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CELLULAR AND MOLECULAR BIOLOGY > TRAFFICKING > Flashcards

TRAFFICKING Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What fidelity to targets have to their destination?

A

High fidelity.

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2
Q

Transport vesicles are coated. What can their coats be made up of?

A

Clathrin
COPI
COPII

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3
Q

Newly made proteins can be translocated into organelles either co or post translationally. What does this mean?

A

Co translational translocation means that as the protein is being translated it is also being translocated into the ER of the lumen.
Post translational means the protein is translocated after being translated.

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4
Q

How leaky is fusion of vesicles onto membranes?

A

Not at all.

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5
Q

What is the function of SNAREs?

A

They provide specificity of fusion and ensures the correct vesicle fuses with the correct target membrane.

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6
Q

What does the Clathrin structure look like?

A

All protein coats are visible through electron microscopy.

Clathrin is distinction by its hexagonal protein arrays.

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7
Q

What is ER translocation?

A

movement of newly made proteins from the cytosol to the ER.

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8
Q

Where does cotranslational translocation occur more frequently?

A

The RER.

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9
Q

What is ‘The Signal Hypothesis’?

A

If a protein has a series of amino acids encoding an ER signal sequence, it can be translated and cotranslated into the ER

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10
Q

What is the process of translocation of a soluble protein?

A

A signal sequence at the end terminus (a stop transfer of the chain embeds into the translocator protein in the ER membrane. The signal sequence acts as a tether, anchoring the polypeptide chain allowing it to enter the ER lumen. A signal peptidase cleaves the signal sequence, releasing the sequence of amino acids into the ER lumen. Now the protein can be folded into the correct tertiary structure, in the ER lumen.

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11
Q

What is the process of insertion of membrane proteins into the ER membrane?

A

The polypeptide chain is fed through the open pore.
A stop transfer sequence on the polypeptide signals to the translocator to close, preventing further translocation. The sequences acts as a TMSD, anchoring the protein in the membrane.
A signal peptidase cuts off the signal peptide.

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12
Q

What is a type 1 membrane protein?

A

Amino terminus is translocated into the ER lumen.

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13
Q

What is a type 2 membrane protein?

A

Carboxyl terminus is translocated into the ER lumen.

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14
Q

What is the function of a chaperone protein?

A

Ensure proper protein folding.

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15
Q

What parts of the cell are rich in chaperones?

A

The ER lumen.

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16
Q

What is BiP?

A

BiP is a chaperone protein in the lumen of the ER that associates with newly made antibody molecules. BiP ensures that antibodies stay in the lumen until they are correctly assembled. After correct assembly, antibodies are packaged into vesicles for transport.

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17
Q

Defects in folding give rise to disease. Give an example.

A

Cystic Fibrosis

18
Q

What does detection of misfolded proteins give rise to?

A

The Unfolded Protein Response

19
Q

What is the Unfolded Protein Response?

A

Recognises that there are too many proteins in the ER lumen and the chaperone system is saturated.
Increases synthesis of ER chaperones and decreases the rate of protein synthesis.

20
Q

Orkambi is used to treat Cystic Fibrosis?

A

Combination drug of a chaperon and a channel opener.

21
Q

What is Gaucher’s disease?

A

Mutations in lysosomal enzymes required for glucosylceramide metabolism.

22
Q

What can liver damage be caused by in terms of failed trafficking?

A

Mutant protein is not degraded and accumulates in hepatocytes.
Carbamazepine can be used to increase autophagy.

23
Q

How is emphysema caused?

A

Deficiency of secretion of alpha1-antitrypsin.

Failure to inactivate neutrophil elastase in the lung.

24
Q

What is the cause of hypothydroidism in terms of trafficking?

A

Production of mutant thyroglobulin.

This causes massive proliferation in the ER in attempt to secrete normal amounts of the hormone.

25
Q

What can ER folding diseases be treated with?

A

Drugs that activate the Unfolded Protein Response.

Pharmacological chaperones.

26
Q

What are pharmacological chaperones?

A

Small molecules that mimic the behaviour of chaperones so misfolded proteins become correctly folded.

27
Q

What are the essential components for all transport vesicle formation?

A

GTPase
Adaptor proteins
Coat proteins

28
Q

What is a GTPase?

A

It is a molecular switch that allows quick response to extracellular signals and regulation.

29
Q

How its GDP converted to GTP and vice versa?

A

Guanine Nucleotide Exchange Factors (GEFs) convert GDP to GTP
GTPase Activating Proteins convert GTP to GDP.

30
Q

Where is GTP usually found?

A

Membrane associated.

31
Q

Where is GDP usually found?

A

In the cytosol.

32
Q

What are the components of COPII?

A

GTPase: Sar1
Adaptor: Sec23/24
Coat: Sec13/31

33
Q

How do COPII vesicles form?

A

Fully folded cargo proteins that are required to be send through the secretory pathway contain an exit signal.
Sar1-GTPase is converted to its active form by a GEF on the ER membrane. Now active, this allows recruitment of adaptor and coat proteins.
The adaptors recognise motifs in the cytoplasmic domains of membrane proteins that allows it to select cargo to ensure specificity and link the cargo to the outer coat. As the coat structure builds up, cargo is selected into the bud. Coat proteins provide a structural scaffold, facilitating pinching off of the bud. The bud is formed from specialised regions of the ER called exit sites.

34
Q

What are the minimal requirements for COPII formation?

A

By reconstitution experiments, we can understand what makes a COPII vesicle. What do you need to add to a test tube produce a COPII vesicle?
Cytosol,ATP,GTP,p58
By fractionating the cytosol to find its components it was found that Sar1(GTPase),Sec23/24 (adaptor), Sec13/31 (coat), ATP and GTP

35
Q

What is the effect of a GDP mutant?

A

Sequesters GEFs so cannot exchange GDP for GTP

Often produces dominant negative effects.

36
Q

What is the effect of a GTP mutant?

A

Cannot hydrolyse GTP

37
Q

What does expression of mutatnt Sar1 inhibit?

A

COPII formation

38
Q

What is the difference between transport vesicles?

A

Select for different cargo.

39
Q

Transport through the secretory pathway is mediated by what?

A

Requirement for the cytoskeleton to move vesicles along microtubule tracts.

40
Q

What is Craniolenticulosutural dysplasia and what is it caused by?

A

Due to a mutation in SEC23A leading to abdnormal endoplasmic reticulum to golgi trafficking.
Problems with ossification of the skull. Fontanel hasnt closed and issues with connective tissue.

41
Q

Using zebrafish to phenocopy the KO of Sec23, what is seen?

A

Defects in the skeleton and cartilage deposition.
Suggests a specific cargo secretion pathway.
Potential that the issue is collagen transportation and the ability of COPII to do this as collagen is such a large molecule.
Only some proteins are affected as Sec23B can compensate for the mutated Sec23A to an extent, but collagen requires a fully functional Sec23A.

CELLULAR AND MOLECULAR BIOLOGY (12 decks)

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