Glycogen degradation requires the following two reactions: Removal of glucose forms the non-reducing ends of glycogen. Using inorganic phosphate (Pi), glycogen phosphorylase cleaves the (1,4) linkages on the outer branches of glycogen to yield glucose-1-phosphate. Glycogen phosphorylase stops when it comes within four glucose residues of a branch point. A glycogen molecule that has been degraded…

When the chain is lengthened to a minimum of eleven glucose residues, the branching enzyme amylo (α 1-4, α 1-6) transglucosidase (Figure 8.12) (glucosyl α 4, 6-transferase) transfers a small fragment of five to eight glucose residues from the non-reducing end of the glycogen chain by breaking α 1-4 linkage to another glucose residue, where…

Glycogen synthase is required for the formation of α 1-4 glycosidic linkages. This enzyme transfers the glucose from UDP-glucose to the glycogen primer to form α 1-4 linkages. The UDP released can be converted again to UTP with the help of nucleotide diphosphate kinase.

A small fragment of pre-existing glycogen must act as a primer to initiate glycogen synthesis. It is recently fount that in the absence of glycogen primer, a specific protein namely glycogenin can accept glucose from UDPG. The hydroxyl group of amino acid tyrosine of glycogenin is the site at which the initial glucose unit is attached. The…

The enzymes hexokinase in muscle and hexokinase in liver convert glucose to glucose 6-phosphate. Phosphoglucomutase catalyses the conversion of glucose 6-phosphate to glucose 1-phosphate. Uridine diphosphate glucose (UDPG) is synthesised from glucose 1-phosphate and UTP by UDP-glucose phosphorylase. Pyrophosphate (PPi) produced in this reaction is hydrolysed to inorganic phosphate, which will ensure the optimal synthesis of…

The synthesis of glycogen from glucose is termed as glycogenesis. Glycogenesis takes place in the cytosol and requires ATP and UTP besides glucose refer Figure 8.11. Overall reaction of glycogen synthesis is   (Glucose)n + glucose + 2ATP → (glucose)n+1 + 2 ADP + Pi Of this two ATP utilised, one is required for the phophorylation of glucose…

The molecular weight of a single glycogen is 108 daltons. Glycogen is present in cytoplasmic granules. The granules contain most of the enzymes necessary for glycogen synthesis and degradation. The structure of glycogen is basically a branched-chain of homopolysaccharides, which consist of α-D-glucose units made of up to 100,000 residues. The glucose units are joined…

Liver stores 6%–8% of glycogen and muscle 1%–2%. Due to more muscle mass, the quantity of glycogen in muscle is about three times higher than that of liver. Liver glycogen stores increase during well-fed state and are depleted during fast. Muscle glycogen is not affected by short period’s fasting (a few days) and is only…

INTRODUCTION Glycogen is the major storage form of carbohydrate in animals and starch in plants. The main stores of glycogen in the body are found in skeletal muscle and liver, although most other cells may store minute amounts. The function of muscle glycogen is to serve as a fuel reserve for the synthesis of ATP during…

The cellular demands of ATP are crucial in controlling the rate of citric acid cycle. The regulation is brought about either by enzymes or the levels of ADP. Three enzymes, namely citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase, regulate citric acid cycle.