# Answers to Biochemistry and Cell Biology Choice --- ## 1. How many protons are pumped from one NADH? - **Correct answer:** **c. 10** NADH donates electrons to Complex I of the electron transport chain. As the electrons move through Complexes I, III, and IV, a total of **10 protons** are pumped from the mitochondrial matrix to the intermembrane space. --- ## 2. Primary regulatory point of the electron transport chain - **Correct answer:** **b. Feedback inhibition on complex I** The primary regulatory point is **Complex I**, which is subject to feedback inhibition. The availability of NADH and ADP, and the ATP/ADP ratio, can regulate the flow of electrons through the chain. --- ## 3. Role of the malate-aspartate and glycerol-3-phosphate shuttles - **Correct answer:** **c. Transport electrons into the mitochondria from the cytoplasm** These shuttles **move electrons (as reducing equivalents) from cytoplasmic NADH into the mitochondrial matrix**, since NADH itself cannot cross the mitochondrial inner membrane. --- ## 4. Glucose symport calculation with sodium gradient ### Given: - [Na+] outside = 145 mM - [Na+] inside = 12 mM - Membrane potential (Δψ) = -50 mV (inside negative) - Faraday’s constant (F) = 96,485 J·V⁻¹·mol⁻¹ - Temperature (T) = 298 K - [Glucose] outside = 10 mM - [Glucose] inside = 100 mM - Assume 1:1 Na⁺:glucose symport ### Step 1: Free energy for Na⁺ influx \[ \Delta G_{Na^+} = RT \ln \left(\frac{[Na^+]_{in}}{[Na^+]_{out}}\right) + zF\Delta\psi \] Where: - \( R = 8.314 \) J·mol⁻¹·K⁻¹ - \( z = +1 \) (charge of Na⁺) - \( \Delta\psi = -.050 \) V Plug in values: \[ \Delta G_{Na^+} = (8.314)(298) \ln \left(\frac{12}{145}\right) + (1)(96,485)(-.050) \] \[ \ln \left(\frac{12}{145}\right) = \ln(.0828) = -2.491 \] \[ (8.314)(298)(-2.491) = -6,183 \text{ J/mol} \] \[ (1)(96,485)(-.050) = -4,824 \text{ J/mol} \] \[ \Delta G_{Na^+} = -6,183 + (-4,824) = -11,007 \text{ J/mol} \] ### Step 2: Free energy required to transport glucose against its gradient \[ \Delta G_{glucose} = RT \ln \left(\frac{[glucose]_{in}}{[glucose]_{out}}\right) \] \[ = (8.314)(298) \ln \left(\frac{100}{10}\right) \] \[ \ln(10) = 2.303 \] \[ (8.314)(298)(2.303) = 5,698 \text{ J/mol} \] ### Step 3: Can one Na⁺ drive one glucose? Compare absolute values: - Energy from 1 mol Na⁺ influx: **-11,007 J/mol** - Energy needed for 1 mol glucose uptake: **+5,698 J/mol** \[ \frac{11,007}{5,698} \approx 1.93 \] So, **one Na⁺ can transport almost 2 glucose molecules** in from outside (theoretically, but in practice, transporters are 1:1). The question asks how many can be transported by the energy from one mole of Na⁺: - **Correct answer:** **c. 2** --- # Summary Table | Question | Correct Answer | Explanation | |----------|----------------|-------------| | 1 | c. 10 | 10 protons per NADH | | 2 | b. Feedback inhibition on complex I | Regulatory point | | 3 | c. Transport electrons into mitochondria | Shuttle function | | 4 | c. 2 | Na⁺ gradient energy can drive 2 glucose molecules |