22 Questions
What is the approximate amount of glycogen stored in the liver?
100-120g
What is the primary function of glycogen in muscle cells?
To provide energy for muscle contraction
What is the key enzyme responsible for the conversion of glucose to glycogen?
Glycogen synthetase
What is the significance of glycogen's branched structure?
It allows for more efficient storage of glucose
What is the primary hormone responsible for regulating glycogen synthesis in the liver?
Insulin
What is the approximate amount of glycogen stored in muscle cells?
250-300g
What is the result of glycogen breakdown by phosphorylase?
Production of glucose-1-phosphate
What is the role of calcium ions in glycogen phosphorylase activation?
Bind to calmodulin domain of glycogen phosphorylase kinase and activate the enzyme
What is the effect of insulin on glycogen phosphorylase?
Inhibit glycogen phosphorylase
What is the function of debranching enzyme in glycogen breakdown?
Hydrolyze 1,6 glycosidic bonds
What is the effect of adrenaline on glycogen phosphorylase?
Activate glycogen phosphorylase
What is the role of AMP in glycogen phosphorylase activation?
Activate glycogen phosphorylase
What is the function of protein kinase in glycogen synthase regulation?
Inhibit glycogen synthase
What is the effect of high glucose levels on glycogen phosphorylase in the liver?
Inhibit glycogen phosphorylase
What type of linkages are present in glycogen?
α-1,6 and α-1,4
What is the function of UDP glucose in glycogen synthesis?
It donates glucose units to the growing glycogen chain
What is the role of glycogenin in glycogen synthesis?
It is the protein primer for glycogen synthesis
What is the net result of the action of branching enzyme?
It introduces branch points in glycogen
What is the function of ATP/UTP/GTP in glycogen synthesis?
They are the energy source for glycogen synthesis
What is the role of the reducing end of glycogen?
It is the site of glycogen breakdown
What type of reaction is the formation of UDP glucose?
Transferase reaction
What is the purpose of tightly regulated enzyme reactions in glycogen synthesis?
To allow for alternative enzymes to be used in the opposite direction
Study Notes
Glycogen Synthesis and Degradation
- Glycogen is a branched polysaccharide with α-1,6 and α-1,4 glycosidic links, and its structure has physiological significance.
- The liver contains 100-120g of glycogen, which is sensitive to blood glucose concentration and plays a crucial role in maintaining constant levels of glucose in the blood.
- Muscle contains 250-300g of glycogen, which is sensitive to energy needs and is used as a rapid source of glucose for muscle contraction.
Features of Biosynthetic Pathways
- ATP, UTP, or GTP are required as cofactors to drive reactions forward.
- One or more enzyme reactions are irreversible, and alternative enzymes are used for the opposite direction.
- Enzyme reactions at the beginning or end of the pathway are tightly regulated.
Glycogen Synthesis
- Glycogen synthesis involves the conversion of glucose to glycogen, with glycogen synthetase as the key enzyme.
- The first stage of glycogen synthesis involves the formation of UDP glucose from glucose-1-P and UTP.
- UDP glucose is then added to a protein primer, glycogenin, to form a glycogen chain.
- Glycogen synthase and branching enzyme work together to produce the branched structure of glycogen.
Regulation of Glycogen Synthesis
- Glycogen synthase is regulated by phosphorylation, which inactivates the enzyme.
- Protein kinase and protein phosphatase play a crucial role in the regulation of glycogen synthase.
Glycogen Breakdown
- Glycogen breakdown involves the conversion of glycogen to glucose, with glycogen phosphorylase as the key enzyme.
- Glycogen phosphorylase breaks down glycogen into glucose-1-phosphate, which is then converted to glucose-6-phosphate.
- Glucose-6-phosphate is then converted to glucose in the liver.
Regulation of Glycogen Breakdown
- Glycogen phosphorylase is regulated by phosphorylation, which activates the enzyme.
- Protein kinase and protein phosphatase play a crucial role in the regulation of glycogen phosphorylase.
- Additional controls include insulin and glucagon, which regulate glycogen phosphorylase in the liver, and adrenaline, calcium, and AMP, which regulate glycogen phosphorylase in muscle.
Assess your knowledge of glycogen synthesis and degradation, including its structure, importance in maintaining blood glucose levels, and regulation. Ideal for MBBS Stage one students.
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