Podcast
Questions and Answers
What is one effect of insulin in muscle cells related to glycogen synthesis?
What is one effect of insulin in muscle cells related to glycogen synthesis?
How do insulin and glucagon act in the regulation of carbohydrate metabolism?
How do insulin and glucagon act in the regulation of carbohydrate metabolism?
Which of the following statements is true regarding muscle cells and blood glucose levels?
Which of the following statements is true regarding muscle cells and blood glucose levels?
What role does epinephrine play in carbohydrate metabolism between liver and muscle cells?
What role does epinephrine play in carbohydrate metabolism between liver and muscle cells?
Signup and view all the answers
Which processes does insulin influence to achieve its effects on carbohydrate metabolism?
Which processes does insulin influence to achieve its effects on carbohydrate metabolism?
Signup and view all the answers
What is the primary outcome of the phosphorolysis mechanism in glycogen degradation?
What is the primary outcome of the phosphorolysis mechanism in glycogen degradation?
Signup and view all the answers
Which cells lack glucose-6-phosphatase, preventing them from regenerating glucose from glucose-6-phosphate?
Which cells lack glucose-6-phosphatase, preventing them from regenerating glucose from glucose-6-phosphate?
Signup and view all the answers
What process involves the conversion of glucose-1-phosphate to glucose-6-phosphate?
What process involves the conversion of glucose-1-phosphate to glucose-6-phosphate?
Signup and view all the answers
Where in the body does gluconeogenesis mainly occur?
Where in the body does gluconeogenesis mainly occur?
Signup and view all the answers
What characterizes glycogen in vertebrates?
What characterizes glycogen in vertebrates?
Signup and view all the answers
What happens to excess glucose in the body?
What happens to excess glucose in the body?
Signup and view all the answers
Which enzyme degrades glycogen on a continuous basis?
Which enzyme degrades glycogen on a continuous basis?
Signup and view all the answers
What is a significant characteristic of glucose as an osmolyte?
What is a significant characteristic of glucose as an osmolyte?
Signup and view all the answers
What is the primary cause of exercise intolerance in McArdle Syndrome?
What is the primary cause of exercise intolerance in McArdle Syndrome?
Signup and view all the answers
Which glycogen storage disease is most prevalent?
Which glycogen storage disease is most prevalent?
Signup and view all the answers
What role does the enzyme glycogenin play in glycogen synthesis?
What role does the enzyme glycogenin play in glycogen synthesis?
Signup and view all the answers
Which of the following processes occurs during the formation of a glycogen branch?
Which of the following processes occurs during the formation of a glycogen branch?
Signup and view all the answers
What triggers covalent modifications to enzymes?
What triggers covalent modifications to enzymes?
Signup and view all the answers
Which factor helps maintain homeostasis in metabolic pathways?
Which factor helps maintain homeostasis in metabolic pathways?
Signup and view all the answers
Which is correct regarding the enzyme Myozyme?
Which is correct regarding the enzyme Myozyme?
Signup and view all the answers
What immediate effect does phosphorylation have on enzymes?
What immediate effect does phosphorylation have on enzymes?
Signup and view all the answers
Which hormone inhibits both glycogen degradation and gluconeogenesis?
Which hormone inhibits both glycogen degradation and gluconeogenesis?
Signup and view all the answers
Which of the following statements regarding the source of the hormones is correct?
Which of the following statements regarding the source of the hormones is correct?
Signup and view all the answers
How does insulin affect fructose-2,6-bisphosphate levels?
How does insulin affect fructose-2,6-bisphosphate levels?
Signup and view all the answers
What is the primary target tissue for glucagon?
What is the primary target tissue for glucagon?
Signup and view all the answers
Which of the following hormones is known to decrease cyclic-AMP levels?
Which of the following hormones is known to decrease cyclic-AMP levels?
Signup and view all the answers
Which enzyme is stimulated by insulin to promote glycogen synthesis?
Which enzyme is stimulated by insulin to promote glycogen synthesis?
Signup and view all the answers
What effect do glucagon and epinephrine have on gluconeogenesis?
What effect do glucagon and epinephrine have on gluconeogenesis?
Signup and view all the answers
Which metabolic pathway is favored by insulin?
Which metabolic pathway is favored by insulin?
Signup and view all the answers
What is the role of fructose 2,6-bisphosphate in glycolysis and gluconeogenesis?
What is the role of fructose 2,6-bisphosphate in glycolysis and gluconeogenesis?
Signup and view all the answers
Which enzyme is allosterically activated by fructose 1,6-bisphosphate?
Which enzyme is allosterically activated by fructose 1,6-bisphosphate?
Signup and view all the answers
What distinguishes glucokinase (hexokinase IV) from other hexokinase isozymes?
What distinguishes glucokinase (hexokinase IV) from other hexokinase isozymes?
Signup and view all the answers
How is pyruvate kinase in the liver uniquely regulated?
How is pyruvate kinase in the liver uniquely regulated?
Signup and view all the answers
Which of the following molecules inhibits glycolysis?
Which of the following molecules inhibits glycolysis?
Signup and view all the answers
What is the primary role of glycogen phosphorylase in glycogen breakdown?
What is the primary role of glycogen phosphorylase in glycogen breakdown?
Signup and view all the answers
What regulatory effect does ATP have on phosphofructokinase (PFK-1)?
What regulatory effect does ATP have on phosphofructokinase (PFK-1)?
Signup and view all the answers
Which factor is a common allosteric regulator of both glycolysis and gluconeogenesis at the level of the first enzymes?
Which factor is a common allosteric regulator of both glycolysis and gluconeogenesis at the level of the first enzymes?
Signup and view all the answers
What is the effect of high glucose levels on glycogen phosphorylase activity?
What is the effect of high glucose levels on glycogen phosphorylase activity?
Signup and view all the answers
The coordinated regulation of glycolysis and gluconeogenesis occurs primarily at which steps?
The coordinated regulation of glycolysis and gluconeogenesis occurs primarily at which steps?
Signup and view all the answers
Which hormone stimulates glycogenolysis in muscle cells?
Which hormone stimulates glycogenolysis in muscle cells?
Signup and view all the answers
What is the characteristic of hexokinases I-III regarding their Km and inhibition?
What is the characteristic of hexokinases I-III regarding their Km and inhibition?
Signup and view all the answers
Which enzyme is responsible for maintaining the balance between glycogen synthesis and breakdown?
Which enzyme is responsible for maintaining the balance between glycogen synthesis and breakdown?
Signup and view all the answers
What initiates the breakdown of glycogen in response to energy needs?
What initiates the breakdown of glycogen in response to energy needs?
Signup and view all the answers
Study Notes
Glucose and Glycogen Regulation
- Glucose levels in blood (glycemia) are tightly controlled by various processes involving glucose production or consumption.
- Excess glucose is stored as glycogen, a storage form that can be broken down when needed to maintain normal blood glucose levels.
Glucose Dynamics in Living Organisms
- Glycogenolysis breaks down glycogen into glucose.
- Glycogenesis synthesizes glycogen from glucose.
- Glycolysis breaks down glucose to lactate.
- Gluconeogenesis produces glucose from non-carbohydrate sources.
- Glucose is a potent osmolyte and cannot be stored in large amounts in its free form.
Glycogen Degradation
- Glycogen is a branched polymer of glucose, with alpha(1→4) and alpha(1→6) linkages.
- In vertebrates, glycogen is primarily stored in the liver (up to 10% weight) and skeletal muscles (up to 1-2% weight).
- Glucose residues are removed from the non-reducing ends by phosphorolysis.
- Phosphorolysis cleaves the glycosidic bond, releasing glucose 1-phosphate.
- Debranching enzymes are necessary to remove branches in glycogen.
- Debranching 1 results in glucose 1-phosphate output.
- Debranching 2 results in free glucose output.
Glycogen Degradation: Debranching
- The debranching process involves two enzymatic activities of a single debranching enzyme.
- The first part is a transferase activity, which moves a block of oligoglucose from a branch to a linear chain.
- The second is a glucosidase activity, which hydrolyzes the remaining alpha(1→6) linked glucose.
Glycogen Degradation and Regulation of Glucose Level
- Glucose 1-phosphate is converted to glucose 6-phosphate.
- Glucose 6-phosphate can undergo glycolysis, the pentose pathway, or gluconeogenesis to replenish glucose.
- Glucose 6-phosphatase is only found in liver and kidney cells, enabling glucose release into the bloodstream (gluconeogenesis).
- Muscle and adipose cells lack glucose 6-phosphatase.
Glycogen Storage Diseases
- Glycogen storage diseases result from defects in enzymes involved in glycogen metabolism.
- Deficiencies in these enzymes can lead to the accumulation of abnormal amounts of glycogen in tissues or result from a lack of glycogen degradation.
- Examples like McArdle syndrome (muscle glycogen phosphorylase deficiency).
Glucose 6-Phosphatase Deficiency (Von Gierke Disease)
- The most common glycogen storage disease.
- Results in glucose 6-phosphatase deficiency, impairing glucose release from the liver.
- Characterized by fasting hypoglycemia, fatty liver, and other symptoms.
Glycogen Synthesis
- The synthesis of glycogen involves the addition of glucose molecules to an existing glycogen chain.
- The process begins with UDP-glucose, which carries glucose to the growing glycogen chain.
- Glycogen synthase is the enzyme responsible for adding glucose residues to the non-reducing end of the glycogen chain.
- Glycogenin is required to initiate the formation of the glycogen primer.
Regulation of Metabolic Pathways
- Cells and organisms maintain a dynamic steady state of metabolic pathways.
- Factors regulating enzyme activity include association with regulatory proteins, sequestration (compartmentation), transcription/translation, turnover, allosteric regulation, and covalent modification.
Covalent Modifications of Enzymes
- Phosphorylation/dephosphorylation is a common covalent modification that alters enzyme activity.
- Kinases add phosphate groups, while phosphatases remove them. This change can potentially affect the conformation or interaction with other proteins.
Assessment of Individual Enzyme Contribution to a Pathway
- Experimental methods can assess the contribution of individual enzymes to metabolic fluxes in pathways.
Coordinated Regulation of Glycolysis and Gluconeogenesis
- Coordinated regulation of glycolysis and gluconeogenesis is crucial to avoid futile cycles.
- The three irreversible reactions in glycolysis and gluconeogenesis are key regulatory points.
- Key regulatory molecules include ATP, citrate, ADP, AMP among others.
Regulation of Glycolysis at Hexokinase Level
- Four isozymes of hexokinase exist.
- Liver isozyme IV (glucokinase) is responsive to increased blood glucose levels. Muscle isozymes are inhibited by glucose-6-phosphate.
Hexokinase Isozyme Regulation
- Isozymes I-III have low Km and Vmax and are inhibited by product glucose-6-phosphate.
- Glucokinase (isozyme IV) has a high Km and is not inhibited by product, thus allowing continuous glucose processing after meals .
Regulation of Glycolysis at PFK Level
- PFK-1 is allosterically regulated by ATP and citrate.
- ATP inhibits PFK 1
Regulation of Glycolysis at Pyruvate Kinase Level
- The enzyme is allosterically inhibited by ATP, acetyl-CoA, fatty acids and alanine.
- It is activated by F-1,6-BP .
Coordinated Regulation of Gluconeogenesis
- Regulatory molecules such as acetyl-CoA regulate the first enzyme in gluconeogenesis.
- The fate of pyruvate is determined by the energy requirements of the cell.
Coordinated Regulation of Glycolysis and Gluconeogenesis (III)
- ATP and citrate inhibit glycolysis and activate gluconeogenesis.
- ADP and AMP activate glycolysis and inhibit gluconeogenesis.
- Fructose 2,6-bisphosphate is a key regulator influencing both pathways.
Fructose 2,6-bisphosphate
- A potent allosteric regulator of PFK-1 and FBPase-1.
- Activates PFK-1 (glycolysis).
- Inhibits FBPase-1 (gluconeogenesis).
PFK-2/FBPase-2
- A bifunctional enzyme with PFK-2 and FBPase-2 activities, crucial for regulating glycolysis and gluconeogenesis.
- Activity is controlled by hormones like insulin and glucagon.
Coordinated Regulation of Glycolysis and Gluconeogenesis (IV)
- Glucose levels regulate both glycolysis and gluconeogenesis through complex interactions among hormones, intermediates and enzymes.
Coordinated Regulation of Glycogen Synthesis and Breakdown
- Glycogen synthesis is regulated by glycogen synthase.
- Glycogen breakdown is regulated by glycogen phosphorylase.
- Hormones like insulin and glucagon impact the activity of these enzymes.
- Hormones like, epinephrine also impact the regulation.
Control of Glycogen Synthesis
- Activation of glycogen synthase is crucial for glycogen synthesis. Inactivation of this enzyme can be achieved by mechanisms including phosphorylation.
- Insulin generally promotes glycogen synthesis
Control of Glycogen Synthesis
- Control of glycogen synthesis involves activation by protein phosphatase 1 (PP1) and activation by a casein kinase and/or a glycogen synthase kinase.
Control of Glycogen Breakdown
- Activation of glycogen phosphorylase involves phosphorylation. This will occur when blood glucose is low/ glucagon or epinephrine are present.
Coordination of Glycogen Synthesis and Breakdown
- Glycogen synthesis and glycogen breakdown are reciprocally regulated to prevent futile cycles.
- Insulin activation will favor glycogen synthesis and glucagon activation will favor glycogen breakdown
Hormones and Glycogen Metabolism
- Insulin promotes glycogen synthesis while glucagon, epinephrine stimulate glycogen breakdown.
- Hormones play a crucial role in regulating the rate of glycogen synthesis and breakdown to maintain blood glucose homeostasis.
Control of Glycogen Synthesis from Blood Glucose in Myocytes
- Insulin promotes GLUT4 translocation to the plasma membrane.
- This allows more glucose to enter the cell.
Carbohydrate Regulation in Liver Cells (Overview)
- Insulin and glucagon have antagonistic effects on glycolysis and gluconeogenesis.
- Insulin stimulates glycolysis and inhibits gluconeogenesis.
- Glucagon stimulates gluconeogenesis and inhibits glycolysis.
Hormones in Carbohydrate Regulation
- Glucagon, epinephrine, and insulin interplay to regulate glucose metabolism homeostasis.
Differences in Carbohydrate Metabolism in Liver and Muscles
- Muscles lack glucose-6-phosphatase and are not involved in maintaining blood glucose levels.
- Glucose metabolism in muscles is primarily for energy production associated with contraction.
Effects of Insulin
- Insulin inhibits glycogen degradation.
- Insulin stimulates Glycogen Synthase and phosphoprotein phosphatase.
- Insulin inhibits cAMP-dependent protein kinase.
Effects of Glucagon and Epinephrine
- Glucagon promotes gluconeogenesis.
- Epinephrine also promotes gluconeogenesis.
- Ephinephrine promotes glycogen breakdown (muscle).
Drugs and Diseases
- Drugs and diseases associated with glycogen metabolism and glucose homeostasis are mentioned.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz explores the complex processes involved in the regulation of glucose and glycogen in living organisms. It covers key concepts such as glycogenolysis, glycogenesis, glycolysis, and gluconeogenesis, shedding light on how the body maintains normal blood glucose levels. Ideal for students studying biochemistry or physiology.
