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

Question 1

protein targeting

Answer 1

delivery of newly synthesized proteins to their proper destination

2 kinds of process

Question 2

2 processes of protein targeting

Answer 2

signal-based targeting

vesible-based trafficking (secretory pathway)

Question 3

signal-based targeting

Answer 3

protein from cytoplasm –> intracellular organelle

occurs during translation or soon after

Question 4

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

Answer 4

insertion of the protein into the lipid bilayer

Question 5

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

Answer 5

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

Question 6

secretory pathway (vesible-based trafficking)

Answer 6

transport of proteins from the ER using vesicles

destination may be outside the cell

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

Question 7

synthesis of all proteins begins by ______ ribosomes

Answer 7

cytosolic

if no signal peptide then product released into cytoplasm

Question 8

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

Answer 8

signal peptide, amino terminus

ex. lysosome/secreted proteins

Question 9

is a signal peptide usually cleaved off later?

Answer 9

yes

Question 10

SRP

Answer 10

signal recognition particle

cytosloic RNP

Question 11

is insulin an example of a secreted protein?

Answer 11

yes, has a SRP –> rough ER

Question 12

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

Answer 12

cis, trans

modified

Question 13

targeting to the nucleus occurs how

Answer 13

mature protein contains a nuclear localization signal

pattern of a few aa directs to nucleus

Question 14

how to test nuclear localization

Answer 14

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

Question 15

targeting to the ER in general

Answer 15

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

Question 16

signal sequence (uptake-targeting sequence/signal peptide)

Answer 16

~20aa in the sequence of the protein itself

directs targeting to a particular organelle destination

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

Question 17

each organelle has specific ______ receptors for specific signal sequences

Answer 17

receptors

Question 18

translocation channel

Answer 18

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

Question 19

ER in general

Answer 19

large organelle made of tubules and flattened sacs

membrane continuous with nuclear membrane

site of lipid and membrane protein biosynthesis

Question 20

pulse-chase experiments with purified ER membrane demonstrated…

Answer 20

that secreted proteins cross the ER memb.

Question 21

what do you find out with pulse-chase

Answer 21

where a tagged molecule ends up

Question 22

pulse-chase experiment with radiolabeled aa

Answer 22

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

Question 23

microsome

Answer 23

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)

Question 24

why is it hard to study memb. proteins?

Answer 24

if you break the membrane, the proteins stop working

Question 25

a homogenizer uses what to break up rough ER

Answer 25

mild detergent then a magnet separates microsomes from microsomes with w/ ribosomes

Question 26

pulse-chase w/ insulin

Answer 26

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

Question 27

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

Answer 27

ER, ribosomes, translocation

Question 28

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

Answer 28

positive

Question 29

cotranslational translocation

Answer 29

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

Question 30

cotranslational translocation is initiated by two GTP hydrolyzing proteins

Answer 30

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

Question 31

what does SRP do

Answer 31

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

Question 32

translocon

Answer 32

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

Question 33

what provides energy of translocation of the proteins into the lumen

Answer 33

energy from chain elongation in the ribosome

Question 34

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

Answer 34

there is a short helical plug

Question 35

signal peptidase

Answer 35

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

Question 36

post-translational translocation

Answer 36

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

Question 37

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

Answer 37

biosynthesis during transport, their orientation is preserved

Question 38

topogenic sequence

Answer 38

direct membrane insertion and orientation of integral proteins

Question 39

what does the topology of a memb. protein refer to

Answer 39

the number of times it spans the memb. the orientation of the membrane spanning segments

Question 40

single pass protein

Answer 40

only span the membrane once classes I, II, III, and tail-anchored proteins

Question 41

type I protein

Answer 41

3 domains (cytoplasmic c-terminal, transmembrane, extracellular n-terminal) signal sequence makes them similar to secreted proteins have a stop transfer sequence

Question 42

type II protein

Answer 42

no signal sequence have an anchor sequence in middle that tells ribosomes to embed protein in rough ER opposite orientation to type I

Question 43

type III protein

Answer 43

same orientation as type I no signal sequence, anchor sequence near N terminus embeds in rough ER

Question 44

multiple pass proteins

Answer 44

class IV - have 2+ membrane spanning segments g-protein coupled receptors (7 pass protein) have multiple internal topogenic sequences

Question 45

stop transfer anchor sequence

Answer 45

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

Question 46

example of type IV protein with N-terminus in cytosol

Answer 46

GLUT transporters (glucose) ion-channel proteins

Question 47

example of type IV protein with N terminus that is extracellular

Answer 47

G protein coupled receptors (7 transmemb. domains)

Question 48

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

Answer 48

phospholipid anchor called GPI signal sequence in luminal domain causes this these proteins can rapidly diffuse laterally

Question 49

deduce topology of a memb. protein by aa sequence

Answer 49

hydropathic index - hydrophobic aa are positive and hydrophilic aa are negative ex. HGH is type I

Question 50

peripheral membane protein

Answer 50

don't cross membrane may be synthesized by rough ER or free ribosomes sticks to memb. by phospholipid

Question 51

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

Answer 51

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

Question 52

glycoprotein

Answer 52

a protein with an attached carbohydrate - begin in rough ER, modified in golgi glycosylation occurs on extracellular domain

Question 53

o-linked oligosaccharide

Answer 53

glycoprotein with carbohydrate chain attached to OH group serine/threonine

Question 54

n-linked oligosaccharide

Answer 54

glycoprotein with carbohydrate chain attached to amide nitrogen asparagine

Question 55

oligosaccharide side chains may promote the _______ and ________ of glycoproteins

Answer 55

folding, stability

Question 56

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

Answer 56

oxidized, reduced

Question 57

disulfide bonds make a protein more ______

Answer 57

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

Question 58

disulfide bonds are only found in which types of proteins

Answer 58

soluble secretory proteins extracellular domains of memb. proteins (ex. insulin)

Question 59

which aa forms disulfide bonds

Answer 59

cysteines

Question 60

what do lectins in the rough ER lumen do

Answer 60

help fold proteins with n-linked oligosaccharides

Question 61

assembly of multisubunit proteins occurs in the ________ __

Answer 61

rough ER ex. immunoglobulins

Question 62

dislocation

Answer 62

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

Question 63

ERAD

Answer 63

ER associated degradation complex channel for dislocation of misfolded proteins

Question 64

p97

Answer 64

member of the AAA ATPase family that couples ATP hydrolysis to disassemble proteins targets ubiquitin on misfolded proteins

Question 65

protein cleavage in rough ER

Answer 65

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