Practice: Oxidative Phosphorylation 2: Videos & Practice Problems

The proton motive force (PMF) is crucial in oxidative phosphorylation as it drives the synthesis of ATP. During electron transport, protons are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This gradient generates an electrochemical potential difference across the inner mitochondrial membrane. ATP synthase, an enzyme complex, utilizes this PMF to catalyze the conversion of ADP and inorganic phosphate (P_i) into ATP. The flow of protons back into the matrix through ATP synthase causes conformational changes in the enzyme, enabling the phosphorylation of ADP to ATP. Without the PMF, ATP synthesis would not occur efficiently.

Uncoupling agents such as DNP (2,4-Dinitrophenol) and FCCP (carbonyl cyanide-p-trifluoromethoxyphenylhydrazone) disrupt oxidative phosphorylation by dissipating the proton gradient across the inner mitochondrial membrane. These agents transport protons back into the mitochondrial matrix without passing through ATP synthase, thereby reducing the proton motive force. As a result, ATP synthesis is inhibited because the necessary proton gradient is not maintained. However, electron transport and oxygen consumption continue, leading to a decreased phosphate-oxygen (P/O) ratio. This means that less ATP is produced per oxygen molecule consumed, highlighting the importance of the proton gradient in ATP production.

The phosphate-oxygen (P/O) ratio is a measure of the efficiency of oxidative phosphorylation. It represents the number of ATP molecules synthesized per oxygen atom reduced in the electron transport chain. A high P/O ratio indicates efficient ATP production, while a low ratio suggests inefficiency. Uncoupling agents, which dissipate the proton gradient, lower the P/O ratio because they allow electron transport and oxygen consumption to continue without effective ATP synthesis. Understanding the P/O ratio helps in assessing the functionality of the mitochondrial electron transport chain and ATP synthase in energy metabolism.

Mitochondrial DNA (mtDNA) is maternally inherited, meaning it is passed down from the mother to her offspring. This form of inheritance is non-Mendelian, as it does not follow the typical patterns of inheritance seen with nuclear DNA. The significance of mtDNA lies in its role in encoding essential components of the mitochondrial electron transport chain and ATP synthesis machinery. Although most mitochondrial proteins are encoded by nuclear DNA, mtDNA provides critical genes for mitochondrial function. Mutations in mtDNA can lead to mitochondrial diseases, highlighting its importance in cellular energy metabolism and overall health.

The chemiosmotic theory, proposed by Peter Mitchell, explains how ATP is generated in mitochondria. According to this theory, the electron transport chain creates a proton gradient across the inner mitochondrial membrane by pumping protons from the matrix to the intermembrane space. This gradient generates a proton motive force, which drives ATP synthesis as protons flow back into the matrix through ATP synthase. The chemiosmotic theory is crucial for understanding mitochondrial function because it links the processes of electron transport and ATP synthesis, providing a comprehensive explanation of how cells produce energy efficiently.