**Question:** Secretory proteins are synthesized in:

**Core Concept:** Secretory proteins are proteins produced and secreted by specialized cells, primarily involved in the defense mechanism of the body. They are synthesized in specific cell organelles.

**Why the Correct Answer is Right:** Secretory proteins are synthesized in the **Endoplasmic Reticulum (ER)** and **Golgi apparatus**. These organelles are crucial for protein folding, modification, and packaging before they are transported to their final destinations, such as lysosomes, plasma membrane, or extracellular space.

**Why Each Wrong Option is Incorrect:**

A. Mitochondria: Mitochondria are responsible for cellular respiration and energy production, not protein synthesis.
B. Lysosomes: Lysosomes contain enzymes for cellular digestion and waste disposal, not protein synthesis.
C. Plasma membrane: Plasma membrane proteins are generated in the ER and Golgi apparatus, but they are not secretory proteins.
D. Plasma membrane: Plasma membrane proteins are generated in the ER and Golgi apparatus, but they are not secretory proteins.

**Clinical Pearl / High-Yield Fact:** The **Golgi apparatus** plays a significant role in post-translational modifications of proteins, including glycosylation, phosphorylation, and sulfation, which are crucial for protein function, stability, and localization.

**Correct Answer:** Secretory proteins are synthesized in the **Endoplasmic Reticulum (ER)** and **Golgi apparatus**.