Chapter 18: Problem 84
Most metabolic pathways are not considered cycles. Why is the citric acid cycle considered to be a metabolic cycle?
Short Answer
Expert verified
The citric acid cycle is considered a cycle because it regenerates its starting molecule, oxaloacetate, allowing the cycle to repeat.
Step by step solution
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Metabolic Pathways
Metabolic pathways are a series of biochemical reactions used by cells to convert substrates into products. They are a vital part of cellular metabolism, helping to extract energy and synthesize necessary compounds.
These pathways are generally linear, meaning they begin with a specific molecule and end with a different one.
The main goal is often the creation of an essential molecule or the extraction of energy for the cell's use.
These reactions occur in specific sequences, guided by enzyme actions that catalyze the conversion steps.
However, not all pathways are linear; some form cycles, notably the citric acid cycle or Krebs cycle.
These pathways are generally linear, meaning they begin with a specific molecule and end with a different one.
The main goal is often the creation of an essential molecule or the extraction of energy for the cell's use.
These reactions occur in specific sequences, guided by enzyme actions that catalyze the conversion steps.
However, not all pathways are linear; some form cycles, notably the citric acid cycle or Krebs cycle.
Enzyme Action
Enzymes are biological catalysts that speed up biochemical reactions. They are crucial in metabolic pathways,
ensuring that reactions occur fast enough to meet the cell's needs. Each enzyme is specific to a particular substrate, which means
it only acts on this specific molecule.
This specificity ensures the correct sequence in metabolic pathways.
Without enzymes, reactions would be too slow or might not occur at all.
In the citric acid cycle, multiple enzymes aid in converting molecules step by step, forming a cycle rather than a linear pathway.
This regular enzyme action ensures that the cycle keeps going, regenerating key molecules like oxaloacetate at the end.
ensuring that reactions occur fast enough to meet the cell's needs. Each enzyme is specific to a particular substrate, which means
it only acts on this specific molecule.
This specificity ensures the correct sequence in metabolic pathways.
Without enzymes, reactions would be too slow or might not occur at all.
In the citric acid cycle, multiple enzymes aid in converting molecules step by step, forming a cycle rather than a linear pathway.
This regular enzyme action ensures that the cycle keeps going, regenerating key molecules like oxaloacetate at the end.
Regeneration of Oxaloacetate
The citric acid cycle starts when acetyl-CoA combines with oxaloacetate to form citrate. This compound then goes through a series of reactions.
During these processes, two molecules of carbon dioxide are released, along with energy captured in the form of electron carriers.
By the end of the cycle, oxaloacetate is regenerated, allowing the cycle to restart with another acetyl-CoA molecule.
This regeneration is crucial because it maintains a supply of oxaloacetate, enabling the cycle to continually process acetyl-CoA.
Without this regeneration step, the cycle would stop, halting energy production and synthesis of necessary metabolites.
During these processes, two molecules of carbon dioxide are released, along with energy captured in the form of electron carriers.
By the end of the cycle, oxaloacetate is regenerated, allowing the cycle to restart with another acetyl-CoA molecule.
This regeneration is crucial because it maintains a supply of oxaloacetate, enabling the cycle to continually process acetyl-CoA.
Without this regeneration step, the cycle would stop, halting energy production and synthesis of necessary metabolites.
Electron Carriers (NADH and FADH2)
As the citric acid cycle progresses, it produces electron carriers like NADH and FADH2.
These molecules capture and store energy released during the reactions.
NADH and FADH2 are crucial because they carry high-energy electrons to the electron transport chain.
Here, their energy is used to produce ATP, the energy currency of the cell, through a process called oxidative phosphorylation.
This makes the citric acid cycle vital for energy production, linking it to other pathways and ensuring the cell's energy demands are met.
Understanding the role of these electron carriers helps to grasp the importance of the citric acid cycle within overall cellular metabolism.
These molecules capture and store energy released during the reactions.
NADH and FADH2 are crucial because they carry high-energy electrons to the electron transport chain.
Here, their energy is used to produce ATP, the energy currency of the cell, through a process called oxidative phosphorylation.
This makes the citric acid cycle vital for energy production, linking it to other pathways and ensuring the cell's energy demands are met.
Understanding the role of these electron carriers helps to grasp the importance of the citric acid cycle within overall cellular metabolism.
