15.2 - Endocytosis Flashcards
What is Endocytosis?
Process by which cells ingest external substances including fluids, molecules, particles, and other cells
What occurs in Endocytosis?
- Plasma membrane pinches inward, forming endocytic vesicles.
- Contents are transported to lysosomes for digestion.
What are the types of Endocytosis?
-Pinocytosis
-Phagocytosis
What is Pinocytosis?
The continuous uptake of fluid and small macromolecules by cells.
What is Phagocytosis?
Ingestion of large vesicles (phagosomes).
What are Specialized Phagocytic Cells?
Cells like macrophages and neutrophils that engulf large particles via phagocytosis.
How do Specialized Phagocytic Cells work?
- Extend pseudopods to engulf the target.
- Form a phagosome by pinching off the engulfed material.
- Fuse the phagosome with a lysosome to create a phagolysosome for digestion.
What are the roles of Specialized Phagocytic Cells?
- Defense against pathogens.
- Recycling of cellular debris.
How much volume do macrophages ingest during Pinocytosis?
Macrophages ingest fluid equivalent to 25% of their cell volume per hour.
How much of their cell membrane do macrophages recycle during Pinocytosis?
About 200% of their cell membrane per hour.
What is Receptor-Mediated Endocytosis?
A selective uptake mechanism for specific macromolecules via plasma membrane receptors.
What happens to Endocytosed Macromolecules?
They are transported to endosomes for sorting, where they may be degraded in lysosomes, recycled, or sent elsewhere in the cell.
What are Endosomes?
Sorting compartments for endocytosed materials.
What are Lysosomes?
Organelles that serve as the primary sites for intracellular digestion.
What is the function of Endocytic Vesicles?
They transport ingested material during endocytosis
What are Pseudopods?
Extensions of a cell’s plasma membrane that engulf targets during phagocytosis.
What is a Phagosome?
A vesicle containing material engulfed by phagocytosis.
What is a Phagolysosome?
A fused structure of a phagosome and lysosome where degradation occurs.
What are Macrophages?
Immune cells involved in phagocytosis and recycling cellular debris.
What are Neutrophils?
Immune cells that engulf pathogens during the immune response.
What is Receptor-Mediated Endocytosis?
Selective uptake of molecules via plasma membrane receptors.
What is Mycoplasma tuberculosis?
A pathogen targeted by phagocytic activity.
Mechanism of Phagocytosis (4 steps)
- Pseudopod Formation
- Engulfment
- Fusion
- Degradation
Explain the process of Pseudopod formation during Phagocytosis.
Specialized phagocytic cells (macrophages, neutrophils) extend their plasma membrane around a target particle (bacterium, etc.)
Explain the process of Engulfment during Phagocytosis.
Pseudopods encircle the target, enclosing it in a membrane-bound compartment known as “Phagosome”
Explain the process of Fusion during Phagocytosis.
Phagosome moves toward and fuses with a lysosome;
forms Phagolysosome
Explain the process of Degradation during Phagocytosis.
Digestive enzymes in the lysosome break down the engulfed material into simpler components; which the cell can either reuse or expel.
Vesicles formed during pinocytosis are recycled back where and why?
Back to the cell surface to maintain membrane balance and to ensure the plasma membrane does not deplete ; supports constant uptake.
What are the 3 steps in the mechanism of Receptor-Mediated Endocytosis?
- Receptor-Binding
- Vesicle Formation
- Transport to Endosomes
Explain Sorting Pathways in Endosomes.
Once Macromolecules are internalized, they are transported to endosomes; which act as sorting stations.
What are the Pathways (destination) in Endosomes?
- Recycling: some materials are sent back to the plasma membrane to be reused.
- Degradation: other materials are transported to lysosomes for breakdown into usable components
- Alternatives: some are directed to specific cellular location, like golgi apparatus for further processes.
