Question
The citric acid cycle has eight steps, each
catalyzed by a specific enzyme
•
explain these 8 steps of citric acid cycle with what they produced in each steps
catalyzed by a specific enzyme
•
explain these 8 steps of citric acid cycle with what they produced in each steps
Answers
GPT-4o mini
The citric acid cycle (also known as the Krebs cycle or TCA cycle) is a crucial metabolic pathway that occurs in the mitochondria of cells. It plays a key role in energy production through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The cycle consists of eight steps, each catalyzed by a specific enzyme, leading to the production of energy-rich molecules.
Here’s a detailed overview of each step, including the enzymes involved and the products produced:
1. **Formation of Citrate**:
- **Enzyme**: Citrate synthase
- **Reactants**: Acetyl-CoA and oxaloacetate (OAA)
- **Product**: Citrate
- **Description**: The acetyl group from acetyl-CoA condenses with oxaloacetate to form citrate. This step is irreversible and initiates the cycle.
2. **Formation of Isocitrate**:
- **Enzyme**: Aconitase
- **Reactant**: Citrate
- **Product**: Isocitrate
- **Description**: Citrate is converted into isocitrate through a rearrangement reaction. This occurs via an intermediary called cis-aconitate.
3. **Oxidation of Isocitrate**:
- **Enzyme**: Isocitrate dehydrogenase
- **Reactant**: Isocitrate
- **Products**: α-Ketoglutarate, NADH, and CO₂
- **Description**: Isocitrate is oxidized to form α-ketoglutarate. In this process, NAD⁺ is reduced to NADH and a molecule of CO₂ is released.
4. **Formation of Succinyl-CoA**:
- **Enzyme**: α-Ketoglutarate dehydrogenase
- **Reactants**: α-Ketoglutarate and CoA
- **Products**: Succinyl-CoA, NADH, and CO₂
- **Description**: α-Ketoglutarate undergoes oxidative decarboxylation to form succinyl-CoA, while another molecule of NAD⁺ is reduced to NADH and another CO₂ is released.
5. **Conversion of Succinyl-CoA to Succinate**:
- **Enzyme**: Succinyl-CoA synthetase
- **Reactants**: Succinyl-CoA
- **Products**: Succinate, CoA, and GTP (or ATP)
- **Description**: Succinyl-CoA is converted into succinate, generating energy that is used to produce GTP (or ATP), and releasing CoA.
6. **Oxidation of Succinate**:
- **Enzyme**: Succinate dehydrogenase
- **Reactants**: Succinate
- **Products**: Fumarate and FADH₂
- **Description**: Succinate is oxidized to fumarate, and in this process, FAD is reduced to FADH₂.
7. **Hydration of Fumarate**:
- **Enzyme**: Fumarase (fumarate hydratase)
- **Reactant**: Fumarate
- **Product**: Malate
- **Description**: Fumarate is hydrated (addition of water) to form malate.
8. **Oxidation of Malate**:
- **Enzyme**: Malate dehydrogenase
- **Reactant**: Malate
- **Products**: Oxaloacetate and NADH
- **Description**: Malate is oxidized back to oxaloacetate, reducing NAD⁺ to NADH. This regenerates oxaloacetate, allowing the cycle to continue.
### Summary of Products:
Overall, for each acetyl-CoA that enters the citric acid cycle, the following products are generated:
- 3 NADH
- 1 FADH₂
- 1 GTP (or ATP)
- 2 CO₂
These reduced coenzymes (NADH and FADH₂) are then utilized in the electron transport chain to produce ATP, while the CO₂ is expelled as a waste product of cellular respiration.
Here’s a detailed overview of each step, including the enzymes involved and the products produced:
1. **Formation of Citrate**:
- **Enzyme**: Citrate synthase
- **Reactants**: Acetyl-CoA and oxaloacetate (OAA)
- **Product**: Citrate
- **Description**: The acetyl group from acetyl-CoA condenses with oxaloacetate to form citrate. This step is irreversible and initiates the cycle.
2. **Formation of Isocitrate**:
- **Enzyme**: Aconitase
- **Reactant**: Citrate
- **Product**: Isocitrate
- **Description**: Citrate is converted into isocitrate through a rearrangement reaction. This occurs via an intermediary called cis-aconitate.
3. **Oxidation of Isocitrate**:
- **Enzyme**: Isocitrate dehydrogenase
- **Reactant**: Isocitrate
- **Products**: α-Ketoglutarate, NADH, and CO₂
- **Description**: Isocitrate is oxidized to form α-ketoglutarate. In this process, NAD⁺ is reduced to NADH and a molecule of CO₂ is released.
4. **Formation of Succinyl-CoA**:
- **Enzyme**: α-Ketoglutarate dehydrogenase
- **Reactants**: α-Ketoglutarate and CoA
- **Products**: Succinyl-CoA, NADH, and CO₂
- **Description**: α-Ketoglutarate undergoes oxidative decarboxylation to form succinyl-CoA, while another molecule of NAD⁺ is reduced to NADH and another CO₂ is released.
5. **Conversion of Succinyl-CoA to Succinate**:
- **Enzyme**: Succinyl-CoA synthetase
- **Reactants**: Succinyl-CoA
- **Products**: Succinate, CoA, and GTP (or ATP)
- **Description**: Succinyl-CoA is converted into succinate, generating energy that is used to produce GTP (or ATP), and releasing CoA.
6. **Oxidation of Succinate**:
- **Enzyme**: Succinate dehydrogenase
- **Reactants**: Succinate
- **Products**: Fumarate and FADH₂
- **Description**: Succinate is oxidized to fumarate, and in this process, FAD is reduced to FADH₂.
7. **Hydration of Fumarate**:
- **Enzyme**: Fumarase (fumarate hydratase)
- **Reactant**: Fumarate
- **Product**: Malate
- **Description**: Fumarate is hydrated (addition of water) to form malate.
8. **Oxidation of Malate**:
- **Enzyme**: Malate dehydrogenase
- **Reactant**: Malate
- **Products**: Oxaloacetate and NADH
- **Description**: Malate is oxidized back to oxaloacetate, reducing NAD⁺ to NADH. This regenerates oxaloacetate, allowing the cycle to continue.
### Summary of Products:
Overall, for each acetyl-CoA that enters the citric acid cycle, the following products are generated:
- 3 NADH
- 1 FADH₂
- 1 GTP (or ATP)
- 2 CO₂
These reduced coenzymes (NADH and FADH₂) are then utilized in the electron transport chain to produce ATP, while the CO₂ is expelled as a waste product of cellular respiration.