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Questions and Answers
What is the major fuel for most tissues?
What is the major fuel for most tissues?
- Nucleic acids
- Proteins
- Glucose (correct)
- Lipids
Which process converts glucose to pyruvate?
Which process converts glucose to pyruvate?
- Glycolysis (correct)
- Glycogenesis
- Gluconeogenesis
- Krebs cycle
What is the end product of anaerobic glycolysis?
What is the end product of anaerobic glycolysis?
- Lactate (correct)
- Acetyl-CoA
- Pyruvate
- ATP
Which pathway does glucose participate in for the synthesis of glycogen?
Which pathway does glucose participate in for the synthesis of glycogen?
What is the precursor of fatty acids and cholesterol in metabolism?
What is the precursor of fatty acids and cholesterol in metabolism?
How does skeletal muscle utilize glucose as a fuel?
How does skeletal muscle utilize glucose as a fuel?
What is the role of insulin in controlling glucose availability for glycolysis in skeletal muscle?
What is the role of insulin in controlling glucose availability for glycolysis in skeletal muscle?
Which enzyme in the liver has a high affinity for glucose and acts at a constant rate to provide glucose-6-phosphate under normal conditions?
Which enzyme in the liver has a high affinity for glucose and acts at a constant rate to provide glucose-6-phosphate under normal conditions?
What is the function of glucokinase in the liver?
What is the function of glucokinase in the liver?
Which cells contain glucokinase to detect high concentrations of glucose?
Which cells contain glucokinase to detect high concentrations of glucose?
What happens as more glucose is phosphorylated by glucokinase in the liver?
What happens as more glucose is phosphorylated by glucokinase in the liver?
How does increased ATP formation due to glucokinase activity affect membrane potential in pancreatic β-islet cells?
How does increased ATP formation due to glucokinase activity affect membrane potential in pancreatic β-islet cells?
What is the main end product of glycolysis in fast-growing cancer cells?
What is the main end product of glycolysis in fast-growing cancer cells?
Which enzyme catalyzes the phosphorylation of glucose to glucose-6-phosphate in glycolysis?
Which enzyme catalyzes the phosphorylation of glucose to glucose-6-phosphate in glycolysis?
What causes lactic acidosis in some cases?
What causes lactic acidosis in some cases?
Which molecule is used for gluconeogenesis in the liver, contributing to hypermetabolism in cancer cachexia?
Which molecule is used for gluconeogenesis in the liver, contributing to hypermetabolism in cancer cachexia?
What inhibits hexokinase allosterically in the process of glycolysis?
What inhibits hexokinase allosterically in the process of glycolysis?
What happens when there is a shortage of oxygen during glycolysis?
What happens when there is a shortage of oxygen during glycolysis?
What leads to the fusion of insulin secretory granules with the cell membrane?
What leads to the fusion of insulin secretory granules with the cell membrane?
Which compound is important at the junction of several metabolic pathways including glycolysis, gluconeogenesis, and glycogenolysis?
Which compound is important at the junction of several metabolic pathways including glycolysis, gluconeogenesis, and glycogenolysis?
How many molecules of ATP are formed in glycolysis per molecule of glucose undergoing the process?
How many molecules of ATP are formed in glycolysis per molecule of glucose undergoing the process?
Which enzyme catalyzes the conversion of fructose to fructose 1-phosphate in glycolysis?
Which enzyme catalyzes the conversion of fructose to fructose 1-phosphate in glycolysis?
What is a consequence of fructose bypassing the main regulatory steps in glycolysis?
What is a consequence of fructose bypassing the main regulatory steps in glycolysis?
Which step in glycolysis involves a dehydration process, forming phosphoenolpyruvate?
Which step in glycolysis involves a dehydration process, forming phosphoenolpyruvate?
What inhibits enolase, an enzyme involved in glycolysis?
What inhibits enolase, an enzyme involved in glycolysis?
Why is the reaction catalyzed by pyruvate kinase considered irreversible under physiological conditions?
Why is the reaction catalyzed by pyruvate kinase considered irreversible under physiological conditions?
What occurs to pyruvate under anaerobic conditions?
What occurs to pyruvate under anaerobic conditions?
Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA under aerobic conditions?
Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA under aerobic conditions?
What happens to the reducing equivalents from NADH formed in glycolysis?
What happens to the reducing equivalents from NADH formed in glycolysis?
Why is glycolysis inhibited when blood samples are taken for glucose measurement?
Why is glycolysis inhibited when blood samples are taken for glucose measurement?
What is the main function of the liver in maintaining blood glucose concentration between meals?
What is the main function of the liver in maintaining blood glucose concentration between meals?
In gluconeogenesis, substrates like lactate and pyruvate from the cytosol enter the mitochondrion to produce which precursor for glucose synthesis?
In gluconeogenesis, substrates like lactate and pyruvate from the cytosol enter the mitochondrion to produce which precursor for glucose synthesis?
Which tissue has a substantial requirement for glucose, even in prolonged fasting?
Which tissue has a substantial requirement for glucose, even in prolonged fasting?
Which pathway occurs in the cytosol of skeletal muscle for synthesizing fatty acids?
Which pathway occurs in the cytosol of skeletal muscle for synthesizing fatty acids?
Where does glycolysis primarily take place within the cell?
Where does glycolysis primarily take place within the cell?
What effect does phosphorylation of fructose to fructose 1-phosphate have on glycolysis?
What effect does phosphorylation of fructose to fructose 1-phosphate have on glycolysis?
Which enzyme catalyzes the formation of fructose 6-phosphate from glucose 6-phosphate?
Which enzyme catalyzes the formation of fructose 6-phosphate from glucose 6-phosphate?
Why is phosphoenolpyruvate formed during glycolysis a critical compound?
Why is phosphoenolpyruvate formed during glycolysis a critical compound?
Which enzyme catalyzes the conversion of fructose to fructose 1-phosphate in glycolysis?
Which enzyme catalyzes the conversion of fructose to fructose 1-phosphate in glycolysis?
What is the primary outcome of the fusion of insulin secretory granules with the cell membrane?
What is the primary outcome of the fusion of insulin secretory granules with the cell membrane?
What is the main function of glucokinase in the liver?
What is the main function of glucokinase in the liver?
Why is glucokinase present in pancreatic β-islet cells?
Why is glucokinase present in pancreatic β-islet cells?
What is the result of increased ATP formation due to glucokinase activity in the liver?
What is the result of increased ATP formation due to glucokinase activity in the liver?
What distinguishes glucokinase from hexokinase in terms of affinity for glucose?
What distinguishes glucokinase from hexokinase in terms of affinity for glucose?
How does hexokinase function in the liver under normal conditions?
How does hexokinase function in the liver under normal conditions?
Why is pyruvate kinase reaction irreversible under physiological conditions?
Why is pyruvate kinase reaction irreversible under physiological conditions?
What happens to NADH formed in glycolysis under anaerobic conditions?
What happens to NADH formed in glycolysis under anaerobic conditions?
What permits the oxidization of NADH and allows another molecule of glucose to undergo glycolysis?
What permits the oxidization of NADH and allows another molecule of glucose to undergo glycolysis?
What happens to pyruvate under aerobic conditions?
What happens to pyruvate under aerobic conditions?
Why does enolase require the presence of Mg2+ or Mn2+ ions?
Why does enolase require the presence of Mg2+ or Mn2+ ions?
What is the main fuel used by most tissues?
What is the main fuel used by most tissues?
In glycolysis, what is the end product when it occurs anaerobically?
In glycolysis, what is the end product when it occurs anaerobically?
Which pathway involves glucose in the synthesis of glycogen?
Which pathway involves glucose in the synthesis of glycogen?
What is the source of reducing equivalents (NADPH) for fatty acid synthesis?
What is the source of reducing equivalents (NADPH) for fatty acid synthesis?
Which compound provides the carbon skeletons for the synthesis of nonessential amino acids?
Which compound provides the carbon skeletons for the synthesis of nonessential amino acids?
What does skeletal muscle form aerobically when utilizing glucose as a fuel?
What does skeletal muscle form aerobically when utilizing glucose as a fuel?
In skeletal muscle, what regulates the availability of glucose for glycolysis?
In skeletal muscle, what regulates the availability of glucose for glycolysis?
What is the function of glucokinase in the liver following a meal?
What is the function of glucokinase in the liver following a meal?
Which enzyme in the liver has a Km much higher than the normal intracellular concentration of glucose?
Which enzyme in the liver has a Km much higher than the normal intracellular concentration of glucose?
What leads to closure of an ATP-potassium channel in pancreatic β-islet cells?
What leads to closure of an ATP-potassium channel in pancreatic β-islet cells?
Which enzyme provides more glucose 6-phosphate than needed for glycolysis in the liver?
Which enzyme provides more glucose 6-phosphate than needed for glycolysis in the liver?
What happens as a result of increased ATP formation due to glucokinase activity in the liver?
What happens as a result of increased ATP formation due to glucokinase activity in the liver?
What is the end product of glycolysis in fast-growing cancer cells?
What is the end product of glycolysis in fast-growing cancer cells?
Which enzyme catalyzes the conversion of glucose to glucose-6-phosphate in glycolysis?
Which enzyme catalyzes the conversion of glucose to glucose-6-phosphate in glycolysis?
What inhibits hexokinase allosterically during glycolysis?
What inhibits hexokinase allosterically during glycolysis?
What is the main fuel for most tissues during energy production?
What is the main fuel for most tissues during energy production?
Why does lactic acidosis occur under certain conditions?
Why does lactic acidosis occur under certain conditions?
Where does gluconeogenesis take place for converting lactate to glucose in the body?
Where does gluconeogenesis take place for converting lactate to glucose in the body?
Why is enolase inhibited by fluoride in blood samples taken for glucose measurement?
Why is enolase inhibited by fluoride in blood samples taken for glucose measurement?
What makes the reaction catalyzed by pyruvate kinase irreversible under physiological conditions?
What makes the reaction catalyzed by pyruvate kinase irreversible under physiological conditions?
What happens to NADH under anaerobic conditions during glycolysis?
What happens to NADH under anaerobic conditions during glycolysis?
Why does pyruvate undergo oxidative decarboxylation to acetyl-CoA under aerobic conditions?
Why does pyruvate undergo oxidative decarboxylation to acetyl-CoA under aerobic conditions?
What is the primary role of lactate dehydrogenase in glycolysis under anaerobic conditions?
What is the primary role of lactate dehydrogenase in glycolysis under anaerobic conditions?
Why is the reaction catalyzed by pyruvate kinase considered irreversible?
Why is the reaction catalyzed by pyruvate kinase considered irreversible?
What is the primary function of skeletal muscle in terms of carbohydrates metabolism?
What is the primary function of skeletal muscle in terms of carbohydrates metabolism?
During gluconeogenesis, where do substrates such as lactate and pyruvate enter to yield oxaloacetate as a precursor for glucose synthesis?
During gluconeogenesis, where do substrates such as lactate and pyruvate enter to yield oxaloacetate as a precursor for glucose synthesis?
What is the significant role of the liver between meals in terms of blood glucose concentration maintenance?
What is the significant role of the liver between meals in terms of blood glucose concentration maintenance?
Which tissue has a substantial requirement for glucose even during prolonged fasting?
Which tissue has a substantial requirement for glucose even during prolonged fasting?
What is the significance of glycolysis, the pentose phosphate pathway, and fatty acid synthesis occurring in the cytosol?
What is the significance of glycolysis, the pentose phosphate pathway, and fatty acid synthesis occurring in the cytosol?
What is essential for tissues like the brain and erythrocytes due to their reliance on glucose for fuel?
What is essential for tissues like the brain and erythrocytes due to their reliance on glucose for fuel?
What is the role of the pyruvate dehydrogenase complex in glucose metabolism beyond glycolysis?
What is the role of the pyruvate dehydrogenase complex in glucose metabolism beyond glycolysis?
Why are erythrocytes completely reliant on glucose as their metabolic fuel?
Why are erythrocytes completely reliant on glucose as their metabolic fuel?
What effect does anoxic conditions have on glycolysis in skeletal muscle?
What effect does anoxic conditions have on glycolysis in skeletal muscle?
What molecular mechanism is responsible for the inhibition of GAPDH by methylglyoxal in cancer cells?
What molecular mechanism is responsible for the inhibition of GAPDH by methylglyoxal in cancer cells?
How does the absence of oxygen influence the function of glycolysis in cancer cells?
How does the absence of oxygen influence the function of glycolysis in cancer cells?
Study Notes
Carbohydrate Metabolism
- Glucose is the major fuel for most tissues, metabolized to pyruvate through glycolysis
- Aerobic tissues metabolize pyruvate to acetyl-CoA, which enters the citric acid cycle for complete oxidation to CO2 and H2O, linked to ATP formation
- Glycolysis can also occur anaerobically, with the end product being lactate
Glucose Metabolic Role
- Glucose and its metabolites participate in other processes, such as:
- Synthesis of glycogen and the pentose phosphate pathway
- Providing reducing equivalents (NADPH) for fatty acid synthesis
- Triose phosphate intermediates giving rise to the glycerol moiety of triacylglycerols
- Pyruvate and citric acid cycle intermediates providing carbon skeletons for nonessential amino acid synthesis
- Acetyl-CoA being the precursor of fatty acids and cholesterol
Skeletal Muscle
- Utilizes glucose as a fuel, both aerobically and anaerobically
- Stores glycogen as a fuel for muscle contraction and synthesizes muscle protein
- Accounts for approximately 50% of body mass, storing protein that can be drawn upon to supply amino acids for gluconeogenesis in starvation
Liver
- Hexokinase has a high affinity for glucose, providing glucose-6-phosphate to meet the liver's needs
- Glucokinase has a higher Km than hexokinase and is involved in:
- Removing glucose from the hepatic portal blood following a meal
- Regulating the concentration of glucose available to peripheral tissues
- Providing more glucose 6-phosphate than required for glycolysis, which is used for glycogen synthesis and lipogenesis
Glycolysis
- Occurs in the cytosol, with all enzymes being cytosolic
- Glucose enters glycolysis by phosphorylation to glucose-6-phosphate, catalyzed by hexokinase
- Hexokinase is inhibited allosterically by its product, glucose-6-phosphate
- In tissues other than the liver and pancreatic β-islet cells, glucose availability for glycolysis is controlled by transport into the cell, regulated by insulin
- Glucokinase is also found in pancreatic β-islet cells to detect high concentrations of glucose
- As more glucose is phosphorylated by glucokinase, there is increased glycolysis, leading to increased ATP formation, which leads to:
- Closure of an ATP-potassium channel
- Membrane depolarization
- Opening of a voltage-gated calcium channel
Glycolysis Regulation
- Major sites of regulation are:
- Hexokinase (and glucokinase)
- Phosphofructokinase
- Pyruvate kinase
- Reactions catalyzed by these enzymes are irreversible
- Most reactions of glycolysis are freely reversible
Fructose Metabolism
-
Fructose enters glycolysis by phosphorylation to fructose 1-phosphate, bypassing the main regulatory steps
-
This leads to increased formation of pyruvate and acetyl-CoA, and can contribute to the development of obesity
-
In the liver and adipose tissue, this leads to increased lipogenesis### Enolase Inhibition
-
Enolase is inhibited by fluoride
-
Fluoride is used in blood sample tubes to inhibit glycolysis when measuring glucose levels
Enolase Dependence
- Enolase requires the presence of either Mg2+ or Mn2+ ions
Pyruvate Kinase Reaction
- Pyruvate kinase catalyzes the transfer of the phosphate from phosphoenolpyruvate to ADP, producing two molecules of ATP per glucose molecule
- The reaction is irreversible under physiological conditions due to:
- Large free energy change
- Spontaneous isomerization of enol-pyruvate to pyruvate, making the product unavailable for the reverse reaction
Anaerobic Conditions
- Under anaerobic conditions, NADH cannot be reoxidized through the respiratory chain
- Pyruvate is reduced to lactate by lactate dehydrogenase, permitting the oxidation of NADH
- This allows another glucose molecule to undergo glycolysis
Aerobic Conditions
- Under aerobic conditions, pyruvate is transported into mitochondria
- Pyruvate undergoes oxidative decarboxylation to acetyl-CoA and then oxidation to CO2 in the citric acid cycle
- Reducing equivalents from NADH formed in glycolysis are taken up into mitochondria for oxidation
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Description
This quiz covers the metabolism of carbohydrates in tissues such as skeletal muscle and liver. Topics include glucose transport into cells, regulation by insulin, glycogen synthesis, and the role of enzymes like hexokinase in the liver.
