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Miscellaneous > MCB Lecture 32 Vesicular Transport > Flashcards

MCB Lecture 32 Vesicular Transport Flashcards

0
Q

What are the features of the Stop Transfer Sequence?

A
  1. Hydrophobic

2. Resistant to peptidase, isn’t cleaved by peptidase

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1
Q

Describe how transmembrane proteins become embedded in the membrane

A
  1. START transfer sequence present on N terminus, as well as STOP transfer sequence present further up
  2. Start transfer sequence binds to the translocator protein bound in the ER membrane
  3. Protein is fed through until it reaches the STOP sequence
  4. Signal peptidase cleaves the START transfer sequence from the rest of the protein.
  5. Translocator dissociates, leaving the protein embedded at the STOP sequence
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2
Q

Describe the orientation of transmembrane proteins and how this can be changed

A

Normally, N terminus is inside, C terminus is outside

To invert the orientation, the START transfer sequence is present further up from the N terminus.
The protein binds to the translocator here, with the N terminus still outside the cell
The protein is fed through, until the C terminus is inside the cell

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3
Q

Describe how multipass proteins become embedded in the membrane

A

There are multiple START and STOP domains

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4
Q

Why does glycosylation occur?

A

This tracks the folding of the protein

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5
Q

Describe the process of glycosylation

A
  1. Oligosaccharyl transferase moves sugars from Dolichol to a Asn residue on the protein as soon asit enters the ER
  2. N-acetyl glucosamine, mannose, and 3 glucoses are added
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6
Q

Describe the sugars on an unfolded protein

A

All three glucose molecules are attached

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7
Q

Describe the sugars on an incompletely folded protein

A

One glucose remains attached

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8
Q

Describe what happens when a protein does not fold properly

A

A glucose molecule will be reattached by glucosyl transferase, and then will bind with calnexin again

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9
Q

What is calnexin?

A

It is a protein bound in the ER membrane.
It binds to the glucose on a protein and helps it fold
The glucose is then cleaved

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10
Q

Describe the process of protein degredation

A

When a protein misfolds:

  1. A chaperone bindso
  2. It is transported out of the ER back into the cytosol
  3. Ubiquitin binds to it
  4. The ubiquitin tagged protein is sent to the proteosome, which degrades it
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11
Q

What is the name of the protein that cleaves the signal sequence

A

Signal peptidase

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12
Q

What is dolichol?

A

It is a lipid in the membrane of the ER with the oligosaccharides that end up of the protein to be folded

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13
Q

What is oligosaccharyl transferase?

A

It transfers the oligosaccharides group from dolichol to the protein

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14
Q

What are the three different pathways that use vesicular transport?

A
  1. Endocytic
  2. Biosynthetic (secretory)
  3. Recycling/retrieval
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15
Q

Describe the biosynthetic pathway

A

Molecules are translated and folded in the ER.
Vesicles bud of and are delivered to the Golgi
The proteins are packaged and altered in the Golgi
From the Golgi, vesicles bud off and are exocytosed

16
Q

What are the three vesicle coat proteins?

A

Clathrin
COP1
COPII

17
Q

Describe the endocytic pathway. How do vesicles form?

A

Endocrine pathway is the endocytosis of stuff from outside the cell. These phagocytotic vesicles become early endosome a, then late endosomes, then lysosomes for degradation of the contents.

  1. Cargo receptors are bound in the membrane
  2. Adaptins bind to the triskelion of the clathrin molecule and the cargo receptor
  3. Clathrin makes the membrane curve out, and concentrates cargo receptors in the clathrin coated pit
  4. Dynamin destabilises the narrowing, so that the vesicle blebs off. (GTP dependent process)
18
Q

What is clathrin?

A

Clathrin is a vesicle coat protein that forms vesicles in the endocytic pathway

19
Q

How are vesicles targeted to specific organelles?

A

There are proteins bound on the outside of the vesicle that moderate targeting.

  1. Rab and v-SNARE are bound to the external side of the vesicle
  2. Tethering molecule on the cell membrane interacts with Rab, bring the vesicle into close proximity
  3. v-SNARE and t-SNARE on the target cell membrane interact, and the vesicle fuses
20
Q

What is Rab-GTP?

A

It is a protein on the outside of a vesicle that is specific to certain organelles, leading to the targeting of organelles to specific organelles

21
Q

What is v-SNARE?

A

This is the vesicle snare molecule that is involved with fusion of the vesicle to the organelle

22
Q

What is t-SNARE?

A

It is the protein on the cell membrane of a vesicle that is involved with fusion of the vesicle to the cell organelle membrane

23
Q

How is specificity of vesicle targeting maintained?

A

There are many different Rab proteins that are specific to different organelles

24
Q

Describe vesicular transport from the ER to the Golgi

A

Vesicles form with COPII

These vesicles are targeted to the Golgi

25
Q

The Golgi apparatus is a series of …

A

Ordered compartments

26
Q

Each compartment in the Golgi has …

A

Specific enzymes involved with processing of enzymes

27
Q

Describe processing in the Golgi

A

In each compartment, different additions are made to the proteins, due to the specific enzymes present in the various compartments

28
Q

By the time a protein reaches the trans face of the Golgi, it has … attached

A

Negatively charged sugars attached

29
Q

What are the two hypotheses for transport through the Golgi apparatus?

A
  1. Vesicular transport
  2. Cisternal maturation: vesicles from the ER fuse to form a cisterna. This cisterna moves along and gets incorporated into the Golgi complex
30
Q

Where does glycosylation occur?

A

In the membrane of the rER

31
Q

When is COP I used?

A

Formation of vesicles moving between the cisternae of the Golgi and formation of vesicles at the trans face for secretion

32
Q

What regulates the Uncoating of vesicles once they have formed?

A

Cytosolic proteins

33
Q

What happens to proteins with the KDEL sequence?

A

They are recycled from the Golgi to the ER in COP I coated vesicles

34
Q

What is the main thing that happens to proteins in the Golgi?

A

Addition and Modification of oligosaccharides

35
Q

To which residue are the dolichol oligosaccharides added during glycosylation in the ER?

A

Asparagine

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