EL CICLO DE KREBS [Paso a paso con repaso y resumen final]

Summary

The Krebs cycle, also known as the citric acid cycle, plays a crucial role in cellular respiration by converting acetyl-CoA into ATP, NADH, FADH2, and CO2. It consists of eight stages, including the conversion of citric acid to isocitrate, the oxidation of isocitrate to alpha-ketoglutarate, and the formation of ATP through substrate-level phosphorylation. This cycle provides energy for the cell by generating electron carriers, which later contribute to ATP production. Despite being oxygen-dependent, the Krebs cycle itself doesn't require oxygen directly, and its regulation is closely linked to energy levels within the cell.

Takeaways

• 😀 The Krebs cycle begins with acetyl-CoA combining with oxaloacetate to form citrate, a 6-carbon molecule.
• 😀 The cycle produces two molecules of CO₂, which are released as waste products.
• 😀 The cycle generates high-energy molecules, including NADH, FADH₂, and ATP, which are essential for cellular energy production.
• 😀 The Krebs cycle is a critical pathway in cellular respiration and occurs in the mitochondrial matrix.
• 😀 The cycle consists of eight stages, starting with citrate formation and ending with the regeneration of oxaloacetate.
• 😀 Enzymes play a crucial role in each step, such as citrate synthase, aconitase, and alpha-ketoglutarate dehydrogenase.
• 😀 The production of NADH and FADH₂ in the cycle feeds into the electron transport chain, which is responsible for ATP production.
• 😀 The cycle is regulated by the energy status of the cell, where high ATP levels inhibit it, while low ATP levels activate it.
• 😀 The Krebs cycle does not require oxygen directly but is closely linked to the electron transport chain, which relies on oxygen.
• 😀 For each molecule of glucose, the Krebs cycle completes two turns, as glucose is split into two molecules of acetyl-CoA during glycolysis.

Q & A

What is the main purpose of the Krebs cycle?

The main purpose of the Krebs cycle is to produce energy-rich molecules such as NADH, FADH2, and GTP (which is equivalent to ATP), and to generate carbon dioxide as a waste product. These molecules are essential for ATP production in later stages of cellular respiration.

How many stages are there in the Krebs cycle and what is the initial molecule involved?

There are eight stages in the Krebs cycle. The initial molecule involved is acetyl-CoA, which combines with oxaloacetate to form citrate at the beginning of the cycle.

What happens during the first stage of the Krebs cycle?

In the first stage, acetyl-CoA (2 carbon atoms) combines with oxaloacetate (4 carbon atoms) to form citrate (6 carbon atoms). This reaction is irreversible and is catalyzed by the enzyme citrate synthase.

What is the role of NADH in the Krebs cycle?

NADH is a high-energy electron carrier that is produced during several steps of the Krebs cycle. It plays a key role in transferring electrons to the electron transport chain, which generates ATP through oxidative phosphorylation.

What is the significance of FADH2 in the Krebs cycle?

FADH2 is another electron carrier produced in the Krebs cycle. Like NADH, it donates electrons to the electron transport chain, contributing to ATP production. It is produced specifically during the conversion of succinate to fumarate.

How does the cycle of the Krebs cycle relate to oxygen consumption?

Although the Krebs cycle itself does not directly require oxygen, it is closely linked to the electron transport chain, which is oxygen-dependent. Oxygen is needed to accept the electrons at the end of the electron transport chain to form water.

Why is the enzyme citrate synthase important in the Krebs cycle?

Citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate, initiating the cycle. This reaction is irreversible, making it a key regulatory point in the cycle.

What happens during the production of alpha-ketoglutarate in the cycle?

During the third stage of the Krebs cycle, isocitrate is oxidized and decarboxylated to form alpha-ketoglutarate, releasing CO2 and generating NADH in the process. This reaction is catalyzed by isocitrate dehydrogenase.

How is ATP produced in the Krebs cycle?

ATP is produced through substrate-level phosphorylation in the fifth stage of the Krebs cycle. The enzyme succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, generating GTP, which can then be converted to ATP.

What regulates the Krebs cycle and how does ATP affect it?

The Krebs cycle is regulated by the energy status of the cell. High levels of ATP and NADH inhibit the cycle, while low levels of these molecules activate it, ensuring that the cycle operates in response to the cell's energy needs.