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Questions and Answers
What effect do high glucose and energy levels have on glycogenesis?
What effect do high glucose and energy levels have on glycogenesis?
Which of the following enzymes is primarily responsible for glycogen breakdown?
Which of the following enzymes is primarily responsible for glycogen breakdown?
In which conditions is glycogenolysis stimulated?
In which conditions is glycogenolysis stimulated?
What is the relationship between glycogen metabolism and glycolysis?
What is the relationship between glycogen metabolism and glycolysis?
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What is an example of a glycogen storage disease (GSD) where a patient might experience severe symptoms?
What is an example of a glycogen storage disease (GSD) where a patient might experience severe symptoms?
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What is glycogen primarily used for in muscle tissue?
What is glycogen primarily used for in muscle tissue?
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Which enzyme initiates the elongation of glycogen chains during glycogenesis?
Which enzyme initiates the elongation of glycogen chains during glycogenesis?
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What is the role of the debranching enzyme in glycogenolysis?
What is the role of the debranching enzyme in glycogenolysis?
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Which disease is caused by a deficiency in glucose 6-phosphatase?
Which disease is caused by a deficiency in glucose 6-phosphatase?
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How does glycogen metabolism get hormonally regulated?
How does glycogen metabolism get hormonally regulated?
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What is a consequence of lysosomal degradation deficiency related to glycogen?
What is a consequence of lysosomal degradation deficiency related to glycogen?
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Which type of glycogen storage disease is characterized by skeletal muscle glycogen phosphorylase deficiency?
Which type of glycogen storage disease is characterized by skeletal muscle glycogen phosphorylase deficiency?
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What is the primary function of glycogen in the liver?
What is the primary function of glycogen in the liver?
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Study Notes
Glycogen Metabolism
- Glycogen is a storage polysaccharide
- Primarily stored in the liver and muscles
- In muscle, glycogen provides ATP during muscle contraction
- In the liver, glycogen maintains blood glucose levels
- Glycogenesis is the synthesis of glycogen
- Glycogenolysis is the degradation of glycogen
- Glycogen synthesis begins with UDP-glucose
- Glycogen synthase elongates glycogen chains
- Branching enzyme creates branches in glycogen
- Glycogen phosphorylase shortens glycogen chains producing glucose-1-phosphate
Degradation of Glycogen
- Glycogen phosphorylase removes glucose from non-reducing ends, yielding glucose-1-phosphate
- A debranching enzyme removes branches with two enzymatic activities
- A(14)-glucosidase is an example of a lysosomal enzyme
- Defects in glycogen-degrading enzymes cause glycogen storage diseases (GSD)
Glycogen Storage Diseases
- Von Gierke disease (Type Ia): Glucose-6-phosphatase deficiency, fasting hypoglycemia
- GSD Type 1 (b): Glucose-6-phosphate translocase deficiency
- Pompe disease (Type II): Lysosomal a(1,4)-glucosidase deficiency
- Cori disease (Type III): Debranching enzyme deficiency
- McArdle disease (Type V): Skeletal muscle glycogen phosphorylase deficiency
- Hers disease (Type VI): Liver glycogen phosphorylase deficiency
Regulation of Glycogen Synthesis and Degradation
- Glycogen synthase and glycogen phosphorylase are hormonally regulated (phosphorylation/dephosphorylation)
- Allosteric regulation by glucose and energy levels.
- Glucagon (liver) and epinephrine (liver and muscle) stimulate glycogen breakdown, leading to increased cAMP and activation of glycogen phosphorylase.
- Glycogen synthesis occurs when glucose and energy levels are high and insulin stimulates glycogen synthesis via protein phosphatase-1
- Calcium is involved in muscle contraction and glycogen degradation
- AMP also activates glycogen degradation in muscle under extreme conditions like anoxia and ATP depletion.
Allosteric Regulation
- Glycogen synthase and phosphorylase are subject to allosteric regulation, reacting to the cell's energy needs
- High glucose and energy levels promote glycogen synthesis
- Low glucose and energy levels promote glycogen breakdown
Metabolic Characteristics
- Glycogen metabolism occurs primarily in the liver and muscle
- Glycogen synthesis requires UTP and produces UDP-glucose
- Ingestion of glucose increases blood glucose levels, triggering insulin release, promoting glycogen synthesis
- Low blood glucose triggers glucagon release, promoting glycogen degradation
Important Note
- Pompe disease affects all organs containing lysosomes
- Early onset of progressive muscle hypotonia, cardiac failure, death before age 2, is associated with this disease.
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Description
This quiz covers important concepts related to glycogen metabolism, including glycogenesis and glycogenolysis. It also discusses glycogen storage diseases, their causes, and symptoms. Test your knowledge of how glycogen functions in the body and the impact of its disorders.
