An antimetabolite is a chemical that inhibits the use of a metabolite, another chemical, part of normal metabolism. Such substances are similar in structure to the metabolite that they interfere with, such as the antifolates that interfere with the use of folic acid. Antimetabolites can be used in cancer treatment, as they interfere with DNA production and therefore cell division and tumor growth; because cancer cells spend more time dividing than other cells, inhibiting cell division harms tumor cells more than other cells. Antimetabolite drugs are used to treat leukemia, cancers of the breast and the gastrointestinal tract, as well as other types of cancers. In the Anatomical Therapeutic Chemical Classification System antimetabolite cancer drugs are classified under L01B. Antimetabolites impair DNA replication machinery, either by incorporation of chemically altered nucleotides or by depleting the supply of deoxynucleotides needed for DNA replication and cell proliferation. Examples of cancer drug antimetabolites include, but are not limited to the following: 5-Fluorouracil 6-Mercaptopurine Capecitabine Cytarabine Floxuridine Fludarabine Gemcitabine Hydroxycarbamide Methotrexate Pemetrexed Anti-metabolites masquerade as a purine or a pyrimidine, chemicals that become the building-blocks of DNA.
They prevent these substances from becoming incorporated into DNA during the S phase, stopping normal development and cell division. Anti-metabolites affect RNA synthesis. However, because thymidine is used in DNA but not in RNA, inhibition of thymidine synthesis via thymidylate synthase selectively inhibits DNA synthesis over RNA synthesis. Due to their efficiency, these drugs are the most used cytostatics. Competition for the binding sites of enzymes that participate in essential biosynthetic processes and subsequent incorporation of these biomolecules into nucleic acids, inhibits their normal tumor cell function and triggers apoptosis, or the cell death process; because of this mode of action, most antimetabolites have high cell cycle specificity and can target arrest of cancer cell DNA replication. Antimetabolites may be antibiotics, such as sulfanilamide drugs, which inhibit dihydrofolate synthesis in bacteria by competing with para-aminobenzoic acid. PABA is needed in enzymatic reactions that produce folic acid, which acts as a coenzyme in the synthesis of purines and pyrimidines, the building-blocks of DNA.
Mammals do not synthesize their own folic acid so they are unaffected by PABA inhibitors, which selectively kill bacteria. Sulfanilamide drugs are not like the antibiotics used to treat infections. Instead, they work by changing the DNA inside cancer cells to keep them from growing and multiplying. Antitumor antibiotics are a class of antimetabolite drugs, they act by binding with DNA molecules and preventing RNA synthesis, a key step in the creation of proteins, which are necessary for cancer cell survival. Anthracyclines are anti-tumor antibiotics that interfere with enzymes involved in copying DNA during the cell cycle. Examples of anthracyclines include: Daunorubicin Doxorubicin Epirubicin IdarubicinAnti-tumor antibiotics that are not anthracyclines include: Actinomycin-D Bleomycin Mitomycin-C Mitoxantrone Antimetabolites mitomycin C, are used in America and Japan as an addition to trabeculectomy, a surgical procedure to treat glaucoma. Antimetabolites have been shown to decrease fibrosis of operative sites.
Thus, its use following external dacryocystorhinostomy, a procedure for the management of nasolacrimal duct obstruction, is being researched. Intraoperative antimetabolite application, namely mitomycin C and 5-fluorouracil, is being tested for its effectiveness of managing pterygium. Main categories of these drugs include: base analogues – structures that can substitute for a normal nucleobases in nucleic acids; this means that these molecules are structurally similar enough the basic components of DNA that they can be substituted in. However, since they are different that the normal bases after they are incorporated into the DNA, the DNA production is halted and the cell dies. Purine analogues – mimic the structure of metabolic purines, the larger bases incorporated into DNA as adenosine and guanosine. Examples: Azathioprine and Fludarabine pyrimidine analogue – mimic the structure of metabolic pyrimidines, the smaller bases incorporated into DNA as cytosine and thymine. Examples: 5-Fluorouracil and Cytarabine nucleoside analogues – nucleosides alternatives which contain a nucleic acid analogue and a sugar.
This means. For the nucleoside analogues either the base or the sugar component can be altered, they are similar enough to the molecules used to build cellular DNA that they are incorporated by the cell into its DNA, but different enough that after being added the cell’s DNA they stop cell growth. Nucleotide analogues – nucleotides alternatives that contain a nucleic acid, a sugar, 1–3 phosphates; this means these molecules look like the pieces used to build DNA in a cell and can be incorporated into a growing cell’s DNA. However, because they are analogues and therefore different than regular nucleotides, causing the cell’s growth to be halted and the cell to die. Antifolates – chemicals that block the acti
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 chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved. There are four types of compounds, depending on how the constituent atoms are held together: molecules held together by covalent bonds ionic compounds held together by ionic bonds intermetallic compounds held together by metallic bonds certain complexes held together by coordinate covalent bonds. A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service: its CAS number.
A compound can be converted to a different chemical composition by interaction with a second chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the interacting compounds, bonds are reformed so that new associations are made between atoms. Any substance consisting of two or more different types of atoms in a fixed stoichiometric proportion can be termed a chemical compound, it follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction, into compounds or substances each having fewer atoms. The ratio of each element in the compound is expressed in a ratio in its chemical formula. A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O.
In the case of non-stoichiometric compounds, the proportions may be reproducible with regard to their preparation, give fixed proportions of their component elements, but proportions that are not integral. Chemical compounds have a unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or the subset of chemical complexes that are held together by coordinate covalent bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they consist of molecules composed of multiple atoms. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service: its CAS number. There is varying and sometimes inconsistent nomenclature differentiating substances, which include non-stoichiometric examples, from chemical compounds, which require the fixed ratios.
Many solid chemical substances—for example many silicate minerals—are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios. It may be argued that they are related to, rather than being chemical compounds, insofar as the variability in their compositions is due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound, or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Compounds are held together through a variety of different types of bonding and forces; the differences in the types of bonds in compounds differ based on the types of elements present in the compound.
London dispersion forces are the weakest force of all intermolecular forces. They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole. Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, to further freeze to a solid state dependent on how low the temperature of the environment is. A covalent bond known as a molecular bond, involves the sharing of electrons between two atoms; this type of bond occurs between elements that fall close to each other on the periodic table of elements, yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on the periodic table tend to have similar electronegativities, which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet.
Ionic bonding occurs when valence electrons are transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions; the metals in ionic bonding
Drug metabolism is the metabolic breakdown of drugs by living organisms through specialized enzymatic systems. More xenobiotic metabolism is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug or poison; these pathways are a form of biotransformation present in all major groups of organisms, are considered to be of ancient origin. These reactions act to detoxify poisonous compounds; the study of drug metabolism is called pharmacokinetics. The metabolism of pharmaceutical drugs is an important aspect of medicine. For example, the rate of metabolism determines the duration and intensity of a drug's pharmacologic action. Drug metabolism affects multidrug resistance in infectious diseases and in chemotherapy for cancer, the actions of some drugs as substrates or inhibitors of enzymes involved in xenobiotic metabolism are a common reason for hazardous drug interactions; these pathways are important in environmental science, with the xenobiotic metabolism of microorganisms determining whether a pollutant will be broken down during bioremediation, or persist in the environment.
The enzymes of xenobiotic metabolism the glutathione S-transferases are important in agriculture, since they may produce resistance to pesticides and herbicides. Drug metabolism is divided into three phases. In phase I, enzymes such as cytochrome P450 oxidases introduce reactive or polar groups into xenobiotics; these modified compounds are conjugated to polar compounds in phase II reactions. These reactions are catalysed by transferase enzymes such as glutathione S-transferases. In phase III, the conjugated xenobiotics may be further processed, before being recognised by efflux transporters and pumped out of cells. Drug metabolism converts lipophilic compounds into hydrophilic products that are more excreted; the exact compounds an organism is exposed to will be unpredictable, may differ over time. The major challenge faced by xenobiotic detoxification systems is that they must be able to remove the almost-limitless number of xenobiotic compounds from the complex mixture of chemicals involved in normal metabolism.
The solution that has evolved to address this problem is an elegant combination of physical barriers and low-specificity enzymatic systems. All organisms use cell membranes as hydrophobic permeability barriers to control access to their internal environment. Polar compounds cannot diffuse across these cell membranes, the uptake of useful molecules is mediated through transport proteins that select substrates from the extracellular mixture; this selective uptake means that most hydrophilic molecules cannot enter cells, since they are not recognised by any specific transporters. In contrast, the diffusion of hydrophobic compounds across these barriers cannot be controlled, organisms, cannot exclude lipid-soluble xenobiotics using membrane barriers. However, the existence of a permeability barrier means that organisms were able to evolve detoxification systems that exploit the hydrophobicity common to membrane-permeable xenobiotics; these systems therefore solve the specificity problem by possessing such broad substrate specificities that they metabolise any non-polar compound.
Useful metabolites are excluded since they are polar, in general contain one or more charged groups. The detoxification of the reactive by-products of normal metabolism cannot be achieved by the systems outlined above, because these species are derived from normal cellular constituents and share their polar characteristics. However, since these compounds are few in number, specific enzymes can remove them. Examples of these specific detoxification systems are the glyoxalase system, which removes the reactive aldehyde methylglyoxal, the various antioxidant systems that eliminate reactive oxygen species; the metabolism of xenobiotics is divided into three phases:- modification and excretion. These reactions act in concert to remove them from cells. In phase I, a variety of enzymes act to introduce polar groups into their substrates. One of the most common modifications is hydroxylation catalysed by the cytochrome P-450-dependent mixed-function oxidase system; these enzyme complexes act to incorporate an atom of oxygen into nonactivated hydrocarbons, which can result in either the introduction of hydroxyl groups or N-, O- and S-dealkylation of substrates.
The reaction mechanism of the P-450 oxidases proceeds through the reduction of cytochrome-bound oxygen and the generation of a highly-reactive oxyferryl species, according to the following scheme: O2 + NADPH + H+ + RH → NADP+ + H2O + ROHPhase I reactions may occur by oxidation, hydrolysis, cyclization and addition of oxygen or removal of hydrogen, carried out by mixed function oxidases in the liver. These oxidative reactions involve a cytochrome P450 monooxygenase, NADPH and oxygen; the classes of pharmaceutical drugs that utilize this method for their metabolism include phenothiazines and steroids. If the metabolites of phase I reactions are sufficiently polar, they may be excreted at this point. However, many phase I products are not eliminated and undergo a subsequent reaction in which an endogenous substrate combines with the newly incorporated functional group to
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to impact the behavior of the receiving individuals. There are alarm pheromones, food trail pheromones, sex pheromones, many others that affect behavior or physiology. Pheromones are used from basic unicellular prokaryotes to complex multicellular eukaryotes, their use among insects has been well documented. In addition, some vertebrates and ciliates communicate by using pheromones; the portmanteau word "pheromone" was coined by Peter Karlson and Martin Lüscher in 1959, based on the Greek φερω pheroo and ὁρμων hormon. Pheromones are sometimes classified as ecto-hormones, they were researched earlier by various scientists, including Jean-Henri Fabre, Joseph A. Lintner, Adolf Butenandt, ethologist Karl von Frisch who called them various names, like for instance "alarm substances".
These chemical messengers are transported outside of the body and affect neurocircuits, including the autonomous nervous system with hormone or cytokine mediated physiological changes, inflammatory signaling, immune system changes and/or behavioral change in the recipient. They proposed the term to describe chemical signals from conspecifics that elicit innate behaviors soon after the German biochemist Adolf Butenandt had characterized the first such chemical, bombykol, a chemically well-characterized pheromone released by the female silkworm to attract mates. Aggregation pheromones function in mate selection, overcoming host resistance by mass attack, defense against predators. A group of individuals at one location is referred to as an aggregation, whether consisting of one sex or both sexes. Male-produced sex attractants have been called aggregation pheromones, because they result in the arrival of both sexes at a calling site and increase the density of conspecifics surrounding the pheromone source.
Most sex pheromones are produced by the females. Aggregation pheromones have been found in members of the Coleoptera, Hemiptera and Orthoptera. In recent decades, the importance of applying aggregation pheromones in the management of the boll weevil, stored product weevils, Sitophilus granarius, Sitophilus oryzae, pea and bean weevil has been demonstrated. Aggregation pheromones are among the most ecologically selective pest suppression methods, they are nontoxic and effective at low concentrations. Some species release a volatile substance when attacked by a predator that can trigger flight or aggression in members of the same species. For example, Vespula squamosa use alarm pheromones to alert others to a threat. In Polistes exclamans, alarm pheromones are used as an alert to incoming predators. Pheromones exist in plants: Certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants; these tannins make the plants less appetizing for the herbivore.
Epideictic pheromones are different from territory pheromones. Fabre observed and noted how "females who lay their eggs in these fruits deposit these mysterious substances in the vicinity of their clutch to signal to other females of the same species they should clutch elsewhere." It may be helpful to note that the word epideictic, having to do with display or show, has a different but related meaning in rhetoric, the human art of persuasion by means of words. Releaser pheromones are pheromones. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. In general, this type of pheromone elicits a rapid response, but is degraded. In contrast, a primer pheromone has a longer duration. For example, rabbit release mammary pheromones that trigger immediate nursing behavior by their babies. Signal pheromones cause short-term changes, such as the neurotransmitter release that activates a response. For instance, GnRH molecule functions as a neurotransmitter in rats to elicit lordosis behavior.
Primer pheromones trigger a change of developmental events. Laid down in the environment, territorial pheromones mark the boundaries and identity of an organism's territory. In cats and dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory. In social seabirds, the preen gland is used to mark nests, nuptial gifts, territory boundaries with behavior described as'displacement activity'. Social insects use trail pheromones. For example, ants mark their paths with pheromones consisting of volatile hydrocarbons. Certain ants lay down an initial trail of pheromones; this trail serves as a guide. As long as the food source remains available, visiting ants will continuously renew the pheromone trail; the pheromone requires continuous renewal. When the food supply begins to dwindle, the trail-making ceases. In at least one species of ant, trails that no longer lead to food are marked with a repellent pheromone; the Eciton burchellii species provides an example of using pheromones to mark and maintain foraging paths.
When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the
Biological pigments known as pigments or biochromes, are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, feathers and hair contain pigments such as melanin in specialized cells called chromatophores. Pigment color differs from structural color in that it is the same for all viewing angles, whereas structural color is the result of selective reflection or iridescence because of multilayer structures. For example, butterfly wings contain structural color, although many butterflies have cells that contain pigment as well. See conjugated systems for electron bond chemistry that causes these molecules to have pigment. Heme/porphyrin-based: chlorophyll, hemocyanin, myoglobin Light-emitting: luciferin Carotenoids: Hematochromes Carotenes: alpha and beta carotene, rhodopsin Xanthophylls: canthaxanthin, lutein Proteinaceous: phytochrome, phycobiliproteins Polyene enolates: a class of red pigments unique to parrots Other: melanin, flavonoids The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll and several colorful pigments that absorb as much light energy as possible.
Other functions of pigments in plants include attracting insects to flowers to encourage pollination. Plant pigments include many molecules, such as porphyrins, carotenoids and betalains. All biological pigments selectively absorb certain wavelengths of light while reflecting others; the principal pigments responsible are: Chlorophyll is the primary pigment in plants. It is the presence and relative abundance of chlorophyll. All land plants and green algae possess two forms of this pigment: chlorophyll a and chlorophyll b. Kelps and other photosynthetic heterokonts contain chlorophyll c instead of b, while red algae possess only chlorophyll a. All chlorophylls serve as the primary means plants use to intercept light in order to fuel photosynthesis. Carotenoids are red, orange, or yellow tetraterpenoids. During the process of photosynthesis, they have functions in light-harvesting, in photoprotection, serve as protein structural elements. In higher plants, they serve as precursors to the plant hormone abscisic acid.
Plants, in general, contain six ubiquitous carotenoids: neoxanthin, antheraxanthin, lutein and β-carotene. Lutein is a yellow pigment found in fruits and vegetables and is the most abundant carotenoid in plants. Lycopene is the red pigment responsible for the color of tomatoes. Other less common carotenoids in plants include lutein epoxide and alpha carotene. In cyanobacteria, many other carotenoids exist such as canthaxanthin, myxoxanthophyll and echinenone. Algal phototrophs such as dinoflagellates use peridinin as a light harvesting pigment. While carotenoids can be found complexed within chlorophyll-binding proteins such as the photosynthetic reaction centers and light-harvesting complexes, they are found within dedicated carotenoid proteins such as the orange carotenoid protein of cyanobacteria. Anthocyanins are water-soluble flavonoid pigments that appear red to blue, according to pH, they occur in all tissues of higher plants, providing color in leaves, plant stem, roots and fruits, though not always in sufficient quantities to be noticeable.
Anthocyanins are most visible in the petals of flowers of many species. Betalains are yellow pigments. Like anthocyanins they are water-soluble, but unlike anthocyanins they are synthesized from tyrosine; this class of pigments is found only in the Caryophyllales, never co-occur in plants with anthocyanins. Betalains are responsible for the deep red color of beets. A noticeable manifestation of pigmentation in plants is seen with autumn leaf color, a phenomenon that affects the green leaves of many deciduous trees and shrubs whereby they take on, during a few weeks in the autumn season, various shades of red, yellow and brown. Chlorophylls degrade into colorless tetrapyrroles known as nonfluorescent chlorophyll catabolites; as the predominant chlorophylls degrade, the hidden pigments of yellow xanthophylls and orange beta-carotene are revealed. These pigments are present throughout the year, but the red pigments, the anthocyanins, are synthesized de novo once half of chlorophyll has been degraded.
The amino acids released from degradation of light harvesting complexes are stored all winter in the tree's roots, branches and trunk until next spring when they are recycled to re‑leaf the tree. Pigmentation is used by many animals for protection, by means of camouflage, mimicry, or warning coloration; some animals including fish and cephalopods use pigmented chromatophores to provide camouflage that varies to match the background. Pigmentation is used in signalling between animals, such as in reproductive behavior. For example, some cephalopods use their chromatophores to communicate; the photopigment rhodopsin intercepts light as the first step in the perception of light. Skin pigments such as melanin may protect tissues from sunburn by ultraviolet radiation. However, some biological structures in animals, such as heme groups that
An aroma compound known as an odorant, fragrance, or flavor, is a chemical compound that has a smell or odor. A chemical compound has a smell or odor when it is sufficiently volatile to be transported to the olfactory system in the upper part of the nose. Molecules meeting this specification have molecular weights of less than 300. Flavors affect both the sense of smell, whereas fragrances affect only smell. Flavors tend to be occurring, fragrances tend to be synthetic. Aroma compounds can be found in food, spices, floral scent, fragrance oils, essential oils. For example, many form biochemically during the ripening of other crops. In wines, most form as byproducts of fermentation. Many of the aroma compounds play a significant role in the production of flavorants, which are used in the food service industry to flavor and increase the appeal of their products. An odorizer may add a detectable odor to a dangerous odorless substance, like propane, natural gas, or hydrogen, as a safety measure. Note: Carvone, depending on its chirality, offers two different smells.
Furaneol 1-Hexanol cis-3-Hexen-1-ol Menthol High concentrations of aldehydes tend to be pungent and overwhelming, but low concentrations can evoke a wide range of aromas. Acetaldehyde Hexanal cis-3-Hexenal Furfural Hexyl cinnamaldehyde Isovaleraldehyde – nutty, cocoa-like Anisic aldehyde – floral, hawthorn, it is a crucial component of chocolate, strawberry, raspberry and others. Cuminaldehyde – Spicy, cumin-like, green Fructone Hexyl acetate Ethyl methylphenylglycidate Cyclopentadecanone Dihydrojasmone Oct-1-en-3-one 2-Acetyl-1-pyrroline 6-Acetyl-2,3,4,5-tetrahydropyridine gamma-Decalactone intense peach flavor gamma-Nonalactone coconut odor, popular in suntan lotions delta-Octalactone creamy note Jasmine lactone powerful fatty-fruity peach and apricot Massoia lactone powerful creamy coconut Wine lactone sweet coconut odor Sotolon Thioacetone A studied organosulfur, its smell is so potent it can be detected several hundred meters downwind mere seconds after a container is opened. Allyl thiol methanethiol, the "mouse thiol", found in mouse urine and functions as a semiochemical for female mice Ethanethiol called ethyl mercaptan 2-Methyl-2-propanethiol called tert-butyl mercaptan, is added as a blend of other components to natural gas used as fuel gas.
Butane-1-thiol called butyl mercaptan, is a chemical intermediate. Grapefruit mercaptan Methanethiol called methyl mercaptan Furan-2-ylmethanethiol called furfuryl mercaptan Benzyl mercaptan Methylphosphine and dimethylphosphine Phosphine Diacetyl Acetoin Nerolin Tetrahydrothiophene 2,4,6-Trichloroanisole Substituted pyrazines Animals that are capable of smell detect aroma compounds with their olfactory receptors. Olfactory receptors are cell-membrane receptors on the surface of sensory neurons in the olfactory system that detect airborne aroma compounds. Aroma compounds can be identified by Gas Chromatography-Olfactometry, which involves a human operator sniffing the GC effluent. In mammals, olfactory receptors are expressed on the surface of the olfactory epithelium in the nasal cavity. In 2005–06, fragrance mix was the third-most-prevalent allergen in patch tests.'Fragrance' was voted Allergen of the Year in 2007 by the American Contact Dermatitis Society. A recent academic study in the United States has shown that "34.7 % of the population reported health problems, such as migraine headaches and respiratory difficulties, when exposed to fragranced products".
The composition of fragrances is not disclosed in the label of products, hiding the actual chemicals of the formula, which raises concerns among some consumers. Fragrances are regulated in the United States by the Toxic Substances Control Act of 1976 that "grandfathered" existing chemicals without further review or testing and put the burden of proof that a new substance is not safe on the EPA; the EPA, does not conduct independent safety testing but relies on data provided by the manufacturer. In 2010 the International Fragrance Association published a list of 3,059 chemicals used in 2011 based on a voluntary survey of its members, it was estimated to represent about 90% of the world's production volume of fragrances. Flavour and Fragrance Journal Fragrances of the World Foodpairing Odor Odor detection threshold Olfaction Olfactory system Olfactory receptor Odorizer, a device for adding an odorant to gas flowing through a pipe Pheromone Aroma of wine Eau de toilette