Structural and functional units

It will already be familiar from introductory courses that proteins, which are either structural or biochemically active molecules, are polypeptides formed from different a-amino acids of general form NHjCHRCOOH (5) strimg together by the peptide link, -CONH- (6). Each monomer unit in the chain is referred to as a peptide residue. About 20 amino acids occur naturally and differ in the nature of the group R. These fundamental building blocks are illustrated in the Atlas of structures. Section A, in the Resource section at the end of the text. 

Nucleic acids, which primarily store and transmit genetic information, ire polynucleotides in which base-sugar-phosphate units are coimected by phos-phodiester bonds built from phosphate-ester links like that shown in (7). In DNA the sugar is P-D-2-deoxyribose (as shown in 8) and the bases are adenine (A), cytosine (C), guanine (G), and thymine (T) see the Atlas of structures. Section B. In RNA the sugar is P-D-ribose and uracil (U) replaces thymine. 

The concept of the structure of a biological macromolecule takes on different meanings for the different levels at which we think about the spatial arrangement of the polypeptide chain  

Examples of secondary structure motifs are random coils and ordered structures, such as helices and sheets, held together primarily by hydrogen bonds (Fig. F.2b). The secondary structure of DNA arises primarily from the winding of two polynucleotide chains around each other to form a double helix (Fig. F.3) held 

Figi F.3 The DNA double helix, in which two polynucleotide chains are linked together by hydrogen bonds between adenine (A) and thymine (T), and between cytosine (C) and guanine (G). 

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It is now apparent that many bacterial cellulases are composed of two or more structural and functional units or domains and it has been suggested that such enzymes arose by a process of domain shuffling (1). The domains may be catalytic or non-catalytic and their occurrence is often indicated in the primary protein structure by an intervening... 

The bile canaliculi form a network, which feed into ductules, which become bile ducts (Fig. 6.3). The structural and functional unit of the liver is the lobule, which is usually described in terms of the hepatic acinus (Fig. 6.5), based on the microcirculation in the lobule. When the lobule is considered in structural terms, it may be described as either a classical or a portal lobule (see "Glossary"). The acinus comprises a unit bounded by two portal tracts and terminal hepatic or central venules, where a portal tract is composed of a portal venule, bile ductile, and hepatic arteriole (Fig. 6.5). Blood flows from the portal tract toward the central... 

Cells Are the Structural and Functional Units of All Living Organisms... 

Cell A small cavity, compartment or locule also the structural and functional unit of plants and animals, consisting of a small mass of cytoplasm and a denser portion (the nucleus) and surrounded by a more or less differentiated semipermeable membrane often the cell secretes a permeable covering or cell wall around itself from which the term was first derived. 

The cell, as the smallest structural and functional unit of all living organisms, is a fascinating system in view of its highly complex and hierarchical machinery. 

Nephron The basic structural and functional unit of the kidney. The basic function of the nephron is to regulate water and soluble substances... 

The kidney tissue has a very intriguing structure. It is organized into several thousand structural and functional units. A single unit - a nephron (Figure 2.15b) - spans the better part of the entire distance between the organ periphery and the renal pelvis, which simply collects the final urine and feeds it into the ureters.. 

Rappaport, A.M., Borowy, Z.J., Longheed, WJM., Lotto, W.N. Subdivision of hexagonal hver lohules into a structural and functional unit role in hepatic physiology and pathology. Anat. Rec. 1954 119 11-34... 

Rappaport, A.M. The structural and functional unit in the human hver (hver acinus). Anat. Rec. 1958 130 673-687... 

Shipway, A.N. Willner, I. Nanoparticles as structural and functional units in surface-confined architectures. Chem. Commun. (Camb.) 2001, 2035-2045. 

The assessment of functional significance of associations between metals and proteins is greatly facilitated when the pure proteins under study exhibit specific enzymatic function. These enzymes may fall in either group of proteins described above. Highly purified proteins which contain a metal firmly and apparently uniquely bound—metalloenzymes—represent particularly useful model systems for the study both of interactions of proteins with metals and of the biological effects of metals. Since the members of this group are structural and functional units, at least three primary parameters can be measured independently to ascertain the interdependence between structure and function ) The protein, 2) the metal, and (3) the activity. 

Rappaport AM. The structural and functional units in the human liver (liver acinus). Microvasc Res 1973 6 212-218. 

Because domains can be considered independent structural and functional units, each domain can be analyzed independently once it has been determined that the query protein contains more than one domain. The identification of functional domains can be performed directly by matching the entire query sequence or a portion of it to a profile from a domain database. Alternatively, the existence of functional domains can be evaluated through indirect inference. For instance, if the query protein contains a well-characterized domain that matches a database profile and the rest of the sequence is not covered by any known domain, that uncovered region (provided it has a reasonable length) can be assumed to contain an additional domain. For cases in which there are no matches to domains or protein families in databases, the existence of multiple domains in the protein of interest can still be inferred through other methods. For example, the connectors between domains tend to be disordered or flexible linkers. Accordingly, predictions of disorder or composition bias, linker predictions, or secondary-structure predictions can be used to infer the spatial location of uncharacterized domains. 

On the one hand, we tried to understand and utilize processes running in animated nature. With the growing understanding of the principles of selforganizing structures and functional units, the knowledge was applied particularly within the areas of life-scientific research and for the development of new materials. 

Wenz G. Cyclodextrins as building blocks for supramolecular structures and functional units. Angew Chem Int Ed 1994 33 803-22. 

Discussion of fat transport in terms of lipoproteins is justified by the fact that each plasma lipid is present in blood as a constituent of lipoproteins. Unfortunately, our knowledge of lipoproteins as structural and functional units is sparse thus any attempt to give an overall view of their role in fat transport is still largely speculative. One of the most difficult problems is that of differentiating the metabolism of transported fats from metabolism of those which are structural constituents of lipoproteins, and the establishment of their interrelationship. Variations from one animal species to another are also be considered and undue generalization avoided until better comparative studies are available. 

The difference in the understanding is centered around the question of whether the primary structural and functional unit for the conductive polymers is the single (eventually oriented) chain, and the main... 

Whole muscles are composed of groups of muscle fibers, which vary from 1 to 400 mm in length and from 10 to 60 tm in diameter. Muscle fibers, in turn, are composed of groups of myofibrils (Fig. 6.2b), and each myofibril is a series of sarcomeres added end to end (Fig. 6.2c). The sarcomere is both the structural and functional unit of skeletal muscle. During contraction, the sarcomeres are shortened to about 70 percent of their uncontracted, resting length. Electron microscopy and biochemical analysis have shown that each sarcomere contains two types of filaments thick filaments, composed of myosin, and thin filaments, containing actin (Fig. 6.2d). Near the center of the sarcomere, thin filaments overlap with thick filaments to form the AI zone (Fig. 6.2c). 

Named proteins and cited them as the most complex biomaterials, built from C, H, O, N and small amounts of S and P Realisation that the cell was the structural and functional unit of all living things... 

The postulate by Nachmansohn and by Belleau that substrate-attachment is likely to Induce conformational changes in acetylcholinesterase has not, as yet, been proved conclusively. Since acetylcholinesterase contains subunits and probably forms a structural and functional unit with the acetylcholine-receptor biopolymers of excitable membranes, it seems very likely that even dien the existence of conformational changes will have been demonstrated conclusively, it will be difficult to Interpret their significance. 

A biological cell is the basic structural and functional unit of all living organisms often called the building block of life. Working at the cellular level is of fundamental importance for biomedical and clinical applications. 

The structural and functional unit of the kidneys consisting of a tuft of capillaries known as the glomerulus attached to the renal tubule. Urine is formed by filtration of blood in the glomerulus and by the selective reabsoiption and secretion of solutes by cells that comprise the walls of the renal tubules. There are approximately 1 million nephrons in each kidney. 

The specific structural and functional unit of the kidney is the nephron. The nephron consists of the Malpighian corpuscle, glomerulus and Bowman s capsule, connected to an elongated tubule component composed of the proximal tuhule, the thin limbs and the distal convoluted tubule. A transitional segment, the connecting tuhules, joins the nephron to the collecting duct system. 

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