Topic 5: Energy transfers: Electron Transport Chain

In the stages of respiration so far, only substrate-level phosphorylation has produced ATP, when a phosphate group is transferred to an intermediate to ADP

Oxidative phosphorylation, the final stage of aerobic respiration, generates ATP by using the flow of protons through ATP Synthase

Where oxidative phosphorylation occurs:

• oxidative phosphorylation occurs across the inner mitochondrial membrane of the cristae

• the cristae are the inner folded membranes in mitochondria where the enzymes and proteins involved in oxidative phosphorylation are located

• some of these proteins are involved in the electron transfer chain: a series of electron carrier molecules in the inner mitochondrial membrane that release energy in stages

Releasing energy in stages allows more energy to be harvested for the benefit of the orgasim,

rather than being released as heat

Reactants

• reduced NAD

• reduced FAD

• Oxygen

• ADP and Pi

Products

• NAD

• FAD

• Water

• ATP

Oxidative phosphorylation has several key stages:

1. Reduced NAD and reduced FAD release hydrogen transferring protons (H+) and electrons (e-) into mitochondrial matrix

2. High energy electrons are passed to an electron carrier from reduced NAD and reduced FAD

3. The electrons are passed along a series of electron carrier molecules in the electron transport chain embedded in the inner mitochondrial membrane, releasing energy as they are transferred

4. The energy is used to actively transport protons across the inner mitochondrial membrane from the mitochondrial matrix into the intermembrane space

5. The accumulation of protons in the intermembrane space sets up a steep electrochemical gradient of protons across the inner membrane

6. Proton diffuse back into the mitochondrial matrix down their electrochemical gradient through ATP Synthase

7. This releases energy and catalyses the synthesis of ATP from ADP and Pi

8. Oxygen is final electron acceptor, and combines with electrons and protons to form water, helping to maintain the proton gradient

In aerobic respiration, chemiosmosis the diffusion of protons across the partially permeable inner mitochondrial membrane, down their electrochemical gradient through ATP Synthase channels

The movement of protons release energy that is used to synthesise ATP. It converts the energy that is used to synthesise ATP. It converts the energy from the electrochemical gradient into chemical energy stored in ATP molecules

Each stage (except the link reaction) contributes to the overall yield of ATP

with oxidative phosphorylation being the most productive