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MCB1 Block 3 > ER & Golgi > Flashcards

ER & Golgi Flashcards

1
Q

What part of ER has ribosome receptors?

A

Rough ER

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2
Q

What is the function of sER?

A

lipid production & detoxification
sterod hormone synthesis
muscle contraction & relaxation
glycogen degradation & gluconeogenesis

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3
Q

The rER is ____ with nuclear membrane

A

continuous

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4
Q

Soluble proteins are ____

A

excreted

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5
Q

Transmembrane proteins become part of ______

A

plasma membrane

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6
Q

What is the function of the rER?

A

proteins destined for ER, golgi, endosomes, lysosomes, plasma membrane & secretion
helps fold proteins
monitors assembly, retention, and degradation of proteins

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7
Q

What cells would have a lot of sER?

A

adrenal cortex, cells of testes (leydig) - they need to make lots of hormones

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8
Q

hepatocyte sER makes what detoxification enzyme?

A

Cytochrome P450

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9
Q

What is the purpose of Glucose-6-phosphatase and where is it located?

A

removes phosphate from G6P, located in sER

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10
Q

If a person is taking medication what might increase in cells to help detoxify?

A

sER

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11
Q

Where are proteins synthesized?

A

Cytosol, unless they have signal sequence that brings them to rER. Otherwise they are translated on ribosome in cytoplasm.

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12
Q

Once mRNA leave nucleus it always combines with ____ _____

A

free ribosome

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13
Q

What are the two ways a protein can be taken from cytoplasm into organelle?

A

co-translational translocation

post-translational translocation

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14
Q

What is co-translational translocation?

A

While a protein is being translated it is transported to rER

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15
Q

What is post-translational translocation?

A

After a protein is made a signal sequence allows it to be transported to an organelle

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16
Q

What does SRP stand for?

A

Signal recognition particle

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17
Q

What is an ER signal sequence and where is it found?

A

A sequence at the N-terminus of protein, signaling for it to be moved to ER. It signals to an SRP

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18
Q

What is the purpose of SRP?

A

it binds to the ER signal sequence and brings the ribosome to a translocon and transfers it, then is displaced

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19
Q

Describe all the steps in cotranslational translocation

A

(pg. 96 in ppt)
1. ER signal sequence on protein
2. SRP binds to signal sequence
3. SRP brings protein over to translocation channel
4. SRP detaches
5. Ribosome transfers growing polypeptide chain through ER membrane at the translocon

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20
Q

What is a translocon?

A

A pore complex on membrane of ER that the growing protein goes through

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21
Q

What does BiP stand for?

A

Binding protein

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22
Q

What will always happen to the N-terminal signal sequence?

A

It will be cleaved off

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23
Q

What cleaves the ER sequence?

A

signal peptidase

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24
Q

What is the purpose of BiP?

A

helps proteins fold, it binds the peptide in the ER lumen and pulls it in

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25
Q

What does it mean that a BiP is a lumeneal ER chaperone?

A

It helps proteins fold

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26
Q

What is a single-pass transmembrane protein?

A

a protein that has a stretch of hydrophobic amino acids and stays in the ER membrane, the rest of protein is translated in cytoplasm

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27
Q

Describe the process of a single-pass transmembrane protein being translated

A

ER terminal sequence (usually N-terminus) - translocation to rER, a hydrophobic sequence in protein anchors it to ER membrane as a STOP sequence, the rest is translated in cytoplasm. When translation complete, N terminal cleaved, but it remains in membrane b/c of hydrophobic region

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28
Q

How does the hydrophobic region of a translocating protein fold?

A

alpha helical structure

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29
Q

What is an internal signal sequence?

A

It is a signal sequence (like ER signal sequence) that is not on the end of a protein - it’s in the middle, and it initiates translocation

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30
Q

Does a single-pass transmembrane protein with internal signal sequence enter cytoplasm with C or N terminus?

A

can be either, depends on sequence

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31
Q

If the signal sequence is internal, is it still cleaved?

A

No

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32
Q

What is a multipass transmembrane protein?

A

It is a protein that has multiple start and stop sequences and is “stitched” into plasma membrane. It’s basically a transmembrane protein with many parts in the membrane (the parts that cross the membrane are alpha-helices)

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33
Q

What is PDI?

A

Protein disulfide isomerase

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34
Q

What are chaperones?

A

They recognize and bind unfolded or misfolded protein, helps fold correctly

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35
Q

Name 3 ER resident proteins

A

BiP, Calnexin, Calreticulin

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36
Q

What does a PDI do?

A

it helps reaction - oxidation of free SH groups on cysteins (S-S bonds) - helps fold protein

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37
Q

Once protein is made in the rER, what happens?

A

disulfide bonds, protein is modified - needs proper folding, addition of carbohydrates, proteolytic cleavage, oligomerisation

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38
Q

Cis golgi receives proteins from the ____

A

ER

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39
Q

What is the function of trans golgi?

A

sorts and packages proteins into vesicles to go to plasma membrane

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40
Q

What happens to proteins if they aren’t folded correctly?

A

They are polyubiquinated - ultimate degradation

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41
Q

Where are sugar chains modified?

A

golgi

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42
Q

Sugar chains are added to protein om ER. What is the last sugar added?

A

Glucose (3 glucose)

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43
Q

How are proteins glycosylated?

A

Dolichol assembles the carbohydrates and puts transfers them to protein. They are added to N terminus of Asn residues. Total of 14 sugars

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44
Q

Where are sugars attached to protein in ER?

A

N-termins of Asn

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45
Q

What is dolichol?

A

a membrane bound lipid that assembles and transfers sugars (oligosaccharide) to protein

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46
Q

What happens to protein and sugar once it is properly folded?

A

Last four sugars are cleaved off - 3 glucose and a mannose. This is signal that it is correctly folded

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47
Q

where are the 4 sugars cleaved off of a properly folded protein?

A

ER

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48
Q

Where do you get specificity of sugar chains?

A

golgi

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49
Q

In golgi, there is more N-linked trimming and/or addition of ______

A

monosaccharides

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50
Q

What is O-linked glycosylation?

A

when sugars are attached to OH of serine and threonine

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51
Q

What does GPI stand for?

A

glycosylphosphatidyl-inositol

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52
Q

Where are GPI linked proteins assembled?

A

ER

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53
Q

GPI linked proteins are commonly found in ___ rafts

A

lipid

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54
Q

Describe what happens with GPI anchors when a protein is destined for a plasma membrane

A

It is covalently attached to GPI anchor in ER, then usually directs protein to lipid raft

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55
Q

If a protein will not fold correctly in the ER, what happens to it?

A

Ejected via translocon to cytosol, where it is deglycosyalated & ubiquilated, taken up by proteasome and degraded

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56
Q

key words: CFTR mutation, fibrosis in lungs, sweat, autosomal recessive, respiratory failure are of what disease?

A

Cystic Fibrosis

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57
Q

What is a Pseudomona?

A

opportunistic infection meaning that some underlying condition or immunosuppression is affecting pt

58
Q

What is the mode of inheritance for cystic fibrosis?

A

Autosomal recessive

59
Q

What disease are these symptoms from? young white kid; normal at birth, failure to thrive, recurrent pneumonia, sputum +pseudomonas; PE: scattered rales/crackles throughout lungs, rhonchi; diagnostic: axillary sweat test; bronchiectasis; respiratory failure is most common cause of death

A

Cystic Fibrosis

60
Q

What is the mechanism for cystic fibrosis?

A

CFTR is misfolded in the ER so it keeps getting ejected back to cytosol and degraded in proteasomes

61
Q

What is CFTR?

A

A protein that is a channel for the movement of Cl- ions across cell

62
Q

What would happen if CFTR protein was transported to plasma membrane?

A

It would function normally - but because it folds incorrectly the body polyubiquinates it

63
Q

What is Bronchiectasis?

A

can develop due to CF. It is a scarring of the lung field.

64
Q

What causes bronchiectasis?

A

chronic infections. they lead to inflammation and scarring

65
Q

Bronchiectasis leads to _____ bronchial dilation and thickened ____ walls

A

irreversible, bronchial

66
Q

What is the most common cause of death in CF pts?

A

respiratory failure

67
Q

What is Hypercholesterolemia?

A

familial high cholesterol

68
Q

These key words: LDL-R, CHD (CAD), plasma cholesterol, Xanthomata, Xanthelasmata are what disease?

A

familial high cholesterol

69
Q

these symptoms are what disease? increased plasma cholesterol levels; increased LDL synthesis; major risk factor for CHD, premature atherosclerosis, Xanthomata, corneal arcus, Xanthelasmata

A

Hypercholesterolemia

70
Q

What is the mechanism for hypercholesterolemia?

A

Mutation inhibits proper folding of LDL-R ! ejected from ER, polyubiquinated, degraded by proteasome
LDL receptor isn’t properly folded. Normally it binds to LDL and brings it in to be broken down and used. This defect means LDL is just circulating and accumualating in vessels and skin

71
Q

Does the LDL protein ever leave the membrane?

A

No - the membrane itself creates the vesicle and brings it to cell membrane

72
Q

Describe what happens to a normal person without Familial hypercholesterolemia

A

This diagram is what normall yhappens: cell needs to pick up LDL, needs LDL receptor (transmembrane proteins), goes to ER, needs to fold properly, when folded correctly goes to golgi, protein undergoes various posttranslational modifications (glycosylations), vesicle to plasma membrane and LDL receptor is now in plasma membrane. The protein in membrane is never leaving the membrane, the membrane itself is what is leaving and going to golgi, plasma membrane. The protein itself doesn’t move.
The LDL receptors on surface can now pick up LDL (low density lipid particles). LDL receptors combine to LDL – triggers endocytosis, invaginate and vesicle enters cell bringing LDL bound to receptor. LDL receptors recycled back to plasma membrane. LDL delivered to lysosome, hydrolytic enzymes break it down. Cholesterol esters can now be used. If cell has enough cholesterol it inhibits production of more LDL receptors and enzyme HMG coA reductase (enzyme that synthesize cholesterol).

73
Q

What is CHD?

A

coronary heart disease

74
Q

Pts with Familial hypercholesterolemia are at major risk for what?

A

CHD

75
Q

If the ER and golgi membrane pinch off with the proteins, how do they not eventually disappear?

A

recycling of membrane

76
Q

What is the roe of microtubules in vesicle transport?

A

The vesicles are walked along the microtubules to their destination via a motor protein

77
Q

What is COPII?

A

It coats the membrane where a vesicle is forming and budding off. Once the vesicle has left the membrane COPII disassembles

78
Q

Do motor proteins walk both directions down the microtubule?

A

No, because microtubules have a + and - side, motor proteins will walk a certain direction

79
Q

What is retrieval transport?

A

Recycles membrane, and puts proteins that are in the wrong spot back in the right spot

80
Q

If a protein doesn’t have a signal sequence, where will it be translated?

A

In cytoplasm

81
Q

If a protein has a NLS signal sequence where will it be translated?

A

Nucleus

82
Q

If a protein has a SKL signal sequence where will it be translated?

A

perixisome

83
Q

What is the pathway for a protein with an ER signal sequence only?

A

It will finish translation in rER, to golgi, to plasma membrane. It will be secreted once at the plasma membrane, unless it is hydrophobic, then it will be a transmembrane protein

84
Q

If a protein has a KDEL signal sequence, where will it be translated?

A

KDEL is a retrieval sequence. It will have KDEL sequence in addition to an ER signal sequence. The KDEL is recognized and trigger COPII formation, which elicts retrieval of protein back to ER

85
Q

If a protein has a KKXX sequence, where will it be translated?

A

ER - this is same mechanism as KDEL sequence. The X just stands for any amino acid (I think)

86
Q

If a protein has an ER signal sequence and then aquires an M6P, where will it be translated?

A

It is translated in ER, then in golgi then golgi phosphorylates it. There are M6P receptors that recognize the sequence and take it to its finally destination, the lysosome

87
Q

What is M6P?

A

It is phosphorylation of a protein. This occurs after protein has been translated and moves to the golgi - the golgi phosphorylates it. M6P is a tag that lets the cel know it needs to be moved to the lysosome

88
Q

If the N terminus is in the lumen of the ER when it is being translated, where will it be once it joins the plasma membrane?

A

The N-terminus will face the extra-cellular space if it is hydrophobic. If hydrophilic the entire thing will be secreted

89
Q

What happens on trans-golgi?

A

It buds and sends proteins to the plasma membrane

90
Q

What is the ERGIC and what does it stand for?

A

ER-Golgi Intermediate compartment. It contains vesicular tubular clusters

91
Q

What side is cis golgi facing?

A

It is facing the rER

92
Q

What does CGN stand for?

A

cis golgi network

93
Q

Vesicles that are leaving need to be coated in COP protein except for where?

A

vesicles budding off of trans golgi do not need COP coat

94
Q

Proteins with KDEL or KKXX tags are ___ resident proteins

A

ER

95
Q

How are proteins that end up in golgi by mistake brought back to ER?

A

Via COPI

96
Q

How are proteins in ER brought to golgi?

A

Via vesicles, need to be coated in COPII

97
Q

What is COPI?

A

It creates a coat to make a vesicle around proteins that are ER resident proteins but are in the golgi. It helps bring them back

98
Q

What is COPII?

A

It creates a coat to make a vesicle around proteins that are in the RER and need to be brought to Cis golgi

99
Q

Is KDEL hydrophobic or hydrophilic?

A

Hydrophilic, it’s soluble

100
Q

Is KKXX hydrophobic or hydrophillic?

A

hydrophobic

101
Q

How does COPI bring back KDEL if it mistakenly enters golgi?

A

KDEL is soluble, and COPI can’t bind to it b/c it’s soluble. There is a KDEL receptor in membrane of golgi, KDEL binds to it. The binding causes a conformational change, and then COPI binds to the receptor and carries it back to the ER

102
Q

How does COPI bring back KKXX if it mistakenly enters golgi?

A

Because KKXX is hydrophobic, COPI can bind directly to it. It binds and carries it back to the ER

103
Q

What are ARF/SAR-GTP

A

G proteins

104
Q

What is ARF/SAR-GTP function?

A

they are involved in COP coat formation to make vesicle

105
Q

What binds to soluble proteins so they can leave membrane of ER?

A

Cargo receptors

106
Q

What needs to happen to ARF/SAR for them to help form COP assembly?

A

They need to be GTP bound

107
Q

Once the vesicle breaks off from the membrane, what happens to the COP coat?

A

It is disassembled

108
Q

What causes the COP coat to disassemble after it buds off from membrane?

A

GTP is hydrolyzed to GDP, so hydrophobic amino aids flip out and COP coat is disassembled

109
Q

Why does the COP coat need to disassemble before the vesicle reaches its destination?

A

so motor proteins can carry the vesicle, so other proteins can interact for vesicle fusion with target membrane

110
Q

What happens once the COP coat disassembles on vesicle?

A

motor proteins bind to vesicle and carry it to target membrane

111
Q

How do carrier proteins get vesicle to target?

A

They “walk” along microtubules

112
Q

What is Rab?

A

G-protein

113
Q

What does V-snare stand for?

A

vesicle snare

114
Q

What does T-snare stand for?

A

target membrane snare

115
Q

Where is V snare located?

A

On vesicle

116
Q

What state is Rab in on the vesicle?

A

GTP bound

117
Q

What is the purpose of the Rab on the vesicle?

A

It interacts with another Rab or a Rab binding protein on the membrane and brings the vesicle close enough to the membrane for V & T snares to interact

118
Q

After the Rab and Rab binding proteins bind, what happens?

A

v-snare on vesicle interacts with t-snare on memrane and brings the vesicle close enough to fuse

119
Q

After the membrane is fused, what happens to V-snare and T-snare

A

a complex of proteins disentangles them, then t-snare stays and v-snare is recycled back to ER

120
Q

What part do v & t snare play in ensuring specificity?

A

If the proteins are supposed to go to golgi, their v-snares will only be compatible with t-snares on golgi. Same if it was going to lysosome, etc.

121
Q

If a cell is secreting a lot of protein, it will have a lot of what two things?

A

ER & Golgi

122
Q

What are the two transport models for how vesicles move through the golgi?

A

Vesicular transport model & Cisternal Transport model

123
Q

Describe the vesicular transport model

A

Each stack of golgi is stationary. Protein goes to cis golgi and leaves via vesicle and fuse with the next membrane stack. Resident enzymes act on it, modifies, then it buds off in a vesicle and goes to next stack, where resident enzymes modify it. Ultimately to trans golgi and to plasma membrane. They are transferred via a vesicle to each stack.

124
Q

Describe the cisternal transport model

A

Cisternal maturation model – vesicles coming off of ER will all fuse together to create a new cis golgi. Enzymes that were present in previous cis golgi will be moved into newly forming cis golgi. So the cis golgi will ultimately mature and become a stack farther up closer to trans. Enzymes move from the previous cis to the newly forming one.

125
Q

Where does the protein receive its M6P tag destining it for the lysosome?

A

In the cis golgi

126
Q

If a protein needs to go to lysosom, what will it be tagged with?

A

M6P

127
Q

Phosphorylation of what makes M6P?

A

mannose

128
Q

What specifically puts the tag on the protein in the golgi for it to go to lysosome?

A

N-acetylglucosamine phosphotransferase

129
Q

What scenario allows a protein to end up in the cytoplasm?

A

No tags at all, or polyubiquinated (because its folded improperly)

130
Q

Name an amino acid is involved in N-linked glycosylation?

A

Asparagine (pt 131)

131
Q

Name an amino acid involved in O-linked glycosylation

A

Threonine (pg 131)

132
Q

A deficiency of N-acetylglucosamine phosphotransferase leads to what disease?

A

I-cell disease

133
Q

what is another name for I-cell disease?

A

Mucolipidosis II

134
Q

What is the mode of inheritance for I-cell disease?

A

Autosomal recessive

135
Q

key words: absence of M6P, waste products in inclusion bodies, coarse facial features, enlarged liver/spleen, death CHF are what disease?

A

I-cell disease

136
Q

What is the mechanism for I-cell disease?

A

Lysosomal enzymes do not receive the M6P tag. Specifically, there is a loss of function of N-acetylglucosamine phosphotransferase, which puts on the M6P tag.. There isn’t anything wrong with the enzymes themselves, they just can’t be sorted correctly. Ultimately, because the proper enzymes aren’t getting to lysosome, there is an accumulation of non-digested things in lysosome. Waste products accumulate as inclusion bodies

137
Q

symptoms: progressive disease; high levels of acid hydrolases in the blood; skeletal abnormalities, coarse facial features, restricted joint movement, psychomotor retardation, enlarged spleen, liver, & heart valves, death due to CHF or RTI are what disease?

A

I-cell disease

138
Q

What is the life expectancy of a pt with I-cell disease?

A

<10 years

139
Q

Where is the mutation located in cystic fibrosis?

A

Delta F508

140
Q

What class is familial hypercholesterolemia where defective transport from rER to Golgi (don’t reach PM

A

Class II

MCB1 Block 3 (15 decks)

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