Cell Organelles - Golgi, Lysosomes, Peroxisomes, Vacuoles, Mitochondria, Chloroplasts, and Endosymbiotic Theory

The Golgi Apparatus

  • The Golgi apparatus is an organelle with bubble-like structures (vesicles) around it.

  • Vesicles: Membrane-bound bubbles that transport substances within the immune cell.

    • Formed from the cell membrane's lipid bilayer.

    • Used in endocytosis (bringing substances into the cell).

    • Used to package and transport waste out of the cell.

    • Used to package and transport specific products out of the cell if the cell's job is to make them.

  • The Golgi acts like a post office or UPS:

    • Receives information.

    • Sorts it.

    • Repackages it if necessary.

    • Ships it out to the next location.

Lysosomes

  • The prefix "lyse" means to break, split, or burst.

  • Lysosomes: Organelles that break things open.

    • Contain catabolic enzymes that break down cell parts.

    • Act like water balloons filled with enzymes that attack and destroy.

    • Important for cleaning up materials inside the cell, including foreign invaders and non-functioning organelles.

    • Break down old organelles into building blocks for reuse.

Peroxisomes

  • Focus on poisonous wastes that are toxic to the cell.

  • Attack and eliminate poisonous substances using enzymes.

Vacuoles

  • Store large amounts of water, especially in plant cells.

  • Important for photosynthesis in plants.

  • Maintain turgor pressure against the cell walls in plants.

Mitochondria

  • Carry out cellular respiration to create energy (ATP) for the cell.

  • Often called the "powerhouse of the cell".

  • Contain their own ribosomes.

  • Contain their own circular DNA, unique to the structure.

  • The job is to create ATP (adenosine triphosphate), and we're gonna go into those steps coming up in the next chapter too.

Chloroplasts

  • Enable organisms to perform photosynthesis.

  • Found in plants, algae, and some fungi, as well as some prokaryotes.

  • Contain pigments that absorb sunlight energy to create sugars (glucose).

  • Glucose is used as a food source for plants and can be used in cellular respiration.

  • Like mitochondria, chloroplasts have their own membrane, ribosomes, and DNA.

Endosymbiotic Theory

  • Explains why mitochondria and chloroplasts have their own ribosomes, membranes, and DNA.

  • Endo: Means within.

  • Symbiosis: An ecological term for two organisms interacting and benefiting each other.

  • Theory: An explanation supported by a lot of evidence but not 100% proven.

  • Theory proposes that mitochondria and chloroplasts were once free-living bacterial cells.

    • Mitochondria were independent bacterial cells with their own DNA, ribosomes, and protective membrane.

    • A host cell engulfed the mitochondria but did not digest it.

    • The host cell benefited from the mitochondria's energy production, and the mitochondria benefited from the safe environment.

    • Over time, the engulfed mitochondria and the host cell began working together symbiotically.

    • The idea is that mitochondria were absorbed first, leading to the first eukaryotic organisms, then some of those absorbed chloroplasts.

  • Evidence for the endosymbiotic theory:

    • Mitochondria and chloroplasts have 70S ribosomes, while eukaryotic cells have 80S ribosomes.

Ribosome Size

  • Mitochondria and chloroplasts contain 70S70S ribosomes, which are smaller than the 80S80S ribosomes found in eukaryotic cells. This supports the idea that they were once prokaryotic organisms.