Refer to the diagram of the citric acid cycle in Figure 12.11 to answer each of the following:


c. Name the reaction that is coupled to GTP formation.

Verified step by step guidance

1. Identify the step in the citric acid cycle where GTP is formed. This occurs during the conversion of succinyl-CoA to succinate.
2. Understand that the formation of GTP is an example of substrate-level phosphorylation, where a phosphate group is directly transferred to GDP to form GTP.
3. Recognize that the enzyme responsible for this reaction is succinyl-CoA synthetase, which catalyzes the conversion of succinyl-CoA to succinate.
4. Note that this reaction involves the hydrolysis of the thioester bond in succinyl-CoA, releasing energy that is used to form GTP from GDP and inorganic phosphate.
5. Conclude that the reaction coupled to GTP formation is the conversion of succinyl-CoA to succinate, catalyzed by succinyl-CoA synthetase.

Key Concepts

Citric Acid Cycle

The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. It takes place in the mitochondria and involves the oxidation of acetyl-CoA to produce ATP, NADH, and FADH2, which are crucial for cellular respiration. Understanding this cycle is essential for identifying specific reactions and their roles in energy production.

GTP Formation

GTP (guanosine triphosphate) is a nucleotide similar to ATP and serves as an energy currency in the cell. In the citric acid cycle, GTP is produced through substrate-level phosphorylation, specifically during the conversion of succinyl-CoA to succinate. Recognizing the conditions and enzymes involved in GTP formation is vital for answering questions related to energy metabolism.

Coupled Reactions

Coupled reactions occur when an energetically unfavorable reaction is driven by an energetically favorable one, allowing the overall process to proceed. In the context of the citric acid cycle, the reaction that produces GTP is coupled with the hydrolysis of succinyl-CoA, which releases energy. Understanding this coupling is important for grasping how energy is efficiently transferred and utilized in metabolic pathways.