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BIOL 2321 - Cell Biology > Endocytosis > Flashcards

Endocytosis Flashcards

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1
Q

Describe endocytosis

A

a process in which cells take up plasma membrane components, fluids, solutes, macromolecules and small particles

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2
Q

How is the ingested material packaged before ingestion?

A

in a small portion of plasma membrane

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3
Q

How does the plasma membrane enclose the to be ingested material?

A

plasma membrane buds inward and pinches off to form an endocytic vesicle

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4
Q

What is an endocytic vesicle?

A

the plasma membrane buds inwards to enclose material that will be ingested by a cell and pinches off to form the vesicle

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5
Q

Where does an endocytic vesicle move through?

A

the endocytic pathway

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6
Q

What are the 3 types of endocytosis?

A

phagocytosis

bulk pinocytosis

receptor-mediated endocytosis (also pinocytosis)

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7
Q

Describe phagocytosis

A

‘cellular eating’

large particles are ingested NON-specifically by packing into large vesicles called phagosomes

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8
Q

T or F: phagocytosis is ingestion of specific particles

A

false! phagocytosis is non-specific

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9
Q

T or F: phagocytosis is the ingestion of large particles

A

true

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10
Q

Describe phagosomes

A

the large vesicles that form by enclosing large particles to be ingested by a cell via phagocytosis

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11
Q

What organisms depend on phagocytosis for feeding?

A

single-cell protists (ex. amoebas) trap small microorganisms as food particles

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12
Q

How do most animals use phagocytosis?

A

as a protective mechanism

specialized cells (macrophages/neutrophils) move through tissues to engulf dead or damaged cells

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13
Q

What will phagosomes fuse with? what occurs when this happens?

A

phagosomes will fuse with lysosomes

the ingested particle will be degraded

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14
Q

Describe pinocytosis

A

‘cellular drinking’

fluid and molecules are ingested by packing into small vesicles called pinocytic vesicles

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15
Q

Describe pinocytic vesicles

A

the small vesicles that form by enclosing fluid or molecules to be ingested by a cell via pinocytosis

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16
Q

T or F: pinocytic vesicles are large

A

False, they are small

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17
Q

What size are pinocytic vesicles limited to?

A

150 nm in diameter

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18
Q

What size can phagosomes be as big as?

A

0.5 um in diameter

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19
Q

What are the 2 kinds of pinocytosis?

A

bulk endocytosis

receptor-mediated endocytosis

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20
Q

Which type of pinocytosis is specific? which is non-specific?

A

bulk endocytosis = non-specific

receptor-mediated endocytosis = specific

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21
Q

Describe bulk pinocytosis

A

the pinocytic vesicles will fuse with the lysosome and any complex molecules will be degraded

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22
Q

Describe receptor-mediated endocytosis

A

A type of pinocytosis

specific ligands (macromolecules) bind to their receptors on the EC surface of the plasma membrane and are brought into the cell

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23
Q

Describe the receptors involved in receptor-mediated endocytosis

A

membrane-bound proteins with ligand-binding domains on one side of the membrane and a functional domain on the other side

24
Q

T or F: all endocytic vesicles have coats

A

False! Not all of them do

25
Q

If an endocytic vesicle has a coat, what type will it always be?

A

clathrin

26
Q

What type of endocytic vesicle always uses a coat?

A

receptor-mediated endocytosis

27
Q

Where are the receptors for receptor-mediated endocytosis always concentrated?

A

receptors are highly concentrated near the clathrin coat

28
Q

What technique would be good to visualize clathrin coats on membranes?

A

Freeze fractured membranes visualized with an SEM

29
Q

What side of the membrane would the ligands be concentrated (in relation to a clathrin coat)?

A

extracellular side of the membrane

30
Q

Before the cargo sinks in during receptor-mediated endocytosis, what structure would the clathrin coat have? Where would this be located?

A

on the cytoplasmic side of the membrane, the clathrin lattice would be flat

31
Q

As the cargo sinks in during receptor-mediated endocytosis, what structure would the clathrin coat have? Where would this be located?

A

the clathrin coat invaginates and gets more spherical - still on the cytoplasmic side of the membrane

32
Q

Briefly describe the steps involved in the receptor-mediated endocytosis of a yolk protein

A
  1. membrane receptors for the protein bind to the protein
  2. the receptors bound to the proteins migrate to one area of the membrane
  3. a clathrin coat forms on the cytoplasmic side to form a coated pit
  4. the coated pits invaginate and pinch off as coated vesicles
33
Q

What is required to pinch off the clathrin coated vesicles from the membrane?

A

dynamin protein

34
Q

How does dynamin pinch off the clathrin coated vesicle from the membrane?

A

it self-assembles to form a helical collar under the budding clathrin-coated vesicle

GTP hydrolysis causes dynamin to constrict and cut off the coated pit = free vesicle

35
Q

What structure does dynamin take on? How does it do this?

A

dynamin self-assembles to form a helical collar

36
Q

What is required for dynamin to function?

A

GTP hydrolysis generates the mechanical force of dynamin

37
Q

What have experiments with a non-hydrolysable analog of GTP shown?

A

dynamin will polymerize and form long neck but will never be able to sever the vesicle head off

38
Q

T or F: endocytosis is not very common

A

FALSE it can be very common in some cell types

ex. macrophages ingest 3% of their own plasma membrane every minute

39
Q

What process often occurs at a similar rate to endocytosis?

A

exocytosis

40
Q

Why does exocytosis have to occur at a similar rate to endocytosis?

A

to ensure the membrane surface area remains the same

41
Q

Where would endocytosis and exocytosis be especially linked? give an example

A

in areas with high membrane turnover

ex. synaptic terminal bulb

42
Q

What happens to the clathrin coat if a vesicle has one after its been pinched off?

A

the clathrin coat is shed off once the membrane vesicle is pinched off and enters the cytoplasm

43
Q

What forms when vesicles fuse?

A

a compartment called the early endosome

44
Q

Describe the early endosome

A

a compartment formed when endocytic vesicles fuse

45
Q

What is the function of an early endosome?

A

sorting occurs here

46
Q

From the early endosome, what happens to empty vesicles?

A

they go back to the plasma membrane

47
Q

From the early endosome, what happens to vesicles with remaining cargo?

A

they move to a second compartment called the late endosome

48
Q

What does the late endosome contain?

A

all the cargo from the endocytic vesicle fusion of the early endosome - very concentrated

49
Q

T or F: the late endosome is very concentrated

A

true

50
Q

How does an endosome mature? What happens to the remaining contents?

A

from an early lysosome to a late endosome

they are committed to degradation

51
Q

Where may the vesicles move from the late endosome?

A

to the lysosome or the Golgi

52
Q

What is the main reason for the connection between the TGN and the late endosome?

A

to recycle the mannose 6 phosphate receptor

53
Q

T or F: as the vesicles move toward the lysosome, the conditions get more and more acidic

A

true because the lysosome is very acidic

54
Q

How re V-type pumps involved in endocytosis?

A

they pump H+ into the lumen and create the acidic conditions required to separate the cargo from the receptor

55
Q

What separates the cargo from the receptor in receptor-mediated endocytosis?

A

acidity

56
Q

Where does the cargo move to in receptor-mediated endocytosis?

A

the late endosome

57
Q

Where does the receptor move to in receptor-mediated endocytosis?

A

back to the plasma membrane

BIOL 2321 - Cell Biology (26 decks)

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