In Part 5 of the Simple Cell series, we took a look at the endoplasmic reticulum and how they were involved with the production of proteins and then sending them on their way through the cell’s FedEx delivery system. In Part 6, we are going to look at the Golgi apparatus which works hand-in-hand with the endoplasmic reticulum and the FedEx delivery system.
The Golgi apparatus also known as the Golgi body was named after its discoverer, Camillo Golgi, an Italian physicist who first identified the organelle in 1898.
Golgi bodies are usually found near the rough endoplasmic reticulum in the cell. They are comprised of a stack of membrane structures known as cisternae.
There are four structural parts to the cisternae: the cis-Golgi, endo-Golgi, medial-Golgi and the trans-Golgi. Each of the different areas of the Golgi cisternae contains different types of enzymes which control a large variety of functions. The cis-Golgi is the section nearest to the endoplasmic reticulum and it is where the Golgi apparatus first receives the cargo vesicles containing the newly synthesized proteins. Most of the various functions of the Golgi apparatus occur as the cargo proteins pass through the endo-Golgi and medial-Golgi sections. Eventually, they end up at the trans-Golgi, located at the opposite end from the cis-Golgi. This is where the finished product is packaged for transportation to the rest of the cell.
The main overall function of the Golgi apparatus is to take the proteins that are manufactured in the endoplasmic reticulum, process them according to specific needs and then send them on to their destinations. These functions include:
- Processes such as phosphorylation and glycosylation are used to modify the various cargo proteins received from the endoplasmic reticulum.
- Nucleotide sugars are imported from the cytosol and used in the phosphorylation and glycosylation processes.
- Production of polysaccharides and glycosaminoglycans to be used in the manufacturing of carbohydrates. Some of the glycosaminoglycans are used elsewhere to form parts of connective tissues.
- Synthesis of proteoglycans by attaching the long non-branched polysaccharides and glycosaminoglycans to some proteins.
- Some cargo proteins are broken down into smaller actively functioning fragments.
- The addition of sulfate groups to some proteins via the help of sulfotransferases. This gives the molecule a negative charge which is an important part of the signaling properties of the molecule.
- The addition of phosphate groups to some proteins.
- Formation of lysosomes for the transportation of lipids to other parts of the cell.
- Formation of core proteins by the polymerization of the glycosaminoglycans.
- The Bcl-2 gene present in the Golgi apparatus plays an important roll in the prevention of apoptosis.
Basically, the Golgi apparatus serves as a processing plant for the products manufactured by the endoplasmic reticulum. It works kind of like the steel industry. The endoplasmic reticulum would be compared to the companies that take the iron ore and combine it with just enough carbon to produce steel. The Golgi apparatus then takes the steel and ads various other elements such as manganese, chromium, vanadium, and tungsten to produce varying forms and grades of steel. Only in the Golgi apparatus, they add sulfates, polysaccharides, phosphates and other molecules to the proteins. It then packages all of the different proteins and ships them out to their various destinations via the FedEx system discussed last week, just like steel products are packaged and shipped to other companies.
Now let’s sum up what we have learned about the cell so far. First they have hundreds of membrane bound proteins that pump things into the cell and other things out of the cell. Then there is the cytoskeleton that acts very much like the infrastructure of a city transporting things in every direction in a very coordinated system. Next were the dynein and kinesin molecules that walk along the microtubules. Then we saw the endoplasmic reticulum that manufactures proteins and acts as a FedEx system to send them throughout the cell. And today, we saw how the Golgi apparatus takes the proteins from the endoplasmic reticulum and process them further for a myriad of specific functions like a steel processing plant.
The more we look into the cell, the more it starts to look like a number of interrelated industries that all work together and far more efficiently than any human industry we see today. And to think that evolutionists still believe that all of this came about by random chance processes. Kind of makes you look at them and say, “Duh!”
Apoptosis – a form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area.
Glycosaminoglycans – any of a group of high molecular weight linear polysaccharides with various disaccharide repeating units and usually occurring in proteoglycans, including the chondroitin sulfates, dermatan sulfates, heparan sulfate and heparin, keratan sulfates, and hyaluronic acid.
Glycosylation – the addition of glycosyl groups to a protein to form a glycoprotein.
Phosphorylation – the addition of phosphate to an organic compound through the action of a phosphorylase or kinase enzyme.
Polymerization – the chaining together of similar molecules to form a compound of high molecular weight.
Polysaccharides – any of a class of carbohydrates, such as starch and cellulose, consisting of a number of monosaccharides joined by glycosidic bonds. Also called glycan.
Proteoglycans – are proteins with glycosaminoglycan chains, are ubiquitously expressed and have a wide range of functions.
Sulfotransferases – an enzyme that catalyzes the transfer of a sulfate group from one compound to the hydroxyl group of another.