C1.2.13 Transfer of energy by reduced NAD (HL) Notes

Introduction to NADH and Energy Transfer

• NADH (Nicotinamide Adenine Dinucleotide, reduced form) is a crucial molecule in cellular respiration that carries high-energy electrons.
• It acts as an energy carrier, transferring electrons from metabolic pathways to the electron transport chain (ETC).

AnalogyThink of NADH as a rechargeable battery that stores energy from food and delivers it to where it's needed for ATP production.

DefinitionNADHA coenzyme that carries high-energy electrons and protons, playing a key role in cellular respiration.

The Role of NADH in Cellular Respiration

• NADH is produced in several stages of cellular respiration:
  • Glycolysis
  • Pyruvate oxidation
  • Krebs cycle
• It carries electrons to the ETC, where energy is extracted to produce ATP.

NoteNADH is the reduced form of NAD⁺, meaning it has gained electrons and protons.

The Electron Transport Chain (ETC)

• The ETC is located in the inner mitochondrial membrane and consists of four protein complexes.
• NADH donates electrons to Complex I, the first protein complex in the chain.

ExampleEach NADH molecule can generate approximately 2.5 ATP molecules through the ETC.

Proton Gradient Formation

• As electrons flow through the ETC, protons (H⁺) are pumped from the mitochondrial matrix to the intermembrane space.
• This creates a proton gradient, also known as the proton motive force.

AnalogyImagine pumping water uphill to create a reservoir. The stored water can later flow downhill to generate electricity. Similarly, the proton gradient stores potential energy.

ATP Synthesis

• Protons flow back into the mitochondrial matrix through ATP synthase, a protein complex that converts ADP + Pi into ATP.
• This process is called chemiosmosis.

DefinitionChemiosmosisThe process of using a proton gradient to drive ATP synthesis.

Regeneration of NAD⁺

• When NADH donates its electrons to the ETC, it is oxidized back to NAD⁺.
• This regeneration is crucial for continuous cellular respiration.

TipWithout NAD⁺ regeneration, glycolysis and the Krebs cycle would halt due to lack of available NAD⁺.

Comparison with FADH₂

• FADH₂ is another electron carrier that donates electrons to Complex II of the ETC.
• It produces less ATP (about 1.5 ATP per FADH₂) because it enters the ETC at a later point.

Don't confuse NADH and FADH₂! They have different entry points in the ETC and yield different amounts of ATP.

Importance of NADH in Energy Production

• NADH is the primary carrier of high-energy electrons in aerobic respiration.
• It enables the efficient production of ATP, the cell's energy currency.

ExampleIn total, one glucose molecule can produce about 30-32 ATP molecules through aerobic respiration, with most of them coming from NADH.