What is the Golgi Apparatus?
The Golgi apparatus is a stack of flattened membrane sacs (cisternae) that receives proteins and lipids from the endoplasmic reticulum, modifies them, and packages them into vesicles for delivery to their final destinations.
The Golgi apparatus is the cell's 'post office' — it modifies, sorts, and packages proteins and lipids received from the ER into vesicles bound for the plasma membrane, lysosomes, or secretion.
- 1↓Cis face receivesTransport vesicles from the ER fuse with the cis (entry) face.
- 2↓ModificationEnzymes add sugars (glycosylation) and tag proteins as they move through the cisternae.
- 3↓SortingThe trans face sorts proteins by their final destination signal.
- 4↓Vesicle buddingFinished proteins are packaged into vesicles that bud off the trans face.
- 5DeliveryVesicles travel to the plasma membrane, lysosomes, or are secreted outside the cell.
Step-by-step worked examples
An antibody protein is finished being processed by the ER. Trace its path through the Golgi to secretion.
The vesicle carrying the antibody fuses with the cis face of the Golgi. As it moves through the cisternae, enzymes glycosylate and finish folding it. At the trans face it's sorted and packaged into a secretory vesicle that fuses with the plasma membrane to release the antibody outside the cell.
A digestive enzyme needs to end up inside a lysosome. How does the Golgi direct it there?
The enzyme enters the Golgi at the cis face and is tagged with a mannose-6-phosphate marker. The trans face recognizes this tag during sorting. The enzyme is packaged into a vesicle that becomes (or fuses with) a lysosome.
A cell needs to build new plasma membrane proteins. What role does the Golgi play?
Membrane proteins arrive from the ER and pass through the Golgi stack for modification. The Golgi sorts them by their destination signal for the plasma membrane. Vesicles bud off and fuse with the plasma membrane, inserting the new proteins.
Flashcards
Quick quiz
Q1.Which face of the Golgi receives material from the ER?
Q2.What happens to proteins as they move through the Golgi cisternae?
Q3.Where do finished vesicles leave the Golgi from?
Q4.A protein tagged with mannose-6-phosphate in the Golgi is most likely headed to…
The full card deck, worked steps and AI-tutor support for “What is the Golgi Apparatus?” are in Notek — study by hand before your exam.
Common mistakes
The Golgi apparatus makes proteins from scratch. — Correct: It modifies and packages proteins already made by ribosomes on the rough ER.
The cis and trans faces are interchangeable. — Correct: The cis face receives from the ER; the trans face ships vesicles out — direction matters.
All Golgi vesicles are secreted outside the cell. — Correct: Many are directed to lysosomes or the plasma membrane, not just secretion.
The Golgi is a single sac. — Correct: It's a stack of several flattened cisternae.
FAQ
What is the Golgi apparatus?
An organelle made of stacked membrane sacs that modifies, sorts, and packages proteins and lipids received from the ER.
What is the function of the Golgi apparatus?
It glycosylates and finishes proteins, then sorts them into vesicles addressed to the plasma membrane, lysosomes, or secretion.
What are examples of Golgi apparatus function?
Packaging antibodies for secretion, tagging digestive enzymes for lysosomes, and preparing membrane proteins for the cell surface.
How does the Golgi apparatus work with the endoplasmic reticulum?
It receives vesicles from the ER at its cis face, processes the contents, then ships them out from its trans face.