Endoplasmic Reticulum- The vesicular network starts from nuclear membrane and spread throughout the cytosol constitutes endoplasmic reticulum (Figure 4.4). There are two different types of endoplasmic reticuli present in the cell, 1) Rough endoplasmic reticulum (RER), and 2) smooth endoplasmic reticulum (SER). RER has ribosome attached to it to give a rough appearance whereas smooth endoplasmic reticulum is devoid of ribosomes. Protein synthesis on ribosome attached to RER are sorted into 3 different catagories, such as integral membrane proteins, proteins for secretion and protein destined for different organelles. Proteins are synthesized with a n-signal peptide and these signal peptides are recognized by signal recognition particle on their the target organelles. For example, if a protein is synthesized with a signal peptide for mitochondria, it will attach to signal recognition particle and receptor onto the outer mitochondrial membrane to deliver the protein. The proteins without any signal peptide tags are supposed to remain in the cytsol.

Functions of endoplasmic reticulum:

1. Synthesis of steroid hormone in gonad cells.
2. Detoxification
3. Ca²⁺ sequestration
4. Synthesis of protein, phospholipid and carbohydrate.
5. Protein sorting to different organelles.
6. Protein modifications such as glycosylation etc.

Golgi Bodies- Golgi bodies were first visualized by a metallic stain invented by Camillo golgi and it is made of flattend, disk like cisternae arranged in a stacked manner to give 3 distinct zones (Figure 4.5). Cis-face receives material or vesicles from endoplasmic reticulum, medial Golgi is the actual place where protein are covalently modified with the sugar. Trans Golgi is the face of Golgi towards plasma membrane and this site sorts vesicle for their destined organelles or plasma membrane.

Functions of golgi bodies

1. Protein sorting
2. Protein modifications (Glycosylation)
3. Proteolysis