Endocytosis

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30 Terms

1
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What is taken up through endocytosis?

  • Nutrients

  • Signals

  • Antibodies

  • Enzymes

  • Viruses

  • Bacteria

  • Membrane

2
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What are the 3 different fates for endocytosed material?

  • recycling

  • transcytosis

  • degradation

3
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What are the 3 main endocytic pathways?

  • small scale clathrin endocytic process

  • micropinocytosis

  • phagocytosis

4
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What is opsonisation?

process by which antibodies or complement proteins coat pathogens, enhancing their recognition and ingestion by immune cells like macrophages

5
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What type of material does phagocytosis allow to take up?

large particles

6
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What are the 4 steps of phagocytosis of a bacteria?

  • ligand coated bacteria approaches phagocyte surface receptors

  • binds to receptors

  • pseudopod forms from mobilisation of actin in phagocyte cytoplasm, engulfing the bacteria

  • destruction of bacteria in the phagocyte

7
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<p>What are the ruffles visible on the membrane of the macrophage? What are the engulfed cells?</p>

What are the ruffles visible on the membrane of the macrophage? What are the engulfed cells?

actin rich pseudopod

RBCs

8
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What type of cell takes up yeast cells? RBCs?

phagocyte // macrophage

9
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Describe frustrated phagocytosis and cell autonomous

immune cells attempt to engulf a same pathogen but are unable to bc of their incompatible ruffles, called cell autonomous ie has to happen within one single cell

10
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How was membrane recycling proven through use of latex beads

macrophages phagocytosed 1.1 uM of latex beads, by counting the beads it was possible to estimate 30% of total membrane was internalised per hour (invagination of membrane necessary for phagocytosis) but there was no change in cell size

11
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What is the difference between a macrophage and a phagocyte?

macrophage is a specific type of phagocyte, specialised in immunity and tissue repair

12
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Explain the similarity and difference between phagocytosis and micropinocytosis

Mechanistically similar to phagocytosis where cells form actin driven ruffles to engulf material HOWEVER is non selective uptake of material

13
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In which types of cells is micropinocytosis often seen and what purpose does it fulfil?

cancer cells to take up nutrients

14
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What’s the pathway of LDL (cholesterol) from the EC to destruction in a cytoplasmic lysosome?

LDL binds to receptor, clathrin coated pit pinches off and takes up cell membrane + receptor bound to the LDL. The newly formed vesicle is uncoated and fuses with an early endosome, becoming a late endosome and finally a lysosome whose enzymes destroy the LDL

15
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How are LDL receptors recycled during clathrin-mediated endocytosis?

as the receptor and LDL are in the early endosome, a small portion buds off containing the LDL receptor which is returned to the plasma membrane

16
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What did Brown and Goldstein contribute to the understanding of endocytosis?

connection between receptor internalization and regulation of metabolism thanks to cross disciplines

17
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<p>What’s depicted on the photo? What are they made of?</p>

What’s depicted on the photo? What are they made of?

clathrin coated pits and vesicles

plasma membrane + cytosol

18
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<p>Why are clathrins termed triskelia ? </p>

Why are clathrins termed triskelia ?

they have 3 arms

19
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Explain the following sentence: “Clathrin triskelia polymerize into lattices “

clathrin molecules come together to form a regular network that helps in the formation of vesicles in cells

<p>clathrin molecules come together to form a regular network that helps in the formation of vesicles in cells</p>
20
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Which protein allows clathrin coated vesicles to pinch off?

dynamin

21
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How is pH gradient related to function of the endocytic pathway? How does it evolve from the plasma membrane to the centre of the cell?

gradient allows maturation of endosomes

pH goes up as we get to the centre of the cell

22
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What are Rab proteins, how are they activated and what is their function?

family of GTPases that act as molecular switches, going from inactive GDP-bound state to active GTP-bound state allowing guidance of vesicles to their target membranes, ensuring proper vesicle formation, transport, docking, and fusion.

23
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What different types of Rab proteins are most important in the function of the endocytic pathway?

  • 5: regulates early endosome formation and vesicle sorting and trafficking

  • 7: late endosome maturation and the fusion of late endosomes with lysosomes

  • 11: recycling endosomes, especially in the recycling of membrane proteins back to the plasma membrane

  • 4: early endosome recycling and sorting

  • 9: protein recycling and retrograde trafficking from late endosomes to the Golgi

<ul><li><p>5: regulates early endosome formation and vesicle sorting and trafficking</p></li><li><p>7: late endosome maturation and the fusion of late endosomes with lysosomes</p></li><li><p>11: recycling endosomes, especially in the recycling of membrane proteins back to the plasma membrane</p></li><li><p>4: early endosome recycling and sorting</p></li><li><p>9: protein recycling and retrograde trafficking from late endosomes to the Golgi</p></li></ul><p></p>
24
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What does overexpression of Rab5 result in? What mediates endosome fusion?

enlarged endosomes

snares

25
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What are lysosomes and what are the 2 main enzymes they contain?

membrane-bound organelles

hydrolases and lipases

26
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What’s the role of hydrolases contained in lysosomes?

catalyse the breakdown of proteins, nucleic acids, carbohydrates, and lipids through the addition of water

27
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What’s the role of lipases contained in lysosomes?

catalyse the hydrolysis of lipids, breaking down fats and phospholipids into fatty acids and glycerol

28
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Which vesicles contain cargo for degradation?

ILVs (intraluminal vesicles)

29
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What is the late endosome also termed because of its structure?

Multivesicular Body (MVB)

30
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What mutation of the endocytic system could cause cancers?

mutation in encapsulation of signal molecules = switch off signalling dysregulated ie over-active signalling if signal molecules aren’t capsulated at the right time