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Cell and Molec > Protein Sorting > Flashcards

Protein Sorting Flashcards

1
Q

Where is a terminal start-transfer sequence of a transmembrane protein?

A

N-terminus as it gets to translocator

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2
Q

What is the stop-transfer sequence of a protein?

A

The area where the protein stops and leaves translocator

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3
Q

Is the stop-transfer sequence hydrophilic or hydrophobic?

A

Hydrophobic

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4
Q

What common domain serves as the membrane-spanning part of the stop transfer signal?

A

A single alpha helix

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5
Q

What’s an internal signal sequence?

A

Signal sequence not on the end of a protein

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6
Q

In an internal signal sequence, what determines if the n-terminus or c-terminus will be on the ER lumen side?

A

Positively charged amino acids > cytosol

Negatively charged > lumen

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7
Q

What part of a double-pass transmembrane protein would get stuck in a membrane?

A

Start + stop transfer sequence

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8
Q

What sequences are present in multipass proteins that get stuck in membranes?

A

Lots of start & stop transfer sequences

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9
Q

How does ‘rough ER’ get its name?

A

It’s the part with a lot of polyribosome sequences on it

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10
Q

What does a signal sequence do to a channel once it gets to it?

A

Pushes out the plug in the channel

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11
Q

What ways can a protein get stuck in the membrane?

A

Single-pass, double-pass, multipass

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12
Q

What ways can a protein get stuck in the membrane?

A

Single-pass, double-pass, multipass

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13
Q

What functions does the ER have besides helping protein synthesis?

A

Add N-linked oligosaccharides

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14
Q

What does ‘N-linked’ oligosaccharide mean?

A

Attached to nitrogens of asparagine side chains

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15
Q

Why do proteins have oligosaccharides added to them?

A

Signal pathway recognition

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16
Q

Where does dolichol hang out?

A

lipid bilayer of ER membrane

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17
Q

What does dolichol do?

A

It’s a carrier that pre-assembles oligosaccharides for protein transfer

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18
Q

Why are proteins glycosylated? (in golgi)

A

Help fold proteins, help for cell recognition / adhesion

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19
Q

What does ‘o-linked’ oligosaccharide mean?

A

Attached to hydroxyl oxygen of serine, threonine, tyrosine, or other oxygens

20
Q

What adds glucose to proteins that aren’t completely folded?

A

glucosyl transferase

21
Q

What does calnexin do?

A

ER chaperone, binds to proteins with single terminal glucose

22
Q

When a protein is fully folded, can it still have an oligosaccharide on it?

A

Yes, N-linked

23
Q

What is a cycle of adding glucose and then trimming it for?

A

To get the protein folded properly

24
Q

Where is the protein as oligosaccharides are getting attached?

A

Still going through Cytosol/ER lumen membrane

25
Q

What happens to misfolded proteins?

A

Get ubiquitin attached to them, then sent to proteosome to get rekt

26
Q

What ubiquitinates misfolded proteins?

A

E3 ubiquitin ligase

27
Q

What’s the unfolded protein response?

A

Signalling protein to get more expression of ER proteins that fold new proteins properly

28
Q

How does the unfolded protein response turn on?

A

Accumulation of misfolded proteins signals transcription activation in nucleus

29
Q

What’s a GPI anchor?

A

Protein that binds to C-terminus of some membrane proteins

30
Q

How are lipid bilayers assembled in the ER?

A

Binding protein attaches ot fatty acid, then it binds to ER membrane

Polar head gets modified

Lipids leave

31
Q

What needs to happen for lipids to flip from one side to another?

A

Enzymes have to catalyze

‘Scramblases’ equilibrate to create symmetry (one-way)

Flippases do the same (two-way)

32
Q

How do cholesterol / ceramide get produced?

A

ER makes them

33
Q

When is a signal sequence on a single-pass transmembrane protein useful a second time before cleavage?

A

It gets recognized by protein translocator and then acts as start-transfer signal

34
Q

What distinguishes start and stop transfer sequences in multipass transmembrane proteins?

A

Nothing really, it’s just based on which sequence goes in first (‘relative order in growing polypeptide chain’)

35
Q

How might a protein stay in the ER after translation?

A

KDEL / KDEL receptor: amino acid sequence at c-terminus of protein keeps it there

36
Q

What does ‘glycosylated’ mean?

A

Carbohydrates (sugars) are added to something

37
Q

What does an oligosaccharyl transferase do?

A

Helps attach sugar precursors (glycosylate) to proteins in lumen rom dolichol

38
Q

What’s the temporal progression of a new dolichol lipid look like?

A

Attach to lipid bilayer > phosphorylated at cytosol side > sugars added at cytosol side > FLIPS > more sugars added to chain on lumen side > 14 sugars total on it

39
Q

What adds sugars to N-glycosylation sites?

A

oligosaccharyl transferase

40
Q

What’s the sugar system that lets proteins get folded properly?

A

Glucose trimming (glucosidase) > glucose addition (glucosyl transferase) > folding (calnexin/reticulum) until it’s folded

41
Q

What marks time a protein has spent in the ER?

A

N-linked oligosaccharides - proteins that can fold faster than sugar is removed don’t get degraded

42
Q

If there are so many misfolded proteins that calnexin/reticulin can’t bind them fast enough, what happens?

A

UPR (unfolded protein response): Sensors (IRE1, PERK, ATF6) sense the misfolded proteins and activate gene expression

43
Q

Where on proteins do GPI anchors attach?

A

C-terminus

44
Q

Why are scramblases necessary for bilayer formation?

A

Lipids are added to bilayer from cytosol side, so ER side doesn’t have any heads. Scramblases need to flip them to make the bilayer equilibrate

45
Q

What do flippases do?

A

Also flip lipids, but specific lipid heads to create asymmetry

46
Q

What is ceramide? How is it made? Where?

A

Just the head of a lipid, useful for signalling. Condense serine with a fatty acid. Made in ER

Cell and Molec (21 decks)

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