Golgi Apparatus

Learning Goals

By the end of this lesson, you will be able to:

• Explain the basic structures of the Golgi apparatus
• Describe the basic process of packaging and secretion of proteins and lipids

Key Vocabulary

• Golgi Apparatus – an organelle found in eukaryotic cells that plays a key role in the modification, sorting, and transport of proteins and lipids

• Cisternae – a flat structure located within the Golgi apparatus and in the endoplasmic reticulum that assists with the packaging of proteins

• Proteins – large, complex macromolecules that are responsible for the structure, function, and regulation of our cells and tissues

• Lipids – macromolecules that play many important roles such as providing energy to cells, protecting our organs, and helping to produce hormones

The Golgi Apparatus

The Golgi apparatus is a key organelle of our cells. The number of Golgi “bodies” there are in a cell is dependent on the function of that particular cell. This organelle is responsible for the modification, sorting, and transport of proteins and lipids within a cell. So, what does that mean?

Well, the word modification means change, so Golgi bodies are responsible for changes being made to proteins. Once proteins are delivered to the Golgi Apparatus, they may be modified. This could mean that a carbohydrate is added to the structure, or a particular amino acid is removed. These modifications are necessary to produce the specific shape and structure of the protein, so it can perform a specific job.

The Golgi Apparatus also sorts proteins based on their final destinations and helps facilitate their transport.

Golgi Apparatus Structure

The Golgi is composed of a series of flattened, stacked cisternae, which are membrane-bound structures. The cisternae are organized into three regions: the cis-Golgi, medial-Golgi, and trans-Golgi.

The cis-Golgi is the region closest to the endoplasmic reticulum (ER) and is responsible for receiving newly synthesized proteins and lipids from the ER. The cis-Golgi is characterized by its cis face, the side of the cisternae facing the ER, where the incoming proteins and lipids enter the Golgi Apparatus.

The medial-Golgi is the region between the cis-Golgi and trans-Golgi and is responsible for further modification of the proteins and lipids. The medial Golgi is characterized by specific enzymes that add carbohydrate and lipid modifications to the proteins and lipids. Once the proteins and lipids have been modified in the medial Golgi, they are transported to the trans-Golgi for sorting and packaging.

The trans-Golgi is the region farthest from the ER and is responsible for sorting and directing the modified proteins and lipids to their final destinations. The trans-Golgi is characterized by its trans face, which is the side of the cisternae facing away from the ER. This side has special sorting receptors that help direct specific proteins and lipids to where they need to go. Once the proteins and lipids are sorted, they are packaged into small containers called vesicles and sent to their final destination, such as the plasma membrane (for secretion) or lysosomes (for degradation). The trans face of the Golgi is important because it makes sure that the right proteins and lipids end up where they’re supposed to be inside the cell.

As you study, keep in mind these key details about the Golgi apparatus:

• The Golgi apparatus is an organelle found in eukaryotic cells that plays a key role in the modification, sorting, and transport of proteins and lipids.
• The Golgi is composed of a series of flattened, stacked cisternae, which are membrane-bound structures organized into three regions: the cis-Golgi, medial-Golgi, and trans-Golgi.
• Each of these sides has a specific role and characteristics:
  • the cis face, the side of the cisternae facing the Endoplasmic Reticulum (ER) which receives newly incoming proteins and lipids from the ER
  • the trans face, the side of the cisternae facing away from the ER, which sorts and directs the proteins and lipids to their final destinations

Quick Quiz Time!