Lecture 15 - Endocytosis 1 Flashcards
What are the types of endocytosis?
Autophagy (cytosolic components are surrounded by plasma membrane)
Endocytosis
Phagocytosis
What is the function of phagocytosis? What happens to phagosomes after a phagocyte ingests harmful material?
Phagocytosis enable cells to eat large material. Phagosomes fuse with lysosomes where their content is digested.
Toxins are eliminated by this method and cells that are too old.
What mediates phagocytosis?
Cells that perform this use actin to do this. The actin pushes the membrane around the cell being phagocytosed.
How is an apoptotic cell eaten by a phagocyte?
Exposure of phosphatidyl serine site during apoptosis induces phagocyte to eat this apoptotic cell.
What is endocytosis?
Ingestion of fluid via small vesicles.
Endocytosis involves exposure of a small segment of plasma membrane which buds inwards to form an intracellular vesicle.
What is the function of endocytosis in combination with exocytosis?
Exocytosis and endocytosis are linked. They allow maintenance of plasma membrane homeostasis. (maintenance of lipid and protein content of the plasma membrane)
What are the components of the clathrin coat?
triskelian made up of:
3 Binding sites for assembly of particles
3 heavy chains
3 light chains at base of heavy chains
1 clathrin coat is comprised of 36 triskelions (12 pentagons and 6 exagons)
How does clathrin coat assemble?
adaptor proteins (AP2) form a coat around the vesicle and under the clathrin coat.
What is the major advantage of clathrin-mediated endocytosis?
Clathrin coated pits represent a specific and highly efficient pathway for uptake of macromolecules, nutrients, and signalling molecules.
What is the problem with clathrin mediated endocytosis?
This pathway is frequently hijacked by pathogens to gain entry into cells.
What is the destination of vesicles of the endocytic pathway?
Endocytic pathway ends at lysosome but many branch points can divert traffic prior to reaching lysosome in a complex pathway.
What are the type of ligands that enter via receptor mediated endocytosis?
Hormones/growth factors
Serum transport factors + antibodies (eg from placenta)
Viruses
Toxins
What are the steps of clathrin-mediated endocytosis?
1) cargo molecules can interact with receptor.
2) adaptor molecule attaches to the cargo receptor.
3) clathrin attaches to the adaptor protein forming a vesicle.
4) vesicle is separated from membrane via dynamin. This is a GTP dependent process.
5) vesicle coat is separated and naked vesicle results.
