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MCBM EXAM 5 DANIELLE > Protein Trafficking > Flashcards

Protein Trafficking Flashcards

1
Q

Do proteins have the same destination after synthesis?

A

no different proteins have different destinations

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2
Q

What are the prokaryotic cells?

A

inner and outer membranes
periplasmic space
secretory proteins

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3
Q

What are the eukaryotic cells?

A

membrane bound compartments
secretory proteins
cytoplasm

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4
Q

What are the 5 membrane bound eukaryotic compartments?

A 
endoplasmic reticulum
nucleus
lysosomes
mitochondria
cell membrane
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5
Q

What type of information do proteins contain?

A

information for targeting

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6
Q

What type of proteins contain signals that determine their ultimate destinations?

A

nascent proteins (or newly synthesized proteins)

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7
Q

What is the difference between free and RER ribosomes?

A

there is no difference!

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8
Q

What determines the location of the ribosome?

A

determined by the protein being synthesized

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9
Q

What 3 types of proteins are made by free ribosomes?

A

nuclear, peroxisomal, and mitochondrial proteins

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10
Q

What does the nucleus have in regards to ribosomes and proteins?

A

internal nuclear localization sequences

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11
Q

What does the peroxisomes have in regards to ribosomes and proteins?

A

C-terminal sequence SKF

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12
Q

What does the mitochondrial matrix have in regards to ribosomes and proteins?

A

N-terminal sequence rich in positive charged amino acids and serine, threonine

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13
Q

Where are long chain fatty acids processed?

A

peroxisomes

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14
Q

What is SKF?

A

serine, lysine, phenylalanine

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15
Q

Ribosomes bound to the endoplasmic reticulum synthesize 3 major classes of protein. What are they?

A

secretory proteins
lysosomal proteins
integral membrane proteins (excluding those of mitochondria)

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16
Q

What are examples of secretory proteins?

A

proteins exported from the cell (collagen, insulin)

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17
Q

What directs the ribosome to attach to the endoplasmic reticulum?

A

an N-terminal signal sequence on the nascent polypeptide

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18
Q

What enzyme is used to remove the signal sequence from the secreted protein by cleavage?

A

signal peptidase

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19
Q

N-terminal secretory peptide signal sequences have ________ _________

A

common features

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20
Q

What are some of the common features that the N-terminal secretory peptide and signal sequences have?

A

they range in length from 13-26 residues
amino-terminal part of signal contains at least one positively charged residue
a highly hydrophobic stretch of usually 10-15 residues forms the center of the signal
residue on the amino-terminal side of the signal peptidase cleavage site usually has a small, neutral side chain (alanine common)

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21
Q

Which amino acid is charged?

A

arg

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22
Q

Which amino acids are hydrophobic?

A

Leu, Ala, Trp

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23
Q

How does protein synthesis begin?

A

by free ribosomes binding to mRNA and commencing synthesis of N-terminal region of polypeptide

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24
Q

What is the first region that is synthesized?

A

the N-terminal

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25
Q

What is the signal recognition particle (SRP)?

A

an RNA-protein complex that recognizes and binds to signal sequences

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26
Q

What temporarily haults translation by a ribosome?

A

binding of SRP

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27
Q

Where does the signal recognition particle receptor direct the peptide?

A

to the translocation complex

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28
Q

What does the SRP receptor do?

A

delivers the signal peptide (and the ribosome) to the peptide translocation complex on the cystolic face of the ER

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29
Q

What happens when SRP binds to the receptor?

A

it releases GDP, GTP binds in its place and SRP is released from ribosome and signal peptide threads through translocation complex

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30
Q

When SRP is released what is hydrolyzed?

A

GTP

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31
Q

What does signal peptidase do?

A

cleaves signal peptide off growing chain

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32
Q

What proteins serve as chaperones to assist correct peptide chain folding?

A

ATP- driven heat shock proteins

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33
Q

Once a protein enters the ER is there a way to return to the cytosol?

A

no once it has entered it is irreversible and cannot return to the cytosol

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34
Q

What do glycoproteins acquire in the ER?

A

core sugars

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35
Q

What are 2 examples of secretory proteins (mucins) that have covalently attached carbohydrate moieties?

A

N-linked to asparagine

O- linked to serine, threonine

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36
Q

What do N-linked oligosaccharides have in common?

A

a pentasaccharide core derived by drimming a 14 residue core oligosaccharide added to specific Asn residues (Asn-X-Ser/Thr)

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37
Q

What is the carrier for N-linked glycoproteins?

A

dolichol phosphate

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38
Q

Where is the dolichol phosphate carrier found?

A

carrier molecule embedded in the ER membrane

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39
Q

What are the 3 characteristics of dolichol phosphate?

A

is an isoprenoid derivative
a lipid
localized to membranes

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40
Q

What is an isoprenoid?

A

5 carbons and then a double bond (structure)

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41
Q

How much of the core oligosaccharides are synthesized on the cystolic side of the ER?

A

about half

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42
Q

What things are combined to form a dolichol pyrophosphate intermediate?

A

nucleotide activated (UDP or GDP coupled) sugar precursors are added stepwise to the phosphate group

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43
Q

What happens to incomplete core-dolichol pyrophosphate?

A

it is translocated across the ER membrane into the lumen

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44
Q

What is GDP?

A

a carrier for manose sugars

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45
Q

2 GlcNAc + 5 mannose =

A

1st 7 sugars

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46
Q

What are dolichol phosphate activated sugars used for?

A

to complete core oligosaccaride

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47
Q

Where are oligosaccharides transferred?

A

to specific Asn residues in protein, releasing dolichol pyrophosphate

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48
Q

Where are activated nucleotide precursors found?

A

on the cytosolic side

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49
Q

Where are the activated dilichol phosphate precursors found?

A

on the lumen side

4 more mannose + 3 glucose added in ER lumen

50
Q

Is dolichol phosphate regenerated?

A

yes it must be regenerated (recycled)

51
Q

What enzyme recycles the dolichol phosphate?

A

phosphatase

52
Q

What 2 drugs affect the addition of sugars?

A

tunicamycin

bacitracin

53
Q

What does tunicamycin do?

A

blocks the first step in oligosaccharide synthesis

54
Q

What does bacitracin do?

A

blocks phosphatase that recycles dolichol phosphate

55
Q

Why is bacitracin a very useful antibiotic?

A

because bacteria use a similar enzyme to recycle an isoprenoid pyrophosphate in cell wall synthesis and the enzyme is very sensitive to bacitracin

56
Q

Where are proteins in the lumen of the ER transported?

A

transported to the cis side of the golgi complex by transport vesicles (transfer vesicles)

57
Q

Where are proteins and carbohydrate moieties additionally modified?

A

in golgi

58
Q

What sorts and directs the proteins to their destination?

A

by transfer vesicles leaving the trans face of the golgi

59
Q

What side of the golgi is closest to the endoplasmic reticulum?

A

the cis side

60
Q

What is closest to the trans side of the golgi?

A

the cell membrane

61
Q

Is membrane asymmetry preserved in vesicular transport?

A

yes

62
Q

What characteristic of the membrane is central to function?

A

membrane asymmetry

63
Q

What corresponds to the luminal side of organelle membranes?

A

external face of plasma membrane

64
Q

What does the luminal side of ER =

A

luminal side of golgi

65
Q

What does the luminal side of golgi =

A

luminal side of transfer vesicle

66
Q

How is phospho-N-acetyl-glucosamine added to a mannose? (which enzyme)

A

phosphotransferase

67
Q

What does the phosphotransferase recognize?

A

the 3D motif in the protein

68
Q

What does the phosphodiesterase remove?

A

N-Ac-Gln leaving mannose - 6- phosphate in core oligosaccharide

69
Q

What does the mannose-6-phosphate and protein bind to?

A

receptor in golgi membrane

70
Q

What is mannose-6-phosphate associated with?

A

lysosome targeting

71
Q

What disease is due to a defect in lysosomal targeting?

A

I-cell disease (mucolipidosis II)

72
Q

What enzyme is deficient in I-cell disease (mucolipidosis II)?

A

phosphotransferase

73
Q

What is the default pathway out of the golgi?

A

secretion

74
Q

What happens to undigested glycosaminoglycans and glycolipids?

A

build up as Inclusions in lysosomes

75
Q

How many hydrolases are needed to break down glycosaminoglycans and glycolipids?

A

eight acid hydrolases are needed

76
Q

Are glycosaminoglycans and glycolipids targeted to lysosomes?

A

no instead they are secreted

77
Q

What does a build up as Inclusion in lysosomes cause?

A

severe psychomotor retardation and skeletal deformities

78
Q

Proteins in ER lumen (ex: heat shock proteins, enzymes) will enter transport vesicles and travel where?

A

to the golgi

79
Q

What is the return signal?

A

the carboxy-terminal sequence Lys-Asp-Glu-Leu (KDEL) on ER proteins is the return signal

80
Q

What happens to proteins after they enter transport vesicles at the golgi?

A

vesicles return proteins to the ER

81
Q

What is receptor mediated endocytosis?

A

a process of import of specific proteins into a cell by protein binding to receptor in plasma membrane and inclusion into vesicles

82
Q

What is receptor mediated endocytosis used for?

A

delivering essential metabolites

83
Q

What modulates response to many protein hormones and growth factors?

A

receptor mediated endocytosis

84
Q

What happens to extracellular proteins?

A

they are targeted for destruction and taken up and delivered to lysosomes (antigen-antibody complexes by phagocytic cells)

85
Q

What is a disadvantage to receptor mediated endocytosis?

A

some toxins and viruses can enter cells by this pathway

86
Q

What is an example of a disease that is caused by disorders of receptor mediated uptake?

A

some forms of familial hypercholesterolemia

87
Q

The cystosolic side of indentation has a thick coat of what type of protein?

A

clathrin protein

88
Q

What are coated pits?

A

specialized regions of plasma membrane that contain many receptors

89
Q

What type of proteins are most cell surface receptors?

A

transmembrane glycoproteins

90
Q

What begins the invagination of coated pit?

A

endocytosis

91
Q

What triggers the invagination of the coated pit?

A

receptor -ligand binding

92
Q

What forms around the coated pit?

A

clathrin forms a lattice around the coated pit, excising it from membrane and forming coated vesicles

93
Q

What happens to the coated vesicle?

A

it rapidly loses clathrin shell and fuses with an enodsome

94
Q

What are endosomes?

A

larger irregular vesicles with acidic lumens

95
Q

How are endosomes acidified?

A

by ATP driven proton pumps in membranes

96
Q

What happens to the protein-receptor complexes in an acidic environment?

A

generally leads to dissociation of these complexes

97
Q

What are the 4 possible fates of receptor protein pairs? (endocytosed proteins)

A 
receptor           protein
recycled           recycled
recycled           degraded
degraded         degraded
transported      transported
98
Q

What is an example of the receptor and protein being recycled?

A

transferrin, MHC proteins

99
Q

What is an example of a recycled receptor and a degraded protein?

A

LDL, transcobalamin II

100
Q

What is an example of a degraded receptor and a degraded protein?

A

EGF, immune complexes

101
Q

what is an example of transported receptor and a transported protein?

A

maternal IgG, IgA

102
Q

What sorts the endocytosed proteins?

A

transferrin - transports iron from sites of absorption and storage to sites of utilization

103
Q

How is transferrin formed?

A

two Fe3+ ions bind/apotransferrin molecule = transferrin (aka ferrotransferrin)

104
Q

What binds to the receptor in coated pits?

A

transferrin but not apotransferrin

105
Q

Why is iron closely guarded?

A

because it can become a method of free radical generation

106
Q

What is bound to iron when transferring through the bloodstream?

A

transferrin

107
Q

How is transferrin processed?

A

the endosome acidifies, Fe3+ dissociates from apotransferrin which remains bound to receptor

108
Q

What is internalized into the endosome?

A

transferrin (transferrin processing slide)

109
Q

What happens to the receptor that was bound to apotransferrin?

A

it is recycled

110
Q

What s ferritin?

A

a storage form of iron (ferritin picks remaining iron in cytosol)

111
Q

What happens to the part of vesicle with apotransferrin bound to its receptor?

A

pinches off and is directed to the plasma membrane

112
Q

What happens when the vesicle is pinched off?

A

it fuses with membrane

113
Q

What happens when the vesicle fuses with the membrane?

A

a sudden shift in PH releases apotransferrin from receptor

114
Q

What do membrane-enveloped viruses do to enter cells?

A

exploit endocytic pathways

115
Q

What is Semliki virus and how is it obtained?

A

related to yellow fever
enters susceptible cells by binding to receptors in coated pits and is endocytosed
the pH change in endosome triggers release of viral nucleocapsid from the membrane

116
Q

How does diphtheria toxin enter cells?

A

by binding to growth factor receptor cells

(Internalized by endocytosis)

117
Q

How are proteins turned over?

A

by ubiquitin tags (signal for destruction)

118
Q

The C-terminal of ubiquitin attaches to what of the target protein?

A

lysine -NH2

119
Q

Which end is more stable due to the signal for ubiquitinylation?

A

N-terminal amino acid is more stable because the ubiquitin attaches at the C- terminal

120
Q

What proteins are poorly ubiquitinylated?

A

Gly,Ala,Cys,Met

121
Q

What are the 4 unstable proteins? (rapidly ubiquitinylated)

A

Arg, His, Ile, Leu

MCBM EXAM 5 DANIELLE (6 decks)

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