Krebs Cycle Functions Quiz

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Questions and Answers

What is the most important function of the Krebs cycle?

Generation of electrons for transfer to the respiratory chain (correct)

Formation of water and ATP units

Production of CO2 for elimination from the body

Conversion of pyruvic acid into glucose

How many ATP molecules are formed at the end of the Krebs cycle?

2 (correct)

What is the fate of hydrogen ions and electrons in the electron transport chain?

Formation of water (correct)

Formation of ATP

Formation of pyruvic acid

Formation of CO2

How many total ATP molecules are generated during aerobic metabolism with complete breakdown of a glucose molecule?

32-33 ATP Signup and view all the answers

Which process refers to the breakdown of ATP without oxygen?

Anaerobic metabolism Signup and view all the answers

What represents an immediate source of energy for muscle cells that can be used to perform work?

Phosphocreatine (PCr) Signup and view all the answers

In which system does energy transfer from PCr play a crucial role during transitions from low to high energy demand?

ATP-PCr system Signup and view all the answers

What is the process called when reversing the hydrolysis of ATP to reform ATP?

Anabolism Signup and view all the answers

What is the main function of anabolism in cells?

Form molecules from smaller units for growth and division Signup and view all the answers

Which of the following is considered a fuel for cells based on the text?

Proteins Signup and view all the answers

During the citric acid cycle, what happens to the acetyl group?

It is oxidized to carbon dioxide Signup and view all the answers

Where does most of a cell's ATP synthesis occur?

Electron transport chain Signup and view all the answers

What is the reduced form of flavin adenine dinucleotide (FAD)?

FADH2 Signup and view all the answers

Which molecule acts as an oxidizing agent in cellular metabolism?

NAD+ Signup and view all the answers

What is the additional group attached to NADP that distinguishes it from NAD?

Phosphate group Signup and view all the answers

What is the primary function of ATP in muscle cells?

To facilitate muscle contraction Signup and view all the answers

What is the end product of the electron transport chain in cellular respiration?

Water Signup and view all the answers

How many ATP molecules are generated from one molecule of glucose throughout both glycolysis and the Krebs cycle?

36-38 ATP Signup and view all the answers

Which macromolecule is primarily broken down to provide substrates for the Krebs cycle?

Carbohydrates Signup and view all the answers

What is the main function of NAD and FAD in the context of the Krebs cycle and electron transport chain?

Facilitate the transfer of electrons to the respiratory chain Signup and view all the answers

What is the primary fate of compounds entering stage 2 of energy extraction from foodstuffs?

Converted to the acetyl group in acetyl coenzyme A Signup and view all the answers

Which process accommodates glycerol from the breakdown of lipids during energy extraction from foodstuffs?

Glycolysis Signup and view all the answers

Where do electrons released by the oxidation of the acetyl group in the citric acid cycle go initially during energy extraction from foodstuffs?

NAD+ and FAD Signup and view all the answers

What is the main function of oxidative phosphorylation in energy extraction from foodstuffs?

Synthesize most of a cell’s ATP Signup and view all the answers

Which enzyme is responsible for the formation of lactic acid from pyruvic acid?

Lactate dehydrogenase Signup and view all the answers

In muscle, which type of LDH is predominantly found?

White muscle LDH Signup and view all the answers

How does Pyruvate Dehydrogenase (PDH) indirectly affect the rate of glycolysis?

By increasing the NADH/NAD+ ratio Signup and view all the answers

Which enzyme competes with mitochondria for pyruvate when glycolysis is slow?

Lactate dehydrogenase Signup and view all the answers

What is the consequence of resting muscle having a large free energy yield from LDH?

Continued lactate formation Signup and view all the answers

What is the primary purpose of a decrease in glycolytic rate due to PFK inhibition at low pH?

To protect muscle fibers and blood from a hazardous pH drop Signup and view all the answers

Which compound activates pyruvate kinase, the enzyme catalyzing the last reaction of glycolysis?

ADP Signup and view all the answers

What is the primary fate of pyruvic acid in the absence of oxygen during glycolysis?

Conversion to lactic acid Signup and view all the answers

During anaerobic metabolism, what determines the fate of pyruvic acid?

Production of lactic acid Signup and view all the answers

Which process is favored during exercise due to changes in ATP, PCr, and ADP concentrations?

Anaerobic glycolysis Signup and view all the answers

How does cytoplasmic reduction of NADH affect glycolysis?

Slows down glycolysis Signup and view all the answers

What is the major precursor for glycolysis during exercise?

Glycogen Signup and view all the answers

At 65% of maximum effort during steady-state exercise, by how much can glycogen breakdown exceed glucose uptake?

Four to five times Signup and view all the answers

What is the primary feedback control mechanism in normal healthy subjects?

Decrease in blood glucose concentration Signup and view all the answers

What type of control is glycolysis under during exercise due to glycogen breakdown acceleration?

Feed-forward control Signup and view all the answers

Which factor is not a feed-forward control for stimulating glycolysis?

Decrease in blood glucose concentration Signup and view all the answers

What happens to the glycolytic rate in muscle during exercise?

Increases by hundreds of times Signup and view all the answers

Which enzyme is a dominant factor in the regulation of glycolysis?

PFK-1 Signup and view all the answers

Which form of PFK predominates in muscle and is considered rate-limiting during rapid glycolysis?

PFK-1 Signup and view all the answers

During exercise, what immediate changes in PFK modulators occur?

Increase in ATP, decrease in citrate, increase in PCr Signup and view all the answers

What is the main difference in ATP usage between breaking down glucose and breaking down glycogen for energy?

Glucose breakdown requires 1 ATP, while glycogen breakdown does not require any ATP. Signup and view all the answers

Which enzyme is the rate-limiting enzyme in glycolysis that helps control the speed of the process?

Phosphofructokinase (PFK) Signup and view all the answers

What is the net gain of ATP molecules when glucose is used for energy production through glycolysis?

2 ATP Signup and view all the answers

During glycolysis, which molecule serves as the ultimate end product?

Pyruvate Signup and view all the answers

What happens to the net gain of ATP molecules when glycogen is utilized for energy production compared to glucose?

Glycogen utilization results in a greater net gain of ATP compared to glucose utilization. Signup and view all the answers

What is the end result of the excess hydrogen ions combining with pyruvate during strenuous exercise?

Lactic acid Signup and view all the answers

Which enzyme catalyzes the formation of lactic acid from pyruvate?

Lactate dehydrogenase (LDH) Signup and view all the answers

In which organ does the Cori Cycle primarily take place?

Liver Signup and view all the answers

Which pathway is the primary metabolic pathway for events lasting from 1-3 minutes?

Anaerobic glycolysis Signup and view all the answers

Which kind of mechanism predominantly accomplishes the fine-tuning of energy supply to demand in glycolysis?

Negative feedback Signup and view all the answers

What triggers the movement of GLUT4 to the plasma membrane in muscle fibers during exercise?

Release of calcium from the sarcoplasmic reticulum Signup and view all the answers

Which molecule inhibits phosphofructokinase (PFK) in resting muscles?

ATP Signup and view all the answers

What enhances the inhibition of PFK by ATP in skeletal muscles?

High levels of phosphocreatine (PCr) Signup and view all the answers

Which factor relieves the inhibition of PFK by ATP in active muscles?

Elevated AMP levels Signup and view all the answers

What is the impact of an acidic pH on phosphofructokinase (PFK) activity?

Inhibition Signup and view all the answers

In resting muscles, which condition leads to the relative inactivity of phosphofructokinase (PFK)?

High ATP and PCr, low AMP Signup and view all the answers

During exercise, what leads to the activation of phosphofructokinase (PFK) in muscle cells?

Decrease in ATP and PCr, increase in AMP levels Signup and view all the answers

What substance binds to PFK and enhances its inhibition by ATP in skeletal muscles?

Phosphocreatine Signup and view all the answers

What is the impact of increased AMP levels on PFK activity during muscle activity?

Activation Signup and view all the answers

What causes the inhibition of PFK during exercise?

Elevated ATP levels Signup and view all the answers

Study Notes

Krebs Cycle and ATP Production

The primary function of the Krebs cycle is to generate electron carriers (NADH and FADH2) for the electron transport chain.
The Krebs cycle produces 1 ATP molecule directly per cycle from each acetyl CoA.
Total ATP yield from one glucose molecule through all pathways (glycolysis, Krebs cycle, and electron transport chain) can reach up to 30-32 ATP.

Electron Transport Chain

Electrons and hydrogen ions from NADH and FADH2 enter the electron transport chain, where they are transferred through protein complexes.
The end product of the electron transport chain is water, formed when electrons reduce oxygen.

Anaerobic and Immediate Energy Sources

Anaerobic metabolism breaks down ATP without oxygen, resulting in lactic acid production in muscles.
Phosphocreatine (PCr) serves as an immediate energy source for muscle cells during high energy demand.

ATP Regeneration and Anabolism

The process of reforming ATP from ADP is called phosphorylation.
Anabolism is crucial for biosynthesis, helping build larger macromolecules from smaller units.

Cellular Metabolism and Fuel Sources

Carbohydrates, particularly glucose, serve as the primary macromolecule broken down for the Krebs cycle.
In the citric acid cycle, acetyl groups from acetyl CoA are oxidized for energy extraction, and released electrons are transferred to NAD+ and FAD.

NAD and FAD Functionality

NADH is the reduced form of NAD; likewise, FADH2 represents the reduced form of FAD.
Both NAD and FAD function as coenzymes, facilitating redox reactions within the Krebs cycle and electron transport chain.

Energy Extraction and Intermediary Metabolism

The primary function of oxidative phosphorylation is to couple electron transport to ATP production.
Enzyme LDH catalyzes the formation of lactic acid from pyruvic acid, which occurs under anaerobic conditions.

Glycolysis Dynamics

Pyruvate Dehydrogenase (PDH) influences glycolysis indirectly by consuming pyruvate when mitochondrial activity is high.
When glycolysis is slow, lactate dehydrogenase (LDH) competes with mitochondria for pyruvate.

pH and Glycolytic Regulation

Low pH inhibits phosphofructokinase (PFK), causing a decrease in the glycolytic rate in resting muscles.
Increased AMP levels activate PFK, promoting glycolysis during muscle activity, whereas elevated ATP enhances PFK inhibition.

Cori Cycle and Metabolic Pathways

The Cori cycle occurs primarily in the liver, converting lactate back to glucose.
Glycolysis operates effectively for 1-3 minute events, mainly powered by anaerobic metabolism.

Glycogen vs. Glucose Utilization

Glycogen breakdown during exercise can exceed glucose uptake, enhancing ATP yield.
Glycogen usage yields a higher net gain of ATP compared to glucose due to fewer energy-invested steps in glycolysis.

Exercise and PFK Activity

Increased acidity during exercise leads to a decrease in PFK activity, while factors like increased ADP or AMP levels help to overcome ATP's inhibitory effects on PFK.
GLUT4 translocation to the plasma membrane during exercise is triggered by insulin and muscle contractions.

Summary of Enzyme Regulation

The rate-limiting step in glycolysis is controlled primarily by PFK, which is influenced by substrates, products, and pH levels.
Changes in PFK activity during exercise are modulated by various intracellular conditions, including AMP, ATP, and pH.

Lactic Acid Formation

Excess hydrogen ions combine with pyruvate to form lactic acid during strenuous exercise, leading to muscle fatigue.

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Description

Test your knowledge on the functions of the Krebs cycle, including the removal of hydrogen atoms, generation of electrons for the respiratory chain, and production of ATP units. Understand how carbon dioxide is removed from pyruvic acid and how water is formed through the electron transport chain.