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Bio 202 Test 2 > Protein Sorting > Flashcards

Protein Sorting Flashcards

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1
Q

What are the two sites of protein synthesis?

A

ER ribosomes and cytosolic ribosomes

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2
Q

What proteins are made by the ER ribosomes, how do they get to their destination?

A

ER proteins

Golgi proteins

Endosomal proteins

Lysosomal proteins

Plasma membrane proteins

Secreted proteins

TRANSPORTED TO DESTINATION VIA VESICLES, MEMBRANE TRANSFER, OR CARRIER PROTEINS

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3
Q

What proteins are made by the cytosol? How do they get to their destination?

A

Cytosolic proteins

mitochondrial and chloroplast proteins

nuclear proteins

peroxisomal proteins

THERE ARE IMPORTED INTO THE ORGANELLES

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4
Q

How do proteins made from cytosolic or ER ribosomes know where to go?

A

They are tagged with specific AA sequences (signal sequences) that allow them to enter specific organelles

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5
Q

Where do untagged proteins remain?

A

in the cytosol

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6
Q

How are cargo proteins imported into the nucleus?

A

their NLS (nuclear localization sequence) binds to importins and direct them through nuclear pores

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7
Q

Are tertiary and quaternary protein structures disrupted during import or export into the nucleus? What about ribosomal subunits?

A

NO NO NO

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8
Q

How are importins dissociated from cargo proteins and brought back to cytoplasm?

A

ran-GTP binds to them and brings them back, then GTP is hydrolyzed to detach

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9
Q

What is the name of the proteins that make up the nuclear pore?

A

nuclear porins

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10
Q

What are some of the functions of the peroxisome?

A

Removal of toxic molecules

metabolism

oxidation (breakdown) of long fatty-acid chains

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11
Q

Do peroxisomes have a lipid bilayer?

A

YES

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12
Q

Can the inside of the peroxisome crystallize due to high enzyme concentration

A

YES

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13
Q

Describe the two paths a protein can take to enter the peroxisome. What is the difference between the PTS1 and PTS2 pathway?

A

A peroxismal targeting signal (PTS) binds to the cargo and brings it through a Docking/RING complex (importer) into the peroxisome.

PTS1 - binds to C terminal

PTS2 - binds to N terminal

BOTH BRING PROTEIN THROUGH IN FOLDED STATE

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14
Q

What import is similar to mitochondrial protein import?

A

Chloroplast

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15
Q

Describe the import process of a protein into the mitochondria. Are the proteins folded or unfolded during this?

A

MTS (mitochondrial signal sequence) must be attached to N-terminal.

Then is recognized by Tom receptor of outer mito membrane

Then is recognized by Tim receptor of inner mito membrane

UNFOLDED VIA HSP70 IN CYTOSOL (CHAPERONIN)

MTS is cleaved off by protease once in the mito matrix via ATP hydrolysis and Hsp70 then folds the protein.

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16
Q

Is the ER more extensive than the plasma membrane?

A

YES, over 30X more membranes.

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17
Q

Where does the translation of ER proteins start?

A

THE CYTOSOL

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18
Q

What happens after ER protein translation starts in the cytosol?

A

SRP (signal recognition particle) recognizes N-terminal sequence and takes the ribosome and partially synthesized protein and mRNA to the ER where SRP binds to receptor on cytosolic surface of ER

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19
Q

After SRP binds to cytosolic surface of ER with partially synthesized ER protein what happens next?

A

The protein continues to be synthesized and goes through a protein translocator into the ER lumen

20
Q

Does just one ribosome usually translate the mRNA at a time?

A

NO, it is commonly a polyribosome

21
Q

What generates the force of translocation through the protein translocator of the ER surface?

A

The ribosome

22
Q

How is the finished ER protein released into the ER lumen?

A

a signal peptidase cleaves the SRP, then it folds into the lumen

23
Q

Is rough ER formed on smooth ER?

A

YES

24
Q

What is the main difference a single-pass ER transmembrane protein has to an ER lumen protein?

A

It is transmembrane and has a stop-transfer sequence that is inserted into the ER membrane

N terminus is on inside of lumen and C terminus is on cytosolic side

25
Q

Does the insertion of proteins into ER membrane happen co-translationally?

A

YES

26
Q

hen does glycosylation of proteins begin?

Where does glycosylation at N-link and ) linked occur?

A

As they are being synthesized

N - Asn (asparagine)

O - serine or threonine

27
Q

Are the proteins and lipid-glycans made separately before the are glycosylated together?

A

YES

28
Q

Where deos protein folding occur for proteins made on ER? Describe this process.

A

In the ER lumen

  1. chaperone protein (BiP) binds to hydrophobic patches via hydrolysis of ATP to ADP of forming protein to prevent misfolding by slowing the folding process down
  2. Eventually ADP is is replaced by ATP, which releases BiP from patch allowing protein to fold.
29
Q

LOOK AT SECRETORY PATHWAY FORM ER TO GOLGI SLIDE 20, 21, 22

A

DO IT

30
Q

Do vesicles have specificity as to where their destination is?

A

YES

31
Q

What is the first destination of a protein from the ER?

A

The golgi, specifically the cis-golgi network

32
Q

What is the difference between retrograde and anterograde transport of ER proteins?

A

Retrograde - towards more cis-golgi network

Anterograde - towards more trans-golgi network

33
Q

Describe how a vesicle is formed. What givens them their specificity? STEP 1

A

GTP-binding protein (GBP) that has GDP associated with it binds to a site of the membrane

When GTP is substituted for GDP coat proteins bind to GBP, this deforms the membrane into a vesicle

The coat proteins then bind membrane cargo proteins,cargo-receptor proteins, THE SOLUBLE CARGO PROTEINs, and v-snare proteins

THE COAT PROTEIN GIVES THEM THEIR SPECIFICITY

34
Q

What are some examples of coat proteins that give the vesicles their specificity?

A

COP1

COP2

EVCP

clathrin

LOOK AT SLIDE 22 TO SEE SPECIFIC TARGETS FOR THESE COAT PROTEINS

35
Q

What coat protein is dynamin specific to?

A

clathrin vesicles

36
Q

When does a vesicle begin to lose its coat protein “coat”? How? STEP 2

A

As is gets closer to the target, GTP is hydrolyzed leading to uncoating

37
Q

Describe how the vesicle fuses to its target. STEP 3

A

The Rab of the vesicle attaches to the tethering protein of the target (tethering)

v-snare of vesicle attaches to t-snare of the target (docking)

Lipid bilayers fuse (fusing) and cargo is delivered

38
Q

What are 2 ways we can visualize the secretory pathway?

A

VSVG linked to GFP in virus to yield green-fluorescent cells

This mutant protein of VSVG is retained in ER at restrictive temp but is released to golgi and then to PM at permissive temp

OR

Radioactively labeled proteins with signal sequence and isolated organelles placed in test tube and they co-sediment

39
Q

Describe the unfolded protein response. What is an unintended consequence of this?

A

sensors for misfolded proteins reside on ER membrane

Can either activate more chaperone proteins, inhibit protein synthesis, or degrade misfolded proteins

DMII - pancreatic cells produce higher levels of insulin than normal, overwhelming the folding machinery and creating a hyperactive UPR AND TRIGGERS CELL DEATH

40
Q

What is the difference between regulated and unregulated exocytosis?

A

Regulated - extracellular signal creates signal transduction pathway in cell that tells secretory vesicle storing proteins to release them the extracellular space

Unregulated - no extracellular signal needed for secretion to occur.

41
Q

What is the purpose of glycosylation and step by step modification of oligosaccharide?

A

to ensure proper protein folding

To maintain protein stability in ER and golgi

Function of transmembrane proteins

Signal in protein that is delivered from trans-golgi network to early endosome

LOOK AT SLIDE 29 FOR EXAMPLES

42
Q

What is the function of adaptin proteins? Examples?

A

contribute to specifity of clathrin vesicles for its CARGO AND TARGET ORGANELLE

AP1 - targets TGN to early endosome

AP3 - targets TGN to lysosome

43
Q

Where do Cop1 vesicles go? Why?

A

retrograde transport

  1. misfolded golgi or ER protein
  2. ER proteins to be returned after glycosylation
  3. for cisternal maturation purposes
  4. for proteins to be recycled for use in anterograde transport.
44
Q

Describe the LDL receptor pathway.

A

LDL binds to LDL receptors on plasma membrane

clathrin coated vesicle forms

uncoated as it reaches target endosome

fuses with endosome

LDL receptor buds off from endosome and returns to PM

endosome delivers LDL to lysosome and is broken down

LACK OF THESE RECEPTORS LEADS TO HYPERCHOLESTEROLEMIA

45
Q

What is the difference between pinocytosis and phagocytosis?

A

pincytosis - small molecules

phagocytosis - whole bacteria

46
Q

What is lowering as the early endosome matures into the lysosome? What does this do?

A

The pH

This activates certain enzymes at certain pH and releases PM receptor at certain pH

Degradation enzymes come from ER/golgi

47
Q

What is the difference between phagocytosis and autophagy?

A

Phagocytosis is the defense against pathogens and dead cells

Autophagy is a defense against damaged organelles

Bio 202 Test 2 (2 decks)

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