After Golgi Body, it is time to look at a different at yet very, really very important organelle of eukaryotic cells. It is none other than the ‘Lysosome’. Lysosomes are unique just like every other cell organelle in a eukaryotic cell and are designed to perform a specific set of tasks that no other organelle can perform. So, the absence of this organelle will just render the cells useless. In this article on lysosome facts, we are going to answer several questions including:
- What are lysosomes?
- Who discovered lysosomes?
- What are the functions of lysosomes?
- Where are they located in a cell?
- What types of cells have lysosomes?
- What produces the lysosomes?
- Why are lysosomes called ‘Suicidal Bags’ of cells?
Well, we will answer these questions but not in the order in which asked the questions. We will answer the questions as and when they appear in the flow of this article. Sounds good? Let’s start with our list of lysosome facts!
Interesting Lysosome Facts: 1-5 | What
1. Lysosomes are cell organelles. These organelles are membrane-bound. This means that the organelles have a protective membrane covering around them.
2. They are typical to eukaryotic cells. This means that lysosomes cannot be found in prokaryotic cells.
3. Though we say that lysosomes are present only in eukaryotic cells, it must be noted that they are found only and only in animal cells. In plant cells, the counterpart of lysosomes is known as ‘vacuoles’.
4. Here is something really important and interesting. Lysosomes are the only vesicles in cells that have a very specific composition of proteins both in its lumen as well as in its plasma membrane. Put in other words, the plasma membrane as well as the lumen of the Lysosome have a specific structure.
5. Inside these vesicles are enzymes – a lot of them. Actually, Lysosomes have 50+ enzymes (according to Wikipedia, they have 60+ enzymes) inside them. These are all hydrolytic enzymes.
Interesting Lysosome Facts: 6-10 | Functions
6. Wondering what’s hydrolytic enzyme? Well, it is a type of enzyme which engages in hydrolysis of biomolecules. In simpler words, the enzyme uses water to break down the biomolecules to make them even smaller.
7. So, here is the most important function of Lysosomes – they help in breaking down biomolecules. In other words, they help in digesting biomolecules. It is because of this, they are known as the stomach of the cells.
8. They can digest because of the hydrolytic enzymes that are present in the lumen. The pH of the lumen is somewhere between 4.5 and 5.0, which is perfect for these enzymes to act.
9. While degrading polymers of biomolecules is the primary job of Lysosomes, that’s not really the only job. There are many more including energy metabolism, cell signaling, repair of plasma membrane as well as secretion.
10. In case you are thinking that that’s all that Lysosomes do, you stand wrong in your opinion. There’s more. These vesicles are also designed in a way that they work as a system of waste disposal for the cells.
Interesting Lysosome Facts: 11-15 | Functions
11. What kind of waste they dispose you ask? Smarty pants! Well, did you know that there are many unwanted materials that are found in the Cytoplasm of a cell. These vesicles digest and dispose those unwanted materials.
12. These unwanted materials have two origins. They are:
- Those that originate from inside the cells. These are basically obsolete and outdated materials that are no longer required.
- Then there are those that are taken in from outside the cells using a method called endocytosis. Basically, it is a process in which the cells engulf these materials and, in the process, use energy.
13. Now, endocytosis can take place in two ways. These two methods are known as pinocytosis and phagocytosis. Pinocytosis is sometimes referred to as ‘cell drinking’ while phagocytosis is sometimes referred to as ‘cell eating’.
14. Pinocytosis is a method in which extracellular fluids and small macromolecules are internalized by the cell. These extracellular materials are carried inside the cells in small vesicles that actually pinch off from the interior side of the plasma membrane.
15. Once inside the cells, these small vesicles carrying extracellular material travel all the way up to endosomes – a type of membrane-bound organelles present inside the cells.
Interesting Lysosome Facts: 16-20 | Functions
16. It is not still clearly understood how the extracellular materials are transported from endosomes to Lysosomes. Some argue that endosomes actually mature in Lysosomes when newly brewed acid hydrolases (basically enzymes present in the Lysosomes) are delivered to the endosomes. A detailed discussion on this is provided in this article here.
17. What about phagocytosis? Before we explain, you need to know that phagocytosis occurs only in very specialized types of cells. It is a process in which large particles get digested. These large particles can be whole organisms or cell debris.
18. What happens in phagocytosis, the cells will create large intracellular vesicles around the engulfed particles. These vesicles carrying the engulfed particles will then fuse with Lysosomes.
19. The fusion will lead to creation of a single organelle bounded by a membrane. Inside the organelle will be the engulfed particle along with the digestive enzymes or acidic hydrolases. These enzymes will then digest and breakdown the ingested materials.
20. That explains endocytosis but what about the obsolete material that originate from inside the cells? These too are processed within the cells by Lysosomes in a process known as autophagy.
These obsolete materials originating within the cells are packed inside vesicles that originate from Endoplasmic Reticulum. These vesicles then carry the materials to Lysosomes where the digestive juices are used by the organelles to digest the obsolete materials.
NOTE: The digested materials (extracellular or intracellular) or broken-down materials are moved back from Lysosomes to the cytoplasm where they are reused as new material for cell building.
Interesting Lysosome Facts: 21-25 | Lysosomal Enzymes Production
21. We said that there are 50+ enzymes in the Lysosomes. The question is, where do these enzymes come from? Here is the answer you seek – these enzymes are synthesized by Rough Endoplasmic Reticulum.
22. Transport vesicles then carry these enzymes to the Golgi Body. Once inside the Golgi Body, these small vesicles are then fused with other larger acidic vesicles. They are then released into the cytoplasm as Lysosomes. This is how the Lysosomes are produced.
23. The question is, how does the Golgi Apparatus identify the enzymes that are meant to be Lysosomal enzymes? The Rough ER takes care of this by tagging those enzymes using a specific molecule known as mannose 6-phosphate.
24. The Golgi Complex is capable of reading this particular tag and sorts out the enzymes into acidic vesicles.
25. Some of the examples of Lysosomal proteins include carbohydrases, lipases, proteases and nucleases. These enzymes are capable of digesting carbohydrates, lipids, proteins and nucleic acids respectively. As a matter of fact, the assorted collection of Lysosomal enzymes can digest almost every type of organic molecules.
Interesting Lysosome Facts: 26-30 | Proton Pumping
26. We said that the lumen of the Lysosomes is acidic by nature. But, what helps to maintain that acidic nature? This is achieved by pumping in protons (or H+ ions) inside the Lysosomes.
27. These protons are pumped in from the cytosol, which maintains a pH of 7.2. The protons taken from the cytosol are pumped inside the Lysosome across the plasma membrane of the Lysosome.
28. Chloride ion channels and proton pumps (which are basically the proteins of the plasma membrane of the Lysosome) are used for pumping in the protons. It is this pumping of the protons that helps to maintaining the acidic condition in the Lysosomes by ensuring low pH.
29. The enzymes present in the Lysosomes can act properly only and only in an acidic condition. This is the reason for maintaining acidic condition inside the Lysosomes.
30. Because these enzymes require acidic conditions to perform their jobs, they are known as acidic hydrolases.
Interesting Lysosome Facts: 31-35 | Structure, Size, Danger
31. Lysosomes are spherical sac-like structures and are completely filled with an assorted range of digestive enzymes.
32. This sac-like structure has a single protective plasma membrane layer. It is this layer that prevents the Lysosomal enzymes from spilling out into the cytoplasm and thereby protects the rest of the cell from these enzymes.
33. The size of Lysosomes can vary. The size range is known to be 0.1µm and 1.2µm.
34. There is a big question that is often asked by many people. Since Lysosomes contain powerful digestive enzymes, can they not digest the organelles inside the cells? They can’t! There are two reasons for this:
- The plasma membrane of the Lysosome prevents the enzymes from getting out into the cytoplasm and digesting other organelles.
- Even if the plasma membrane of the Lysosome leaks the enzymes into the cytoplasm, the pH of the cytosol prevents the enzymes from functioning properly. These enzymes require acidic condition to work while the cytosol is alkaline and thereby prevents the enzymes from working.
35. Here is another important question: “why the enzymes don’t digest the plasma membrane of the Lysosomes?” Well, scientists are not really clear about this and they are seeking answer to this question.
Interesting Lysosome Facts: 36-40 | Suicide Bags, Discovery, LSD
36. Lysosomes were once known as the Suicide Bags or Suicide Sacs. The reason for such name was that it was originally thought that these organelles played a very vital role in apoptosis (programmed cell death). However, further research has proven that Lysosomes play a very minor role in apoptosis and hence, they are no longer referred to as Suicide Bags.
37. It was Christian de Duve and his team who discovered the Lysosomes in 1949 but they eventually named the organelle in 1955. Christian de Duve worked in Belgium’s Catholic University of Louvian as the Chairman of Physiological Chemistry.
38. Lysosomes are susceptible to disorders. The diseases that show up because of the disorders of Lysosomes are known as Lysosomal Storage Diseases (LSD). LSDs are a result of either lack of or, malfunctioning of specific acidic hydrolases.
39. Lack of or malfunctioning of these enzymes can lead to build up of various molecules that were meant to be digested. The build up of these molecules inside the cells can lead to an assorted range of physical problems and genetic defects that can even lead to death.
40. The reason we say ‘genetic defects’ is that lysosomal enzymes synthesis is dependent on nuclear genes. If these genes mutate, the synthesis of lysosomal enzymes can go wrong, leading to genetic defects. There are 30 such known LSDs.
Some of the well-known LSDs are Tay-Sachs Disease, Gaucher’s Disease, Lysosomal Glycogen Storage Disease or Acid Maltase Deficiency.
This completes our lists of Lysosome facts. In case you think we have missed something really vital, you can let us know so that we can fix the problem quickly.