Use this worksheet to practice with Chapter 8 content 1. Review the steps of aerobic respiration - glycolysis, the citric acid cycle, and the electron transport chain. For each step, list all the inputs and outputs, including their counts. Include: Glucose, pyruvate, NAD+, FAD, NADH, FADH2, ATP, ADP, water, oxygen, and carbon dioxide. If we noted any special intermediary molecules, also include those in your summary of the steps of aerobic respiration.

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**Glycolysis**  
- **Input per 1 Glucose molecule:**  
  - $$1 \, 	ext{Glucose}$$  
  - $$2 \, 	ext{NAD}^+$$  
  - $$2 \, 	ext{ADP} + 2 \, 	ext{P}_	ext{i}$$

- **Output:**  
  - $$2 \, 	ext{Pyruvate}$$  
  - $$2 \, 	ext{NADH}$$  
  - $$2 \, 	ext{ATP}$$ (net gain; note that 4 ATP are produced but 2 are consumed in early steps)  
  - $$2 \, 	ext{H}_2	ext{O}$$

*Additional note:* Glycolysis also involves several intermediary molecules (e.g., glucose-6-phosphate, fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate), but the summary here emphasizes the key inputs and outputs.

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**Pyruvate Oxidation (Link Reaction)**  
For each of the $$2 \, 	ext{Pyruvate}$$ from glycolysis:

- **Input (per pyruvate):**  
  - $$1 \, 	ext{Pyruvate}$$  
  - $$1 \, 	ext{NAD}^+$$  
  - Coenzyme A (CoA)

- **Output (per pyruvate):**  
  - $$1 \, 	ext{Acetyl-CoA}$$  
  - $$1 \, 	ext{NADH}$$  
  - $$1 \, 	ext{CO}_2$$

*Thus, per glucose (2 pyruvate):*  
- **Input:** $$2 \, 	ext{Pyruvate}$$, $$2 \, 	ext{NAD}^+$$  
- **Output:** $$2 \, 	ext{Acetyl-CoA}$$, $$2 \, 	ext{NADH}$$, $$2 \, 	ext{CO}_2$$

---

**Citric Acid Cycle (Krebs Cycle)**  
For each turn of the cycle (per acetyl-CoA):

- **Input (per acetyl-CoA):**  
  - $$1 \, 	ext{Acetyl-CoA}$$  
  - $$1 \, 	ext{Oxaloacetate}$$ (a cyclical intermediate that is regenerated)  
  - $$3 \, 	ext{NAD}^+$$  
  - $$1 \, 	ext{FAD}$$  
  - $$1 \, 	ext{ADP} + 1 \, 	ext{P}_	ext{i}$$  
  - $$2 \, 	ext{H}_2	ext{O}$$

- **Output (per acetyl-CoA):**  
  - $$2 \, 	ext{CO}_2$$  
  - $$3 \, 	ext{NADH}$$  
  - $$1 \, 	ext{FADH}_2$$  
  - $$1 \, 	ext{ATP}$$ (or GTP in some cells)  
  - Regenerated $$1 \, 	ext{Oxaloacetate}$$ (allowing the cycle to continue)

*Thus, per glucose (2 acetyl-CoA):*  
- **Total Input:**  
  - $$2 \, 	ext{Acetyl-CoA}$$  
  - $$6 \, 	ext{NAD}^+$$  
  - $$2 \, 	ext{FAD}$$  
  - $$2 \, 	ext{ADP} + 2 \, 	ext{P}_	ext{i}$$  
- **Total Output:**  
  - $$4 \, 	ext{CO}_2$$  
  - $$6 \, 	ext{NADH}$$  
  - $$2 \, 	ext{FADH}_2$$  
  - $$2 \, 	ext{ATP}$$

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**Electron Transport Chain (Oxidative Phosphorylation)**

- **Primary Inputs:**  
  - All reduced coenzymes produced in previous steps:  
    - From glycolysis: $$2 \, 	ext{NADH}$$  
    - From pyruvate oxidation: $$2 \, 	ext{NADH}$$  
    - From the citric acid cycle: $$6 \, 	ext{NADH}$$ and $$2 \, 	ext{FADH}_2$$  
    - *Totals:* $$10 \, 	ext{NADH}$$ and $$2 \, 	ext{FADH}_2$$  
  - $$ 	ext{Oxygen} $$ is essential as the final electron acceptor:  
    - Approximately $$6 \, 	ext{O}_2$$ molecules per glucose are used (since each NADH effectively transfers electrons that, when paired with protons, reduce half a molecule of oxygen to water).

- **Process:**  
  - Electrons from $$ 	ext{NADH} $$ and $$ 	ext{FADH}_2 $$ travel through a series of carriers, creating a proton gradient across the inner mitochondrial membrane.  
  - The flow of protons back into the mitochondrial matrix via ATP synthase drives the production of ATP.

- **Output:**  
  - Oxidized coenzymes: $$10 \, 	ext{NAD}^+$$ and $$2 \, 	ext{FAD}$$  
  - $$ \approx 28 \, 	ext{ATP} $$ molecules synthesized by the ATP synthase complex (the exact number may vary with cell type and efficiency)  
  - $$6 \, 	ext{H}_2	ext{O}$$ molecules formed as oxygen accepts electrons and protons

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**Overall Summary of Aerobic Respiration (per 1 Glucose):**

- **Glycolysis:**  
  - Inputs: $$1 \, 	ext{Glucose}$$, $$2 \, 	ext{NAD}^+$$, $$2 \, 	ext{ADP} + 2 \, 	ext{P}_	ext{i}$$  
  - Outputs: $$2 \, 	ext{Pyruvate}$$, $$2 \, 	ext{NADH}$$, $$2 \, 	ext{ATP}$$, $$2 \, 	ext{H}_2	ext{O}$$

- **Pyruvate Oxidation:**  
  - Inputs (total for 2 pyruvate): $$2 \, 	ext{NAD}^+$$  
  - Outputs: $$2 \, 	ext{Acetyl-CoA}$$, $$2 \, 	ext{NADH}$$, $$2 \, 	ext{CO}_2$$

- **Citric Acid Cycle:**  
  - Inputs (total for 2 acetyl-CoA): $$6 \, 	ext{NAD}^+$$, $$2 \, 	ext{FAD}$$, $$2 \, 	ext{ADP} + 2 \, 	ext{P}_	ext{i}$$  
  - Outputs: $$4 \, 	ext{CO}_2$$, $$6 \, 	ext{NADH}$$, $$2 \, 	ext{FADH}_2$$, $$2 \, 	ext{ATP}$$

- **Electron Transport Chain:**  
  - Inputs: $$10 \, 	ext{NADH}$$ and $$2 \, 	ext{FADH}_2$$ from earlier stages; approximately $$6 \, 	ext{O}_2$$ molecules  
  - Outputs: $$10 \, 	ext{NAD}^+$$, $$2 \, 	ext{FAD}$$, $$\approx 28 \, 	ext{ATP}$$ from oxidative phosphorylation, $$6 \, 	ext{H}_2	ext{O}$$

This complete pathway summarizes the key inputs and outputs, including the counts for $$ 	ext{Glucose} $$, $$ 	ext{Pyruvate} $$, $$ 	ext{NAD}^+/	ext{NADH} $$, $$ 	ext{FAD}/	ext{FADH}_2 $$, $$ 	ext{ATP}/	ext{ADP} $$, oxygen, water, and carbon dioxide along with special intermediates like Acetyl-CoA and oxaloacetate.
**Aerobic Respiration Summary:** - **Glycolysis:** - **Inputs:** 1 Glucose, 2 NAD⁺, 2 ADP + 2 Pi - **Outputs:** 2 Pyruvate, 2 NADH, 2 ATP, 2 H₂O - **Pyruvate Oxidation:** - **Inputs:** 2 NAD⁺ - **Outputs:** 2 Acetyl-CoA, 2 NADH, 2 CO₂ - **Citric Acid Cycle:** - **Inputs:** 6 NAD⁺, 2 FAD, 2 ADP + 2 Pi - **Outputs:** 4 CO₂, 6 NADH, 2 FADH₂, 2 ATP - **Electron Transport Chain:** - **Inputs:** 10 NADH, 2 FADH₂, 6 O₂ - **Outputs:** 10 NAD⁺, 2 FAD, ~28 ATP, 6 H₂O **Total Outputs:** - **ATP:** ~30 (from glycolysis: 2, citric acid cycle: 2, electron transport chain: ~28) - **CO₂:** 6 - **H₂O:** 8 (from glycolysis: 2, pyruvate oxidation: 2, citric acid cycle: 4, electron transport chain: 6)

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