In contrast, both RNA and proteins are normally single-stranded. In DNA and RNA, this can take the form of Watson-Crick base pairs (G-C and A-T or A-U), although many more complicated interactions can and do occur.īecause of the double-stranded nature of DNA, essentially all of the nucleotides take the form of Watson-Crick base pairs between nucleotides on the two complementary strands of the double-helix. In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into a very long chain. In general, they are all unbranched polymers, and so can be represented in the form of a string. The simple summary is that DNA makes RNA, and then RNA makes proteins.ĭNA, RNA, and proteins all consist of a repeating structure of related building blocks ( nucleotides in the case of DNA and RNA, amino acids in the case of proteins). Each of these molecules is required for life since each plays a distinct, indispensable role in the cell. This comes from macromolecules excluding other molecules from a large part of the volume of the solution, thereby increasing the effective concentrations of these molecules.Īll living organisms are dependent on three essential biopolymers for their biological functions: DNA, RNA and proteins. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules, through an effect known as macromolecular crowding. Similarly, many proteins will denature if the solute concentration of their solution is too high or too low. Many require salts or particular ions to dissolve in water. Īnother common macromolecular property that does not characterize smaller molecules is their relative insolubility in water and similar solvents, instead forming colloids. Macromolecules often have unusual physical properties that do not occur for smaller molecules. ( May 2013) ( Learn how and when to remove this template message) Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources in this section. This section needs additional citations for verification. In British English, the word "macromolecule" tends to be called " high polymer". Complicated biomacromolecules, on the other hand, require multi-faceted structural description such as the hierarchy of structures used to describe proteins. The structure of simple macromolecules, such as homopolymers, may be described in terms of the individual monomer subunit and total molecular mass. īecause of their size, macromolecules are not conveniently described in terms of stoichiometry alone. For example, a single polymeric molecule is appropriately described as a "macromolecule" or "polymer molecule" rather than a "polymer," which suggests a substance composed of macromolecules. Īccording to the standard IUPAC definition, the term macromolecule as used in polymer science refers only to a single molecule. For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry, the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not readily dissociate. Usage of the term to describe large molecules varies among the disciplines. At that time the term polymer, as introduced by Berzelius in 1832, had a different meaning from that of today: it simply was another form of isomerism for example with benzene and acetylene and had little to do with size. The term macromolecule ( macro- + molecule) was coined by Nobel laureate Hermann Staudinger in the 1920s, although his first relevant publication on this field only mentions high molecular compounds (in excess of 1,000 atoms). If a part or the whole of the molecule fits into this definition, it may be describedĪs either macromolecular or polymeric, or by polymer used adjectivally. This statementįails in the case of certain macromolecules for which the properties may beĬritically dependent on fine details of the molecular structure.Ģ. In many cases, especially for synthetic polymers, a molecule can be regardedĪs having a high relative molecular mass if the addition or removal of one or aįew of the units has a negligible effect on the molecular properties. Molecules of low relative molecular mass.ġ. A molecule of high relative molecular mass, the structure of which essentiallyĬomprises the multiple repetition of units derived, actually or conceptually, from
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