The Golgi apparatus is an organelle found in eukaryotic cells that modifies, sorts, and packages molecules for use inside or outside the cell. It is especially important for proteins and lipids that come from the endoplasmic reticulum. Because many cell products must be delivered to exact destinations, the Golgi acts like a cellular processing and shipping center.
Without it, secretion, membrane renewal, and many enzyme deliveries would not work correctly.
The Golgi is made of stacked, flattened membrane sacs called cisternae, with a receiving side called the cis face and a shipping side called the trans face. Transport vesicles bring newly made proteins and lipids to the cis face, where enzymes begin modifying them. As molecules move through the cisternae, they may be tagged with sugars or other chemical groups, then sorted at the trans face into new vesicles.
These vesicles can deliver cargo to the plasma membrane, lysosomes, secretory granules, or other parts of the cell.
Key Facts
- The Golgi apparatus is a membrane-bound organelle in eukaryotic cells.
- Cisternae are the flattened membrane sacs that form the Golgi stack.
- The cis face receives vesicles from the endoplasmic reticulum.
- The trans face sorts and ships modified molecules in vesicles.
- Secretory pathway: ER to Golgi to vesicle to plasma membrane or target organelle.
- A common Golgi modification is glycosylation, where sugars are added to proteins or lipids.
Vocabulary
- Golgi apparatus
- A eukaryotic organelle that modifies, sorts, and packages proteins and lipids for transport.
- Cisterna
- One flattened membrane sac within the Golgi apparatus.
- Cis face
- The receiving side of the Golgi apparatus where vesicles from the endoplasmic reticulum arrive.
- Trans face
- The shipping side of the Golgi apparatus where molecules are sorted into outgoing vesicles.
- Vesicle
- A small membrane-bound sac that transports materials within or out of a cell.
Common Mistakes to Avoid
- Calling the Golgi the place where most proteins are made is wrong because ribosomes build proteins, often on the rough endoplasmic reticulum, while the Golgi mainly modifies and sorts them.
- Mixing up the cis and trans faces is wrong because the cis face receives incoming vesicles and the trans face sends outgoing vesicles to their destinations.
- Thinking vesicles move randomly is wrong because many vesicles carry targeting signals and follow organized routes through the secretory pathway.
- Assuming the Golgi handles only proteins is wrong because it also processes lipids and helps form some carbohydrate-rich molecules.
Practice Questions
- 1 A protein is made on a ribosome attached to the rough ER. List the next three major steps it may take to be secreted outside the cell.
- 2 A Golgi stack has 6 cisternae. If a diagram shows 4 vesicles arriving at the cis face and 7 vesicles leaving the trans face, how many total vesicles are shown interacting with the Golgi?
- 3 In a cell, 120 proteins enter the Golgi. If 50 are sent to the plasma membrane, 30 are sent to lysosomes, and the rest are secreted outside the cell, how many proteins are secreted?
- 4 A mutation disrupts enzymes that add sugar groups to proteins in the Golgi. Explain how this could affect protein function or delivery.