During which of the following processes is ATP produced?

• A. Citric acid cycle (Krebs cycle)
• B. Glycolysis
• C. Electron transport chain and oxidative phosphorylation
• D. Transcription

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the processes listed in the problem. ATP (adenosine triphosphate) is the primary energy currency of the cell, and its production is a key feature of cellular respiration. Cellular respiration includes glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain coupled with oxidative phosphorylation.
2. Step 2: Analyze glycolysis. Glycolysis occurs in the cytoplasm and involves the breakdown of glucose into pyruvate. During this process, ATP is produced directly through substrate-level phosphorylation. This is one of the pathways where ATP is generated.
3. Step 3: Examine the citric acid cycle (Krebs cycle). This cycle occurs in the mitochondrial matrix and generates high-energy electron carriers (NADH and FADH2) that are used later in the electron transport chain. While ATP is produced in small amounts via substrate-level phosphorylation during this cycle, its main role is to provide electron carriers for further ATP production.
4. Step 4: Investigate the electron transport chain and oxidative phosphorylation. This process occurs in the inner mitochondrial membrane. Electrons from NADH and FADH2 are transferred through protein complexes, creating a proton gradient. ATP is then synthesized by ATP synthase as protons flow back into the mitochondrial matrix, a process called chemiosmosis.
5. Step 5: Clarify transcription. Transcription is the process of synthesizing RNA from a DNA template. It does not involve ATP production as it is not part of cellular respiration. Therefore, transcription is not a correct answer to the question.