This editable Main Article has an approved citable version (see its Citable Version subpage). While we have done conscientious work, we cannot guarantee that this Main Article, or its citable version, is wholly free of mistakes. By helping to improve this editable Main Article, you will help the process of generating a new, improved citable version. [edit intro]
Macromolecule structure and properties are important in biology. Inman M ( ) Shape of a common protein module suggests role as molecular switch. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.”.
Macromolecular chemistry (from macro = large) is the study of the physical, biological and chemical structure, properties, composition, and reaction mechanisms of macromolecules. A macromolecule is a molecule that consists of one or more types of repeated ‘building blocks’. The building blocks are called monomeric units (monomers).
(also known as polymer molecules) appear in daily life in the form of plastic, styrofoam, nylon, etc. The artificial polymer molecules usually exist of long repetitions of identical monomers, either in chains or networks.
In molecular biology macromolecules (biopolymers) play a very important role: the well known molecules DNA, RNA, and polypeptides (proteins) are examples of macromolecules. In molecular biology one is mostly interested in macromolecules in solution, usually dissolved in water. The biological function of macromolecules in living cells is a highly relevant and widely studied topic of research. Although, strictly speaking, biopolymers belong to the class of polymer molecules, there is a tendency not to use the latter name in biological applications, but to speak of macromolecules. The term “polymer” is usually reserved for the substances (plastic, nylon, etc.) manufactured in bulk by the chemical industry.
In industry, the value of synthetic macromolecules as plastics and nylon, has risen enormously over the last 60 years. They have made it possible to mould shapes that would have been impossible to create without them. When they were first developed, their resistance to rupture and degradation was seen as a profound advantage, but nowadays we seek more biologically degradable plastics such as polyethyleneglycol that pollute the environment less.
include, besides the molecules already mentioned, enzymes, and polysaccharides, such as cellulose and starch. The better understanding of the basic behavior of polymer molecules has enhanced our knowledge of these biological molecules, and studies of partially charged polyelectrolytes have led to a deeper insight into their biological function. The investigations of the three dimensional structure of macromolecules, (their configuration and conformation), have led to the identification of specific regions that perform specialized activities. A good example is the catalytic role of particular amino acid residues in polypeptide enzymes and the role of functional groups such as biotin or riboflavin in cellular metabolism. The folding of macromolecules is now a topic of much scientific investigation, since the correct folding of these polymers is a critical factor for normal function.
have a molecular mass larger than most simple molecules; in general, they have a mass of more than 1000 Dalton (or unified atomic mass unit), but the molecular weight of some can be as large as millions of Daltons (even billions in the case of DNA). Their mass and size often leads to them breaking up into smaller pieces simply due to the shear resistance experienced by the macromolecule in a solvent. Any macromolecule, staying in a simple unfolded stretched filament configuration, is experiencing stress shear due to its length and overall mass. For that reason macromolecules have a practical way to avoid these excess forces by folding. Some macromolecules in a solvent fold into an alpha helix shape, some in more complex folding structures, but all according to the possible biological functions that these molecules should exert when in a cellular environment. Complex molecules like DNA, RNA and many proteins also use coiling and super coiling to regain a functional three dimensional conformation. Often these long molecules hide their basic backbones, but ensure stability and functionality essence their own existence and safety. In the laboratory artificial macromolecules are used with a mean molecular mass up to 5 million Dalton with a small spread in the weight have a sample suitable for research. (Long and heavy molecules tend to get disrupted, leading to smaller chains that can influence the measurements done on these molecules, and make it hard to understand results in an unambiguous way. Because of these shear breaks the average molecular weight of a macromolecular sample will have a large deviation around the mean value.)
The mechanism of supercoiling and folding is presently being researched in detail, as its biological function, and failure therein, has reportedly been connected to diseases like Alzheimer’s and Creutzfeldt Jakob disease (CJD).
Large biological molecules seem to use another mechanism similar to the so called Khohlov implosion of macromolecules, a kind of implosive diminishing of the size of the dissolved molecule where its hydrodynamic radius diminishes by a factor of 1000 or more. This can be visualized by the super coiled structure of DNA when inactive. DNA then has the same cigar resulting shape and consists of the total of all of the molecule in one chromosome comprised in a very compac adidas superstar t way.
This implosion seems to be based upon specific environmental conditions based upon charge effects and low concentrations of (possibly) interfering other kinds of macromolecules.
Substances made from macromolecules can have very unusual properties that can be exploited in a wide range of applications. Importantly, plastics and other polymeric substances contribute substantially to the global economy. Whole industries are based on the use of plastics, including the packaging industries, toy manufacturers, automotive industry and household appliances. The downside, however, is the resistance of plastics to chemical degradation, causing them to persist in the environment and the food chain. Plastic bags lead to the death of many animals, be it by animals swallowing the plastic directly, or, later in the food chain, by predators eating plastic containing prey. New artificial materials have been produced that are more easily part of chains of decay and composting. The PET bottle is an example of these new materials. PET (polyethylene terephthalate) is a thermoplastic polymer resin of the polyester family that is used for making synthetic fibers as well as drink containers. PET is fully recyclable, as two depolymerisation methods methanolysis and glycolosis can be used to reduce PET to either a monomer or the original raw materials.
Sources of raw material
Natural polymers do occur. The most familiar is natural rubber, also k adidas superstar nown as latex. It has been used for the production of tires (after vulcanization), paint, and even by the clothing industries. Natural rubber is an elastic and has been artificially created by polymerization of isoprene. A byproduct of the research into these industrial rubbers was Silly Putty. Most (artificial) plastics are made from refined crude oil. Because they are hard to produce otherwise, their continued availability is tied to petroleum security. However, some newer biological process, such as polylactide production, and Dupont’s biological polyethylene glycol monomer synthesis route, use biological feed stocks instead.For more information, see Polymer chemistry.
are the products of polymerization reactions. Polymerization reactions are known for their exothermic nature (their ability to release energy in the form of heat) and their fast kinetics. They continue until one of the reactants has been used, as for instance in the formation of polyurethane. As demonstrated in many high school classes, adding small amounts of ethene and urea to an acidic solution of water results in a high volume polymer in a seemingly never ending process. A very well known biological polymer is starch. Starch is a complex carbohydrate that contains two molecules: amylose and amylopectin, both of which are large polymers of glucose. Starch is soluble in water, and is used as a way of storing excess glucose by plants; it is mainly found in their fruit, seed rhizomes or tubers. Starch also plays a role in storing energy in the bodies of animals, although the two kinds of starch differ in composition. Some artificial polymers exhibit behavior not seen in other materials; for example, kevlar is a composite material that is stronger than steel but which weighs very little in comparison and is very flexible. Such materials have found many uses, from bullet proof vests to enforcing more rigidity in the hull of aeroplanes. Another polymer of importance is silicone, famous by now for its application in the building industry as well as in medicine, reconstructive surgery as well as cosmetic surgery. Silicone is a polymer with a repetitive siloxane group as the backbone.
The behavior of a large group of polymers can be divided in two groups, the thermoplasts and the thermoharders. Thermoplasts respond to heat by becoming more fluid in their behavior, enabling them to be molded to any desired shape. This behavior can also be achieved by adding substances to the polymer (or plastic) called weakeners. Thermoharders are characterized by responding with a more crystalline structure upon heating, ultimately creating a granular resulting material. Many composite materials use these two behaviors in making plastics for special purposes. The thermoplastic behavior of polymers used for clothing, nylon, polyester makes them easier to wash and handle, but also introduces a danger. When heated extendedly they turn into a very hot liquid state, some to the point of burning.
For more information, see Protein structure.
One of the first artificial polypeptides made was nylon. Most nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that amide bonds form at both ends of each monomer in a process analogous to polypeptide biopolymers. Because the reaction also produces H2O the reaction is called a condensation. The most common variant is nylon 6 6, which refers to the fact that the diamine (hexamethylene diamine) and the diacid (adipic acid) each donate six carbons to the polymer chain (the numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second). As with other regular copolymers, like polyesters and polyurethanes, the ‘repeating unit’ consists of one of each monomer, so that they alternate adidas superstar in the chain. As each monomer has the same reactive group on both ends, the direction of the amide bond reverses between each monomer, unlike natural polyamide proteins which have overall directionality: C terminal N terminal. In the laboratory, nylon 6,6 can adidas superstar also be made using adipoyl chloride instead of adipic acid.
The best known biological macromolecules are deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins and polysaccharides. There is a huge diversity of these molecules in living organisms, and not all of their functions are completely known. All of them have a polarity and are synthesised by condensation reactions that add monomers to a defined end of the polymer. The (biological) chemistry and chemical functions of biological macromolecules are discussed further in Biochemistry.