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Questions and Answers
What role does glycogenin play in glycogen metabolism?
What role does glycogenin play in glycogen metabolism?
- It catalyzes the synthesis of glucose from pyruvate.
- It is responsible for the breakdown of glycogen into glucose.
- It acts as a regulator for glucose storage.
- It serves as the initial acceptor of glucose residues for glycogen synthesis. (correct)
Which of the following accurately describes the attachment site for the first glucosyl unit in glycogenin?
Which of the following accurately describes the attachment site for the first glucosyl unit in glycogenin?
- The hydroxyl group of a specific tyrosine side chain. (correct)
- The amine group of a lysine side chain.
- The carboxyl group of a glutamic acid side chain.
- The hydroxyl group of a specific serine side chain.
What type of linkage does glycogenin use to transfer the first few glucose molecules?
What type of linkage does glycogenin use to transfer the first few glucose molecules?
- β-1,6 linkages
- α-1,4 linkages (correct)
- β-1,4 linkages
- α-1,3 linkages
Where is glycogenin primarily located within the glycogen molecule?
Where is glycogenin primarily located within the glycogen molecule?
What type of reaction does UDP-glucose pyrophosphorylase catalyze?
What type of reaction does UDP-glucose pyrophosphorylase catalyze?
Which statement best describes glycogenin's function after glycogen synthesis?
Which statement best describes glycogenin's function after glycogen synthesis?
What initiates the process of glycogen synthesis?
What initiates the process of glycogen synthesis?
Glycogenin's function in glycogen synthesis primarily revolves around which of the following?
Glycogenin's function in glycogen synthesis primarily revolves around which of the following?
What is the relationship between glycogenin and finished glycogen molecules?
What is the relationship between glycogenin and finished glycogen molecules?
What is the primary function of Glucosyl 4:6 Transferase in glycogen metabolism?
What is the primary function of Glucosyl 4:6 Transferase in glycogen metabolism?
During glycogen synthesis, which of the following is required as a coenzyme for the branching enzyme?
During glycogen synthesis, which of the following is required as a coenzyme for the branching enzyme?
What is the significance of the nonreducing end of the glycogen chain in branching?
What is the significance of the nonreducing end of the glycogen chain in branching?
What does the branching enzyme provide in the context of glycogen structure?
What does the branching enzyme provide in the context of glycogen structure?
How does the action of the branching enzyme affect glycogenolysis?
How does the action of the branching enzyme affect glycogenolysis?
What type of bond does the Glucosyl 4:6 Transferase form during the branching process?
What type of bond does the Glucosyl 4:6 Transferase form during the branching process?
What limitation does glycogenolysis face due to the structure introduced by the branching enzyme?
What limitation does glycogenolysis face due to the structure introduced by the branching enzyme?
What initiates the branching process in glycogen synthesis?
What initiates the branching process in glycogen synthesis?
Where do the cleaved glucosyl residues go after the action of the branching enzyme?
Where do the cleaved glucosyl residues go after the action of the branching enzyme?
What is the primary component of glycogen metabolism?
What is the primary component of glycogen metabolism?
Which edition of Harper's Illustrated Biochemistry is referenced?
Which edition of Harper's Illustrated Biochemistry is referenced?
Which institution published the 5th edition of Biochemistry, Molecular Biology & Genetics?
Which institution published the 5th edition of Biochemistry, Molecular Biology & Genetics?
Who are the authors of the 5th edition of Biochemistry, Molecular Biology & Genetics?
Who are the authors of the 5th edition of Biochemistry, Molecular Biology & Genetics?
What is an essential sugar involved in human metabolism that is derived from glycogen degradation?
What is an essential sugar involved in human metabolism that is derived from glycogen degradation?
Which of the following best describes the role of glycogen in the human body?
Which of the following best describes the role of glycogen in the human body?
What is the primary role of pyrophosphatase in glycogen metabolism?
What is the primary role of pyrophosphatase in glycogen metabolism?
What does phosphoglucomutase primarily convert in glycogen metabolism?
What does phosphoglucomutase primarily convert in glycogen metabolism?
During glycogen synthesis, what type of bond does glycogen synthase form?
During glycogen synthesis, what type of bond does glycogen synthase form?
What is the mechanism by which glycogen is degraded?
What is the mechanism by which glycogen is degraded?
What happens to UDP after a new α-1,4 linkage is formed during glycogen synthesis?
What happens to UDP after a new α-1,4 linkage is formed during glycogen synthesis?
Which two enzymes are primarily involved in the degradation of glycogen?
Which two enzymes are primarily involved in the degradation of glycogen?
How does branching of glycogen contribute to its function?
How does branching of glycogen contribute to its function?
What is a key characteristic of how glycogen phosphorylase functions?
What is a key characteristic of how glycogen phosphorylase functions?
Which of the following best describes the reaction UTP + ATP ↔ UTP + ADP?
Which of the following best describes the reaction UTP + ATP ↔ UTP + ADP?
What is the result of glycogen branching on metabolic processes?
What is the result of glycogen branching on metabolic processes?
What is the primary genetic defect associated with Type VI Glycogen Storage Disease?
What is the primary genetic defect associated with Type VI Glycogen Storage Disease?
Which of the following is NOT a common manifestation of Type VI Glycogen Storage Disease?
Which of the following is NOT a common manifestation of Type VI Glycogen Storage Disease?
What typical liver condition is associated with Type VI Glycogen Storage Disease?
What typical liver condition is associated with Type VI Glycogen Storage Disease?
What is the average number of residues from which the new branch points are formed in glycogen?
What is the average number of residues from which the new branch points are formed in glycogen?
Which enzyme activities are performed by the bifunctional debranching enzyme?
Which enzyme activities are performed by the bifunctional debranching enzyme?
Which metabolic condition is the least likely to be observed in patients with Type VI Glycogen Storage Disease?
Which metabolic condition is the least likely to be observed in patients with Type VI Glycogen Storage Disease?
What primarily causes growth retardation in Type VI Glycogen Storage Disease?
What primarily causes growth retardation in Type VI Glycogen Storage Disease?
What is a key step in glycogenolysis regarding the removal of branches in glycogen?
What is a key step in glycogenolysis regarding the removal of branches in glycogen?
What is the consequence of the partial deficiency of liver phosphorylase in Type VI Glycogen Storage Disease?
What is the consequence of the partial deficiency of liver phosphorylase in Type VI Glycogen Storage Disease?
Which condition is least likely to directly result from Type VI Glycogen Storage Disease?
Which condition is least likely to directly result from Type VI Glycogen Storage Disease?
Study Notes
Glycogenin
- Serves as the protein anchor for glycogen.
- Functions as a glucose residue acceptor in the absence of glycogen fragments.
- Initial attachment site for glucosyl units is the hydroxyl group of a specific tyrosine side chain.
- Catalyzes the transfer of the first few glucose molecules using α-1,4 linkages.
- Remains associated with the completed glycogen molecule at its center.
Glycogen Synthesis Enzymes
- UDP-Glucose Pyrophosphorylase: Reversible reaction for synthesizing UDP-glucose.
- Pyrophosphatase: Hydrolyzes inorganic pyrophosphate, making glycogen synthesis irreversible.
- Phosphoglucomutase: Converts glucose 6-phosphate to glucose 1-phosphate necessary for glycogen synthesis.
- Glycogen Synthase: Transfers glucose from UDP-glucose to the growing glycogen chain, forming new glycosidic bonds.
Glycogen Degradation
- Glycogen breakdown occurs via phosphorolysis, using a phosphate ion to break bonds.
- Enzymes involved in degradation include glycogen phosphorylase and the debranching enzyme.
- UDP released during the formation of new α-1,4 linkages is converted back to UTP by nucleoside diphosphate kinase.
Branch Formation
- Glucosyl 4:6 Transferase: Enzyme responsible for creating branches by forming α-1,6 linkages.
- Breaks an α-1,4 bond from 6-8 glucosyl residues and attaches them to a non-terminal glucosyl residue via an α-1,6 bond.
- Resulting branches enhance the molecule’s synthesis sites and solubility, allowing continued elongation by glycogen synthase.
Type VI Glycogen Storage Disease (Hers' Disease)
- Caused by a genetic deficiency of liver phosphorylase.
- Patients exhibit partial deficiency in glycogen metabolism.
- Manifestations:
- Hepatomegaly (enlarged liver).
- Moderate hypoglycemia.
- Mild acidosis.
- Growth retardation.
Branch Removal
- Branches in glycogen are removed by a bifunctional protein, the debranching enzyme, possessing both glucosyl 4:4 transferase and α-1,6-glucosidase activities.
- New branch points maintain a minimum of 4 residues, usually 7 to 11 residues from existing branches.
Key Notes on Glycogenolysis
- Glycogen degradation is distinct from synthesis, utilizing a different set of enzymes.
- Glycogen phosphorylase plays a vital role in the rate-limiting step during glycogenolysis.
- Continues hydrolyzing α-1,4 linkages until approaching a branch point.
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Description
This quiz explores the role of glycogenin in glycogen storage. It discusses how glycogenin acts as a protein to which glycogen is attached and its function as an acceptor of glucose residues in the absence of glycogen fragments. Test your understanding of this essential protein in carbohydrate metabolism.
