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From Molecules to Cells > Lecture 5: The endomembrane system > Flashcards

Lecture 5: The endomembrane system Flashcards

1
Q

What is vesicular transport?

A

How proteins and lipids are moved between membrane enclosed organelles in vesicles

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2
Q

What is symmetric growth in the synthesis of membrane lipids?

A
  1. Enzymes on cytosolic face of the ER membrane synthesise new phospholipids which adds to cytosolic half of bilayer
  2. Scramblase catalyses the transfer of random phospholipids from one monolayer to another
  3. This means both sides of the bilayer grow symmetrically
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3
Q

What is asymmetric growth in the synthesis of membrane lipids?

A
  1. New membrane is delivered from the ER
  2. Flippase catalyses the transfer of specific phospholipids to the cytosolic membrane
  3. Only certain ones being transported allows asymmetric growth
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4
Q

Where are flippase transporters found?

A

Golgi apparatus

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5
Q

What is the secretory pathway?

A

Vesicular transport
Proteins and lipids move from ER through the golgi and plasma membrane
Move outwards

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6
Q

What is the endocytic pathway?

A

Vesicular transport
Proteins and other molecules move from the plasma membrane to the cell interior
Moves inwards

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7
Q

In what way is the membrane orientation maintained during vesicular transport?

A

Cytosolic surface stays facing cytosol
Other side faces outwards

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8
Q

How are vesicles formed?

A
  1. Protein coat is formed and helps deform the membrane and capture correct cargo
  2. Dynamin assembles and helps the bud pinch off
  3. Vesicle is released and protein coats are removed through uncoating
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9
Q

What are some different types of coated vesicles?

A

Clathrin coated
COPII coated
COPI coated

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10
Q

2 variants of Clathrin coated vesicles

A

Clathrin + adaptin 1 or adaptin 2

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11
Q

Clathrin + adaptin 1

A

Origin : Golgi
Destination : Lysosome

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12
Q

Clathrin + adaptin 2

A

Origin : Plasma membrane
Destination : Endosome

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13
Q

COPI

A

Origin : Golgi
Destination : ER

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14
Q

COPII

A

Origin : ER
Destination : Golgi

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15
Q

What is clathrin?

A

Has a role at the plasma membrane and golgi
Part of endocytic pathway
Shapes membrane into bud and vesicle
Captures cargo

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16
Q

What are the three stages of forming a vesicle?

A

Cargo selection
Vesicle budding
Vesicle uncoating

17
Q

What occurs during cargo selection?

A
  1. Adaptins help clathrin attach to membrane
  2. Clathrin coated pit forms on cytosolic face of membrane
  3. Or will bind to cargo receptors and recruit them to recognise specific sorting signals on the cargo
18
Q

What happens during vesicle budding?

A
  1. Clathrin assembles into a cage
  2. Membrane invaginates into a bud
  3. Dynamin makes a ring around the neck of the bud and helps it pinch off
19
Q

What happens during vesicle uncoating?

A
  1. After budding coat proteins are removed
  2. Needs molecular chaperones and ATP
  3. Produces naked transport vesicle that can fuse with the target membrane
20
Q

What is dynamin and how does it work?

A
  1. When it hydrolyses GTP it changes conformation
  2. This constricts the neck of the bud and the vesicle pinches off
21
Q

What is mutant dynamin?

A
  • A temperature sensitive type in Drosophila
  • The vesicles can’t pinch off which causes loss of neurotransmitter vesicles in synapses
22
Q

How does the vesicle reach the right destination?

A

Transported along microtubules to reach the correct place

23
Q

What are the 2 proteins that help vesicles tether to a membrane

A
  • Rab proteins
  • SNARE proteins
24
Q

What happens when a vesicle fuses to the target membrane using Rab proteins?

A
  1. Rab protein on vesicle binds to a tethering protein on target membrane
  2. There are Rab and tether pairs so this happens correctly
25
Q

What happens when the vesicle binds to the target membrane using SNARES?

A
  1. Vesicle SNARE pairs with target SNARE
  2. The Rab binding draws vesicle closer
  3. Vesicle snare and target snare interact and vesicle is docked onto target membrane as they wrap around eachother
26
Q

Process of fusion

A

Transport vesicle dock
Membranes coalesce
Lipid bilayers fuse

27
Q

What must happen for the SNARE proteins to interact?

A

Bilayers are within 1.5nm
Water is displaced

28
Q

What are the two methods of protein sorting in the secretory pathway?

A

ER retention and retrieval signal
Other sorting signals

29
Q

How does the ER retention and retrieval signal work?

A
  1. KDEL sequence at C terminus of protein is recognised by KDEL receptor in golgi
  2. Protein then Recruited into COPI vesicles that return protein to ER
  3. Protein prevented from secretion
30
Q

How do other sorting signals work to sort proteins?

A
  1. Addition of Mannose-6-phosphate to N-linked glycans of some glycoproteins at the golgi
  2. Causes sorting to lysosomes
  3. Short transmembrane domain retains proteins in the golgi
31
Q

What is the structure of the golgi apparatus?

A

Near nucleus
Stack of membrane enclosed sacs called cisternae

32
Q

What are the two transport models for how proteins move through the golgi?

A

Vesicular transport
Cisternal maturation

33
Q

What is the vesicular transport model for movement through the golgi?

A
  1. Vesicles bud from one cisterna and fuse with the next
  2. This transports cargo through each cisterna
34
Q

What is the cisternal maturation transport model for how proteins move through the golgi?

A
  1. Cargo enters Cisterna
  2. As each cisterna matures it migrates outwards carrying the cargo with it
  3. Cargo is then released once the Cisterna has fully matured and buds off on its own
35
Q

What are the two functions of the golgi apparatus?

A

Protein modification
Protein sorting

36
Q

3 examples of protein modification in the Golgi

A
  • O-linked oligosaccharides are added to some -OH side chains of serine and threonine residues in proteins travelling across golgi
  • N-linked oligosaccharides that are added to protein in the ER can be trimmed and rebuilt in golgi
  • N-linked oligosaccharides on lysosomal proteins are modified with mannose-6-phosphate
37
Q

How does protein sorting work in the golgi apparatus?

A

Cis = Resident proteins are sorted back to ER and cargo proteins carry on
Trans = Cargo proteins sorted into transport vesicles

From Molecules to Cells (23 decks)

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