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MBB 231 > Lecture 11 - Endomembranes & ER > Flashcards

Lecture 11 - Endomembranes & ER Flashcards

1
Q

def: sites for protein and lipid synthesis, processing and sorting

A
  • rough and smooth ER
  • golgi complex
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2
Q

def: carry and sort material bought into the cell

A

endosomes

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3
Q

def: digest ingested material and unneeded cellular components

A

lysosomes

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4
Q

def: move molecules between the compartments and plasma membrane

A

transition, transport and secretory vesicles

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5
Q

def: house hydrogen peroxide generating reactions

A

peroxisomes

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6
Q

def: store ions, sugars, amino acids, and toxic compounds

A

vacuoles

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7
Q

from the protein synthesis perspective, what is the start of the endomembrane system?

A

the rough endoplasmic reticulum

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8
Q

the rough ER consists of tubular membranes and flattened sacs called _______

A

cisternae

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9
Q

about ___ of the proteins are synthesized in the RER

A

1/3

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10
Q

where are these proteins produced in the cell:
- secreted proteins
- transmembrane proteins
- soluble proteins that reside in the ER, Golgi complex, lysosomes, endosomes vesicles, and vacuoles

A

rough ER

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11
Q

where are these proteins synthesized:
- ones destined to remain in the cytosol
- peripheral proteins of the cystolic surface membranes
- proteins that are transported to the nucleus
- proteins that are incorporated into peroxisome, chloroplasts and mitochondria

A

on “free” cytosolic ribsomes

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12
Q

where do all proteins BEGIN synthesis?

A

on ribosomes in the cytosol

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13
Q

how do proteins know where they need to go?

A

information is coded in the primary sequence: ER signal sequence or sorting signal

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14
Q

how can the compartments of the eukaryotic cell be divided?

A
  1. the endomembrane system
  2. the cytosol
  3. the mitochondria, chloroplasts, peroxisomes, and the interior of the nucleus
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15
Q

what are the 2 pathways for routing the protein products?

A
  1. free ribosomes
  2. ER docked ribosomes
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16
Q

most membrane proteins take which pathway of protein synthesis?

A

ER-docked ribosomes

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17
Q

what are the 2 pathways of protein sorting?

A
  1. co-translational import
  2. post-translational import
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18
Q

def: protein sorting - proteins carrying an ER signal sequences direct the ribosomes-polypeptide complex to the rough ER, translation is completed on the rough ER and then process and sorted in the ER and Golgi

A

co-translation import

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19
Q

def: protein sorting - proteins lacking an ER signal sequence complete their synthesis on ribosomes that are free in the cytoplasm, proteins are released into the cytoplasm and the ones with an organelle-specify sorting signal are imposed into the organelle

A

post-translational import

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20
Q

do cytoplasmic proteins have sorting signals

A

no they remain in the cytoplasm

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21
Q

co-translational import is considered a _________ pathway while post-translational import is a _____________ pathway

A

secretory, non-secretory

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22
Q

def: multiple ribosomes synthesizing the same mRNA

A

polysome

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23
Q

sorting signals direct proteins to _______ __________-

A

their compartments

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24
Q

an ER signal sequence directed the polypeptide/ribosme to the __ __________

A

ER membrane

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25
Q

co-translational translocation of _______ ______ deposits the polypeptide into the ER lumen by a ribosome that is attached to the ER membrane

A

soluble proteins

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26
Q

def: proposes that intrinsic molecular signals determine the localizations of some polypeptides

A

signal hypothesis

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27
Q

what happens if a sorting signal is lost?

A

targeting of the protein is lost

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28
Q

what happens if a sorting signal is transplanted to another protein?

A

targeting is imparted to the recipient protein

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29
Q

ER signal sequences usually have _________ ________ region and a _______ region near where the cleavage from the mature protein will take place

A

hydrophobic N-terminal region, polar region

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30
Q

def: particle that bind the Ribosome-mRNA-Polypeptide complex to the ER protein

A

signal recognition particle (SRP)

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31
Q

contact with the ER is mediated by __, which binds the __ _____ _______ of the newly forming polypeptide

A

SRP, ER signal sequence

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32
Q

what does the SRP contain

A

proteins and RNA

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33
Q

polypeptide synthesis proceeds until the ___ ______ sequence has been formed

A

ER signal sequecne

34
Q

what happens when the SRP binds to the signal sequence?

A

blocks further translation

35
Q

where does the SRP bind to on the ER membrane?

A

to the SRP receptor, which is an integral membrane protein

36
Q

the ER signal sequence is inserted into the _________, a channel protein in the membrane once the SRP has been released

A

translocon

37
Q

what happens once the ER signal sequence makes contact with the interior of the translocon?

A

the plug is displaced and the channel opens to the ER lumen

38
Q

def: cleaves ER signal sequence during polypeptide elongation

A

signal peptidase

39
Q

def: bind the nascent peptide to facilitate folding

A

chaperones

40
Q

G proteins can acts as ______ ______ as seen in the SRP and SRP receptor proteins

A

molecular switches

41
Q

in GTP-bound form, SRP and SRP receptor have _____ affinity for each other

A

high

42
Q

when hydrolysis of GTP occurs, affinity for SRP to SRP receptor _______ causing their release

A

decreases

43
Q

the orientation of multi-pass protein integral membrane protein is determined by _____ _____ of the first transmembrane domain

A

charge/orientation

44
Q

what are the two kinds of transmembrane proteins?

A

single pass or multi-pass

45
Q

when is transmembrane protein orientation established?

A

during their synthesis

46
Q

__________ chains are always present on the non-cytosolic side

A

oligosaccharide

47
Q

asymmetry of transmembrane proteins reflects their ______

A

function

48
Q

hydrophobic transmembrane domains can ________ into the lipid bilayer through a seam along one side of the translocon

A

dissolve

49
Q

each subsequent transmembrane domain must have _________ ________-

A

opposite charge/orientation

50
Q

what can help but in a subsequent transmembrane domain

A

ribosomes

51
Q

in terms of protein synthesis, what are 3 specific functions of the rough ER?

A
  1. glycolysation
  2. folding of polypeptide chains and subunit assembly
  3. disulphide bond formation
52
Q

in terms of recognition, what are 2 specific functions of the rough ER?

A
  1. ER associated degradation (ERAD) proteins that are incorrectly folded, modified, or assembled are exported
  2. degradation occurs in cytosolic proteasome
53
Q

most proteins synthesized in the rough ER are _________ on the amide nitrogen of an asparagine rescue by the addition of a pre-formed oligosacharride. what is this process called?

A

glycosylated, N-linked glycosylation

54
Q

where are O-linked sugars added ?

A

in the Golgi

55
Q

what are the 3 functions of carbohydrate groups?

A
  1. macromolecule binding sites
  2. aid in protein folding
  3. increase stability
56
Q

def: when oligosaccharide is added to the recipient protein as the polypeptide is being synthesized

A

co-translational glycosylation

57
Q

what do the lectins Calnexin and Clareticulin do ?

A

bind to N-linked oligosaccharides preventing aggregation and promoting proper folding

58
Q

calnexin and clareticulin recognize a _______ _____ glucose and therefor bind only ______ the oligosaccharide precursor has begun

A

single terminal, after

59
Q

when can the protein dissociate from its chaperone and leave the ER

A

when the third glucose is removed

60
Q

binding of calnexin and calreticulin _______ _______ and drives ______ ______ formation

A

prevents aggregation and drives disulphide bond formation

61
Q

def: abundant chaperone in the ER lumen, member of Hsp70 chaperones

A

BiP (binding proteins)

62
Q

what does BiP do?

A

binds to hydrophobic regions of polypeptide chains and prevents aggregation of polypeptides with similar regions

63
Q

what does BiP prevent?

A

interaction between hydrophobic regions of different proteins

64
Q

if the protein folds correctly, the hydrophobic region is where?

A

buried in the interior of the molecule

65
Q

if the protein does not fold correctly, what happens?

A

it will have to interact with BiP again

66
Q

def: enzyme that catalyzes disulfide bond formation in the lumen of the ER

A

protein disulfide isomerase (PDI)

67
Q

disulfide bond in the active site of PDI is __________ to a protein

A

transferred

68
Q

where are disulfide bonds only formed in eukaryotic cells?

A

only in the ER

69
Q

def: a cellular stress response pathway in which sensor molecules in the ER detect the misfiled proteins

A

unfolded protein respones (UPR)

70
Q

what do phosphorylate translation factors do?

A

inhibit protein synthesis to decrease the flow of proteins to the ER

71
Q

what do UPR’s up regulate?

A
  1. ER based chaperones
  2. transport that move proteins out of the ER
  3. protein degradation machinery
72
Q

def: component of the UPR that recognizes misfolded or unassembled proteins

A

ER-associated degradation (ERAD)

73
Q

what degrades misfiled proteins ?

A

proteasomes

74
Q

def: large protein degrading structures, predominant proteases of the cytosol

A

proteasomes

75
Q

what do proteasome bind to?

A

ubiquitin-labeled proteins

76
Q

def: small protein containing 76 amino acids

A

ubiquitin

77
Q

ubiquitin is joined to target proteins by a process involving 3 enzymes:

A
  • ubiquitin activating enzyme
  • ubiquitin conjugating enzyme
  • substrate recognition protein, or ubiquitin ligase
78
Q

ER is the primary source of ________ _______

A

membrane lipids

79
Q

fatty acids for membrane phospholipids are synthesized in the _________ and incorporated into the ER membrane on the cytosolic side

A

cytosol

80
Q

what transfers fatty acids for membrane phospholipids to the lumen side of the bilayer of the ER?

A

phospholipid translocators (flippases)

81
Q

T or F: the ER cannot form contact sites with other organelles

A

false, it can

82
Q

def: proteins that exchange lipids between the compartments of the ER

A

lipid transfer proteins

MBB 231 (19 decks)

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