Understanding Gibbs Free Energy Changes in Cellular Respiration

Hard Biochemistry Bioenergetics

In cellular respiration, organisms convert biochemical energy from nutrients into adenosine triphosphate (ATP), which is then used to power cellular activities. Glycolysis is the first step in this process, occurring in the cytosol, and it produces a small yield of ATP through substrate-level phosphorylation. Following glycolysis, pyruvate enters the mitochondria where it undergoes further processing to enter the citric acid cycle (CAC). A key step in this pathway is the conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex (PDC).

One of the critical aspects of bioenergetics is understanding how these metabolic processes relate to changes in Gibbs free energy (ΔG). A significant portion of the total available energy from the complete oxidation of glucose is captured from glycolysis and is subsequently used in oxidative phosphorylation. During the electron transport chain, electrons derived from NADH and FADH₂ are transferred through a series of protein complexes, resulting in the pumping of protons across the mitochondrial membrane and creating an electrochemical gradient.

Which of the following statements correctly describes a fundamental principle of bioenergetics based on the processes discussed?

The exergonic reaction of substrate-level phosphorylation directly produces ATP without the involvement of the electron transport chain.

The conversion of glucose to pyruvate in glycolysis increases the total entropy of the system.

The Gibbs free energy change (ΔG) of a reaction can be influenced by both the concentration of reactants and products.

Oxidative phosphorylation yields a greater amount of ATP than substrate-level phosphorylation, but does not require an electrochemical gradient.

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