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Cellular and Molecular Biology > Exam 3: Ch 13 Targeting & Insertion of Proteins (ER) > Flashcards

Exam 3: Ch 13 Targeting & Insertion of Proteins (ER) Flashcards

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1
Q

protein targeting

A

delivery of newly synthesized proteins to their proper destination

2 kinds of process

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2
Q

2 processes of protein targeting

A

signal-based targeting

vesible-based trafficking (secretory pathway)

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3
Q

signal-based targeting

A

protein from cytoplasm –> intracellular organelle

occurs during translation or soon after

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4
Q

for memb. proteins, signal-based targeting leads to…

A

insertion of the protein into the lipid bilayer

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5
Q

for water-soluble proteins, signal-based targeting leads to…

A

translocation of the protein across the membrane into the aqueous interior of an organelle

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6
Q

secretory pathway (vesible-based trafficking)

A

transport of proteins from the ER using vesicles

destination may be outside the cell

integral memb. proteins transported to golgi, lysosome, and membrane

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7
Q

synthesis of all proteins begins by ______ ribosomes

A

cytosolic

if no signal peptide then product released into cytoplasm

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8
Q

memb. bound proteins and some organelles have a _____ peptide at the _______ terminus

A

signal peptide, amino terminus

ex. lysosome/secreted proteins

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9
Q

is a signal peptide usually cleaved off later?

A

yes

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10
Q

SRP

A

signal recognition particle

cytosloic RNP

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11
Q

is insulin an example of a secreted protein?

A

yes, has a SRP –> rough ER

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12
Q

vesicles on Golgi go from the ___ to ____ face and are ____

A

cis, trans

modified

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13
Q

targeting to the nucleus occurs how

A

mature protein contains a nuclear localization signal

pattern of a few aa directs to nucleus

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14
Q

how to test nuclear localization

A

put nuclear localization signal into a diff protein and see if it ends up in the nucleus

some TF are held inactive in the cytoplasm until another protein finds that has a nuclear localization signal

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15
Q

targeting to the ER in general

A

involves nascent proteins being synthesized on a ribosome –> when finished, extruded into ER memb. –> lumen

in lumen, chaperones help fold proteins

folded proteins undergo post-translational modifications –> transported out of ER

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16
Q

signal sequence (uptake-targeting sequence/signal peptide)

A

~20aa in the sequence of the protein itself

directs targeting to a particular organelle destination

found at N terminus (1st part of protein synthesized)

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17
Q

each organelle has specific ______ receptors for specific signal sequences

A

receptors

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18
Q

translocation channel

A

allows the targeted protein to enter the target organelle through the membrane

occurs after the signal sequence has interacted w/ the receptor on the organelle

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19
Q

ER in general

A

large organelle made of tubules and flattened sacs

membrane continuous with nuclear membrane

site of lipid and membrane protein biosynthesis

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20
Q

pulse-chase experiments with purified ER membrane demonstrated…

A

that secreted proteins cross the ER memb.

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21
Q

what do you find out with pulse-chase

A

where a tagged molecule ends up

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22
Q

pulse-chase experiment with radiolabeled aa

A

pulse: add radiolabeled aa glycine that gets incorporated into secretory proteins in rough ER

collect samples and homogenize them

chase: add lots of unlabeled glycine

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23
Q

microsome

A

little portions of rough ER memb. after cell is broken open (homogenized)

capable of protein translocation

showed that proteins synthesized by ribosomes on outside end up on the inside of the microsome (rough ER)

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24
Q

why is it hard to study memb. proteins?

A

if you break the membrane, the proteins stop working

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25
Q

a homogenizer uses what to break up rough ER

A

mild detergent

then a magnet separates microsomes from microsomes with w/ ribosomes

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26
Q

pulse-chase w/ insulin

A

homogenize –> microsomes then ribosome Ab to separate rough ER microsomes from others

grind everything with detergent then insulin Ab to isolate insulin and analyze

shows newly synthesized insulin in rough ER microsomes 1st, then insulin goes somewhere else

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27
Q

after synthesis of a secretory protein begins on free ribosomes in the cytosol, an __ signal sequence in the nascent protein directs the _______ to the ER membrane and initiates ______ of the growing pp across the ER membrane

A

ER, ribosomes, translocation

28
Q

signal sequences contain 1+ ______ aas adjacent to a stretch of hydrophobic residues

A

positive

29
Q

cotranslational translocation

A

transport of most secretory proteins into the ER lumen begins while the protein is still bound to the ribosome

30
Q

cotranslational translocation is initiated by two GTP hydrolyzing proteins

A

the signal recognition particles and its receptor located in the ER membrane

31
Q

what does SRP do

A

binds the ER signal sequence in a growing pp and the large ribosomal subunit

brings this complex to the ER membrane and docks to SRP receptor

32
Q

translocon

A

a complex of proteins that forms a channel in the Er membrane

growing pp goes through the central pore of the translocon into ER lumen

33
Q

what provides energy of translocation of the proteins into the lumen

A

energy from chain elongation in the ribosome

34
Q

why don’t other molecules go through the translocon pore?

A

there is a short helical plug

35
Q

signal peptidase

A

enzyme in the translocon that cleaves the signal peptide as it enters the lumen of the rough ER

36
Q

post-translational translocation

A

secretory proteins in yeast enter ER lumen after translation has been completed

doesn’t use SRP, only the translocon + signal peptide

uses ATP hydrolysis as the driving force

37
Q

the final orientation of integral membrane proteins is established during their _______

A

biosynthesis

during transport, their orientation is preserved

38
Q

topogenic sequence

A

direct membrane insertion and orientation of integral proteins

39
Q

what does the topology of a memb. protein refer to

A

the number of times it spans the memb.

the orientation of the membrane spanning segments

40
Q

single pass protein

A

only span the membrane once

classes I, II, III, and tail-anchored proteins

41
Q

type I protein

A

3 domains (cytoplasmic c-terminal, transmembrane, extracellular n-terminal)

signal sequence makes them similar to secreted proteins

have a stop transfer sequence

42
Q

type II protein

A

no signal sequence

have an anchor sequence in middle that tells ribosomes to embed protein in rough ER

opposite orientation to type I

43
Q

type III protein

A

same orientation as type I

no signal sequence, anchor sequence near N terminus embeds in rough ER

44
Q

multiple pass proteins

A

class IV - have 2+ membrane spanning segments

g-protein coupled receptors (7 pass protein)

have multiple internal topogenic sequences

45
Q

stop transfer anchor sequence

A

type I proteins

tells translocon to stop transport of mRNA/protein when 22aa hydrophobic sequence is reached

allows the hydrophobic transmembrane segment to be anchored in bilayer

46
Q

example of type IV protein with N-terminus in cytosol

A

GLUT transporters (glucose)

ion-channel proteins

47
Q

example of type IV protein with N terminus that is extracellular

A

G protein coupled receptors (7 transmemb. domains)

48
Q

some cell-surface proteins are tethered to the membrane by a ________ anchor

A

phospholipid anchor called GPI

signal sequence in luminal domain causes this

these proteins can rapidly diffuse laterally

49
Q

deduce topology of a memb. protein by aa sequence

A

hydropathic index - hydrophobic aa are positive and hydrophilic aa are negative

ex. HGH is type I

50
Q

peripheral membane protein

A

don’t cross membrane

may be synthesized by rough ER or free ribosomes

sticks to memb. by phospholipid

51
Q

4 modifications membrane and soluble secretory proteins synthesized on the rough ER undergo before reaching their destinations

A

covalent addition and processing of carbs (glycosylation) in ER and golgi

formation of disulfide bonds in ER

proper folding and assembly in ER

proteolytic cleavages in ER, golgi, and secretory vesicles

52
Q

glycoprotein

A

a protein with an attached carbohydrate - begin in rough ER, modified in golgi

glycosylation occurs on extracellular domain

53
Q

o-linked oligosaccharide

A

glycoprotein with carbohydrate chain attached to OH group

serine/threonine

54
Q

n-linked oligosaccharide

A

glycoprotein with carbohydrate chain attached to amide nitrogen

asparagine

55
Q

oligosaccharide side chains may promote the _______ and ________ of glycoproteins

A

folding, stability

56
Q

the lumen is an ______ environment, while the cytoplasm is a _______ environment

A

oxidized, reduced

57
Q

disulfide bonds make a protein more ______

A

stable

happens in an oxidation rxn (only in lumen of rough ER)

58
Q

disulfide bonds are only found in which types of proteins

A

soluble secretory proteins

extracellular domains of memb. proteins (ex. insulin)

59
Q

which aa forms disulfide bonds

A

cysteines

60
Q

what do lectins in the rough ER lumen do

A

help fold proteins with n-linked oligosaccharides

61
Q

assembly of multisubunit proteins occurs in the ________ __

A

rough ER

ex. immunoglobulins

62
Q

dislocation

A

when misfolded proteins in the ER are targeted for transport to cytosol for degradation

63
Q

ERAD

A

ER associated degradation complex

channel for dislocation of misfolded proteins

64
Q

p97

A

member of the AAA ATPase family that couples ATP hydrolysis to disassemble proteins

targets ubiquitin on misfolded proteins

65
Q

protein cleavage in rough ER

A

pro-proteins are precursors to the real protein (become proteins after post-translational modifications)

insulin is a pre-pro-protein (pre designates signal sequence)

cleave signal sequence to turn into pro-protein

Cellular and Molecular Biology (34 decks)

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