Advanced Placement (AP) Biology Practice Exam

Which metabolic pathway is responsible for acetyl-CoA processing?

1. Glycolysis

2. Krebs cycle

3. Fermentation

4. Calvin cycle

The correct answer is: Krebs cycle

The Krebs cycle, also known as the citric acid cycle, is the metabolic pathway responsible for processing acetyl-CoA. Acetyl-CoA is a central metabolite derived from carbohydrates, fats, and proteins. When carbohydrates are broken down through glycolysis, the resulting pyruvate is converted into acetyl-CoA before entering the Krebs cycle. This cycle occurs in the mitochondria and plays a crucial role in cellular respiration, as it not only processes acetyl-CoA but also generates electron carriers, NADH and FADH2, and releases carbon dioxide as a waste product. Through a series of enzymatic reactions, the Krebs cycle leads to the production of ATP and provides precursors for various biosynthetic pathways. It is a vital step in aerobic respiration, linking the breakdown of organic fuels to the production of energy in the form of ATP. Understanding the role of the Krebs cycle is essential for grasping how cells convert energy from food into a usable form, underlining its importance in metabolic processes.