted. Marine bacteriophages are significant parasites of unicellular marine cyanobacteria. Cyanobacteria growth is favored in ponds and lakes where waters are calm and have less turbulent mixing, their life cycles are disrupted when the water or artificially mixes from churning currents caused by the flowing water of streams or the churning water of fountains. For this reason blooms of cyanobacteria occur in rivers unless the water is flowing slowly. Growth is favored at higher temperatures, making increasing water temperature as a result of global warming more problematic. At higher temperatures Microcystis species are able to outcompete green algae; this is a concern because of the production of toxins produced by Microcystis.
Based on environmental trends and observations suggest cyanobacteria will increase their dominance in aquatic environments. This can lead to serious consequences the contamination of sources of drinking water. Cyanobacteria can interfere with water treatment in various ways by plugging filters and by producing cyanotoxins, which have the potential to cause serious illness if consumed. Consequences may lie within
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
In chemistry, pH is a scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher pH. At room temperature, pure water is neither acidic nor basic and has a pH of 7; the pH scale is logarithmic and approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in a solution. More it is the negative of the base 10 logarithm of the activity of the hydrogen ion. At 25 °C, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic; the neutral value of the pH depends on the temperature, being lower than 7 if the temperature increases. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for strong acids and bases respectively; the pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode.
The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator. Measurements of pH are important in chemistry, medicine, water treatment, many other applications; the concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", as so: pH; the exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation, pH stands for "power of hydrogen". It has been suggested that the "p" stands for the German Potenz, others refer to French puissance. Another suggestion is that the "p" stands for the Latin terms pondus hydrogenii, potentia hydrogenii, or potential hydrogen, it is suggested that Sørensen used the letters "p" and "q" to label the test solution and the reference solution.
In chemistry, the p stands for "decimal cologarithm of", is used in the term pKa, used for acid dissociation constants. Bacteriologist Alice C. Evans, famed for her work's influence on dairying and food safety, credited William Mansfield Clark and colleagues with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little and colleagues knew about Sørensen's work a few years prior, she said: In these studies Dr. Clark's attention was directed to the effect of acid on the growth of bacteria, he found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration; these methods replaced the inaccurate titration method of determining acid content in use in biologic laboratories throughout the world.
They were found to be applicable in many industrial and other processes in which they came into wide usage. The first electronic method for measuring pH was invented by Arnold Orville Beckman, a professor at California Institute of Technology in 1934, it was in response to local citrus grower Sunkist that wanted a better method for testing the pH of lemons they were picking from their nearby orchards. PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. PH = − log 10 = log 10 For example, for a solution with a hydrogen ion activity of 5×10−6 we get 1/ = 2×105, thus such a solution has a pH of log10 = 5.3. For a commonplace example based on the facts that the masses of a mole of water, a mole of hydrogen ions, a mole of hydroxide ions are 18 g, 1 g, 17 g, a quantity of 107 moles of pure water, or 180 tonnes, contains close to 1 g of dissociated hydrogen ions and 17 g of hydroxide ions. Note that pH depends on temperature. For instance at 0 °C the pH of pure water is 7.47.
At 25 °C it's 7.00, at 100 °C it's 6.14. This definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst equation, for the hydrogen ion can be written as E = E 0 + R T F ln = E 0 − 2.303 R T F pH where E is a measured potential, E0 is the standard electrode potential, R is the gas const
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