Answer and Explanation:
When mRNA leaves the nucleus and meets a free ribosome in the cytosol, it starts the protein building. Ribosomes read the mRNA code and begin protein synthesis by adding the correct amino acid using transference RNA.
Ribosomes attached to the RER membrane are responsible for synthesizing membrane proteins, exportation proteins, or enzymes.
The synthesis of proteins destined to become enzymes, membrane proteins, or exportation proteins starts in the cytoplasm with the production of a molecule portion known as a signal aminoacidic sequence. This signal sequence in the amino extreme of the synthesizing protein, and when it reaches a certain length, it meets the signal recognizing particle that leads the synthesizing protein and associated ribosome to the Rough endoplasmic reticulum, where it continues the protein building until finishing the elongation process. When the new protein synthesis is complete, the polypeptide is released into the reticulum lumen, suffering a few posterior steps related to conformation and structure, such as folding to become functional and the initial glycosylation stages.
The new proteins get packaged into vesicles that carry them to the Golgi complex where occurs the final association of carbohydrates and lipids with proteins, to originate glycoproteins and glycolipids.
Enzymes destined for exportation are packaged and sent from the Golgi complex to the cell membrane into vesicles. When the secretory vesicle reaches the target, its membrane fuses with the cell membrane, releasing its content to the extracellular space. This secreting process is known as exocytosis.
