Number of ATPs formed per cycle of TCA –

**Core Concept**
The Tricarboxylic Acid (TCA) cycle, also known as the Citric Acid cycle or Krebs cycle, is a key metabolic pathway that generates energy through the oxidation of acetate derived from carbohydrates, fats, and proteins into carbon dioxide and water. The **TCA cycle** is a crucial step in cellular respiration, taking place in the **mitochondrial matrix**. It produces **NADH** and **FADH2** as by-products, which are then used in the electron transport chain to generate **ATP**.

**Why the Correct Answer is Right**
In one cycle of the TCA cycle, three **NAD+** molecules are reduced to **NADH**, one **FAD** molecule is reduced to **FADH2**, and one **GTP** molecule is produced, which is equivalent to one **ATP**. The **NADH** and **FADH2** molecules then donate electrons to the electron transport chain. Each **NADH** results in approximately 2.5 **ATP** molecules, and each **FADH2** results in approximately 1.5 **ATP** molecules. Therefore, the total number of **ATP** molecules produced per cycle is calculated as follows: (3 **NADH** * 2.5 **ATP/NADH**) + (1 **FADH2** * 1.5 **ATP/FADH2**) + 1 **GTP** (or **ATP**) = 7.5 + 1.5 + 1 = 10 **ATP**.

**Why Each Wrong Option is Incorrect**
**Option A:** This option underestimates the yield of **ATP** from **NADH** and **FADH2**.
**Option B:** This option does not account for the **GTP** (or **ATP**) produced directly in the cycle.
**Option D:** This option overestimates the yield, not aligning with the electron transport chain's efficiency.

**Clinical Pearl / High-Yield Fact**
The TCA cycle is a critical energy-producing pathway, and its dysregulation can lead to various metabolic disorders. Understanding the **ATP** yield per cycle is essential for appreciating the energy metabolism in cells.

**Correct Answer:** B. 10