**Question:** Highest amount of protein is seen in: (1987)

**Core Concept:** Protein synthesis and distribution in cells and tissues.

**Why the Correct Answer is Right:** The correct answer, **Option D:** Mitochondria, refers to the organelle responsible for cellular respiration and energy production. Within mitochondria, there is a specific structure called the mitochondrial matrix where proteins are synthesized through the process of translation. The mitochondrial matrix plays a crucial role in maintaining cellular structure and function, as well as performing essential biochemical reactions.

**Why Each Wrong Option is Incorrect:**

A. Nucleus (Option A): While the nucleus does contain DNA that codes for proteins, proteins are synthesized in the mitochondrial matrix rather than directly within the nucleus.

B. Ribosome (Option B): Ribosomes are the sites of protein synthesis, but they are found in the cytoplasm, not specifically in mitochondria.

C. Mitochondria (Option C): While mitochondria are involved in protein synthesis, the correct answer focuses on the mitochondrial matrix where proteins are synthesized, not the entire organelle.

**Why Option D is Right:** Proteins synthesized in the mitochondrial matrix are essential for maintaining mitochondrial function, including enzymes involved in the Krebs cycle and oxidative phosphorylation. These proteins contribute to ATP (adenosine triphosphate) production, which is crucial for cellular energy supply.

**Clinical Pearl / High-Yield Fact:** The high protein content in mitochondria is especially important in tissues with high energy demands, such as cardiac and skeletal muscles, where ATP production is vital for maintaining contractile function. This is particularly relevant in understanding the cellular basis of muscle fatigue and its relation to mitochondrial protein content.

**Correct Answer:** Mitochondria