14 Questions
What is the primary source of energy for muscular activity in muscles?
Glucose-6-phosphate
What is the enzyme responsible for adding glucose units to a glycogen primer molecule?
Glycogen synthase
What type of linkage is formed when glucose units are added to a glycogen primer molecule?
Alpha-1,4 glycosidic linkage
Where is lactate converted to glucose via the gluconeogenic pathway?
Liver
What is the purpose of the branching enzyme in glycogen synthesis?
To create alpha-1,6 glycosidic linkages
What is the purpose of glycogenolysis?
To maintain blood glucose levels between meals
What is the reactant in the first step of glycogen synthesis?
Glucose-1-phosphate
What is the byproduct of the reaction catalyzed by UDP-glucose pyrophosphorylase?
UDP
What is the byproduct of anaerobic oxidation of bloodborne glucose in skeletal muscles?
Lactate
What is the role of the Cori cycle in lactic acidosis?
To remove lactic acid from blood circulation
What is the enzyme responsible for dephosphorylating glucose-6-phosphate to free glucose in the liver?
Glucose-6-phosphatase
What is the product of phosphorolysis of glycogen in the presence of glycogen phosphorylase?
Glucose-1-phosphate
What is the purpose of the enzyme glucosyl transferase in glycogenolysis?
To remove branches from limit dextrins
What is the destination of lactate produced in skeletal muscles?
Liver
Study Notes
Cori Cycle (Lactic Acid Cycle)
- Lactate is produced in strongly contracting skeletal muscles during anaerobic oxidation of bloodborne glucose.
- The produced lactate cannot be further metabolized in skeletal muscles and diffuses out of the muscles, entering blood circulation.
- Lactate is carried to the liver, where it is converted to glucose via the gluconeogenic pathway and released back into blood circulation.
- The reformed glucose becomes available for utilization in skeletal muscles.
Glycogenolysis
- Glycogenolysis is the breakdown of glycogen stored in liver and muscles.
- It maintains blood glucose levels between meals and provides energy for muscular activities.
Steps of Glycogenolysis
- Step 1: Glycogen undergoes phosphorolysis to yield glucose-1-phosphate and limit dextrin in the presence of enzyme glycogen phosphorylase.
- Step 2: The branches of limit dextrins are removed with the help of enzyme glucosyl transferase.
- Step 3: The branching point with a single glucose residue is cleaved by debranching enzyme, releasing the free glucose residue.
- Steps 4 and 5: Glucose-1-phosphate is converted to glucose-6-phosphate in the presence of enzyme phosphoglucomutase.
Fate of Glucose-6-Phosphate
- In liver: Glucose-6-phosphate is dephosphorylated to free glucose, which diffuses out of hepatic cells and enters blood circulation.
- In muscles: Glucose-6-phosphate is utilized in glycolysis as a source of energy for muscular activities.
Glycogenesis
- Glycogen synthesis occurs by a pathway distinctly different from the reversal of glycogen breakdown.
- Steps of glycogenesis:
- Activation of glucose: UDP-glucose is formed from glucose-1-phosphate and UTP by the catalytic activity of UDP-glucose pyrophosphorylase.
- Glycogen synthesis: Activated glucose units are sequentially added by the enzyme glycogen synthase.
- Branching enzyme: Creates alpha-1,6 linkages, making the molecule more globular.
Learn about the Cori cycle, where lactate is produced in skeletal muscles during anaerobic glucose oxidation, and how it's converted back to glucose in the liver.
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