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Questions and Answers
What is the net energy cost in terms of phosphate ( ~P) for the Cori cycle?
What is the net energy cost in terms of phosphate ( ~P) for the Cori cycle?
How does lactate produced in muscles reach the liver?
How does lactate produced in muscles reach the liver?
What role does the Cori cycle play in skeletal muscle during exercise?
What role does the Cori cycle play in skeletal muscle during exercise?
In the context of cancer, what triggers a shift to anaerobic metabolism in solid tumors?
In the context of cancer, what triggers a shift to anaerobic metabolism in solid tumors?
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What happens to glucose produced in the liver as part of the Cori cycle?
What happens to glucose produced in the liver as part of the Cori cycle?
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What is the primary consequence of the energy dissipation caused by the Cori cycle in late-stage cancer?
What is the primary consequence of the energy dissipation caused by the Cori cycle in late-stage cancer?
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How many NADH molecules are involved in the formation of lactate during the Cori cycle?
How many NADH molecules are involved in the formation of lactate during the Cori cycle?
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What is the primary metabolic state of muscle tissue during prolonged exertion like a marathon run?
What is the primary metabolic state of muscle tissue during prolonged exertion like a marathon run?
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Which of the following statements is true regarding the Cori cycle?
Which of the following statements is true regarding the Cori cycle?
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What is a major source of energy for tumor cells when faced with low oxygen levels?
What is a major source of energy for tumor cells when faced with low oxygen levels?
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What is the main purpose of the Cori cycle in the human body?
What is the main purpose of the Cori cycle in the human body?
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During glycolysis in muscle cells, what is the primary output produced per cycle under normal oxygen conditions?
During glycolysis in muscle cells, what is the primary output produced per cycle under normal oxygen conditions?
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What happens when the demand for energy exceeds the liver's capacity to convert lactate to glucose?
What happens when the demand for energy exceeds the liver's capacity to convert lactate to glucose?
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What is the cost of gluconeogenesis in the liver for maintaining the Cori cycle?
What is the cost of gluconeogenesis in the liver for maintaining the Cori cycle?
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What is lactic acidosis primarily associated with following prolonged vigorous exercise?
What is lactic acidosis primarily associated with following prolonged vigorous exercise?
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What role does adenosine triphosphate (ATP) play within the Cori cycle?
What role does adenosine triphosphate (ATP) play within the Cori cycle?
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Which process mainly supplies ATP after phospho-creatine is exhausted during strenuous activity?
Which process mainly supplies ATP after phospho-creatine is exhausted during strenuous activity?
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What are the gifts of pyruvate and lactate to the cellular energy process?
What are the gifts of pyruvate and lactate to the cellular energy process?
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In which scenario is the Cori cycle primarily engaged?
In which scenario is the Cori cycle primarily engaged?
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What characteristic defines lactic acid's effect on the body's pH level during rigorous activity?
What characteristic defines lactic acid's effect on the body's pH level during rigorous activity?
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What reaction does 6-Phospho-glucono-lactonase primarily catalyze?
What reaction does 6-Phospho-glucono-lactonase primarily catalyze?
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What is the product of the reaction catalyzed by Phospho-gluconate Dehydrogenase?
What is the product of the reaction catalyzed by Phospho-gluconate Dehydrogenase?
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Why is 6-phospho-glucono-lactone considered potentially toxic?
Why is 6-phospho-glucono-lactone considered potentially toxic?
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What type of reaction occurs during the conversion of 6-phospho-gluconate to ribulose-5-phosphate?
What type of reaction occurs during the conversion of 6-phospho-gluconate to ribulose-5-phosphate?
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What is the role of NADP+ in the reactions described?
What is the role of NADP+ in the reactions described?
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Which statement correctly describes the role of enzymes in the reactions discussed?
Which statement correctly describes the role of enzymes in the reactions discussed?
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What occurs during the reaction catalyzed by 6-Phospho-glucono-lactonase?
What occurs during the reaction catalyzed by 6-Phospho-glucono-lactonase?
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What metabolic pathway does the transformation involving 6-phospho-glucono-lactone and 6-phospho-gluconate belong to?
What metabolic pathway does the transformation involving 6-phospho-glucono-lactone and 6-phospho-gluconate belong to?
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What is the significance of NADPH produced in these reactions?
What is the significance of NADPH produced in these reactions?
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What is the role of NADPH in metabolic pathways?
What is the role of NADPH in metabolic pathways?
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Which enzyme regulates the committed step of the Pentose Phosphate Pathway?
Which enzyme regulates the committed step of the Pentose Phosphate Pathway?
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During the Pentose Phosphate Pathway, ribulose-5-phosphate can be converted to which of the following products?
During the Pentose Phosphate Pathway, ribulose-5-phosphate can be converted to which of the following products?
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What happens to NADP+ concentration as NADPH is utilized in reductive synthesis?
What happens to NADP+ concentration as NADPH is utilized in reductive synthesis?
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What is the overall reaction of the Pentose Phosphate Pathway starting with 3 molecules of ribulose-5-phosphate?
What is the overall reaction of the Pentose Phosphate Pathway starting with 3 molecules of ribulose-5-phosphate?
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Which of the following enzymes is NOT involved in the Pentose Phosphate Pathway?
Which of the following enzymes is NOT involved in the Pentose Phosphate Pathway?
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How do the products of the Pentose Phosphate Pathway vary based on cellular needs?
How do the products of the Pentose Phosphate Pathway vary based on cellular needs?
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What is the electron transfer process involved in the reduction of NADP+?
What is the electron transfer process involved in the reduction of NADP+?
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What product provides a source for NADPH in the Pentose Phosphate Pathway?
What product provides a source for NADPH in the Pentose Phosphate Pathway?
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In the Pentose Phosphate Pathway, which product is primarily generated from xylulose-5-P?
In the Pentose Phosphate Pathway, which product is primarily generated from xylulose-5-P?
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What is the primary output of the Pentose Phosphate Pathway when producing ribulose-5-phosphate?
What is the primary output of the Pentose Phosphate Pathway when producing ribulose-5-phosphate?
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Which two products are formed that can re-enter the Pentose Phosphate Pathway to maximize NADPH production?
Which two products are formed that can re-enter the Pentose Phosphate Pathway to maximize NADPH production?
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What key function does ribose-5-phosphate serve in cellular metabolism?
What key function does ribose-5-phosphate serve in cellular metabolism?
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During which scenario does the Pentose Phosphate Pathway primarily produce both NADPH and ATP?
During which scenario does the Pentose Phosphate Pathway primarily produce both NADPH and ATP?
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What allows ribose-1-phosphate from nucleoside catabolism to enter glycolysis?
What allows ribose-1-phosphate from nucleoside catabolism to enter glycolysis?
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What metabolic role does the Pentose Phosphate Pathway serve in relation to glycolysis?
What metabolic role does the Pentose Phosphate Pathway serve in relation to glycolysis?
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How many molecules of NADP+ are reduced during the Pentose Phosphate Pathway?
How many molecules of NADP+ are reduced during the Pentose Phosphate Pathway?
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What transformation is necessary for glyceraldehyde-3-phosphate to participate in ATP production?
What transformation is necessary for glyceraldehyde-3-phosphate to participate in ATP production?
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Which of the following accurately describes the focus of scenario two in the Pentose Phosphate Pathway?
Which of the following accurately describes the focus of scenario two in the Pentose Phosphate Pathway?
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What is the role of fructose-6-phosphate in the context of the Pentose Phosphate Pathway?
What is the role of fructose-6-phosphate in the context of the Pentose Phosphate Pathway?
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What is the primary role of NADPH produced in the pentose phosphate pathway?
What is the primary role of NADPH produced in the pentose phosphate pathway?
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Which intermediate is produced from glucose-6-phosphate during the linear part of the pentose phosphate pathway?
Which intermediate is produced from glucose-6-phosphate during the linear part of the pentose phosphate pathway?
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What metabolic process is directly connected to the pentose phosphate pathway?
What metabolic process is directly connected to the pentose phosphate pathway?
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What enzyme catalyzes the first reaction of the pentose phosphate pathway involving glucose-6-phosphate?
What enzyme catalyzes the first reaction of the pentose phosphate pathway involving glucose-6-phosphate?
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Which of the following is a precursor for nucleotide synthesis derived from the pentose phosphate pathway?
Which of the following is a precursor for nucleotide synthesis derived from the pentose phosphate pathway?
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Which compound acts as an electron acceptor during the reactions of the pentose phosphate pathway?
Which compound acts as an electron acceptor during the reactions of the pentose phosphate pathway?
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What is the primary function of the linear part of the pentose phosphate pathway?
What is the primary function of the linear part of the pentose phosphate pathway?
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What is the relationship between the activity of gluconeogenesis and glucose-6-phosphate levels?
What is the relationship between the activity of gluconeogenesis and glucose-6-phosphate levels?
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What occurs to glucose-6-phosphate when it undergoes oxidation in the pentose phosphate pathway?
What occurs to glucose-6-phosphate when it undergoes oxidation in the pentose phosphate pathway?
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Which alternative name is used for the pentose phosphate pathway?
Which alternative name is used for the pentose phosphate pathway?
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Study Notes
Cori Cycle Overview
- Facilitates the consumption of glucose by muscles while producing lactate.
- Lactate is transported to the liver to be converted back into glucose.
Lactate Production and Utilization
- Muscle cells generate energy via aerobic metabolism when oxygen is available.
- Anaerobic conditions lead to glucose breakdown through glycolysis, resulting in lactate output.
- Lactate is effectively a soluble form of lactic acid, circulating back into the bloodstream.
Gluconeogenesis and Blood Sugar Regulation
- The liver conducts gluconeogenesis, synthesizing glucose from non-carbohydrate sources to maintain blood sugar levels.
- Adenosine triphosphate (ATP) is crucial as a catalytic coenzyme in these reactions.
Glycolysis in Muscle Cells
- Under normal oxygen levels, glycolysis produces two ATP and two pyruvate molecules.
- Pyruvate is essential for continuing energy production through the Krebs cycle (citric acid cycle).
Energy Cycle and ATP Costs
- The liver processes lactate to convert it back into pyruvate and then glucose, reentering the bloodstream to support muscle energy demands.
- The Cori cycle is not completely closed; it uses more ATP in gluconeogenesis than it produces during glycolysis.
Exercise and Energy Demand
- Vigorous physical activity rapidly activates the Cori cycle to generate and recycle glucose anaerobically.
- Lactic acidosis can occur if energy needs surpass the liver's capacity to convert lactate to glucose, leading to lowered blood pH and potential tissue damage.
Effects of Lactic Acidosis
- Symptoms include hyperventilation, vomiting, and abdominal cramps.
- Lactic acidosis is related to rigor mortis post-mortem due to continuous glucose consumption by muscles.
ATP Utilization and Phospho-Creatine
- Initially, muscle cells utilize ATP stored in phospho-creatine for quick energy bursts.
- Once phospho-creatine is depleted, glycolysis primarily supports ATP production through glycogen breakdown and glucose from the blood.
Cori Cycle Energy Costs
- The Cori cycle requires six ATP equivalents (6 ~P) in the liver for each two produced (2 ~P) in muscles, resulting in a net cost of four ATP equivalents (4 ~P).
Cori Cycle in Cancer
- An analogous process to the Cori cycle occurs in cancer, particularly when tumor growth exceeds blood vessel supply, leading to hypoxia and a shift to anaerobic metabolism.
- This metabolic shift may contribute to the weight loss observed in late-stage cancer patients, despite normal food intake.
Pentose Phosphate Pathway Overview
- Major source of NADPH for anabolic processes, operating in parallel with glycolysis.
- Directly linked to gluconeogenesis; increased glucose-6-phosphate activity boosts gluconeogenesis.
- Known as Phosphogluconate Pathway or Hexose Monophosphate Shunt.
Pathway Mechanics
- Begins with glucose-6-phosphate (G-6-P) and involves oxidation and decarboxylation reactions.
- Results in the production of ribulose-5-phosphate (R-5-P), a precursor for nucleotide synthesis.
- Key enzyme: Glucose-6-phosphate Dehydrogenase catalyzes the oxidation of G-6-P.
Enzymatic Steps
- Glucose-6-phosphate Dehydrogenase converts G-6-P to 6-phospho-glucono-lactone, generating NADPH.
- 6-Phospho-glucono-lactonase hydrolyzes the lactone to form 6-phospho-gluconate.
- Phospho-gluconate Dehydrogenase catalyzes oxidative decarboxylation, yielding ribulose-5-phosphate, releasing CO2 and reducing NADP+ to NADPH.
Regulation of the Pathway
- Regulation hinges on Glucose-6-phosphate Dehydrogenase, the pathway's key control point.
- Increase in NADP+ concentration stimulates the pathway to replenish NADPH as it's consumed in biosynthetic processes.
Interconversion of Sugars
- Ribulose-5-P can be converted to either ribose-5-P or other sugars (glyceraldehyde-3-P and fructose-6-P) through isomerization and epimerization.
- Additional enzymes involved include Isomerase, Epimerase, Transketolase, and Transaldolase for sugar interconversion.
Pathway Modes and Outputs
- Three primary modes of operation:
- Producing NADPH and ribose-5-phosphate for nucleotide synthesis.
- Maximizing NADPH production through diversion to glyceraldehyde-3-P and fructose-6-P.
- Producing both NADPH and ATP by channeling sugars into glycolysis.
Glycolytic Connection
- Glyceraldehyde-3-P and fructose-6-P can enter glycolysis for ATP production.
- Ribose-1-phosphate from nucleoside catabolism can also feed into glycolysis after conversion to ribose-5-phosphate.
- Overall, the pentose phosphate pathway facilitates entry into glycolysis for both 5-carbon and 6-carbon sugars.
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Description
Explore the intricacies of the Cori Cycle, including how lactate is produced, utilized, and converted back into glucose in the liver. This quiz covers key metabolic processes such as glycolysis, gluconeogenesis, and ATP production, highlighting their role in energy regulation within muscle cells.
