Abiomolecule orbiological molecule is loosely defined as amolecule produced by a livingorganism and essential to one or more typicallybiological processes.[1] Biomolecules include largemacromolecules such asproteins,carbohydrates,lipids, andnucleic acids, as well assmall molecules such as vitamins and hormones. A general name for this class of material isbiological materials. Biomolecules are an important element of living organisms. They are oftenendogenous,[2] i.e. produced within the organism,[3] but organisms usually also needexogenous biomolecules, for example certainnutrients, to survive.
The uniformity of both specific types of molecules (the biomolecules) and of certainmetabolic pathways are invariant features among the wide diversity of life forms; thus these biomolecules and metabolic pathways are referred to as "biochemical universals"[4] or "theory of material unity of the living beings", a unifying concept in biology, along withcell theory andevolution theory.[5]
Nucleosides can bephosphorylated by specifickinases in the cell, producingnucleotides. BothDNA andRNA arepolymers, consisting of long, linear molecules assembled bypolymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, and T, while RNA uses the ribonucleotides (which have an extra hydroxyl(OH) group on the pentose ring) C, G, A, and U. Modified bases are fairly common (such as with methyl groups on the base ring), as found inribosomal RNA ortransfer RNAs or for discriminating the new from old strands of DNA after replication.[6]
DNA structure is dominated by the well-knowndouble helix formed by Watson-Crickbase-pairing of C with G and A with T. This is known asB-form DNA, and is overwhelmingly the most favorable and common state of DNA; its highly specific and stable base-pairing is the basis of reliable genetic information storage. DNA can sometimes occur as single strands (often needing to be stabilized by single-strand binding proteins) or asA-form orZ-form helices, and occasionally in more complex 3D structures such as the crossover atHolliday junctions during DNA replication.[7]
Stereo 3D image of a group I intron ribozyme (PDB file 1Y0Q); gray lines show base pairs; ribbon arrows show double-helix regions, blue to red from 5' to 3'[when defined as?] end; white ribbon is an RNA product.
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 constitutemessenger RNA molecules. Those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops, bulges, and junctions.[8] Examples are tRNA, ribosomes,ribozymes, andriboswitches. These complex structures are facilitated by the fact that RNA backbone has less local flexibility than DNA but a large set of distinct conformations, apparently because of both positive and negative interactions of the extra OH on the ribose.[9] Structured RNA molecules can do highly specific binding of other molecules and can themselves be recognized specifically; in addition, they can perform enzymatic catalysis (when they are known as "ribozymes", as initially discovered by Tom Cech and colleagues).[10]
Monosaccharides are the simplest form ofcarbohydrates with only one simple sugar. They essentially contain analdehyde orketone group in their structure.[11] The presence of an aldehyde group in a monosaccharide is indicated by the prefixaldo-. Similarly, a ketone group is denoted by the prefixketo-.[6] Examples of monosaccharides are thehexoses,glucose,fructose,Trioses,Tetroses,Heptoses,galactose,pentoses, ribose, and deoxyribose. Consumed fructose andglucose have different rates of gastric emptying, are differentially absorbed and have different metabolic fates, providing multiple opportunities for two different saccharides to differentially affect food intake.[11] Most saccharides eventually 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.[6] Examples of disaccharides includesucrose,maltose, andlactose.
Polysaccharides are polymerized monosaccharides, or complex carbohydrates. They have multiple simple sugars. Examples arestarch,cellulose, andglycogen. They are generally large and often 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, and some polysaccharides form thick colloidal dispersions when heated in water.[6] Shorter polysaccharides, with 3 to 10 monomers, are calledoligosaccharides.[12]A fluorescent indicator-displacement molecular imprinting sensor was developed for discriminating saccharides. It successfully discriminated three brands of orange juice beverage.[13] The change in fluorescence intensity of the sensing films resulting is directly related to the saccharide concentration.[14]
Lignin is a complex polyphenolic macromolecule composed mainly of beta-O4-aryl linkages. After cellulose, lignin is the second most abundant biopolymer and is one of the primary structural components of most plants. It contains subunits derived fromp-coumaryl alcohol,coniferyl alcohol, andsinapyl alcohol,[15] and is unusual among biomolecules in that it isracemic. The lack of optical activity is due to the polymerization of lignin which occurs viafree radical coupling reactions in which there is no preference for either configuration at achiral center.
Lipids (oleaginous) are chieflyfatty acidesters, and are the basic building blocks ofbiological membranes. Another biological role is energy storage (e.g.,triglycerides). Most lipids consist of apolar orhydrophilic head (typically glycerol) and one to three non polar orhydrophobic fatty acid tails, and therefore they areamphiphilic. Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone (saturated fatty acids) or by both single anddouble bonds (unsaturated fatty acids). The chains are usually 14-24 carbon groups long, but it is always an even number.
For lipids present in biological membranes, the hydrophilic head is from one of three classes:
Amino acids contain bothamino andcarboxylic acidfunctional groups. (Inbiochemistry, the term amino acid is used when referring to those amino acids in which the amino and carboxylate functionalities are attached to the same carbon, plusproline which is not actually an amino acid).
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification aftertranslation (protein synthesis). For example, phosphorylation of serine bykinases and dephosphorylation byphosphatases is an important control mechanism in thecell cycle. Only two amino acids other than the standard twenty are known to be incorporated into proteins during translation, in certain organisms:
Selenocysteine is incorporated into some proteins at a UGAcodon, which is normally a stop codon.
Pyrrolysine is incorporated into some proteins at a UAG codon. For instance, in somemethanogens in enzymes that are used to producemethane.
The particular series of amino acids that form a protein is known as that protein'sprimary structure. This sequence is determined by the genetic makeup of the individual. It specifies the order of side-chain groups along the linear polypeptide "backbone".
Proteins have two types of well-classified, frequently occurring elements of local structure defined by a particular pattern ofhydrogen bonds along the backbone:alpha helix andbeta sheet. Their number and arrangement is called thesecondary structure of the protein. Alpha helices are regular spirals stabilized by hydrogen bonds between the backbone CO group (carbonyl) of one amino acid residue and the backbone NH group (amide) of the i+4 residue. The spiral has about 3.6 amino acids per turn, and the amino acid side chains stick out from the cylinder of the helix. Beta pleated sheets are formed by backbone hydrogen bonds between individual beta strands each of which is in an "extended", or fully stretched-out, conformation. The strands may lie parallel or antiparallel to each other, and the side-chain direction alternates above and below the sheet. Hemoglobin contains only helices, natural silk is formed of beta pleated sheets, and many enzymes have a pattern of alternating helices and beta-strands. The secondary-structure elements are connected by "loop" or "coil" regions of non-repetitive conformation, which are sometimes quite mobile or disordered but usually adopt a well-defined, stable arrangement.[16]
When two or morepolypeptide chains (either of identical or of different sequence) cluster to form a protein,quaternary structure of protein is formed. Quaternary structure is an attribute ofpolymeric (same-sequence chains) orheteromeric (different-sequence chains) proteins likehemoglobin, which consists of two "alpha" and two "beta" polypeptide chains.
Anapoenzyme (or, generally, an apoprotein) is the protein without any small-molecule cofactors, substrates, or inhibitors bound. It is often important as an inactive storage, transport, or secretory form of a protein. This is required, for instance, to protect the secretory cell from the activity of that protein.Apoenzymes become active enzymes on addition of acofactor. Cofactors can be either inorganic (e.g., metal ions andiron-sulfur clusters) or organic compounds, (e.g., [Flavin group|flavin] andheme). Organic cofactors can be eitherprosthetic groups, which are tightly bound to an enzyme, orcoenzymes, which are released from the enzyme's active site during the reaction.
Isoenzymes, or isozymes, are multiple forms of an enzyme, with slightly differentprotein sequence and closely similar but usually not identical functions. They are either products of differentgenes, or else different products ofalternative splicing. They may either be produced in different organs or cell types to perform the same function, or several isoenzymes may be produced in the same cell type under differential regulation to suit the needs of changing development or environment. LDH (lactate dehydrogenase) has multiple isozymes, whilefetal hemoglobin is an example of a developmentally regulated isoform of a non-enzymatic protein. The relative levels of isoenzymes in blood can be used to diagnose problems in the organ of secretion .
^Gayon, J. (1998). "La philosophie et la biologie". In Mattéi, J. F. (ed.).Encyclopédie philosophique universelle. Vol. IV, Le Discours philosophique. Presses Universitaires de France. pp. 2152–2171.ISBN9782130448631 – via Google Books.
^abcdSlabaugh, Michael R. & Seager, Spencer L. (2007).Organic and Biochemistry for Today (6th ed.). Pacific Grove:Brooks Cole.ISBN978-0-495-11280-8.
^Kruger K, Grabowski PJ, Zaug AJ, Sands J, Gottschling DE, Cech TR (1982). "Self-splicing RNA: autoexcision and autocyclization of the ribosomal RNA intervening sequence of Tetrahymena".Cell.31 (1):147–157.doi:10.1016/0092-8674(82)90414-7.PMID6297745.S2CID14787080.
^Jin, Tan; Wang He-Fang & Yan Xiu-Ping (2009). "Discrimination of Saccharides with a Fluorescent Molecular Imprinting Sensor Array Based on Phenylboronic Acid Functionalized Mesoporous Silica".Anal. Chem.81 (13):5273–80.doi:10.1021/ac900484x.PMID19507843.
^Bo Peng & Yu Qin (2008). "Lipophilic Polymer Membrane Optical Sensor with a Synthetic Receptor for Saccharide Detection".Anal. Chem.80 (15):6137–41.doi:10.1021/ac800946p.PMID18593197.
^K. Freudenberg; A.C. Nash, eds. (1968).Constitution and Biosynthesis of Lignin. Berlin: Springer-Verlag.
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