From DNA to Secretory Protein: A Journey Inside the Cell

How is a secretory protein processed in a cell?

Answer: D. Describe, using labeled diagrams and words the steps that occur as a secretory protein is processed from the DNA to mRNA to protein, including how it is inserted into the rough endoplasmic reticulum, then further modified and sorted by the Golgi apparatus, transported and finally secreted by the cell.

Secretory Protein Synthesis Process

Secretory proteins are synthesized beginning with DNA transcription in the nucleus, followed by their translation in the rough endoplasmic reticulum (RER), modification and sorting in the Golgi apparatus, and finally secretion outside the cell via exocytosis.

Explanation:

The process of secreting a protein begins with the transcription of DNA into mRNA in the nucleus. During this process, segments known as introns are removed, and the remaining exons are spliced together to form a mature mRNA strand. This mRNA strand exits the nucleus and attaches to a ribosome on the RER, where translation into a protein occurs.

The growing peptide chain enters the RER lumen, where a signal peptide guides the emerging protein into the RER. Once inside the RER, proteins undergo modifications, such as glycosylation.

Next, the protein is packaged into vesicles and transported to the Golgi apparatus via microtubules. Here, it undergoes further modifications and is properly sorted. Eventually, the protein is targeted to the correct destination, encapsulated in vesicles, which bud from the Golgi's trans face. These vesicles are then transported to the plasma membrane, where they will either become part of the membrane or release their contents outside the cell through exocytosis.