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Y2 Mol Bio > Secretory Pathway > Flashcards

Secretory Pathway Flashcards

1
Q

Describe the oath of the secretory pathway

A

ER to golgi to plasma membrane

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2
Q

Describe the path of the endocytic pathway

A

Cell surface to endosome to golgi/ER/endosome

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3
Q

How does material move from the rough ER to golgi?

A

Vesicle fusion

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4
Q

What does the trans golgi do?

A

Sorts out constitutively secreted proteins without the ned for signals

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5
Q

Where does glycoslation take place?

A

ER

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6
Q

What sorts of glycosylation can take place?

A

N- linked on Asp
O- linked on S/T

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7
Q

Describe how an Asp N-link forms

A
  1. Pre-formed oligosaccharide is added to an Asp in the ER
  2. Oligosaccharides are added and processed throughout the secretory pathway
  3. Oligosaccharides are trimmed and more sugars are added in the golgi
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8
Q

Why are proteins glycosylated?

A

Assist in folding
Can act as a ligand for intracellular trafficking/sorting and interactions with the extracellular matrix + proteins/sugars on other cells

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9
Q

What makes a suitable model organism to study cellular processes?

A

Simplicity- so single celled organisms
Allows analysis of specific types of secretion

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10
Q

What are some advantages of studying yeast for the secretory pathway?

A

Can do genetic studies between haploid and diploid
The entire genome sequence is known and fundamental pathways have been conserved
Cheap and easy to grow in large quantities
Limited gene diversity

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11
Q

What are some disadvantages of studying yeast for the secretory pathway?

A

Limited cell-cell contact, so not informative for multicellular organisms
Small (5μm) so high resolution imaging is difficult
Cell wall can prevent some studies such as microinjections

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12
Q

What hypothesis did Novick and Schekman have in 1980?

A

If proteins couldn’t be secreted (sec-), the cell density would increase as vesicles carrying the protein accumulates

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13
Q

What experiment did Novick and Schekman do in 1980?

A

Cells were analysed for their abilities to secrete invertase and acid phosphate at permissive and restictive temperatures
Secretory mutants synthesised by didn’t secrete them.
Heavier cells were analysed with electron microscopy to find alterations in ultrastructure, e.g accumulation of vesicles

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14
Q

How many genes were identified in Novick and Schekman’s experiments?

A

23
These were ordered by combining mutants from different classes

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15
Q

Describe the progress of α factor throughout the secretory pathway

A
  1. Modified in the ER by oligosaccharides
  2. Sugars are added in the golgi
  3. Proteolytically cleaved into 4 peptides before secretion
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16
Q

Why weren’t all the genes in secretory and exocytic pathway identified by Novick and Schekman?

A

Only temperature sensitive mutants were identified
Only secretion to the plasma membrane was identified- nothing to endosome or vacuole
Redundantly (rarely) functioning genes wouldn’t be identified

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17
Q

Where does the decision to traffic to the surface or lysosome take place?

A

Trans-golgi network

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18
Q

What pathways are affected by mutations between the endosome and lysosome?

A

Biosynthetic and degradative pathways

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19
Q

What is endocytosis?

A

Process where the plasma membrane invaginates into the cell
Produces a vesicle that can fuse with endosomes and enter the endo-lysosomal membrane system

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20
Q

What is the importance of endocytosis?

A

Retrieves molecules from the secretory vesicle for recycling
Downregulates certain signals
Remodels the cell surface

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21
Q

Describe the path of endocytosis

A

Plasma membrane
Endocytic vesicle
Early endosome
Late endosome
Golgi or vacuole

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22
Q

How were mutants in endosomal pathway identified?

A

End- screens looked at mutatants tht could not internalise lucifer yellow or an α-factor (pheromone)

23
Q

What does the lysosome (vacuole) do?

A

Degrades extracellular material from endocytosis
Degrades intracellular components through autophagy
It’s proteolytic enzymes are kept separate from the rest of the cell

24
Q

How are lysosome enzymes transported to the lysosome?

A

Secretory pathway and sorted at the trans-golgi network

25
Q

How was vacuolar protein sorting (VPS) studied?

A

Carboxypeptidase Y (CPY) moves ER -> Golgi -> Lysosome
This can be tracked with a colour based assay
vps mutant strains were combined to find the order of action of genes

26
Q

How is carboxypeptidase Y recycled?

A

It has an adaptor protein which binds to its tail and leads to it moving to the golgi to be recycled

27
Q

what receptor recognises CPY in the late golgi?

A

Vsp10

28
Q

What does the transport step of CPY require

A

Clathrin and 2 adaptors: Gga1 and Gga2

29
Q

Describe the nuclear pore

A

Formed at inner and outer membranes of the nuclear envelope
30 different nucleoporins
Important in DNA histone synthesis in the cytosol

30
Q

Where are ribosomes synthesised

A

The nucleus, so have to diffuse out

31
Q

How can proteins be recognised for trafficking through the nuclear pore?

A

Peptide sequence on the end of a protein.
Rich in Lys, Arg and Pro

32
Q

What sort of experiments were used to work out machinery for translocating proteins?

A

In vitro experiments, e.g protein import into nucleus

33
Q

What signals are recognised for a protein to move from nucleus to cytosol?

A

N-terminal sequence is recognised by sec61 and fed through
When the stop transfer sequence is reached, the C-terminus enters the cytosol

34
Q

Describe how chaperones in the ER assist protein folding

A

BiP (chaperone) associates with newly folded protein to ensure it correctly folds.
It is bound until the protein folds correctly, so it can be packaged.
e.g light chains forming on an antibody

35
Q

What stimulates the unfolded protein response in cystic fibrosis?

A

CFTRδ508 misfolds proteins, stimulating the UPR. This is becuase the ER is overwhelmed

36
Q

What happens in the unfolded protein response (UPR)?

A

Translation shuts down
Too many proteins activates apoptotic pathways
Upregulated chaperone synthesis

37
Q

Describe how proteins move into mitochondria

A

N-terminal is recognised by TOM
Protein translocates though TOM and chaperones in intermembrane space assemble polypeptides. They move through TIM23 into the matrix

38
Q

How does TOM recognise proteins?

A

Recognises structure, rather than amino acids
Hydrophobic residues bind in a hydrophobic groove

39
Q

What are some features of vesicular transport?

A

Vesicles are targeted to their destination with high fidelity
Cargo buds off the donor membrane
Fusion is non-leaky
Transport vesicles are coated

40
Q

What are the main features of vesicle formation?

A

GTPase
Adaptor proteins (recognise cargo)
Coat

41
Q

What is the founding member of the GTPase family involved in vesicular transport

A

Ras
Family includes Rabs, Arfs, Ran, Rho

42
Q

What is a COPII coated vesicle made up of?

A

GTPase: Sar1 (Arf) Sec12(GEF)
Adaptor: Sec23/24 complex 23 binds Sar1, 24 binds cargo
Coat: Sec 13/31 complex

43
Q

How is the COPII coated vesicle suited to its function

A

Sec23/24 has a bow-tie shape allowing it to recognise a curved shape
High SA:V of the bud

44
Q

How is COPII studied?

A

Reconstitution with ER membranes containing ribophorin. These are mixed with COPII vesicles containing p58.
These are separated on a sucrose gradient and centrifuged to see if ER has taken up p58

45
Q

What is a GDP mutant?

A

Mutant where GEFs have been sequestered

46
Q

What is a GTP mutant?

A

Mutant where GTP cannot be hydrolysed

47
Q

What effect does Sar1GDP have on COPII formation?

A

Inhibits it

48
Q

What do COPII and COPI carry?

A

COPI- Retrived/newly synthesised proteins
COPII- Newly synthesised proteins

49
Q

What do adaptor proteins do?

A

Recognise and select cargo, ensuring specificity
Link the coat to membrane
Recognise motifs in cytoplasmic domains of membrane proteins

50
Q

What sorting signal does TfR (Transferrin receptor) have?

A

Tyrosine-based YxxPhi

51
Q

What sorting signal does acetylcholine have?

A

Di leucine [DE]xxxLL

52
Q

What is AP2?

A

Major clathrin adaptor
Recognises a variety of peptide motifs
At the plasma membrane

53
Q

Where are AP1 and AP3 located?

A

AP1- endosomes and TGN
AP3- TGN and lysosomal related organelles

54
Q

Describe AP1 and AP2 structures

A

Appendages that interact with proteins
β2 binds to clathrin
μ2 and σ2 recognise signals on TM proteins

Y2 Mol Bio (10 decks)

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