Chapter 13 Flashcards
1
Q
What is vesicular transport?
A
The exchange of components between membrane compartments by the budding of transport vesicles from a donor compartment followed by fusion of the vesicle to the target compartment
2
Q
Vesicular transport is the exchange of components between membrane compartments by the budding of transport vesicles from a donor compartment followed by what?
A
Fusion of the vesicle to the target compartment
3
Q
Identify A and B
A
A: Donor compartment B: Target compartment
4
Q
In eukaryotes, transport along the secretory and endocytic pathways occur by what?
A
The fusion of topologically equivalent membrane bound compartments
5
Q
This flow of material between topologically equivalent membrane compartments is highly what? (3 answers)
A
Organized, balanced, and directional
6
Q
The flow of material between topologically equivalent membrane compartments allows for what? (3 answers)
A
- The secretion of select proteins, 2. The uptake of extracellular material 3. The remodeling of the plasma membrane
7
Q
The secretory pathway (red arrows) includes the outward movement of material from what? (3 answers)
A
- The ER to the Golgi 2. The Golgi to the plasma membrane 3. The Golgi to the lysosome
8
Q
The endocytic pathway (green arrows) is uptake of what? Their fusion with what?
A
The uptake of plasma membrane material and their fusion with the lysosome
9
Q
The retrieval pathway is what?
A
The movement from the plasma membrane to the Golgi and from the Golgi to the ER
10
Q
Formation of transport vesicles requires a what? where?
A
A specialized ‘protein coat’ on the outside of the membrane vesicle
11
Q
The specialized ‘protein coat’ perform what two main functions?
A
- Selects the membrane proteins required for transport 2. Generates the shape of the vesicle by influencing the curvature of the membrane
12
Q
What is flat and stiff due to its cholesterol rich composition and its attachment to the underlying cytoskeleton?
A
The plasma membrane
13
Q
For the plasma membrane, what are essential for the generation of the force required to introduce membrane curvature?
A
Coat proteins
14
Q
What based vesicle formation is less dependent on coat-proteins for membrane curvature as vesicles form at curved regions of the membrane?
A
Golgi based
15
Q
For the Golgi, coat proteins are primarily used for what?
A
Cargo selection
16
Q
What are the 3 major types of coated vesicles distinguished by their coat proteins?
A
- Clathrin-coated vesicles 2. COPI-coated vesicles 3. COPII coats
17
Q
What vesicles were the first identified and the best characterized coat type?
A
Clathrin-coated vesicles
18
Q
What vesicles form on buds that exit from the Golgi
A
COPI-coated vesicles
19
Q
Vesicles form at the plasma membrane and are ssential for endocytosis?
A
Clathrin-coated vesicles
20
Q
What form on vesicles leaving the ER
A
COPII coats
21
Q
Identify pathway A (in green):
A
Clathrin
22
Q
Identify pathway B (in blue):
A
COPI
23
Q
Identify pathway C (in red):
A
COPII
24
Q
The formation of transport vesicles are mediated by the formation of what? where?
A
A specialized ‘protein coat’ on the cytosolic side of the membrane vesicle.
25
Specialized 'protein coats' on the cytosolic side of the membrane vesicle perform what two main functions?
1. Select the membrane proteins required for transport 2. Generate the shape of the vesicle by influencing the curvature of the membrane
26
In general, there are 3 types of coated vesicles which are distinguished by their coat proteins with each type of coat being used for what?
Different transport steps
27
What kind of transport do clathrin-coated vesicles perform?
Plasma membrane mediated endocytosis
28
Where do COPI coated vesicles exit from?
They exit from the Golgi cisternae
29
Where do COPII coated vesicles exit from?
They exit from the ER
30
In general, coat formation requires what four things?
1. Coat-recruitment GTPases 2. Adaptor proteins 3. Cargo receptors4. Coat proteins
31
What are monomeric GTPases that are responsible for the recruitment of coat proteins to the membrane surface for vesicle formation?
Coat-recruitment GTPases
32
What links the coat proteins to the vesicle membrane and interacts with cargo receptors.
Adaptor proteins
33
Not all coated vesicles have adaptor proteins as some cargo may directly bind to what?
Coat proteins
34
What are transmembrane proteins that capture specific soluble cargo for packaging into the vesicle?
Cargo receptors
35
What are proteins that form a cage-like structure over the vesicle to promote membrane curvature and bud formation?
Coat proteins
36
Give the four steps of protein coating
1. Coat assembly and cargo selection 2. Bud formation 3. Vesicle formation 4. Uncoating
37
Give the steps in the formation of COPII coated vesicles
1. Coat-recruitment GTPases 2. Recruitment of adaptor proteins 3. Recruitment of cargo 4. Assembly of coat proteins vesicle budding
38
What are found at high concentrations in the cytosol in an inactive GDP-bound form (Sar1-GDP)?
Coat-recruitment GTPases
39
When coat-recruitment GTPases interact with a specific membrane bound guanine exchange factor (GEF), their bound GDP is replaced with what?
GTP
40
Upon binding GTP, what undergoes a conformational change that exposes its amphiphilic helix leading to insertion into the outer leaflet of the ER membrane?
Sar1
41
The mechanism of activation and membrane tethering is common for what?
Other coat-recruitment GTPases.
42
What are coat-recruitment GTPases?
1. They members of the monomeric GTPases 2. Their activity is regulated by the state of the guanine nucleotide bound 3. They are similar to Ran-GTP and nuclear transport
43
Give the steps for protein binding to ER using GTPases
1. SAR-GDP - The GDP is replaced with GTP by Sar1-GEF 2. Sar1 undergoes conformational change that exposes it's alpha helix 3. It is inserted into outer leaflet of ER membrane
44
When the coat recruitment protein associates with the membrane it recruits what molecules to the ER membrane?
Adaptor molecules
45
The adaptor molecules bind to what?
The carboxy terminal tail domain of select transmembrane "receptor" proteins
46
Proteins bound to these transmembrane receptors are selected as the what?
Vesicle cargo
47
GTP- and membrane-bound Sar1 recruits what two adaptor molecules to the membrane?
The Sec23 and Sec24 adaptor molecules
48
Which adaptor molecule (Sec23 or Sec24) has affinity for the C-terminal tails of receptor proteins and is therefore tethered to the vesicle cargo.
Sec24
49
Which adaptor molecule (Sec23 or Sec24) can bind to multiple receptors? How many of them?
Sec24, one
50
Identify 1 - 5
1: Sec24 2: Sec23 3. Sar1-GTP 4. Cargo receptor 5. Cargo
51
What two coat proteins assemble to form the outer shell of the coat?
Sec13 and Sec31
52
The subsequent recruitment of additional adaptor proteins and outer coat proteins by membrane-bound GTP-Sar1 promotes
Membrane deformation and vesicle formation.
53
Once in the cytosol, hydrolysis loss of GTP by Sar1 results in what? (2 answers)
The disassembly of the coat-adaptor complex and generation of a naked vesicle.
54
It is thought that Sar1 has a slow rate of GTP hydrolysis. What is it that influences coat disassembly?
Time
55
What kind of vesicles form only if bud formation occurs faster than Sar1 GTP hydrolysis?
Fully formed vesicles
56
What are the molecular players in COPII coat formation?
1. Coat recruitment GTPase: (Sar1) 2. Adaptor proteins: (Sec23 and 24) (dimer) 3. Coat protein: (Sec13 and 31) (tetramer) 4. Cargo receptors: (Select transmembrane domain proteins)
57
Formation of COP1 coated vesicles utilizes what components? (3 answers)
1. Coat recruitment proteins 2. Adaptors 3. Cargo receptors
58
What does ARF mean?
ADP-ribosylation factor
59
ARF, or ADP-ribosylation factor, is used as the what?
The coat recruitment protein
60
What is the first step of the formation of COI vesicles?
ARF is recruited to the membrane through the exchange of its bound GDP for GTP through a membrane bound GEF
61
What is the second step of the formation of COI vesicles?
Binding of GTP induces a conformational change that triggers membrane insertion
62
What is the third step of the formation of COI vesicles?
Membrane bound ARF recruits coat proteins for coat formation and adaptors for cargo selection
63
What is the last step of the formatin of COI vesicles?
Assembly of sufficient coat proteins results in vesicle formation. GTP hydrolysis of ARF leads to coat disassembly in the cytosol
64
What are the molecular players in clathrin coat formation:
1. Coat recruitment: (GTPase ARF1) 2. Adaptor proteins: (20 different adaptor proteins) (AP) 3. \_-arrestin 4. Coat protein: (Clathrin complex) 5. Cargo receptors: (Transmembrane proteins)
65
Coat recruitment GTPase ARF1 is involved in the formation of what two kinds of coats?
COPI and clathrin coats
66
COPI and clathrin vesicles utilize a common coat recruitment GTPase. How do they differ?
1.Their use of adaptor proteins, cargo receptors, and coat proteins. 2. They form on distinctly different membrane surfaces. 3. The final membrane 'pinching off' process requires an additional protein factor
67
What kind of vesicles were the first transport vesicles identified and hence, the best characterized?
Clathrin-coated vesicles
68
Clathrin-coated vesicles are involved in what? (2 answers)
1. The endocytosis of transmembrane receptors 2. The delivery of lysosomal hydrolases from the TGN to the lysosome.
69
What does TGN mean?
Trans Golgi Network
70
Clathrin-coated vesicles are composed of what?
Clathrin
71
Each subunit contains three large and three small polypeptide subunits arranged in a three-legged structure called a what?
Triskelion
72
Clathrin triskelons assemble into a cage-like structure that promotes the formation of what?
Membrane vesicles
73
The last step in the formation of an internalized clathrin-coated vesicle requires a membrane tethered GTPase called what?
Dynamin
74
What kind of structure does dynamin assemble into around the neck of a forming bud?
A ring-like structure
75
Activation of dynamin and its associated proteins, leads to what two events?
1. The 'pinching off' of the vesicle 2. Release into the cytosol.
76
In the cytosol the coat is released through the activity of what multiple proteins?
1. HSC70, 2. cytosolic Hsp70 chaperone, 3. Auxillin, 4. A PIP phosphatase enzyme whose activity weakens the binding of the adaptor proteins to the membrane
77
What is essential for the formation of completely endocytosed vesicles?
Functional dynamin
78
What is X?
Dynamin
79
Because of a mutation in dyamin in the nerve cells of the fruit fly, Drosophila, the clathrin vesicles fail to release. This failure causes an accumulation of clathrin vesicles and leads to what?
Paralysis due to a failure in synaptic vesicle recycling.
80
What are available that are capable of interacting with a single coat protein?
Multiple adapter proteins
81
Even a single coat type can carry many different cargos depending on what? (2 answers)
The adaptor and the site of vesicle formation
82
What is another membrane vesicle type that assembles on endosomes. It is involved in the retrieval of endosomal proteins back to the trans-Golgi network and is dedicated to a specific cargo: transmembrane receptors like the mannose 6-phosphate receptor?
Retromer
83
Retromer formation occurs on endosomal membranes only when what three conditions have been met?
1. It is bound to the cytoplasmic tails of specific cargo receptors, 2. It directly interacts with a curved phospholipid bilayer, and 3. It binds to the endosomal marker, phosphoinositide (PI(3)P)
84
Retromer formation can therefore only occur when and where?
At a defined time and on a defined membrane
85
Give some examples of retromers?
1. Vps29 2. Vps35 (cargo binding) 3. Vps26 4. Snx1 (PI(3)P binding)
86
What cargo does retromer coat proteins cover?
Transmembrane proteins
87
What can undergo cycles of phosphorylation and dephosphorylation?
Sugar heads
88
Different organelles in the secretory pathway contain distinct sets of what due to the unique localization of PIP kinases and PIP phosphatases?
Phosphoinositides
89
Many of the proteins involved in vesicular transport recognize different what?
PIP species
90
Differential PIP pattern establishes a highly controlled flow of what?
Vesicular trafficking
91
What proteins are monomeric GTPases associated with the membranous organelles of the secretory pathway. They are selectively distributed to different organelles and act as guides for vesicular transport?
Rab proteins
92
Rab cycles between what two forms based on the status of their guanine nucleotide?
Cytosolic and membrane bound
93
When bound to GDP, Rab is what?
Inactive and cytosolic.
94
When bound to GTP, Rab is what?
Active and tightly associated with membrane.
95
What kind of Rab is found on both transport vesicles and target membrane.
Activated Rab
96
The specificity of vesicle-membrane fusion is controlled by what? Found where?
Protein markers found on the surface of the vesicle
97
Protein markers on the surface of the vesicle are recognized by specific receptors found only These markers are recognized by specific receptors found only where?
On the Correct target membrane
98
Rab proteins are example factors that act as what?
Surface markers
99
Monomeric GTPases cycle between cytosolic and membrane bound forms depending on what?
The guanine nucleotide bound
100
In the cytosol (membrane free), Rab is in a what form?
A GDP bound form
101
When activated by a membrane bound Rab-specific GEF, Rab exchanges GDP for what and becomes tightly bound to the what?
GTP, membrane
102
Membrane bound GTP-Rab recruits additional proteins called "what" to facilitate membrane tethering and fusion between the transport vesicles and target membrane?
Rab effectors
103
Membrane bound GTP-Rab recruits additional proteins called "what" to facilitate what? (2 answers)
Membrane tethering and fusion between the transport vesicles and target membrane
104
Individual Rab proteins can interact with multiple "Rab effectors" providing additional layers of what?
System flexibility.
105
Once a vesicle has been tethered to a target membrane by a Rab effector protein, what happens next?
The two lipid bilayers must be brought in close proximity to facilitate fusion and vesicle unloading.
106
A fusion event is mediated by another group of proteins called what?
SNAREs.
107
Give the steps of Rab mediated vesicle capture:
1. Tethering 2. Docking 3. Fusion
108
What proteins are membrane bound proteins that mediate the fusion of transport vesicles with their target organelle?
SNARE proteins
109
What does SNARE stand for?
Soluble NSF Attachment Receptor
110
There are over 60 different SNARE proteins that are generally broken down into what two complementary sets:
1. v-SNARE (vesicle) 2. t-SNARE (target)
111
Where are v-SNARE proteins found?
On transport vesicles
112
Where are t-SNARE proteins found?
On target compartments
113
SNAREs have what two important roles:
1. They provide specificity to the transport process by ensuring that only correctly targeted vesicles fuse to a membrane, 2. They catalyze the membrane fusion reaction between vesicle and target.
114
The nomenclature of v-SNARE and t-SNAREs has become obsolete as more and more what proteins have been identified?
SNARE
115
Which SNARE (v-SNARE or t-SNARE) are single polypeptide chains and always a transmembrane protein?
v-SNARE
116
Which SNARE (v-SNARE or t-SNARE) has two to three polypeptide chains; one of which is always a transmembrane protein; they others may, or may not, be transmembrane proteins.
t-SNARE
117
v-SNARE association with t-SNARE forms a what?
4-\_-helix bundle
118
The 4-\_-helix bundle is so stable that even elevated temperatures and strong detergents are unable to do what to them?
Pry them apart
119
The availability of SNAREs for membrane fusion are regulated by what?
Rab proteins.
120
t-SNAREs in target membranes are often associated with inhibitory proteins that must be released prior to their interaction with what?
v-SNAREs
121
Rab proteins and their effector proteins control what?
The release of these inhibitory proteins and ultimately membrane fusion.
122
Identify A, B and C
A: v-SNARE (synaptobrevin) B: t-SNARE (Snap25) C: t-SNARE (syntaxin)
123
Intertwined SNARE complexes catalyze membrane fusion using the energy released when the \_-helices do what? Excluding any what?
Wrap around each other to pull the two membranes together excluding any water.
124
In close contact, the outer lipid bilayer will fuse first, followed by what fusion?
Inner bilayer fusion
125
Give the steps of SNARE mediated vesicle membrane fusion:
1. Water is released 2. Stalk formation 3. Hemifusion 4. Fusion
126
The interaction between v- and t-SNARE proteins is very strong, so strong that the complex needs to be physically pried apart after what?
Membrane fusion.
127
What use the energy of ATP hydrolysis to unravel the SNARE complex to prepare them for the next round of fusion?
The cytsolic proteins, NSF and SNAP
128
What does NSF stand for?
N-ethylmaleimide-sensitive factor
129
What does SNAP stand for?
Soluble NSF attachment protein
130
Proteins destined for organelles in the secretory pathway include what organelles?
The ER, the Golgi, the lysosome, the plasma membrane or proteins destined for secretion from the cell
131
Proteins start by co-translational transport into the ER through the what?
Sec61 membrane transport channel
132
In the ER, these proteins move along in the pathway by what?
Vesicle mediated transport
133
Proteins imported into the ER are processed how?
Amino terminal signal removed, modified by glycosylation, and correctly folded
134
Only proteins that are correctly folded ER can do what?
Leave the ER
135
What system ensures that only folded proteins are selectes as cargo for incorporation into transport vesicles?
The calreticulin/calnexin chaperone system
136
Proteins targeted to the Golgi or later organelles in the secretory pathway will leave the ER in what vesicles?
COPII coated vesicles.
137
Vesicles bud from specialized sites on the ER that lack ribosomes called what?
Transitional ER or ER exit sites
138
Cargo selection is an active one; soluble proteins contain amino acids sequences that are recognized by what? Function as what?
Transmembrane proteins that function as receptors for COPII transport.
139
Proteins that are found at high concentrations can also get packaged in what? Without what?
Transport vesicles without selection
140
Proteins intended as ER resident proteins can be mistakenly incorporated into what?
Transit vesicles
141
These accidental passengers are returned to the ER through the what?
The 'retreival' pathway
142
Identify A - D
A: Forming ER transport vesicle
B: Sar1-GTP
C: Subunits of COPII coat
D: Chaperone proteins (bound to folded or misfolded proteins)
143
In addition to the calreticulun/calnexin monitoring system, unassembled proteins can be retained in the ER by what?
The ER lumenal chaperone BiP
144
How is an IgG antibody composed/assembled/transported in the ER?
1. It is composed of two large heavy chain polypeptides (dark green) and two smaller light chain molecules (light green) 2. Only when the protein is fully assembled can it exit the ER through transport vesicles
145
What binds to ER export signals preventing their recruitment into budding vesicles?
BiP
146
When assembled ,the BiP is released exposing the ER export signal promoting transport to the what?
Golgi
147
Quality-control steps place pretty strict rules on the continued movement of proteins through the what?
The secretory pathway
148
For some proteins, what percentage of the protein synthesized never makes it past this checkpoint and are degraded
90%
149
The stringent monitoring system can have a significant downside; Name one resulting illness?
Cystic fibrosis
150
Many of cystic fibrosis patients have a deletion in the gene that codes the what?
The plasma membrane channel, CFTR
151
CFTR encodes what?
A 12 transmembrane domain chloride channel
152
CFTR localizes where?
The plasma membrane of epithelial cells
153
CFTR maturation is very inefficient; only what percentage of the WT protein passes ER quality control?
25%
154
Mutant CFTR protein is significantly slowed in folding and never leaves the what? Is targeted for what?
The ER and is targeted for degradation
155
Mutated CFTR protein can function as a what channel if it made it to the plasma membrane, but because it takes too long to fold in the ER it never makes it out of this organelle
Chloride channel
156
Soon after budding from tER sites, COPII coats are disassembled from the vesicles and they begin to fuse, in a SNARE dependent manner, to form a "Pre-Golgi" compartment called the what?
Vesicular tubular cluster
157
Vesicular tubular clusters are not 'true' ER or Golgi as they lack what?
The required processing enzymes of these compartments.
158
What proteins, moving along microtubule tracks, transports this 'enlarged' vesicle to the cis Golgi network to deliver the enclosed cargo.
Motor proteins
159
Shortly after generation, vesicles bud off of the vesicular tubular cluster in a COPI dependent manner to return material to the ER by the what?
Retrieval pathway
160
Material returned to the ER include what?
1. ER resident proteins that were accidentally packaged into transport vesicles, 2. Cargo receptors that participated in the selection of cargo for transport
161
Identify A-D
A: COPII coat
B: Motor protein
C: Vesicular tubular cluster
D: COPI coat
162
The retrieval pathway is a what kind of process?
A signal sequence dependent process
163
ER proteins that accidentally get packaged can be selected for transport where?
Back to the ER
164
ER retrieval signals for membrane proteins consists of a highly conserved what sequence located within their carboxy terminus?
KKXX (Di-lysine motif)
165
Soluble proteins contain what sequence?
The conserved KDEL amino acid sequence
166
For soluble proteins, the KDEL sequence directs its interaction with what?
Membrane bound KDEL receptor proteins
167
Both di-lysine motif containing transmembrane proteins and KDEL containing soluble proteins bound to KDEL receptors are packaged into what? For their retrograde transport where?
COPI coated vesicles for their retrograde transport back to the ER
168
Not all proteins returned to the ER contain what kind of signal?
Retrieval signal
169
The presence of a retrieval signal increases the efficiency of what?
Retrograde transport
170
Identify A and B
A: COPII coat B: COPI coat
171
Identify 1, 2 and 3
1. cis Golgi network
2. Golgi stack
3. trans Golgi network
172
Identify 1, 2 and 3
1. KDEL
2. Empty KDEL receptor
3. COPI coat
173
Proteins destined for the Golgi enter the stacks from what face?
The cis face
174
What face in the Golgi is closest to the nucleus?
The cis face
175
In what kind of cells, the Golgi is a single complex composed of many stacks?
Mammalian cells
176
In what kind of cells, the Golgi are often many stacked complexes throughout the cytoplasm
Plant cells
177
Proteins that enter the cis side of the Golgi move forward into the what or are returned to the what by the retrieval pathway?
Forward: Golgi network Return: ER
178
Identify the five functional domains of the Golgi (A-E):
A: cis Golgi network (CGN)
B: cis cisterna
C: medial cisterna
D: trans cisterna
E: trans Golgi network (TGN)
179
Identify the two faces of the Golgi (1 and 2):
1. cis face
2. trans face
180
At the trans face of the Golgi, where can the proteins go?
They can be returned to an earlier compartment or moved along to the next destination
181
If the proteins leave the trans face of the Golgi, where can they go?
Lysosomes, secretory vesicles, or the plasma membrane
182
What are organized stacks of distinct biochemical compartments responsible for the successive modification and sorting of proteins as they move from the cis to the trans cisternae?
The Golgi
183
The Golgi are organized stacks of distinct biochemical compartments responsible for what as they move from the cis to the trans cisternae?
The successive modification and sorting of proteins
184
The spatial and biochemical compartmentalization of the Golgi is not absolutely necessary since each processing enzyme can only accept what as a substrate after it has been properly processed by the proceeding enzyme?
A glycoprotein
185
Each compartment of the Golgi has a unique role in modifying the what that pass through the Golgi stacks?
The proteins
186
Spatial distribution in the Golgi of each enzyme establishes an 'ordering' component to these post translational modifications with processing occuring in a stepwise manner in what direction?
Cis to trans direction
187
What kind of modifications happen in the cis Golgi network?
Phosphorylation of oligosaccharides on lysosomal proteins
188
What kind of modifications happen in the cis cisterna?
Removal of Man (mannose)
189
What kind of modifications happen in the medial cisterna?
Removal of Man (mannose) and addition of GlcNAc (N-Acetylglucosamine)
190
What kind of modifications happen in the trans cisterna?
Addition of Gal (galactose) and NANA (N-acetylneuraminic acid)
191
What kind of modifications happen in the trans Golgi network?
Sulfation of tyrosines and carbohydrates
192
What kind of sugar moiety gets added to substrate proteins in the ER?
An N-linked sugar moiety
193
A 14 sugar oligosaccharide is initially trimmed in the ER and further modified where? What is removed and added?
In the Golgi with sugars removed and added
194
The Golgi is also responsible for what? It is the addition of sugars to serine and threonine residues
O-linked glycosylation
195
What is removed in step 1?
1. Glucosidase I 2. Glucosidase I (two of them) 3. ER Mannosidase
196
What is removed in step 2?
Golgi Mannosidase I (three of them)
197
What is added in step 3?
N-acetylglucosamine transferase I
198
What is removed in step 4?
Golgi Mannosidase II (two of them)
199
What is added in step 5? What is the end result?
1. N-acetylglucosamine 2. 5 UDP 3. 3 CMP Complex oligosaccharide
200
The enzymes responsible for N-linked gylcosylation are found in the ER and the process utilizes what kind of enzymes?
Both soluble and membrane bound enzymes
201
The enzymes responsible for O-linked addition are found in the Golgi and the process utilizes what kind of enzymes?
Only membrane bound enzymes
202
All Golgi resident proteins are what kind of proteins?
Single-pass transmembrane proteins
203
Which modification (N-linked or O-linked) occurs en bloc; the 14 sugar moiety is added in one step to a protein substrate?
N-linked
204
Which modification (N-linked or O-linked) is through the addition of one sugar molecule at a time?
O-linked
205
N-linked addition is through the amino group of a what?
An asparagine
206
O-linked modification occurs on the hydroxyl residue of what?
Serine and threonine
207
What kind of glycosylation is A (N-linked or O-linked)?
N-linked (N-linked addition is through the amino group of an asparagine)
208
What kind of glycosylation is B (N-linked or O-linked)?
O-linked (O-linked modification occurs on the hydroxyl residue of serine and threonine)
209
What are the two prevailing models for how the Golgi is able to maintain its polarized structure and how proteins are moved from one cisterna to another?
1. Vesicular Transport Model 2. Cisternal Maturation Model
210
The vesicular transport model states that the Golgi cisterna are what?
Stable membrane compartments with their associated membrane-bound enzymes
211
The vesicular transport model states that proteins move through these stacks in sequence in what direction? What are the proteins carried by?
From the cis to the trans and are carried by transport vesicles
212
According to the vesicular transport model, the forward movement through the stacks (red arrows) is mediated by what?
COPI coated vesicles
213
(Vesicular transport model) The selection of cargo at different points along the pathway is facilitated by the use of different what?
Adaptor proteins
214
(Vesicular transport model) What pathway is responsible for the return of escaped and recycled proteins back to the ER
The retrieval pathway
215
According to the Cisternal maturation model, The Golgi stacks are what? What moves? What direction?
Dynamic such that the Golgi stacks migrate from the cis to the trans face of the apparatus
216
(Cisternal maturation model) Vesicular tubular clusters fuse to become the what?
cis Golgi network
217
(Cisternal maturation model) Each stack progressively matures to become the next compartment such that the secretory vesicles that leave the ER eventually mature to become the what?
trans Golgi network.
218
(Cisternal maturation model) Everything moves forward as the what matures?
Cisternae
219
(Cisternal maturation model) The flow of material in what direction has a significant role in maintaining Golgi function?
Retrograde
220
(Cisternal maturation model) The COPI based retrograde traffic is essential for what?
The collection and return of enzymes back to earlier stacks where they function
221
The two models are not mutually exclusive and it is likely that transport occurs in what way?
Through a combination of both pathways
222
What transport model is this (vesicular or cisternal maturation)?
Vesicular transport
223
What transport model is this (vesicular or cisternal maturation)?
Cisternal maturation model
224
What membrane bound organelle is involved in intracellular digestion?
Lysosome
225
The lysosome contains \>40 acid what which are active only at acidic pH?
Hydrolases
226
Besides the hydrolases, the lysosome contains what?
Lipases, nucleases, phosphatases, and glycosidases
227
The membrane proteins of the lysosome are highly what?
Glycosylated
228
The low pH of the lysosome is maintained by the what which pumps protons into the organelle?
Vacuolar H+ ATPase
229
What is used to drive transport of small metabolites out of the lysosome?
Generated membrane potential
230
The end-products of digested macromolecules (amino acids, sugar, nucleotides) are exported from the what? Into the what? For what purpose?
From the lysosome and into the cytosol for recycling
231
The acid proteases in the lysosome require low pH for activity; Would they be active if they were to escape into the cytosol ?
No
232
What are highly glycosylated which protects them from digestion by lysosomal proteases?
Lysosomal membrane proteins
233
What generates a membrane potential which used to drive the transport of metabolites out of the lysosome?
The proton gradient
234
The membrane potential facilitates the export of what?
End-products
235
The lysosome has how many membranes?
One
236
The lysosome is found in what kind of organisms?
All eukaryotes
237
How are lysosomes generated?
They are generated from the Golgi apparatus as well as material by endocytosis from the plasma membrane
238
The vacuole takes up to how much volume in a plant cell?
30%
239
What are the functions of a vacuole? (4 answers)
1. Storage of nutrients and waste products 2. Maintains cytosolic pH through regulation of H+ flux 3. Controls turgur pressure
240
What does a vacuole contain?
It contains hydrolytic enzymes
241
Material degraded by lysosomes are acquired from what 3 sources?
1. Phagocytosis 2. Endocytosis 3. Autophagy
242
What is the uptake of large extracellular molecules/microbes?
Phagocytosis
243
What is the internalization of plasma membrane proteins?
Endocytosis
244
What is the disposal of old intracellular organelles or microbes?
Autophagy
245
The hydrolytic enzymes responsible for the degradation of these materials are provided by what?
Vesicular transport from the ER-Golgi based secretory pathway
246
Which route (A, B or C) shows endocytosis?
B
247
Which route (A, B or C) shows autophagy?
C
248
Give the steps that lysosomal proteins take from translation to the ER?
1.Translation on cytosolic ribosomes 2. SRP recognition and co-translational transport into the ER via the Sec61 channel
249
While in the ER, what happens to the lysosomal proteins?
They are modified by N-linked oligosaccharide addition
250
Where and by what are lysosomal proteins transported out of the ER?
Into the cis Golgi network by COPII coated vesicles
251
In the cis Golgi, what is added to the lysosomal proteins? By what?
N-acetyl glucosamine (GluNac) is added to the mannose residue of the N-linked oligosaccharide by N-acetyl glucosamine phosphotransferase
252
In the trans Golgi, the N-acetyl glucosamine is removed from the lysosomal protein to generate what?
Mannose 6-phosphate (M6P)
253
Mannose 6-phosphate modified proteins are recognized by transmembrane receptors which in turn are recognized by what? For assembly into what?
Adaptor proteins for assembly into clathrin-coated vesicles
254
Clathrin-coated vesicles bud from what?
trans Golgi Network
255
Coat proteins are lost upon hydrolysis of what?
GTP bound ARF
256
Uncoated vesicles fuse with the what?
The early endosome
257
The low pH of the pre-lysosomal compartment (pH 6.0) leads to what?
The disassociation of the M6P receptor and its cargo.
258
The empty receptors are recycled back to the what?
trans Golgi Network
259
At the lower pH the phosphate group on the mannose sugar is hydrolyzed which prevents what?
Tts recycling back to the Trnas Golgi Network with the receptor.
260
Early endosomes then deliver their contents to what?
Lysosomes
261
pH influences what binding?
M6P receptor-cargo binding
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At pH 6.5-6.7, the pH of the TGN, M6P receptors bind or release cargo?
Bind cargo
263
M6P binds or releases cargo at more acidic pH?
Releases cargo
264
Give the steps in the targeting pathway for lysosomal proteins?
1. Addition of P-GlcNac
2. Uncovering of the M6P signal
3. Binding to M6P receptor
4. Receptor-Dependent transport
5. Dissociation at acidic pH
6. Removal of phosphate
7. Receptor recycling
265
The mannose-6-phosphate tag acts as a marker for what?
Lysosomal targeting
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Since mannose-6-phosphate is added to an N-linked oligosaccharide with a terminal mannose residue and all glycoproteins leaving the ER contain this carbohydrate modification, the Golgi enzymes responsible for mannose-6-phosphate addition must recognize something in addition to the oligosaccharide. What contributes to their recognition?
A specific cluster of neighboring amino acids on the surface of a target protein(signal patch)
267
The N-acetyl glucosamine phosphotransferase enzyme contains what two functional sites:?
1. One responsible for recognizing the surface 'signal patch' 2. A second site that binds UDP-GluNac and the N-linked oligosaccharide
268
After the transfer of GluNAc phosphate to the mannose residue a second enzyme catalyzes the removal of what? To generate what?
The removal of N-acetylglucosamine to generate mannose 6-phosphate
269
What is the process by which cells take up extracellular macromolecules
Endocytosis
270
The two main types of endocytosis differ according what?
The size of the vesicles formed during the uptake process
271
What are the two types of endocytosis?
1. Phagocytosis 2. Pinocytosis
272
What is the uptake of large molecules such as microorganisms and dead cells?
Phagocytosis (cell eating)
273
In what kind of organisms, this process supplies nutients and is viewed as a mode of 'feeding'?
In protozoans
274
In what kind of organisms, phagocytosis is carried out by specialized cells such as macrophages and neutrophils
Mammalian cells
275
To be phagocytosed, the material to be ingested must be recognized by what?
Surface receptors
276
Once recognized by surface receptors, binding triggers pseudopod formation through what?
Actin polymerization and re-organization
277
To complete engulfment, the actin network at the base of the pseudopod is depolymerized by the activity of a PI-3 kinase that converts PI(4,5)P2 to what which promotes actin reorganization?
PI(3,4,5)P3
278
This is phagocytosis. What is X and Y?
X: PI(4,5)P2 Y: PI (3,4,5)P3
279
What kind of endocytosis is carried out by all eukaryotes and is a continual process used for the ingestion of fluid and solutes?
Pinocytosis
280
What varies by cell type but can range as high as 3% of its plasma membrane/minute?
Rate of membrane internalization
281
What is mediated by clathrin-coated vesicles
Pinocytosis
282
To ensure no change in cell size endocytosis is balanced by what?
Exocytosis
283
Extracellular fluid internalized by this process is called what?
Fluid-phased endocytosis
284
What is the specific uptake of molecules from the extracellular fluid by clathrin coated pits?
Receptor mediated endocytosis
285
Extracellular molecules bind to transmembrane receptors and accumulate in coated pits for entry into the cell by what?
Clathrin-coated vesicles
286
Receptor binding allows for the efficient concentration of ligands to ensure that even minor components in the extracellular fluid are what?
Endocytosed
287
\>25 receptors may participate in receptor mediated endocytosis; all use what for internalization?
Clathrin
288
Signals in the what terminus of these receptors interact with adaptor proteins in the clathrin-coat?
Carboxy
289
Association with adaptor proteins results in clathrin-coated pits preferentially collecting a subset of what?
Plasma membrane receptor
290
Give an example of receptor mediated endocytosis?
The uptake of cholesterol in mammalian cells
291
Most cholesterol is transported in the blood in what?
Low density lipoproteins (LDLs)
292
Each LDL particle is composed of what? (3 answers)
1. ~1,500 cholesteryl ester molecules 2. Cholesterol containing phospholipid monolayer 3. 500 kD protein that mediates binding to LDL receptors
293
Give the the steps of LDL particle binding to LDL receptors (3 steps)
1. With low intracellular levels of cholesterol, the cell increases plasma membrane levels of the LDL receptor 2. These receptors diffuse in the plane of the membrane until they associate with clathrin-coated pits 3. The receptors are rapidly internalized, regardless of their ligand binding status
294
With high intracellular levels of cholesterol, the cell decreases synthesis of what?
LDL receptors
295
Individuals with defects in the gene coding for the LDL receptor are unable to aquire cholesterol from the what?
Circulating blood
296
Individuals with defects in the gene coding for the LDL receptor are unable to aquire cholesterol from the circulating blood. These individuals have an increased risk of what?
A heart attack from coronary artery disease
297
Give two identified LDL receptor mutations
1. Receptors that lack extracellular LDL binding sites, 2. Receptors that are unable to bind to clathrin coat proteins,
298
Once internalized, vesicles are targeted to the what?
The early endosome
299
The acidic pH of the early endosome releases what particles from their receptors?
The LDL particles
300
Once the LDL particles are released, what happens to the receptors?
They are recycled back to the plasma membrane
301
How many trips does a single LDL receptor make into the cell during its lifetime?
Hundreds
302
LDL particles released in the early endosome are targeted to the what in a multi step process?
The lysosomes
303
In the lysosome, LDL is degraded to what? For use in what process?
Free cholesterol for use in membrane biosynthesis
304
Give the steps of receptor mediated endocytosis
1. endocytosis 2. uncoating 3. fusion with endosome 4. fusion with lysosome
305
Give the steps in the recycyling of receptors?
1. Budding off in transport vesicles 2. Return of LDL receptors to plasma membrane
306
Are all endocytosed receptors returned to the plasma membrane?
No
307
Endocytosed receptors with their bound ligands have 1 of 3 fates when they reach the early endosomal compartment. What are they?
A. In transcytosis the endocytosed receptors are returned to another domain of the plasma membrane. B. The transferrin receptor follows the recycling pathway C: Signaling receptors (epidermal growth factor receptor, or EGF receptor) are degraded along with their bound ligand in the lysosome
308
The early endosome acts as a what for the endocytic pathway?
Sorting station
309
Endosomal compartments are heterogeneous, membrane-enclosed tubes that extend from the what to the what?
Cell periphery (early endosomes) to a perinuclear location (late endosomes)
310
The presence of vacuolar H+ ATPases generates endosomes that are acidic; ranging from a pH of 6.0 for the what?
The early endosomes
311
The presence of vacuolar H+ ATPases generates endosomes that are acidic; ranging from a pH of 6.0 for the early endosomes to pH 5 for the what?
Lysosome
312
Identify structures A - D
A: Early endosome
B: Late endosome
C: Endolysosome
D: Lysosome
313
What is the movement of macromolecules from one domain of the plasma membrane to another and cccurs most often in polarized cells?
Transcytosis
314
What movement requires material be endocytosed and targeted to the early endosomes?
Transcytosis
315
(Transcytosis) In the early endosome the material is moved to an intermediate compartment called what?
A recycling endosome
316
Recycling endosomes serve as what? For what?
An intracellular storage compartment for membrane proteins whose subsequent targeting to the plasma membrane can be regulated
317
Give an example of transcytosis:
The acquision of maternally provided antibodies
318
In the newborn, what are removed from ingested milk through the activity of receptors localized on the apical side of gut epithelial cells?
Antibodies
319
Under the acidic conditions of the lumen of the gut, maternally provided antibodies do what?
Bind to their receptor and are endocytosed by clathrin-coated pits for targeting to the early endosome
320
The antibody-receptor complex is then targeted to the what which targets vesicles to the basolateral domain of the plasma membrane?
Recycling endosome
321
Once presented to the neutral pH of the extracellular fluid, the antibodies dissociate from their receptors entering the newborns what?
Bloodstream
322
The transport of material from the recycling endosome to the plasma membrane can be what kind of event?
A regulated event
323
In muscle or fat cells the recycling endosome is an intracellular store for what?
Plasma membrane glucose transporters
324
Plasma membrane glucose transporters can be relocalized to what to increase glucose uptake by the cell under specific conditions such as insulin signaling?
the plasma membrane
325
What is this transport system?
Transcytosis
326
What is a mechanism for transcellular transport in which a cell encloses extracellular material in an invagination of the cell membrane to form a vesicle, then moves the vesicle across the cell to eject the material through the opposite cell membrane by the reverse process?
Transcytosis
327
What transport process uses vesicles that fuse with the plasma membrane to deliver material to the plasma membrane and for extracellular secretion
Exocytosis
328
What two pathways do transport vesicles that leave the trans Golgi network?
1. The constitutive secretory pathway, or 2. The regulated secretory pathway
329
What pathway has vesicles that continually fuse with the plasma membrane, delivers both soluble secretory proteins and new material to the plasma membrane and operates in all cell types?
Constitutive secretory pathway
330
What pathway are present only in secretory cells specialized for the on demand delivery of hormones, neurotransmitters, or digestive enzymes?
Regulated secretory pathway
331
What pathway is this? Proteins are selected in the trans Golgi network for storage in secretory vesicles.
Regulated secretory pathway
332
This pathway has vesicles that retain high concentrations of materials until an extracellular signal stimulates their fusion with the plasma membrane. What is it?
Regulated secretory pathway
333
What pathway is A?
Constitutive secretory pathway
334
What pathway is B?
Regulated secretory pathway
335
The trans Golgi network is responsible for sorting proteins into one of three pathways. What are they?
1. Proteins with a mannose-6-phosphate will be diverted to the lysosome. 2. Proteins in the regulated secretory pathway are targeted for storage in secretory vesicles where they will remain until a extracellular signal is received for their release 3. Proteins are delivered to the cell surface in a constitutive manner
336
Secretory vesicles form where?
At the trans Golgi network
337
Proteins destined for regulated secretion are packaged through what? Mediated by what?
A selection mechanism mediated by protein aggregation
338
Secretory proteins contain patches of amino acids that promote their what?
Aggregation
339
Aggregated proteins are segregated into secretory vesicles which fuse to form what?
Immature secretory vesicles
340
Immature secretory vesicles become what through the fusion of additional secretory vesicles coupled with the continuous retrieval of membrane back to the TGN?
Mature secretory vesicles
341
The recycling of membrane concentrates vesicle contents and increases the concentration of what?
Membrane localized ATP driven protonpumps
342
What activity acidifies this compartment leading to the further condensation of enclosed aggregated material?
V-type ATPase
343
Give the structures of the secretory pathway
1. Golgi 2. trans Golgi network 3. Immature secretory vesicle 4. Mature secretory vesicle
344
Densely packed secretory granules contain what? Localized where?
Large amounts of electron dense material that are typically localized adjacent to the plasma membrane
345
Upon receipt of an external signal, these vesicles fuse with the plasma membrane releasing their contents to what?
The extracellular space
346
Extracellular signals are what? That bind to what? To generate what?
Chemical messengers (hormone) that bind to plasma membrane receptor to generate an intracellular signal
347
An example cue for exocytosis is the increase in intracellular what? Generated by what?
Intracellular calcium generated by voltage gated calcium channels
348
Membrane fusion events associated with regulated exocytosis are balanced by what? To prevent what?
Endocytosis to prevent an increase in plasma membrane surface area
349
Endocytic events remove secretory vesicle membrane proteins for what? (2 answers)
Recycling or targeted lysosomal degradation
350
Give the steps in exocytosis of secretory vesicles
1. Docking 2. Fusion 3. Release
351
Most cells are what, having 2 or more distinct plasma membrane domains that serve different functions and therefore require the delivery of a different set of proteins?
Polarized
352
The segregation of proteins destined for the apical versus the basolateral surface of a cell occurs where?
In the TGN, and not before.
353
Work in polarized epithelial cells have shown that proteins from the ER that are destined for different domains travel where and how?
Through the ER and the cis and medial Golgi together
354
Only at what are proteins segregated into vesicles for transport to the apical or basolateral surface of a cell?
The trans Golgi network
355
What transport has coat protein recognition in the Trans Golgi Network and sortings signal in C-terminus of proteins?
Basolateral membrane transport:
356
What transport has GPI modified proteins accumulate in a modified lipid environment of the TGN
Apical membrane transport
357
In one case, targeting is directed by an amino acid sequence within the C-terminus of the cargo protein. In the other, it is the association of the protein with what?
A particular lipid environment in the TGN that influences its targeting.
358
In most epithelial cells, the apical plasma membrane proteins are linked to the lipid bilayer through the attachment of a what?
GPI anchor
359
GPI anchored proteins are thought to associate with glycosphingolipids in
Lipid rafts
360
Lipid rafts help select specific cargo molecules in the TGN for transport to the what?
Apical domain of the plasma membrane
361
Proteins targeted to the basolateral membrane contain sorting signals in their cytosolic tail which are recognized by coat proteins for what?
Packaging into transport vesicles transported to the basolateral membrane.
362
What pathway has proteins that are delivered to all regions of the cell surface indiscriminately?
Indirect targeting pathway
363
Proteins are selectively retained at their location or actively removed and retargeted to what?
Their appropriate membrane domain
364
The retargeting of proteins from one plasma membrane domain to another occurs through what?
Transcytosis
365
What kind of proteins are retrieved by endocytosis, transported to the early endosome and then redirected to their correct membrane domain?
Incorrectly localized membrane proteins
366
The indirect targeting pathway is used only in certain cells such as what cells for the redirection of proteins to the apical domain that line the bile ducts
Liver hepatocytes
