If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:5:43

Lysosomes and peroxisomes

Video transcript

- [Voiceover] Lysosomes are membrane-bound organelles that are found in a cell. What do they do? Well, if you look at the word "lysosome", you can see the root "lys", which means to "cut or digest." So, lysosomes digest various molecules and substances. We can break this down into two different processes. The first is "Autophagy" and the second is "Crinophagy". Autophagy literally means "self-eating". So, autophagy is when the lysosomes digest molecules that are part of the cell itself, or other cells. So, for example, if there are organelles in the cell that are no longer functional, they will be digested by the lysosomes. So, if there are some mitochondria or other organelles floating around that are old and not functioning properly, the lysosomes will break them down. Another example of autophagy, would be the macrophages of the immune system. So, macrophages of the immune system will engulf bacteria and viruses, and then they will go to the lysosomes and be broken-down over there. Let"s focus on Crinophagy. Crinophagy is when the lysosomes digest excess secretory products. So let"s say, for example, a certain cell is producing a hormone to be secreted and the cell, for some reason, produced some extra of that hormone. All the extra hormones will be broken down by the lysosomes. In both Autophagy and Crinophagy, after the lysosome finishes breaking down the molecules, it will release into the cytoplasm, the building blocks that have just formed. It didn"t exactly form those building blocks, but it broke the molecules down into their most basic, basic parts, and those basic parts will be put into the cytoplasm and be reused. So, for example, let"s say the lysosomes digested some extra hormones that were lying around, and those hormones were made up of proteins. They will break those proteins down into the individual amino acids and then those amino acids will be released into the cytoplasm, and they"ll be used for something else. What"s the environment like in the lysosomes? The enzymes in the lysosomes are known as "acid hydrolases". They"re known as acid hydrolases because they require an acidic environment in order to work properly. So the pH inside a lysosome will be approximately five. This acts as a safety mechanism for the cell. How so? Let"s take a look at the lysosome right here, on bottom. Let"s say for some reason, it burst and released into the cytoplasm, all the acid hydrolases that we just learned are capable of digesting organelles. We said in order for them to work properly, they need to be in an acidic environment, but the cytoplasm has a pH of approximately 7.4. Therefore, these acid hydrolases are not going to function properly. You might say "Well, when the lysosome bursts, "doesn"t it release some acid into the cytoplasm?" That"s true, however, it"s still going to be a pretty small amount and it"ll get diluted in the cytocell, and the cytoplasm will still remain, overall, at a pH of about 7.4. However, if many lysosomes burst at the same time, it would release a larger amount of acid into the cytoplasm. Then the cytoplasm might actually become more acidic and the acid hydrolases will start to work, and will start to digest the various organelles. This, generally speaking, would not be a good thing for the cell. Let"s talk about another membrane-bound organelle that"s pretty similar to lysosomes. They"re known as "Peroxisomes". Peroxisomes are responsible for a variety of metabolic activities. In some cells they"re essential for lipid break down. They help liver cells detoxify chemicals and drugs. We"re gonna focus on one important task that they carry out. Let"s zoom in on one peroxisome. Here it is. So what do they do? Well, there are various enzymes in a cell, that as a result of their activity, they produce a by-product, hydrogen peroxide, which looks like this. Hydrogen peroxide happens to be pretty dangerous for the cell, so what peroxisomes will do is, they"re going to isolate it so the hydrogen peroxide ends up in the peroxisome. Each peroxisome has an enzyme known as "catalase". This enzyme is able to break down hydrogen peroxide. Let"s write out the reaction. Hydrogen peroxide in the presence of the enzyme catalase, will become water and oxygen. I"m just gonna put 1/2 there to keep the ratio correct. So, peroxisomes protect the cell from the damaging effects of hydrogen peroxide by isolating it, and by then breaking it down into water and oxygen.