Carbohydrate Metabolism: Glycogen Metabolism

Flashcards reviewing glycogen synthesis and breakdown.

What is glycogen?

A highly branched polymer of α,D-glucose.

What type of linkages unite glucose residues within glycogen branches?

α 1, 4-glucosidic linkages.

What type of linkages are found at the branching points of glycogen?

α 1, 6 linkages.

How many glucose residues are typically found in glycogen branches?

13-14 glucose residues.

What is glycogenesis?

The synthesis of glycogen from glucose.

What are the four steps of glycogenesis?

Glucose activation, glycogen priming, chain elongation, and branching.

What is the first step of glycogenesis?

Glucose activation.

What is the second step of glycogenesis?

Glycogen priming.

What is the third step of glycogenesis?

Chain elongation.

What is the fourth step of glycogenesis?

Branching.

What protein is at the center of glycogen granules?

Glycogenin.

What is the function of Glycogenin?

Autocatalytic glycosyltransferase.

How many glucose molecules does each subunit of glycogenin catalyze the addition of?

8 glucose molecules.

What enzyme is key for chain elongation in glycogenesis?

Glycogen synthase.

How many glucose residues are required for glycogen synthase to function?

At least 4 glucose residues.

What type of linkage does glycogen synthase create?

α-1,4 linkage.

How does branching affect glycogen solubility?

Increases the solubility of the glycogen molecule.

How does branching affect enzyme accessibility in glycogen?

Makes glycogen more accessible to enzymes.

What is the function of branching regarding the rate of glycogenolysis or glycogenesis?

Increases the potential rate.

What is glycogenolysis?

The breakdown of glycogen.

What is the main product of glycogenolysis?

Glucose-1-phosphate.

What enzymes are involved in glycogenolysis?

Phosphorylase and Debranching enzyme.

What are the two functions of Debranching enzyme?

Glucosyl-transferase and Glucosidase.

What is the function of Phosphorylase in Glycogenolysis?

Breaks the α1,4 glucosidic bond by adding phosphate.

What is the key regulatory enzyme in glycogenolysis?

Phosphorylase.

What is the function of transferase in glycogenolysis?

Shifts a block of 3 glucose residues from outer branch.

What is the function of α-1,6-glucosidase in glycogenolysis?

Hydrolyzes 1,6 linkage by adding water.

What is the fate of glucose-1-phosphate in muscle during exercise?

Feeds into glycolysis to produce energy.

What is the fate of glucose-1-phosphate in the liver during fasting?

Converted to free glucose and released into the bloodstream.

Which organ contains glucose-6-phosphatase?

Liver.

What can muscle glycogen be converted to during muscular exercise?

Lactate to supply energy.

What is the glucose-alanine cycle?

An indirect pathway to convert muscle glycogen into glucose during starvation.

What does insulin stimulate in glycogen regulation?

Glucose uptake, glycolysis and glycogenesis.

What happens to excess glucose when insulin is high?

Excess glucose is stored as glycogen, any surplus can be converted to TAG.

What happens to glycogen stores during fasting?

Glycogen stores are mobilized, to maintain glucose levels.

What happens to glycogen stores during exercise?

Glycogen is broken down, especially for high intensity anaerobic exercise.

What causes glycogen storage diseases?

Defects in the processing of glycogen synthesis or breakdown.

What is a key feature of Type I glycogen storage disease?

Hypoglycemia due to impairment of glycogenolysis and gluconeogenesis.

What is McArdle disease?

Glycogen storage disorder type V, a deficiency of muscle glycogen phosphorylase.

What are some consequences of McArdle disease?

Poor tolerance of exercise, muscle weakness, cramps, and early fatigue.