Cori Cycle and Metabolism Overview

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Questions and Answers

What is the net energy cost in terms of phosphate ( ~P) for the Cori cycle?

8 ~P

4 ~P (correct)

6 ~P

2 ~P

How does lactate produced in muscles reach the liver?

Via the bloodstream (correct)

Through direct cellular exchange

Via lymphatic system

By diffusion through tissue

What role does the Cori cycle play in skeletal muscle during exercise?

It enhances aerobic metabolism.

It accommodates fluctuations in energy requirements. (correct)

It decreases lactate production.

It converts glucose to glycogen.

In the context of cancer, what triggers a shift to anaerobic metabolism in solid tumors?

Decreased blood vessel development Signup and view all the answers

What happens to glucose produced in the liver as part of the Cori cycle?

It travels back to the muscle for glycolysis. Signup and view all the answers

What is the primary consequence of the energy dissipation caused by the Cori cycle in late-stage cancer?

Weight loss Signup and view all the answers

How many NADH molecules are involved in the formation of lactate during the Cori cycle?

2 NADH Signup and view all the answers

What is the primary metabolic state of muscle tissue during prolonged exertion like a marathon run?

Aerobic fat metabolism Signup and view all the answers

Which of the following statements is true regarding the Cori cycle?

It primarily occurs in the liver and muscle. Signup and view all the answers

What is a major source of energy for tumor cells when faced with low oxygen levels?

Glucose from the liver Signup and view all the answers

What is the main purpose of the Cori cycle in the human body?

To provide a means for muscles to quickly regenerate glucose from lactate. Signup and view all the answers

During glycolysis in muscle cells, what is the primary output produced per cycle under normal oxygen conditions?

Two units of pyruvate and two units of ATP. Signup and view all the answers

What happens when the demand for energy exceeds the liver's capacity to convert lactate to glucose?

Lactic acid accumulates, causing lactic acidosis. Signup and view all the answers

What is the cost of gluconeogenesis in the liver for maintaining the Cori cycle?

Six ATP molecules are consumed. Signup and view all the answers

What is lactic acidosis primarily associated with following prolonged vigorous exercise?

Decreased pH in the blood causing tissue damage. Signup and view all the answers

What role does adenosine triphosphate (ATP) play within the Cori cycle?

It provides energy for muscle contractions. Signup and view all the answers

Which process mainly supplies ATP after phospho-creatine is exhausted during strenuous activity?

Glycogen breakdown and glycolysis. Signup and view all the answers

What are the gifts of pyruvate and lactate to the cellular energy process?

They provide substrates for Krebs cycle to produce ATP. Signup and view all the answers

In which scenario is the Cori cycle primarily engaged?

When energy needs significantly increase during exercise. Signup and view all the answers

What characteristic defines lactic acid's effect on the body's pH level during rigorous activity?

It lowers the blood pH, leading to acidosis. Signup and view all the answers

What reaction does 6-Phospho-glucono-lactonase primarily catalyze?

Hydrolysis of the ester linkage Signup and view all the answers

What is the product of the reaction catalyzed by Phospho-gluconate Dehydrogenase?

Ribulose-5-phosphate Signup and view all the answers

Why is 6-phospho-glucono-lactone considered potentially toxic?

It is a highly reactive compound Signup and view all the answers

What type of reaction occurs during the conversion of 6-phospho-gluconate to ribulose-5-phosphate?

Oxidative decarboxylation Signup and view all the answers

What is the role of NADP+ in the reactions described?

It acts as a reducing agent receiving electrons Signup and view all the answers

Which statement correctly describes the role of enzymes in the reactions discussed?

Enzymes lower the activation energy of reactions. Signup and view all the answers

What occurs during the reaction catalyzed by 6-Phospho-glucono-lactonase?

Ring opening of a cyclic ketone Signup and view all the answers

What metabolic pathway does the transformation involving 6-phospho-glucono-lactone and 6-phospho-gluconate belong to?

Pentose phosphate pathway Signup and view all the answers

What is the significance of NADPH produced in these reactions?

It plays a role in biosynthetic reactions. Signup and view all the answers

What is the role of NADPH in metabolic pathways?

Functions as a reductant in anabolic pathways Signup and view all the answers

Which enzyme regulates the committed step of the Pentose Phosphate Pathway?

Glucose-6-phosphate Dehydrogenase Signup and view all the answers

During the Pentose Phosphate Pathway, ribulose-5-phosphate can be converted to which of the following products?

Glyceraldehyde-3-P and Ribose-5-P Signup and view all the answers

What happens to NADP+ concentration as NADPH is utilized in reductive synthesis?

It stimulates the Pentose Phosphate Pathway Signup and view all the answers

What is the overall reaction of the Pentose Phosphate Pathway starting with 3 molecules of ribulose-5-phosphate?

3 C5 à 2 C6 + C3 Signup and view all the answers

Which of the following enzymes is NOT involved in the Pentose Phosphate Pathway?

Pyruvate Kinase Signup and view all the answers

How do the products of the Pentose Phosphate Pathway vary based on cellular needs?

They can operate to maximize production of ribose-5-P, NADPH, or ATP Signup and view all the answers

What is the electron transfer process involved in the reduction of NADP+?

Transfer of 2 e- and 1 H+ Signup and view all the answers

What product provides a source for NADPH in the Pentose Phosphate Pathway?

Glucose-6-phosphate Signup and view all the answers

In the Pentose Phosphate Pathway, which product is primarily generated from xylulose-5-P?

Fructose-6-P Signup and view all the answers

What is the primary output of the Pentose Phosphate Pathway when producing ribulose-5-phosphate?

NADPH Signup and view all the answers

Which two products are formed that can re-enter the Pentose Phosphate Pathway to maximize NADPH production?

Fructose-6-phosphate and glyceraldehyde-3-phosphate Signup and view all the answers

What key function does ribose-5-phosphate serve in cellular metabolism?

Substrate for nucleotide synthesis Signup and view all the answers

During which scenario does the Pentose Phosphate Pathway primarily produce both NADPH and ATP?

When redirecting products into glycolysis Signup and view all the answers

What allows ribose-1-phosphate from nucleoside catabolism to enter glycolysis?

Conversion to ribose-5-phosphate Signup and view all the answers

What metabolic role does the Pentose Phosphate Pathway serve in relation to glycolysis?

It acts as a precursor pathway supplying essential sugars. Signup and view all the answers

How many molecules of NADP+ are reduced during the Pentose Phosphate Pathway?

Two molecules per cycle Signup and view all the answers

What transformation is necessary for glyceraldehyde-3-phosphate to participate in ATP production?

Recycling to glucose-6-phosphate Signup and view all the answers

Which of the following accurately describes the focus of scenario two in the Pentose Phosphate Pathway?

Maximizing the output of NADPH Signup and view all the answers

What is the role of fructose-6-phosphate in the context of the Pentose Phosphate Pathway?

It can re-enter the linear pathway for additional NADPH. Signup and view all the answers

What is the primary role of NADPH produced in the pentose phosphate pathway?

To supply reducing power for anabolic processes Signup and view all the answers

Which intermediate is produced from glucose-6-phosphate during the linear part of the pentose phosphate pathway?

6-Phosphogluconate Signup and view all the answers

What metabolic process is directly connected to the pentose phosphate pathway?

Gluconeogenesis Signup and view all the answers

What enzyme catalyzes the first reaction of the pentose phosphate pathway involving glucose-6-phosphate?

Dehydrogenase Signup and view all the answers

Which of the following is a precursor for nucleotide synthesis derived from the pentose phosphate pathway?

Ribulose-5-phosphate Signup and view all the answers

Which compound acts as an electron acceptor during the reactions of the pentose phosphate pathway?

NADP+ Signup and view all the answers

What is the primary function of the linear part of the pentose phosphate pathway?

Oxidize glucose-6-phosphate Signup and view all the answers

What is the relationship between the activity of gluconeogenesis and glucose-6-phosphate levels?

Directly proportional Signup and view all the answers

What occurs to glucose-6-phosphate when it undergoes oxidation in the pentose phosphate pathway?

It is converted to ribulose-5-phosphate Signup and view all the answers

Which alternative name is used for the pentose phosphate pathway?

Hexose monophosphate shunt Signup and view all the answers

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.