Glycogen chemical structure

Biochemical studies follow several themes. For example, investigations can be focussed on the chemical structures of molecules, (for example the structure of glycogen, DNA or protein conformation) or the structural inter-relationship between molecules (e.g. enzymes with their substrates, hormones with their receptors). The other branch of biochemical enquiry is into those numerous dynamic events known collectively as metabolism , defined here as all of the chemical reactions and their associated energy changes occurring within cells . The purpose of metabolism is to provide the... 

Describe, using chemical structural formulas, the reactions involved in the breakdown of glycogen to glucose 1-phosphate and the synthesis of glycogen from glucose 1-phosphate. 

Fig. 62. Chemical structure of a section of a glycogen molecule. The letters A, B, C, D denote the functional groups95 ...

Details of the chemical structure of glycogen remained unknown, however, until the polysaccharide attracted the attention of Haworth, Hirst, and Bell, and their respective collaborators. 

The chemical structure of a polymer can also cause a contraction of the polymer coil compared to the unperturbed dimensions at theta-conditions. In this case the exponent a of the [ ]]-M-relationship shows values of a<0.5. A contraction of the coil occurs if the attractive intramolecular interactions between the polymer segments become larger than the interactions with the solvent molecules. In extreme cases, the solvent is forced out of the polymer coil and the chain segments start to form compact aggregates. The density of the polymer coil is then independent of the molar mass and the intrinsic viscosity is constant. In this case the exponent a is zero. An example is shown in Fig. 6.12 for compact glycogen in aqueous solution. 

Plants store polysaccharides as food reserve in all types of cell but primarily in special storage cells or organs such as parenchymous cells or roots, tubers, and pith. The most important of these food reserves are starches, fructans, mannans, and galactomannans. The mannans are sometimes food reserves and sometimes structural material in the plant cell wall. In animals the chief reserve polysaccharide is glycogen, which in chemical structure is much like one of the components of starch (see Part II of this chapter.). 

A number of other polysaccharides, such as glycogen, dextran, chitin, etc., possess interesting structures for chemical modification [103,104]. Dextran has been used as a blood plasma substitute. Although it can be converted to films and fibers, chitin s relatively small resource restricts its commercialization. 

Observation of an abnormally large shift in the position of fluorescent emission of pyridoxal phosphate (PLP) in glycogen phosphorylase answered an interesting chemical question.187188 A 330 nm (30,300 cm ) absorption band could be interpreted either as arising from an adduct of some enzyme functional group with the Schiff base of PLP and a lysine side chain (structure A) or as a nonionic tautomer of a Schiff base in a hydrophobic environment (structure B, Eq. 23-24). For structure A, the fluorescent emission would be expected at a position similar to that of pyridoxamine. On the other hand, Schiff bases of the... 

As indicated in Table 4.12, four regions which constitute the catalytic regions of amylolytic enzymes are conserved in the starch-branching isoenzymes of maize endosperm, rice seed and potato tuber, and the glycogen-branching enzymes of E. coli.286,281 It would be of interest to know whether the seven highly conserved amino acid residues of the a-amylase family listed in bold letters in Table 4.12 are also functional in branching enzyme catalysis. Further experiments, such as chemical modification and analysis of the three-dimensional structure of the BEs, would be needed to determine the nature of its catalytic residues and mechanism. 

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