Question
The
Stages of Cellular Respiration: A Preview
•
Cellular respiration has three stages:
–
Glycolysis (breaks down glucose into two
molecules of pyruvate)
–
The citric acid cycle (completes the
breakdown of glucose)
–
Oxidative phosphorylation (accounts for
most of the ATP synthesis)
note: explain the stages of cellular respiration
Stages of Cellular Respiration: A Preview
•
Cellular respiration has three stages:
–
Glycolysis (breaks down glucose into two
molecules of pyruvate)
–
The citric acid cycle (completes the
breakdown of glucose)
–
Oxidative phosphorylation (accounts for
most of the ATP synthesis)
note: explain the stages of cellular respiration
Answers
GPT-4o mini
Cellular respiration is a metabolic process that cells use to convert glucose into energy in the form of ATP (adenosine triphosphate). This process occurs in three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation. Here’s a closer look at each stage:
### 1. Glycolysis
- **Location**: Cytoplasm of the cell
- **Process**: Glycolysis is the first step in cellular respiration, which begins with one molecule of glucose (a six-carbon sugar) and ends with two molecules of pyruvate (a three-carbon compound).
- **Steps**:
- **Energy Investment Phase**: The initial steps of glycolysis consume two ATP molecules to phosphorylate glucose and its derivatives, facilitating subsequent breakdown.
- **Energy Payoff Phase**: The conversion of glucose into pyruvate produces four ATP molecules (a net gain of two ATP) and two NADH (an electron carrier) as glucose is oxidized.
- **Net Gain**: 2 ATP, 2 NADH, and 2 pyruvate molecules.
### 2. The Citric Acid Cycle (Krebs Cycle)
- **Location**: Mitochondrial matrix
- **Process**: Before the citric acid cycle begins, each pyruvate is converted to Acetyl-CoA, with the release of one carbon dioxide molecule and the production of one NADH. The citric acid cycle then processes Acetyl-CoA to harvest high-energy electrons.
- **Steps**:
- Acetyl-CoA enters the cycle, combining with a four-carbon molecule (oxaloacetate) to form citric acid (citrate).
- The cycle consists of a series of reactions that regenerate oxaloacetate while producing energy-rich molecules: three NADH, one FADH₂ (another electron carrier), and one ATP (or GTP, depending on the cell type) are generated per cycle, along with two carbon dioxide molecules released as waste.
- **Net Gain per Acetyl-CoA**: 3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂.
### 3. Oxidative Phosphorylation
- **Location**: Inner mitochondrial membrane
- **Process**: This stage includes the electron transport chain and chemiosmosis, where most of the ATP is generated.
- **Steps**:
- Electrons from NADH and FADH₂ are transferred through a series of protein complexes (the electron transport chain), which creates a proton gradient across the inner mitochondrial membrane.
- Protons move back across the membrane through ATP synthase (a protein complex), powering the synthesis of ATP from ADP and inorganic phosphate.
- As electrons move through the chain, they ultimately reduce oxygen to form water (the final electron acceptor).
- **Net Gain**: Approximately 28-32 ATP, depending on the efficiency and conditions of the cell.
### Summary
In total, the aerobic respiration of one glucose molecule can yield up to about 36-38 ATP molecules:
- **Glycolysis**: 2 ATP
- **Citric Acid Cycle**: 2 ATP (from two cycles for the two pyruvate)
- **Oxidative Phosphorylation**: 28-32 ATP
This energy production process is crucial for cellular functions and overall metabolism in aerobic organisms.
### 1. Glycolysis
- **Location**: Cytoplasm of the cell
- **Process**: Glycolysis is the first step in cellular respiration, which begins with one molecule of glucose (a six-carbon sugar) and ends with two molecules of pyruvate (a three-carbon compound).
- **Steps**:
- **Energy Investment Phase**: The initial steps of glycolysis consume two ATP molecules to phosphorylate glucose and its derivatives, facilitating subsequent breakdown.
- **Energy Payoff Phase**: The conversion of glucose into pyruvate produces four ATP molecules (a net gain of two ATP) and two NADH (an electron carrier) as glucose is oxidized.
- **Net Gain**: 2 ATP, 2 NADH, and 2 pyruvate molecules.
### 2. The Citric Acid Cycle (Krebs Cycle)
- **Location**: Mitochondrial matrix
- **Process**: Before the citric acid cycle begins, each pyruvate is converted to Acetyl-CoA, with the release of one carbon dioxide molecule and the production of one NADH. The citric acid cycle then processes Acetyl-CoA to harvest high-energy electrons.
- **Steps**:
- Acetyl-CoA enters the cycle, combining with a four-carbon molecule (oxaloacetate) to form citric acid (citrate).
- The cycle consists of a series of reactions that regenerate oxaloacetate while producing energy-rich molecules: three NADH, one FADH₂ (another electron carrier), and one ATP (or GTP, depending on the cell type) are generated per cycle, along with two carbon dioxide molecules released as waste.
- **Net Gain per Acetyl-CoA**: 3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂.
### 3. Oxidative Phosphorylation
- **Location**: Inner mitochondrial membrane
- **Process**: This stage includes the electron transport chain and chemiosmosis, where most of the ATP is generated.
- **Steps**:
- Electrons from NADH and FADH₂ are transferred through a series of protein complexes (the electron transport chain), which creates a proton gradient across the inner mitochondrial membrane.
- Protons move back across the membrane through ATP synthase (a protein complex), powering the synthesis of ATP from ADP and inorganic phosphate.
- As electrons move through the chain, they ultimately reduce oxygen to form water (the final electron acceptor).
- **Net Gain**: Approximately 28-32 ATP, depending on the efficiency and conditions of the cell.
### Summary
In total, the aerobic respiration of one glucose molecule can yield up to about 36-38 ATP molecules:
- **Glycolysis**: 2 ATP
- **Citric Acid Cycle**: 2 ATP (from two cycles for the two pyruvate)
- **Oxidative Phosphorylation**: 28-32 ATP
This energy production process is crucial for cellular functions and overall metabolism in aerobic organisms.