Questions and Answers
What is the process that occurs in the mitochondria, specifically in the inner mitochondrial membrane?
Where do NADH and FADH2 drop off their electrons?
What is the purpose of the proton gradient?
How many protons are pumped out by Complex I?
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What is the role of Coenzyme Q?
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What is the byproduct of the electron transport chain?
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What is the purpose of ATP synthase?
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How many ATP are produced from one NADH?
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What is the process by which ATP is generated in the electron transport chain?
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Where do the electrons from NADH and FADH2 ultimately end up?
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Study Notes
Electron Transport Chain
- The electron transport chain is a process that occurs in the mitochondria, specifically in the inner mitochondrial membrane
- The process starts with NADH and FADH2, which are produced in the citric acid cycle and oxidative steps of cellular respiration
- NADH drops off its electrons at Complex I, which then passes them to Coenzyme Q
- FADH2 drops off its electrons at Complex II, which then passes them to Coenzyme Q
Complex I (NADH Dehydrogenase)
- NADH drops off its electrons at Complex I
- Electrons are passed from NADH to Complex I, which then passes them to Coenzyme Q
- Complex I pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons
Complex II (Succinate Dehydrogenase)
- FADH2 drops off its electrons at Complex II
- Electrons are passed from FADH2 to Complex II, which then passes them to Coenzyme Q
- Complex II does not pump protons out of the mitochondrial matrix
Coenzyme Q (Ubiquinone)
- Coenzyme Q is a mobile molecule that accepts electrons from Complex I and II
- Coenzyme Q passes electrons to Complex III
Complex III (Cytochrome b-c1 Complex)
- Coenzyme Q passes electrons to Complex III
- Electrons are passed from Coenzyme Q to Complex III, which then passes them to Cytochrome C
- Complex III pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons
Cytochrome C
- Cytochrome C is a mobile molecule that accepts electrons from Complex III
- Cytochrome C passes electrons to Complex IV
Complex IV (Cytochrome c Oxidase)
- Cytochrome C passes electrons to Complex IV
- Electrons are passed from Cytochrome C to Complex IV, which then passes them to Oxygen
- Complex IV pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons
Proton Gradient
- The proton gradient is the accumulation of protons in the intermembrane space due to the pumping of protons from Complex I, III, and IV
- The proton gradient is used to generate ATP through the process of chemiosmosis
ATP Synthesis
- ATP synthesis occurs through the process of chemiosmosis
- Protons move from high concentration in the intermembrane space to low concentration in the mitochondrial matrix through ATP synthase
- The movement of protons drives the rotation of the rotor and rod in ATP synthase
- The rotation of the rotor and rod absorbs potential energy, which is used to drive the production of ATP from ADP and inorganic phosphate
ATP Synthase
- ATP synthase is a complex of proteins that spans the mitochondrial membrane
- The structure of ATP synthase includes a rotor, rod, catalytic knob, and stat
- The catalytic knob is where ADP and inorganic phosphate are bound
- The rotation of the rotor and rod drives the production of ATP from ADP and inorganic phosphate### Oxidative Phosphorylation
- In oxidative phosphorylation, energy from NADH and FADH2 is used to convert ADP and inorganic phosphate to ATP
- This process occurs through a specific type of phosphorylation
Electrons and Protons
- One NADH drops off electrons, which pass through complex 1, Q, complex 3, cytochrome C, and complex 4
- At complex 1, one proton is pumped out
- At complex 3, another proton is pumped out
- At complex 4, a third proton is pumped out, resulting in a total of 3 protons
- Since 2 electrons are coming from one NADH, this means one NADH gives 3 protons
- For every proton moving down its concentration gradient, one ATP is produced, so one NADH gives 3 ATP
- One FADH2 drops off electrons, which pass through complex 2, Q, complex 3, cytochrome C, and complex 4
- At complex 3, one proton is pumped out
- At complex 4, another proton is pumped out, resulting in a total of 2 protons
- Since 2 electrons are coming from one FADH2, this means one FADH2 gives 2 protons, or 2 ATP
ATP Production
- Total ATP production from one NADH: 3 ATP
- Total ATP production from one FADH2: 2 ATP
Krebs Cycle and Electron Transport Chain
- From the Krebs cycle:
- 6 NADH produced (18 ATP)
- 2 FADH2 produced (4 ATP)
- 2 ATP produced by substrate-level phosphorylation
- From the transition step:
- 2 NADH produced (6 ATP)
- From glycolysis:
- 2 NADH produced (6 ATP)
- 2 ATP produced by anaerobic mechanisms
Total ATP Production
- Total ATP production under aerobic conditions: 36 ATP
- Total ATP production including anaerobic ATP from glycolysis: 38 ATP
Electron Transport Chain
- The electron transport chain occurs in the mitochondria's inner membrane.
- NADH and FADH2, produced in the citric acid cycle and oxidative steps of cellular respiration, start the process.
Electron Carriers
- NADH drops off its electrons at Complex I, which passes them to Coenzyme Q.
- FADH2 drops off its electrons at Complex II, which passes them to Coenzyme Q.
- Coenzyme Q is a mobile molecule that accepts electrons from Complex I and II and passes them to Complex III.
- Cytochrome C is a mobile molecule that accepts electrons from Complex III and passes them to Complex IV.
Proton Pumping
- Complex I pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons.
- Complex III pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons.
- Complex IV pumps protons out of the mitochondrial matrix into the intermembrane space as it accepts electrons.
Proton Gradient
- The proton gradient is the accumulation of protons in the intermembrane space due to proton pumping.
- The proton gradient is used to generate ATP through chemiosmosis.
ATP Synthesis
- Protons move from high concentration in the intermembrane space to low concentration in the mitochondrial matrix through ATP synthase.
- The movement of protons drives the rotation of the rotor and rod in ATP synthase, producing ATP from ADP and inorganic phosphate.
ATP Synthase
- ATP synthase is a transmembrane protein complex with a rotor, rod, catalytic knob, and stat.
- The catalytic knob is where ADP and inorganic phosphate are bound.
- The rotation of the rotor and rod drives ATP production from ADP and inorganic phosphate.
Oxidative Phosphorylation
- Energy from NADH and FADH2 is used to convert ADP and inorganic phosphate to ATP through oxidative phosphorylation.
ATP Production
- One NADH produces 3 ATP through the electron transport chain.
- One FADH2 produces 2 ATP through the electron transport chain.
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Test your knowledge of the electron transport chain process in mitochondria, including NADH and FADH2 reactions and Complex I and II mechanisms.