Amylopectin

Amylopectin is one of the biggest molecules in nature being the principal component in the majority of starches. Starches with varying amylose and amylopectin content are of particular interest due to their ability to influence and modify the texture, quality and stability of starch-based food products.

Starch normally contains about 20–30% amylose and 70–80% amylopectin. Amylopectin consists of numerous chains that are much shorter than the major chains found in amyloses.

The branched amylopectin molecule contains regions with low and high levels of branches. The branches in amylopectin constitute about 5% of the molecule, which results in a very complex molecular structure. Short chains of amylopectin form double-helices, which crystalize and contribute to the semi-crystalline nature of the starch granules.

In highly branched regions, side-chains of amylopectin are grouped, forming crystalline zones (clusters). Side chains of the amylopectin molecule can be divided in A, B, and C chains. The A chains are the shortest.

C chains constitute the backbones of the amylopectin molecules, to which B-chains are linked that at the same time carry one or more branches. The B chains are classified into B1, B2, B3 and B4 depending on their length and the number of clusters that they span.
Amylopectin

Glycogen – History and Property

Glycogen – History and Property
Glycogen is the only homopolysaccharides of important in human metabolism. Glycogen presence in liver was first detected in 1856 by Claude Bernard, who recognized the relationship between the glycogen of the liver and the sugar present in the blood. Subsequently other researcher proved that the common monosaccharides give rise to liver glycogen. Although the total quantity of glycogen in the human body is low, considerably less than one-tenth percent of the total body weight, its role is primarily that of a storage carbohydrate, similar to the role of starch in plants cells. It occurs predominantly in the liver where it is important in the homeostatic mechanism regulating glucose level of the blood.

Hepatocytes have the highest concentration of glycogen – up to 8% of the fresh weight in well fed state, or 100 – 120 g in an adult. In skeletal muscle, glycogen serves as a source of energy for muscle contraction. In the muscles, glycogen is found in a much lower concentration (1% of the muscle mass), but the total amount exceeds that in liver.

Glycogen is a branched chain polymer of 6,000 to 30,000 glucose units. It is similar to amylopectin in structure but is more highly branched. The average chain length is only 10 to 24 glucose units with 3 to 4 glucose units between branching points. The size of the molecules varies with its source and with the metabolic state of the body. Muscle glycogen is estimated to have a molecular weight of about 1000000 where as the liver of glycogen molecule is much larger, approximately 5 X 1000000. Both molecules, however, constantly change in size as glucose molecules are added or removed.

Glycogen plays an important role in the glucose cycle. The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted.
Glycogen – History and Property

Definitions for Polysaccharides

Definitions for Polysaccharides
Polysaccharides are complex polymers containing only one monosaccharide, homopolysaccharides, or several different monosaccharides or monosaccharide derivatives, heteropolysaccharides. Many polysaccharides exist in the plant and animal kingdoms. However, only a few of these are known to be significant in mammalian nutrition, either as dietary constituents or as human cell metabolites.

The most common digestible polysaccharides in plants is starch, a polymer of glucose. Starch is present primarily in the cells of grains, fruits and tubers in the form of granules that, under microscopes examinations, appear to be typical for each starch. The composition of starches also differs somewhat, but all types contain both amylase, a straight chain polymer of glucoses, and amylopectin, a branch chain polymer. The average chain contains 20 to 25 glucose units with approximately 5 to 8 glucose molecules between branching points within the chain. On hydrolysis in the intestinal tract, starch yields dextrin and maltose and, eventually glucose.

Cellulose is a straight chain polymer of glucose. It is a constituent of the cell walls of plants and gives rigidity to the plant structure much as the skeleton supports to human body. It is not attacked by digestive enzymes of the human and although it provides bulk to the diet it does not contribute significantly to the nutrition of body cells. Cellulose tends to be affected little by usual acid hydrolysis and requires the action of strong mineral acids. Plants also contain indigestible hemicellulose, which are unrelated chemically to cellulose and are homopolysaccharides containing D-xylose. Pectin, present in fruit, is an indigestible heteropolymer and contains arabinose, galactose, and galacturonic acid.
Definitions for Polysaccharides