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39-434: An A-frame is a basic structure designed to bear a load in a lightweight economical manner. The simplest form of an A-frame is two similarly sized beams , arranged in an angle of 45 degrees or less, attached at the top, like an uppercase letter 'A'. These materials are often wooden or steel beams attached at the top by rope, welding , gluing , or riveting . A-frames can be used as-is, as part of shears , or set up in

78-415: A hierarchical organization , but hierarchy makes it easier for a listener to understand and remember the music. In analogy to linguistic terminology, motifs and phrases can be combined to make complete musical ideas such as sentences and phrases . A larger form is known as the period . One such form that was widely used between 1600 and 1900 has two phrases, an antecedent and a consequent , with

117-417: A pointer that links them together in a particular order. Out of these any number of other data structures can be created such as stacks , queues , trees and hash tables . In solving a problem, a data structure is generally an integral part of the algorithm . In modern programming style, algorithms and data structures are encapsulated together in an abstract data type . Software architecture

156-506: A crystal have a structure that involves repetition of a basic unit called a unit cell . The atoms can be modeled as points on a lattice , and one can explore the effect of symmetry operations that include rotations about a point, reflections about a symmetry planes, and translations (movements of all the points by the same amount). Each crystal has a finite group, called the space group , of such operations that map it onto itself; there are 230 possible space groups. By Neumann's law ,

195-404: A half cadence in the middle and a full cadence at the end providing punctuation. On a larger scale are single-movement forms such as the sonata form and the contrapuntal form , and multi-movement forms such as the symphony . A social structure is a pattern of relationships. They are social organizations of individuals in various life situations. Structures are applicable to people in how

234-478: A hydroxyoxazolidine (Ser/Thr) or hydroxythiazolidine (Cys) intermediate]. This intermediate tends to revert to the amide form, expelling the attacking group, since the amide form is usually favored by free energy, (presumably due to the strong resonance stabilization of the peptide group). However, additional molecular interactions may render the amide form less stable; the amino group is expelled instead, resulting in an ester (Ser/Thr) or thioester (Cys) bond in place of

273-457: A multilevel hierarchy of structures employing biominerals and proteins , at the bottom of which are collagen fibrils . In biology , one of the properties of life is its highly ordered structure, which can be observed at multiple levels such as in cells , tissues , organs , and organisms . In another context, structure can also observed in macromolecules , particularly proteins and nucleic acids . The function of these molecules

312-415: A primary structure, although the usage is not standard. The primary structure of a biological polymer to a large extent determines the three-dimensional shape ( tertiary structure ). Protein sequence can be used to predict local features , such as segments of secondary structure, or trans-membrane regions. However, the complexity of protein folding currently prohibits predicting the tertiary structure of

351-494: A protein from its sequence alone. Knowing the structure of a similar homologous sequence (for example a member of the same protein family ) allows highly accurate prediction of the tertiary structure by homology modeling . If the full-length protein sequence is available, it is possible to estimate its general biophysical properties , such as its isoelectric point . Sequence families are often determined by sequence clustering , and structural genomics projects aim to produce

390-461: A redundant structure is needed so that if a component fails it has backups. A high redundancy is an essential part of the design of several systems in the Space Shuttle . As a branch of philosophy, logic is concerned with distinguishing good arguments from poor ones. A chief concern is with the structure of arguments. An argument consists of one or more premises from which a conclusion

429-511: A row along a longitudinal beam for added stability, as in a saw horse . More complex structures will often have crossmembers connecting the A-frames at different angles, forming a truss . Structure Buildings , aircraft , skeletons , anthills , beaver dams , bridges and salt domes are all examples of load -bearing structures. The results of construction are divided into buildings and non-building structures , and make up

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468-434: A society is as a system organized by a characteristic pattern of relationships. This is known as the social organization of the group. Sociologists have studied the changing structure of these groups. Structure and agency are two confronted theories about human behaviour. The debate surrounding the influence of structure and agency on human thought is one of the central issues in sociology. In this context, agency refers to

507-471: A variety of diagrams called structural formulas . Lewis structures use a dot notation to represent the valence electrons for an atom; these are the electrons that determine the role of the atom in chemical reactions. Bonds between atoms can be represented by lines with one line for each pair of electrons that is shared. In a simplified version of such a diagram, called a skeletal formula , only carbon-carbon bonds and functional groups are shown. Atoms in

546-408: Is inferred . The steps in this inference can be expressed in a formal way and their structure analyzed. Two basic types of inference are deduction and induction . In a valid deduction, the conclusion necessarily follows from the premises, regardless of whether they are true or not. An invalid deduction contains some error in the analysis. An inductive argument claims that if the premises are true,

585-434: Is determined by their shape as well as their composition, and their structure has multiple levels. Protein structure has a four-level hierarchy. The primary structure is the sequence of amino acids that make it up. It has a peptide backbone made up of a repeated sequence of a nitrogen and two carbon atoms. The secondary structure consists of repeated patterns determined by hydrogen bonding . The two basic types are

624-413: Is harder because of the reverse information loss (from amino acids to DNA sequence). The current lossless data compressor that provides higher compression is AC2. AC2 mixes various context models using Neural Networks and encodes the data using arithmetic encoding. The proposal that proteins were linear chains of α-amino acids was made nearly simultaneously by two scientists at the same conference in 1902,

663-489: Is the specific choices made between possible alternatives within a framework. For example, a framework might require a database and the architecture would specify the type and manufacturer of the database. The structure of software is the way in which it is partitioned into interrelated components. A key structural issue is minimizing dependencies between these components. This makes it possible to change one component without requiring changes in others. The purpose of structure

702-420: Is to optimise for (brevity, readability, traceability, isolation and encapsulation, maintainability, extensibility, performance and efficiency), examples being: language choice , code , functions , libraries , builds , system evolution , or diagrams for flow logic and design . Structural elements reflect the requirements of the application: for example, if the system requires a high fault tolerance, then

741-434: The cyclol hypothesis advanced by Dorothy Wrinch , proposed that the linear polypeptide underwent a chemical cyclol rearrangement C=O + HN → {\displaystyle \rightarrow } C(OH)-N that crosslinked its backbone amide groups, forming a two-dimensional fabric . Other primary structures of proteins were proposed by various researchers, such as the diketopiperazine model of Emil Abderhalden and

780-406: The active site of the protein, inhibiting its function. The protein is activated by cleaving off the inhibitory peptide. Some proteins even have the power to cleave themselves. Typically, the hydroxyl group of a serine (rarely, threonine) or the thiol group of a cysteine residue will attack the carbonyl carbon of the preceding peptide bond, forming a tetrahedrally bonded intermediate [classified as

819-516: The amino -terminal end through to the carboxyl -terminal end. Either a three letter code or single letter code can be used to represent the 22 naturally encoded amino acids, as well as mixtures or ambiguous amino acids (similar to nucleic acid notation ). Peptides can be directly sequenced , or inferred from DNA sequences . Large sequence databases now exist that collate known protein sequences. In general, polypeptides are unbranched polymers, so their primary structure can often be specified by

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858-521: The encoded 22, and may be cyclised, modified and cross-linked. Peptides can be synthesised chemically via a range of laboratory methods. Chemical methods typically synthesise peptides in the opposite order (starting at the C-terminus) to biological protein synthesis (starting at the N-terminus). Protein sequence is typically notated as a string of letters, listing the amino acids starting at

897-648: The infrastructure of a human society. Built structures are broadly divided by their varying design approaches and standards, into categories including building structures, architectural structures , civil engineering structures and mechanical structures. The effects of loads on physical structures are determined through structural analysis , which is one of the tasks of structural engineering . The structural elements can be classified as one-dimensional ( ropes , struts , beams , arches ), two-dimensional ( membranes , plates, slab , shells , vaults ), or three-dimensional (solid masses). Three-dimensional elements were

936-575: The protein has been synthesized on the ribosome , typically occurring in the endoplasmic reticulum , a subcellular organelle of the eukaryotic cell. Many other chemical reactions (e.g., cyanylation) have been applied to proteins by chemists, although they are not found in biological systems. In addition to those listed above, the most important modification of primary structure is peptide cleavage (by chemical hydrolysis or by proteases ). Proteins are often synthesized in an inactive precursor form; typically, an N-terminal or C-terminal segment blocks

975-405: The pyrrol/piperidine model of Troensegaard in 1942. Although never given much credence, these alternative models were finally disproved when Frederick Sanger successfully sequenced insulin and by the crystallographic determination of myoglobin and hemoglobin by Max Perutz and John Kendrew . Any linear-chain heteropolymer can be said to have a "primary structure" by analogy to the usage of

1014-415: The α-helix and the β-pleated sheet . The tertiary structure is a back and forth bending of the polypeptide chain, and the quaternary structure is the way that tertiary units come together and interact. Structural biology is concerned with biomolecular structure of macromolecules. Chemical structure refers to both molecular geometry and electronic structure. The structure can be represented by

1053-528: The 1920s when he argued that rubber was composed of macromolecules . Thus, several alternative hypotheses arose. The colloidal protein hypothesis stated that proteins were colloidal assemblies of smaller molecules. This hypothesis was disproved in the 1920s by ultracentrifugation measurements by Theodor Svedberg that showed that proteins had a well-defined, reproducible molecular weight and by electrophoretic measurements by Arne Tiselius that indicated that proteins were single molecules. A second hypothesis,

1092-523: The 74th meeting of the Society of German Scientists and Physicians, held in Karlsbad. Franz Hofmeister made the proposal in the morning, based on his observations of the biuret reaction in proteins. Hofmeister was followed a few hours later by Emil Fischer , who had amassed a wealth of chemical details supporting the peptide-bond model. For completeness, the proposal that proteins contained amide linkages

1131-419: The conclusion is likely. Protein primary structure Protein primary structure is the linear sequence of amino acids in a peptide or protein . By convention, the primary structure of a protein is reported starting from the amino -terminal (N) end to the carboxyl -terminal (C) end. Protein biosynthesis is most commonly performed by ribosomes in cells. Peptides can also be synthesized in

1170-661: The individual human capacity to act independently and make free choices. Structure here refers to factors such as social class , religion , gender , ethnicity , customs, etc. that seem to limit or influence individual opportunities. In computer science , a data structure is a way of organizing information in a computer so that it can be used efficiently. Data structures are built out of two basic types: An array has an index that can be used for immediate access to any data item (some programming languages require array size to be initialized ). A linked list can be reorganized, grown or shrunk, but its elements must be accessed with

1209-455: The laboratory. Protein primary structures can be directly sequenced , or inferred from DNA sequences . Amino acids are polymerised via peptide bonds to form a long backbone , with the different amino acid side chains protruding along it. In biological systems, proteins are produced during translation by a cell's ribosomes . Some organisms can also make short peptides by non-ribosomal peptide synthesis , which often use amino acids other than

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1248-996: The main option available to early structures such as Chichen Itza . A one-dimensional element has one dimension much larger than the other two, so the other dimensions can be neglected in calculations; however, the ratio of the smaller dimensions and the composition can determine the flexural and compressive stiffness of the element. Two-dimensional elements with a thin third dimension have little of either but can resist biaxial traction. The structure elements are combined in structural systems . The majority of everyday load-bearing structures are section-active structures like frames, which are primarily composed of one-dimensional (bending) structures. Other types are Vector-active structures such as trusses , surface-active structures such as shells and folded plates, form-active structures such as cable or membrane structures, and hybrid structures. Load-bearing biological structures such as bones, teeth, shells, and tendons derive their strength from

1287-407: The peptide bond. This chemical reaction is called an N-O acyl shift . The ester/thioester bond can be resolved in several ways: The compression of amino acid sequences is a comparatively challenging task. The existing specialized amino acid sequence compressors are low compared with that of DNA sequence compressors, mainly because of the characteristics of the data. For example, modeling inversions

1326-438: The protein can undergo a variety of post-translational modifications , which are briefly summarized here. The N-terminal amino group of a polypeptide can be modified covalently, e.g., The C-terminal carboxylate group of a polypeptide can also be modified, e.g., Finally, the peptide side chains can also be modified covalently, e.g., Most of the polypeptide modifications listed above occur post-translationally , i.e., after

1365-420: The sequence of amino acids along their backbone. However, proteins can become cross-linked, most commonly by disulfide bonds , and the primary structure also requires specifying the cross-linking atoms, e.g., specifying the cysteines involved in the protein's disulfide bonds. Other crosslinks include desmosine . The chiral centers of a polypeptide chain can undergo racemization . Although it does not change

1404-428: The sequence, it does affect the chemical properties of the sequence. In particular, the L -amino acids normally found in proteins can spontaneously isomerize at the C α {\displaystyle \mathrm {C^{\alpha }} } atom to form D -amino acids, which cannot be cleaved by most proteases . Additionally, proline can form stable trans-isomers at the peptide bond. Additionally,

1443-557: The symmetry of a crystal determines what physical properties, including piezoelectricity and ferromagnetism , the crystal can have. A large part of numerical analysis involves identifying and interpreting the structure of musical works. Structure can be found at the level of part of a work, the entire work, or a group of works. Elements of music such as pitch , duration and timbre combine into small elements like motifs and phrases , and these in turn combine in larger structures. Not all music (for example, that of John Cage ) has

1482-468: The term for proteins, but this usage is rare compared to the extremely common usage in reference to proteins. In RNA , which also has extensive secondary structure , the linear chain of bases is generally just referred to as the "sequence" as it is in DNA (which usually forms a linear double helix with little secondary structure). Other biological polymers such as polysaccharides can also be considered to have

1521-574: Was made as early as 1882 by the French chemist E. Grimaux. Despite these data and later evidence that proteolytically digested proteins yielded only oligopeptides, the idea that proteins were linear, unbranched polymers of amino acids was not accepted immediately. Some scientists such as William Astbury doubted that covalent bonds were strong enough to hold such long molecules together; they feared that thermal agitations would shake such long molecules asunder. Hermann Staudinger faced similar prejudices in

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