**Question:** Cori's cycle is concerned with transport of -

A. Glucose
B. Lactate
C. Pyruvate
D. Amino acids

**Correct Answer:** C. Pyruvate

**Core Concept:** Cori's cycle, also known as the citric acid cycle or Krebs cycle, is an essential process in cellular respiration that occurs within the mitochondria. It is responsible for producing ATP (adenosine triphosphate), NADH (nicotinamide adenine dinucleotide), and FADH2 (flavin adenine dinucleotide), which are crucial coenzymes involved in the electron transport chain and ultimately lead to the generation of energy in the form of ATP.

**Why the Correct Answer is Right:** Cori's cycle primarily involves the transport and conversion of pyruvate, which is derived from glycolysis, into acetyl-CoA. This process occurs in the mitochondria, where pyruvate is oxidized, generating CO2, H2O, NADH, and FADH2. The cycle is regulated by various enzymes, including pyruvate dehydrogenase and citrate synthase.

**Why Each Wrong Option is Incorrect:**

A. Glucose (6-carbon sugar) is not involved in Cori's cycle directly. It is the intermediate product of glycolysis, which is the initial step preceding the cycle.
B. Lactate (3-carbon sugar) is also not a key component of Cori's cycle. Lactate arises from anaerobic conditions, while Cori's cycle occurs in aerobic conditions, typically in the presence of oxygen.
D. Amino acids are not the main focus of Cori's cycle. While some amino acids can be oxidized in the cycle, the primary substrate is pyruvate derived from glucose.

**Clinical Pearl:** Understanding the role of Cori's cycle in cellular respiration is essential for medical students, as it contributes to generating energy for the cell and maintaining the redox balance within the mitochondria. Adequate knowledge of this process is also crucial for interpreting laboratory values, as it can help diagnose diseases affecting cellular respiration, such as pyruvate dehydrogenase complex deficiency, which leads to lactic acidosis and ketosis, a condition known as lactic acidosis.