Siklus Krebs /Siklus Asam Trikarboksilat (TCA)

Summary

This video explains the Krebs Cycle, an essential part of aerobic respiration, taking place in the mitochondria. It covers the eight key stages, starting with the condensation of Acetyl-CoA with Oxaloacetate to form Citrate, and ending with the regeneration of Oxaloacetate. The process produces important molecules like NADH, FADH2, and ATP. Key enzymes are involved at each stage, and the cycle runs twice for every glucose molecule, ultimately generating energy that powers cellular activities. Understanding the Krebs Cycle is vital for comprehending metabolism and energy production in living organisms.

Takeaways

• 😀 The Krebs Cycle is the third stage of aerobic respiration, following oxidative decarboxylation.
• 😀 The cycle takes place in the mitochondria matrix, unlike glycolysis which happens in the cytoplasm.
• 😀 Acetyl-CoA, a two-carbon molecule, condenses with oxaloacetate to form citric acid, initiating the cycle.
• 😀 The first step in the cycle forms citric acid (or citrate), which has six carbon atoms.
• 😀 Citrate undergoes isomerization, converting into isocitrate, with the same number of carbon atoms (six).
• 😀 Isocitrate is then converted into alpha-ketoglutarate (five-carbon molecule) through a decarboxylation reaction, releasing CO2 and producing NADH.
• 😀 Alpha-ketoglutarate undergoes another decarboxylation, converting into succinyl-CoA (four-carbon molecule), releasing CO2 and producing NADH.
• 😀 Succinyl-CoA is converted into succinate, producing GTP (or ATP) through a substrate-level phosphorylation.
• 😀 Fumarate, a four-carbon molecule, is produced from succinate, with electrons transferred to FAD, forming FADH2.
• 😀 Malate is produced from fumarate, which is then converted back into oxaloacetate, producing NADH in the process, completing the cycle.
• 😀 Each complete cycle of Krebs results in the production of 3 NADH, 1 FADH2, and 1 ATP (or GTP).

Q & A

What is the Krebs Cycle and why is it important?

The Krebs Cycle, also known as the Citric Acid Cycle, is the third stage in aerobic respiration. It is crucial because it generates energy-rich molecules like NADH, FADH2, and ATP, which are essential for cellular energy production.

Where does the Krebs Cycle occur within the cell?

The Krebs Cycle takes place in the mitochondrial matrix, while glycolysis occurs in the cytoplasm.

What is the role of acetyl-CoA in the Krebs Cycle?

Acetyl-CoA, which contains two carbon atoms, combines with oxaloacetate (four carbon atoms) to form citric acid (six carbon atoms) at the beginning of the cycle.

What is the first step of the Krebs Cycle?

The first step involves the condensation of acetyl-CoA with oxaloacetate, forming citric acid (also known as citrate), a six-carbon compound.

What happens during the isomerization of citric acid?

Citric acid undergoes isomerization to form isocitrate, with the help of the enzyme aconitase. This process involves both dehydration and hydration reactions.

How is NADH produced in the Krebs Cycle?

NADH is produced when electrons are transferred to NAD+ during dehydrogenation reactions, such as when isocitrate is converted to alpha-ketoglutarate and when alpha-ketoglutarate is converted to succinyl-CoA.

What is the significance of the decarboxylation reactions in the Krebs Cycle?

Decarboxylation reactions involve the removal of carbon dioxide (CO2) from molecules. These reactions occur during the conversion of isocitrate to alpha-ketoglutarate and alpha-ketoglutarate to succinyl-CoA.

How is ATP generated during the Krebs Cycle?

ATP is produced when GDP (or ADP) is phosphorylated by inorganic phosphate, transferring a phosphate group to form GTP or ATP during the conversion of succinyl-CoA to succinate.

What is the role of FAD in the Krebs Cycle?

FAD accepts electrons during the conversion of succinate to fumarate, forming FADH2, which plays a crucial role in the electron transport chain for further ATP production.

How does the Krebs Cycle regenerate oxaloacetate?

At the end of the cycle, malate is converted back into oxaloacetate, completing the cycle. This reaction also produces NADH.

What is the overall output of one complete turn of the Krebs Cycle?

One turn of the Krebs Cycle produces 3 NADH, 1 FADH2, 1 ATP (or GTP), and 2 CO2 molecules, which are used in the subsequent stages of aerobic respiration to produce more ATP.