A pancreas cell makes proteins (enzymes) that it releases to the small intestine. Which of the following best describes the path of these proteins from synthesis to exocytosis at the pancreatic cell's plasma membrane (PM)? a. Golgi → rough ER → PM, b. smooth ER → Golgi → lysosome → PM, c. rough ER → Golgi → PM, d. nucleus → Golgi → PM.

Verified step by step guidance

1. Step 1: Understand where protein synthesis occurs in the cell. Proteins, especially enzymes, are synthesized by ribosomes attached to the rough endoplasmic reticulum (rough ER), not the smooth ER or Golgi apparatus.
2. Step 2: Recognize the role of the rough ER. After synthesis, proteins enter the rough ER where they undergo initial folding and modifications.
3. Step 3: Identify the next organelle in the pathway. Proteins are then transported from the rough ER to the Golgi apparatus for further processing, sorting, and packaging.
4. Step 4: Determine the final destination before secretion. After processing in the Golgi, proteins are packaged into vesicles that move to the plasma membrane (PM) for exocytosis.
5. Step 5: Eliminate incorrect options based on organelle functions. For example, the nucleus is not directly involved in protein transport, and lysosomes are for degradation, not secretion. Therefore, the correct path is rough ER → Golgi → PM.

Key Concepts

Protein Synthesis in the Rough Endoplasmic Reticulum (Rough ER)

Proteins destined for secretion are synthesized by ribosomes attached to the rough ER. This organelle provides a site for folding and initial modifications of these proteins before they are transported to the Golgi apparatus.

Role of the Golgi Apparatus in Protein Processing and Sorting

The Golgi apparatus modifies, sorts, and packages proteins received from the rough ER. It directs proteins to their final destinations, such as secretion outside the cell via vesicles that fuse with the plasma membrane.

Exocytosis and Protein Secretion

Exocytosis is the process by which vesicles containing proteins fuse with the plasma membrane, releasing their contents outside the cell. This is essential for pancreatic cells to secrete enzymes into the small intestine.