Why must NADH be reoxidized? How does this happen in an organism that uses respiration? Fermentation?

Verified step by step guidance

1. Understand the role of NADH in cellular metabolism: NADH is a crucial electron carrier in metabolic pathways, such as glycolysis and the citric acid cycle, where it is produced by the reduction of NAD+.
2. Recognize the need for NADH reoxidation: NADH must be reoxidized to NAD+ to ensure a continuous supply of NAD+ for glycolysis and other metabolic processes, allowing the cell to produce ATP efficiently.
3. Explore reoxidation in respiration: In organisms using aerobic respiration, NADH is reoxidized in the electron transport chain, where it donates electrons to the chain, ultimately reducing oxygen to water and regenerating NAD+.
4. Examine reoxidation in fermentation: In anaerobic conditions, organisms use fermentation to reoxidize NADH. For example, in lactic acid fermentation, NADH donates electrons to pyruvate, forming lactate and regenerating NAD+.
5. Compare the efficiency: Respiration is more efficient in ATP production compared to fermentation, as the electron transport chain allows for a greater yield of ATP per molecule of glucose oxidized.

Key Concepts

Role of NADH in Metabolism

NADH is a crucial electron carrier in cellular metabolism, particularly in glycolysis and the citric acid cycle. It functions by accepting electrons during the oxidation of substrates, thus becoming reduced to NADH. This reduction is essential for the continuation of metabolic pathways, as NADH must be reoxidized to NAD+ to allow glycolysis to proceed and to maintain the flow of electrons through the electron transport chain.

Reoxidation of NADH in Respiration

In organisms that utilize respiration, NADH is reoxidized primarily through the electron transport chain located in the inner mitochondrial membrane. Here, NADH donates electrons, which are transferred through a series of protein complexes, ultimately leading to the reduction of oxygen to water. This process not only regenerates NAD+ but also drives ATP synthesis via oxidative phosphorylation, making it a highly efficient energy-producing mechanism.

Reoxidation of NADH in Fermentation

In fermentation, NADH is reoxidized through substrate-level phosphorylation and the conversion of pyruvate into various end products, such as lactic acid or ethanol. This process allows for the regeneration of NAD+ without the need for an electron transport chain, enabling glycolysis to continue in anaerobic conditions. Fermentation is less efficient than respiration in terms of ATP yield but is vital for organisms that thrive in low-oxygen environments.