Golgi apparatus

All living things are composed of cells. Within all cells are small, membrane-enclosed structures called organelles. Each organelle is designed for a specific function and purpose. The Golgi apparatus is a cellular organelle responsible for modifying and packaging cellular products and transporting them to where they need to go within the cell or outside the cell. When transported to the cell membrane, these products help repair damage as well as strengthen cell-to-cell communication.

The Golgi apparatus is part of an elaborate arrangement of organelles called the endomembrane system. The entire system works together to construct proteins and lipids and then transport them to their final destination. Like most organelles within the cell, the Golgi cannot operate on its own. It requires cooperation from other organelles so that it can perform its functions as efficiently as possible.

Brief History

It was in 1898 that the Golgi apparatus was formally discovered as an organelle within cells. The first person to report its existence was Camillo Golgi, a biologist from Italy whose primary area of focus was the nervous system. While researching nerve cells and their functions, he noticed a small, reticular object located within the inner part of the cell.

Golgi later concluded that the same structure could be found in many different types of cells. It would be a long time before Golgi’s claims would be accepted within the scientific community. The birth of electron microscopy in the 1930s helped to settle the Golgi debate. Electron microscopes allowed scientists to confirm the existence of the Golgi apparatus within cells. Golgi’s contributions greatly impacted biomedical sciences in the twentieth century.

Overview

The Golgi apparatus is often referred to as the Golgi body, and if one were to take a look at a eukaryotic cell underneath a microscope, this organelle would look like a sack of flattened pancakes. The region of the Golgi that is closest to the nucleus, where DNA is housed, is called the cis face, while the side furthest away from the nucleus is called the trans face. Whenever a protein arrives at this organelle, it is pushed through the center of the Golgi, where it is modified in various ways—like adding a sugar to it for example—followed by shipping it off to other parts of the cell.

Before it reaches the Golgi apparatus, a protein molecule is first built by a ribosome. The protein then passes through the endoplasmic reticulum, which continues the assembly process, including the crucial step of recognizing the protein’s destination tag. After this, the protein is sealed in a vesicle and carried to the cis face of the Golgi body. The modified protein cannot simply enter the Golgi—it needs to fuse with the cis face membrane before gaining access to the lumen of the Golgi, where it will be further modified.

Molecules brought to the Golgi for modification and transport enter on the cis face side of the organelle. Next they proceed to the Golgi stack, the main processing area within the organelle. When viewed under a microscope, the stack looks like several flattened sacs (called cisternae) all folded in on one another. It is here that the molecules receive the bulk of their modifications. The Golgi packs protein molecules in something called a transport vesicle. A transport vesicle could be compared to an envelope that you would mail a letter in. They provide the protein with protection from the outside environment. The molecules then exit through the trans Golgi network. Here, a few more final reactions take place before the molecules are sealed into transport vesicles and shipped off to where they need to go within the cell.

Once molecules have been modified within the Golgi apparatus, their final destination is the cell membrane, where they help repair damage and promote signaling between cells. Other molecules are transported outside of the cell. This is accomplished when the transport vesicle carrying the modified molecule fuses with the cell membrane, releasing the product outside of the cell.

Aside from synthesizing molecules and shipping them to where they need to go, the Golgi is also responsible for a number of other functions within the cell. For instance, it is responsible for the production of lysosomes. A lysosome is an organelle within the cell that recycles cellular waste and thus helps keeps cellular function at optimal levels. Hence, a working Golgi apparatus is indirectly responsible for ensuring that cellular waste does not accumulate to a dangerous level within the cell.

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