Structural hierarchy tertiary

The Danish biochemist Kai Linderstrom-Lang coined the terms "primary," "secondary," and "tertiary" structure to emphasize the structural hierarchy in... 

Figure 1.3 Folding of a polypeptide chain illustrating the hierarchy of protein structure from primary structure through secondary structure and tertiary structure.

Figure 11.4 The structural hierarchy in proteins, (a) A segment of primary structure (b) secondary structure illustrated as a segment of alpha helix (c) tertiary structure in which helices are interspersed with coils, and (d) quaternary structure. (Illustration, Irving Geis/Geis Archive Trust. Copyright Howard Hughes Medical Institute. Reproduced with permission.)...

Certain properties, common to all types of macromolecule, can be derived from such analyses. All seem to have a certain individuality and many have the ability to specifically recognize and interact with other substances. They are all, to a greater or lesser extent, flexible molecules, capable of adapting their shape in response to their particular microenvironment within the cell. They ail have a pronounced intolerance to extreme conditions, a fragility that makes them fall apart if treated harshly. Finally they all may be described in terms of a structural hierarchy of primary, secondary and tertiary structures that we need to look at in a little more detail. 

Tertiary structure is the level above secondary structure in the hierarchy of structures. For example, in the zinc-finger motif mentioned above, there are regions of secondary structure, a-helix, and b-sheet. These interact to form a specific higher-order structure, the tertiary structure. 

Figure 15.22 The structural hierarchy of proteins. A typical protein s structure can be viewed at different levels. Primary structure (shown as a long string of balls leaving and returning to the picture frame) is the sequence of amino acids. Secondary structure consists of highly ordered regions that occur as an a-helix or a p-sheet. Tertiary structure combines these ordered regions with more random sections. In many proteins, several tertiary units interact to give the quaternary structure.

A description of the protein-structure hierarchy is incomplete without a discussion of structural motifs, which are critical to an understanding of protein structure [17]. Identification of recurring motifs in protein structures has refined our knowledge of the protein-structure hierarchy these motifs occur at all levels from primary to tertiary. The Phe-Asp-Thr-Gly-Ser sequence found in the active site of all aspartic acid proteinases, and the Gly-Gly-X-Leu sequence (where X represents any amino acid residue) that predicts a 3-strand for the last two residues [17], are examples of sequence motifs a-helices, P-strands, and turns are examples of secondary-structural motifs PaP and PxP units, P-hairpins, and Greek keys are examples of supersecondary-structural motifs and four-a-helix bundles and TIM barrels are examples of tertiary-structural motifs. The tertiary fold of a protein is characterized by its tertiary-structural motif. 

There are several structural tiers that exist in a folded protein, sometimes referred to as the hierarchy of protein structure. Although different types of proteins can fold in very different ways, this structural hierarchy can be applied generally to all proteins primary, secondary, tertiary, and quaternary structure. 

Figure 13 The structural hierarchy of polysoaps involves three levels. The primary structure, the monomer sequence, is set hy the chemistry (a). The intrachain micelles introduce a secondary structure (b). The configurations of the micellar string, linear (c), branched (d), or globular (e), define the tertiary structure. (Adapted from Refs. 45 and 66.)...

Fig. 3.2 Structural hierarchy of heteropoly compounds (a) Keggin cluster (primary particle), (b) secondary structure and (c) tertiary structure (texture particle size, porosity, surface area, etc.) (Adapted with permission fiorn Ref. [16]. Copyright 2001, Royal Society of Chemistry)...

Many proteins consist of two or more interacting polypeptide chains of characteristic tertiary structure, each of which is commonly referred to as a subunit of the protein. Subunit organization constitutes another level in the hierarchy of protein structure, defined as the protein s quaternary (4°) structure (Figure 5.10). Questions of quaternary structure address the various kinds of subunits within a protein molecule, the number of each, and the ways in which they interact with one another. 

Protein domains are conserved regions of a limited number of amino acids that can bind diverse partner molecules to form structures of a higher complexity. The domains have a heterogeneous internal organization that consist of amino acid interactions and comprise multiple functionally distinct sectors or subdivisions. The sectors are regions of proteins that are distinct from the hierarchy of primary, secondary, tertiary, and quaternary structures. 

The structure of any one protein is described in terms of a hierarchy of structures primary, secondary, tertiary, and quaternary. The primary structure is the sequence of amino acids along the polypeptide chain. This is generally synonymous with the covalent structure of the protein, except that any disulfide bridges may alternately be... 

There is a natural hierarchy in proteins (see Figure 15.1) which allows the complex three-dimensional structure to be simplified and categorized as combinations of smaller motifs. At the atom level there are patterns of side-chain interactions at the backbone level we see formation of secondary structure (a helix, P sheet and yS turn) and loop families these combine to give supersecondary structures (e.g. P hairpins) and motifs (e.g. Greek key) and ultimately the whole tertiary and quaternary structure. In this chapter we present an overview of current patterns which are observed... 

One of the most remarkable properties of self-assembly is its ability to generate exceedingly coinplica ted supramolecular structures from fairly simple components. Perhaps the most elegant embodiment of this phenomenon is protein stmcture. Proteins exhibit at least four hierarchies of stmcture primary, secondary, tertiary, and quaternary stmctures. Primary stmcture describes the covalent connections making up the sequence of amino acids in each strand. Secondary stmcture involves local architectural elements created when portions of a strand... 

These levels of organization are hierarchical, because each level eaimot exist without the preceding level. For example, a tertiary stmcture requires the presence of secondary stmctural elements. These cannot exist without a primary structure. When viewed in a widening perspective, from an atomic level to a more macroscopic level, each of the hierarchies of organization becomes progressively obvious. 

Going into the physics of biopoljmiers, the first thing to understand is the hierarchy of their structiu-e. As you must have guessed from the title of this Section, there is a primary, a secondary, and a tertiary structure, and sometimes even a quaternary one. 

There is just one more question we would like to broach to conclude this chapter. We have been using the words primary, secondary, tertiary. And what comes next Sometimes the name quaternary structure is introduced when a few protein globules are stuck together, or when one protein chain forms a number of little globules. Clearly, there is the whole hierarchy of structures There are complexes of chains, these complexes form parts of cells, the cells make up tissues, and so on. 

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