Polypeptides gelatin chains

Photographic material containing gelatin can be hardened during manufacture the process involves cross-linking between the gelatine polypeptide chains induced by hardener. 

Gelatin stmctures have been studied with the aid of an electron microscope (23). The stmcture of the gel is a combination of fine and coarse interchain networks the ratio depends on the temperature during the polymer-polymer and polymer-solvent interaction lea ding to bond formation. The rigidity of the gel is approximately proportional to the square of the gelatin concentration. Crystallites, indicated by x-ray diffraction pattern, are beUeved to be at the junctions of the polypeptide chains (24). 

When collagen is heated, it is denaturated, losing its structure the polypeptide chains separate and unwind, and, as the collagen cools down, it soaks up surrounding water and forms gelatin. 

The usual alkali employed is lime. The raw material for gelatine is tropocollagen, which is present in the original hides or bones. This protein consists of three polypeptide chains arranged in a triple helix. In contrast, gelatine consists of several free or interassociated chains, ranging in molecular weight from around ten thousand to several hundred thousand. On extraction, monomers (a-chains MW 100 000), dimers (P-chains) and trimers ( -chains) and some lower order peptides are released. 

Nature often uses cystine knots of variable complexity to assemble polypeptide chains in the correct order and to stabilize the structure of the resulting proteins. Classical examples are proteins of the extracellular matrix with collagens and gelatines as the main components. This simple cystine-knot approach has been applied to synthetic constructs to ligate in a desired order helix bundles. [166 170 194-1%] It has also been used to mimic natural multiple-chain containing proteins like collagen.[83 1691971... 

The dissociation of the polypeptide chains of collagen by thermal or chemical processes leads to products variously termed gelatin. In the present section we propose to consider certain of the physicochemical properties of gelatin, looking toward a deeper understanding of the structure and chemistry of collagen. 

In spite of the above drawbacks. Equations 6.1 and 6.2 are popular mainly due to their simple form and have been used to estimate Me of protein (e.g., egg, gelatin) and other gels from shear modulus-concentration data (Table 6-2) (Fu, 1998). Its successful application to protein gels initially has been attributed to the greater flexibility of polypeptide chains in comparison to polysaccharide chains that are relatively stiff. In addition, the inability to employ low strain rates in early experimental studies on polysaccharide gels could be another reason. 

C. Robinson and M. J. Bott. Nature 168, 325-6 (1951). Optical rotation and chain folding in synthetic polypeptides and gelatin. 

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