Golgi apparatus

The Golgi apparatus, also called the Golgi complex, Golgi body, or simply the Golgi, is a tiny structure inside most eukaryotic cells. It is part of the endomembrane system and lives in the cytoplasm. Its main job is to package proteins into tiny bags called membrane-bound vesicles, which then travel to where they are needed in the cell.

The Golgi apparatus is very important because it helps prepare proteins for secretion. It has special tools called glycosylation enzymes that add sugar pieces to proteins as they move through it.

This important structure was first seen in 1898 by an Italian scientist named Camillo Golgi. Later, in the 1910s, it was named after him.

Discovery

The Golgi apparatus was one of the first tiny parts inside cells to be found and studied. An Italian doctor named Camillo Golgi discovered it in 1898 while looking at the nervous system. He saw it through his microscope and called it the "internal reticular apparatus." At first, some people thought it might just be a trick of the microscope. But as better microscopes were made in the 1900s, scientists confirmed that the Golgi apparatus really exists. Over time, it was called by different names before settling on "Golgi apparatus."

Subcellular localization

The Golgi apparatus can be found in different places inside cells depending on the type of cell. In animals, there is usually one Golgi apparatus close to the center of the cell, near a special area called the centrosome. In yeast cells, many smaller Golgi apparatuses are spread out. In plant cells, the Golgi stacks are not gathered in one spot and do not form ribbons. What they all have in common is that they are next to areas where the endoplasmic reticulum sends out material.

Structure

In most cells, the Golgi apparatus is made of a series of compartments formed from flattened, disk-like structures called cisternae. These come from small groups of bubbles that break off from another part of the cell called the endoplasmic reticulum. A typical animal cell has about 40 to 100 stacks of these disks, with each stack usually containing between four and eight cisternae.

The Golgi is divided into different parts, called the cis Golgi network and the trans Golgi network. The cis part is where the process starts, and the trans part is where it ends, packing proteins into small bags called vesicles. These vesicles then carry proteins to other parts of the cell or to the outside.

The size and number of Golgi structures can vary depending on the cell. For example, cells that make and release a lot of substances, like certain immune cells, have larger and more noticeable Golgi structures. Each stack of cisternae has an entry side and an exit side, and they contain special enzymes that change the proteins in specific ways, helping decide where each protein goes next.

Function

The Golgi apparatus is like a busy post office inside cells. It takes proteins made in a part of the cell called the endoplasmic reticulum and puts them into small packages called vesicles. These vesicles then join the Golgi apparatus, where the proteins are changed and prepared for their next journey. Some proteins are sent out of the cell, while others stay inside to help the cell work.

The Golgi apparatus also helps move fats called lipids and makes special parts of the cell called lysosomes. It changes proteins in many ways, adding sugar molecules and other groups to them. These changes help the proteins know where to go next in or around the cell. The Golgi also helps build important molecules called proteoglycans that are found outside the cell.

Vesicular transport

The tiny bags of material that leave the part of the cell called the rough endoplasmic reticulum move to the cis face of the Golgi apparatus. There, they join with the Golgi's membrane and let their contents inside.

Once inside, the molecules get changed and then sorted to go to their next places in the cell.

These proteins that need to go to places outside the endoplasmic reticulum or the Golgi move through the Golgi towards the trans face. There, they reach a special area called the trans-Golgi network (TGN). This is where proteins are sorted and sent to where they need to go, placed into different types of bags based on the signals they carry.

Current models of vesicular transport and trafficking

In cell theory, scientists are still trying to figure out exactly how proteins move through the Golgi apparatus. There are several models that try to explain this process.

One model suggests the Golgi is made of stable sections, each with special enzymes that change proteins. Proteins move from one section to the next using tiny bags called vesicles. Another model suggests these sections form and change over time, with proteins moving as the sections mature. A newer model thinks the Golgi has stable sections controlled by special proteins called Rab GTPases. Each model has strengths and weaknesses, and scientists are still working to understand how proteins move through the Golgi.

Brefeldin A

Brefeldin A (BFA) is a substance made by fungi that scientists use to study how the Golgi apparatus works. When added to cells, BFA stops some important proteins from working properly. This causes the Golgi apparatus to break apart and its proteins to move to other parts of the cell. This helps researchers learn more about how cells send out materials.