Lysosomes and peroxisomes | Cells | MCAT | Khan Academy

00:05:43
https://www.youtube.com/watch?v=OZdmaf2R9ys

Summary

TLDRThe video delves into the functions of lysosomes and peroxisomes within cells. Lysosomes are membrane-bound organelles that perform digestion through two main processes: "Autophagy" and "Crinophagy." Autophagy involves the lysosomes digesting the cell's own obsolete organelles or ingested materials, while crinophagy specifically targets the breakdown of excessive secretion products like surplus hormones. After digestion, lysosomes release the resulting basic molecules back into the cytoplasm for reuse. The internal pH of a lysosome is approximately 5, which is necessary for its acid hydrolase enzymes to function. This acidity also acts as a safeguard, as escaped enzymes won’t perform effectively in the cell's neutral pH environment of 7.4. Peroxisomes, similar to lysosomes, are involved in metabolic activities such as lipid metabolism and detoxification in liver cells. A crucial role of peroxisomes is to neutralize hydrogen peroxide, a toxic by-product of some enzymatic reactions in cells. They achieve this with the enzyme catalase, converting hydrogen peroxide into water and oxygen, ensuring cellular safety from oxidative stress.

Takeaways

  • 🧬 Lysosomes are essential for cellular digestion processes.
  • 🔍 Autophagy involves digesting obsolete cell organelles.
  • 🔄 Crinophagy deals with excess secretory products.
  • 🔑 Lysosomal enzymes require a pH of 5 to function.
  • 🛡️ Acidic environment in lysosomes protects the cell.
  • 🔬 Peroxisomes assist in metabolic activities.
  • 🔄 They break down lipids and help detoxify cells.
  • 💧 Peroxisomes convert toxic hydrogen peroxide to water and oxygen.
  • ⚙️ Catalase is the enzyme that facilitates this conversion.
  • ⚠️ Multiple lysosome bursts can be harmful to cells.

Timeline

  • 00:00:00 - 00:05:43

    Lysosomes are organelles responsible for digesting molecules through processes like autophagy and crinophagy. In autophagy, lysosomes break down cell components such as non-functional organelles or engulfed pathogens. In crinophagy, they digest excess secretory products like extra hormones. Lysosomes release basic building blocks back into the cytoplasm for reuse. They contain enzymes called acid hydrolases, which require an acidic environment (pH ~5) to function. This acidic condition acts as a safety mechanism; if lysosomes burst, the neutral cytoplasm (pH ~7.4) prevents the enzymes from damaging the cell. However, multiple bursts could lower the pH, activating the enzymes and harming the cell. Peroxisomes, similar to lysosomes, carry out metabolic functions such as breaking down lipids and detoxifying chemicals in the liver. They contain catalase, an enzyme that breaks down the harmful by-product hydrogen peroxide into water and oxygen, thus protecting the cell.

Mind Map

Video Q&A

  • What is autophagy?

    Autophagy is a process where lysosomes digest molecules that are part of the cell itself or other cells.

  • What is crinophagy?

    Crinophagy is the process where lysosomes digest excess secretory products such as extra hormones.

  • How do lysosomes contribute to autophagy?

    Lysosomes digest old or non-functional organelles and recycle their basic components into the cytoplasm.

  • Why do lysosomal enzymes require an acidic environment?

    Lysosomal enzymes, known as acid hydrolases, require an acidic environment to function properly, typically with a pH of about 5.

  • What is the role of peroxisomes in the cell?

    Peroxisomes handle various metabolic activities, including lipid breakdown and detoxification, and they break down hydrogen peroxide into water and oxygen.

  • What happens if lysosomes burst in a cell?

    If lysosomes burst, they can release acid hydrolases into the cytoplasm; however, these enzymes do not function well in the cytoplasm's neutral pH unless many lysosomes burst simultaneously.

  • How does peroxisomes protect the cell from hydrogen peroxide?

    Peroxisomes contain catalase, which breaks down hydrogen peroxide into water and oxygen, thus preventing damage to the cell.

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  • 00:00:03
    - [Voiceover] Lysosomes are membrane-bound
  • 00:00:05
    organelles that are found in a cell.
  • 00:00:08
    What do they do?
  • 00:00:09
    Well, if you look at the word "lysosome",
  • 00:00:12
    you can see the root "lys", which means to "cut or digest."
  • 00:00:15
    So, lysosomes digest various molecules and substances.
  • 00:00:26
    We can break this down into two different processes.
  • 00:00:29
    The first is "Autophagy"
  • 00:00:34
    and the second is "Crinophagy".
  • 00:00:40
    Autophagy literally means "self-eating".
  • 00:00:46
    So, autophagy is when the lysosomes digest molecules
  • 00:00:50
    that are part of the cell itself, or other cells.
  • 00:01:00
    So, for example, if there are organelles in the cell
  • 00:01:03
    that are no longer functional,
  • 00:01:05
    they will be digested by the lysosomes.
  • 00:01:13
    So, if there are some mitochondria or other organelles
  • 00:01:16
    floating around that are old and not functioning properly,
  • 00:01:19
    the lysosomes will break them down.
  • 00:01:21
    Another example of autophagy,
  • 00:01:23
    would be the macrophages of the immune system.
  • 00:01:30
    So, macrophages of the immune system will engulf
  • 00:01:34
    bacteria and viruses, and then they will go
  • 00:01:36
    to the lysosomes and be broken-down over there.
  • 00:01:39
    Let"s focus on Crinophagy.
  • 00:01:42
    Crinophagy is when the lysosomes
  • 00:01:44
    digest excess secretory products.
  • 00:01:53
    So let"s say, for example, a certain cell is producing
  • 00:01:56
    a hormone to be secreted and the cell,
  • 00:01:58
    for some reason, produced some extra of that hormone.
  • 00:02:01
    All the extra hormones will be broken down by the lysosomes.
  • 00:02:05
    In both Autophagy and Crinophagy,
  • 00:02:08
    after the lysosome finishes breaking down the molecules,
  • 00:02:11
    it will release into the cytoplasm,
  • 00:02:14
    the building blocks that have just formed.
  • 00:02:22
    It didn"t exactly form those building blocks,
  • 00:02:24
    but it broke the molecules down into their most basic,
  • 00:02:28
    basic parts, and those basic parts will
  • 00:02:30
    be put into the cytoplasm and be reused.
  • 00:02:32
    So, for example, let"s say the lysosomes digested some
  • 00:02:36
    extra hormones that were lying around,
  • 00:02:37
    and those hormones were made up of proteins.
  • 00:02:40
    They will break those proteins down
  • 00:02:41
    into the individual amino acids
  • 00:02:43
    and then those amino acids will be released
  • 00:02:45
    into the cytoplasm, and they"ll be used for something else.
  • 00:02:49
    What"s the environment like in the lysosomes?
  • 00:02:53
    The enzymes in the lysosomes are known as "acid hydrolases".
  • 00:03:00
    They"re known as acid hydrolases because
  • 00:03:02
    they require an acidic environment
  • 00:03:04
    in order to work properly.
  • 00:03:05
    So the pH inside a lysosome will be approximately five.
  • 00:03:09
    This acts as a safety mechanism for the cell.
  • 00:03:12
    How so?
  • 00:03:13
    Let"s take a look at the lysosome right here, on bottom.
  • 00:03:16
    Let"s say for some reason, it burst and released
  • 00:03:19
    into the cytoplasm, all the acid hydrolases
  • 00:03:23
    that we just learned are capable of digesting organelles.
  • 00:03:27
    We said in order for them to work properly,
  • 00:03:30
    they need to be in an acidic environment,
  • 00:03:32
    but the cytoplasm has a pH of approximately 7.4.
  • 00:03:37
    Therefore, these acid hydrolases are
  • 00:03:39
    not going to function properly.
  • 00:03:41
    You might say "Well, when the lysosome bursts,
  • 00:03:45
    "doesn"t it release some acid into the cytoplasm?"
  • 00:03:46
    That"s true, however, it"s still going
  • 00:03:49
    to be a pretty small amount and it"ll get diluted
  • 00:03:52
    in the cytocell, and the cytoplasm will still remain,
  • 00:03:54
    overall, at a pH of about 7.4.
  • 00:03:58
    However, if many lysosomes burst at the same time,
  • 00:04:02
    it would release a larger amount of acid into the cytoplasm.
  • 00:04:05
    Then the cytoplasm might actually become more acidic
  • 00:04:09
    and the acid hydrolases will start to work,
  • 00:04:11
    and will start to digest the various organelles.
  • 00:04:14
    This, generally speaking, would not
  • 00:04:16
    be a good thing for the cell.
  • 00:04:19
    Let"s talk about another membrane-bound organelle
  • 00:04:22
    that"s pretty similar to lysosomes.
  • 00:04:25
    They"re known as "Peroxisomes".
  • 00:04:29
    Peroxisomes are responsible for a
  • 00:04:31
    variety of metabolic activities.
  • 00:04:33
    In some cells they"re essential for lipid break down.
  • 00:04:36
    They help liver cells detoxify chemicals and drugs.
  • 00:04:39
    We"re gonna focus on one important task that they carry out.
  • 00:04:43
    Let"s zoom in on one peroxisome.
  • 00:04:46
    Here it is. So what do they do?
  • 00:04:49
    Well, there are various enzymes in a cell,
  • 00:04:52
    that as a result of their activity,
  • 00:04:54
    they produce a by-product, hydrogen peroxide,
  • 00:04:58
    which looks like this.
  • 00:05:00
    Hydrogen peroxide happens to be pretty dangerous
  • 00:05:03
    for the cell, so what peroxisomes will do is,
  • 00:05:05
    they"re going to isolate it so the hydrogen peroxide
  • 00:05:08
    ends up in the peroxisome.
  • 00:05:10
    Each peroxisome has an enzyme known as "catalase".
  • 00:05:14
    This enzyme is able to break down hydrogen peroxide.
  • 00:05:17
    Let"s write out the reaction.
  • 00:05:19
    Hydrogen peroxide in the presence of the enzyme catalase,
  • 00:05:25
    will become water and oxygen.
  • 00:05:29
    I"m just gonna put 1/2 there to keep the ratio correct.
  • 00:05:32
    So, peroxisomes protect the cell from the damaging effects
  • 00:05:36
    of hydrogen peroxide by isolating it,
  • 00:05:39
    and by then breaking it down into water and oxygen.
Tags
  • Lysosomes
  • Peroxisomes
  • Autophagy
  • Crinophagy
  • Membrane-bound organelles
  • Acid hydrolases
  • pH
  • Catalase
  • Hydrogen peroxide
  • Cell metabolism