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Cell Bio > Chapter 8: Endomembrane Systems > Flashcards

Chapter 8: Endomembrane Systems Flashcards

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1
Q

Organelles in the endomembrane system

A 
ER
Golgi Complex
Endosomes
Lysosomes
Vacuoles
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2
Q

Materials are shuttled between organelles in membrane-bound __________

A

Materials are shuttled between organelles in membrane-bound TRANSPORT VESICLES

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3
Q

The membrane of a vacuole is called the ____

A

tonoplast

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4
Q

Biosynthetic pathway

A

synthesis, modification, and transport of proteins

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5
Q

Secretory pathway:

constitutive vs regulated secretion

A

Secretory pathway: when proteins are discharged from cell.

Constitutive Secretion: in a CONTINUOUS FASHION
Regulated Secretion: in response to STIMULI

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6
Q

During regulated secretion, materials to be secreted are stored in large, membrane-bound ____ _____

A

secretory granules

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7
Q

T/F: Cells remain alive in the experimental approach of autoradiography and electron microscopy

A

False. Cells are fixed (killed)

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8
Q

T/F. Cells remain alive in the experimental approach of green fluorescent protein labelling

A

True

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9
Q

Which experimental approach involves the fractionation of cells?

A

Biochemical analyses

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10
Q

Pulse-Chase experiment object and general method

A

Purpose: to track proteins from pancreatic mucus-secreting cells using AUTORADIOGRAPHY.

Method: A pulse of radioactive amino acids was given to the cell followed by a chase (addition of non-radioactive amino acids).
First trial = 3 min pulse. No chase.
Second Trial = 3 min pulse. 17 min chase.
Third Trial = 3 min pulse. 117 min chase.

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11
Q

Results of the pulse-chase experiment

A

NOTE: This was the first developed strategy of observing movement of proteins from ER to Golgi.

First trial = 3 min pulse. No chase.
Result: radioactive aa’s incorporated in the rough ER

Second Trial = 3 min pulse. 17 min chase.
Result: radioactive aa’s incorporated in the Golgi Complex and some in vesicles.

Third Trial = 3 min pulse. 117 min chase.
Result: radioactive aa’s incorporated in secretory vesicles and in the extracellular side.

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12
Q

GFP?

A
  • stands for Green Fluorescent Protein.
  • isolated from jellyfish
  • GFP is fused to DNA encoding the protein to be studied
  • useful for tracking protein movement and protein synthesis
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13
Q

Describe the experiment involving GFP and VSV virus

A
  • VSVG gene in the VSV virus was fused with GFP causing green proteins to be synthesized in the cell.
  • VSVG also contained a temp-sensitive mutation that prevented newly-synthesized VSVG to leave the ER at 40 degrees.
  • mutated VSVG accumulated in the ER when left at 40 degrees.
  • after a 10 minute incubation at 32 degrees, VSVG was observed to move to the Golgi Complex.
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14
Q

Describe the successive fractions and pellets after every centrifugation

A
  1. centrifuge homogenate:
    • postnuclear supernatant
    • nuclear pellet: contains whole cells and nuclei
  2. centrifuge postnuclear nupernatant:
    • post-mitochondrial supernatant
    • mitochondrial pellet
  3. centrifuge post-mitochondrial supernatant:
    • post-microsomal supernatant
    • microsomal pellet: contains microsomes
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15
Q

How to separate smooth and rough ER

A
  • centrifuge homogenized smooth and rough ER in a tube with gradient of INCREASING SUCROSE CONCENTRATION.
  • smooth microsomes have a low density, stop sedimenting, and will float at low sucrose concentration.
  • rough microsomes have high density, stop sedimenting, and float at high sucrose concentration.
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16
Q

What is a cell-free system?

A
  • method of analysis which does not contain full cells.
  • provides info about the roles of the proteins involved in membrane trafficking.
    ex: extraction of rough ER via diff. centrifugation after homogenization. Isolated ribosomes continue to synthesize proteins.
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17
Q

What occurred when the gene for vesicle formation in the ER was mutated? (Sec12 mutant)

A
  • When Sec12 was mutated, protein build up occured in the ER due to inability of vesicles to bud off.
  • ER INCREASED IN VOLUME.
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18
Q

What occurred when the gene for vesicle fusion in the ER was mutated? (Sec 17 mutant)

A
  • When Sec17 was mutated, vesicles could not fuse with Golgi.
  • ACCUMULATION OF UNFUSED VESICLES IN THE CYTOPLASM.
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19
Q

Describe RNA interference

A
  • RNA interference is a process in which cells produce small RNAs (siRNAs) that bind to SPECIFIC mRNAs and inhibit the translation of these into proteins.
  • process allows scientists to identify genes involved in a particular process by determining which siRNAs interfere with that process.
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20
Q

Network of flattened sacs in the RER is called ____

A

cistenae

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21
Q

T/F: the luminal or cisternal space inside ER membranes has the same composition as the surrounding cytosol

A

FALSE

ya ninny

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22
Q

The ribosomes on the rough ER are present on the ______ space

A

CYSTOLIC space

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23
Q

Functions of SER

A
  • Synthesis of steroid hormones in endocrine cells.
  • Detoxification in the liver of various organic compounds
  • sequestration of calcium ions into the cytoplasm of muscle cells.
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24
Q

Functions of RER

A

-starting point of the BIOSYNTHETIC PATHWAY. Aka, it is the site of synthesis of proteins, carbohydrate chains, and phospholipids that journey through the membranous compartments of the cell.

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25
Q

Polypeptides synthesized by membrane-bound vs. free ribosomes.

A
  • Polypeptides synthesized by ribosomes in the RER include secreted proteins, integral membrane proteins, and soluble proteins of organelles.
  • Polypeptides synthesized by free ribosomes include 1/3 of those encoded by the human genome, cytosolic proteins, peripheral membrane proteins, nuclear proteins, and proteins incorporated into chloroplasts, mitochondria, and peroxisomes
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26
Q

What is the N-terminal portion of a polypeptide?

A

The first part to emerge from the ribosome during protein synthesis

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27
Q

Secretory proteins contain a ___________ at their N-terminus that directs the emerging polypeptide and ribosome to the __________

A

Secretory proteins contain a SIGNAL SEQUENCE at their N-terminus that directs the emerging polypeptide and ribosome to the ER MEMBRANE.

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28
Q

What do polypeptides move through to reach the cisternal space of the ER?

A

polypeptides move through a protein-lined, aqueous channel

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29
Q
  1. Cotranslational movement

2. Posttranslational movement

A
  1. Cotranslational movement
    - polypeptides moving through the membrane as they are being synthesized.
  2. Posttranslational movement
    - polypeptides are synthesized fully in the cytosol and then imported into ER lumen
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30
Q

Secretory proteins synthesized on RER ribosomes have their signal sequence recognized by ________.

A

SRP (Signal Recognition Particles)

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31
Q

What does SRP do?

A

as a signal sequence emerges from a free ribosome, it binds to SRP, which stops translation until the SRP-ribosome complex can make contact with the ER membrane.

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32
Q

To what does the SRP-ribosome complex attach?

A

The SRP-ribosome complex collides with and binds to an SRP RECEPTOR situated WITHIN THE ER MEMBRANE.

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33
Q

What occurs upon the binding of an SRP-ribosome complex with an SRP-receptor on the ER membrane?

A
  1. The SRP is released (along with the hydrolysis of GTP)
  2. The ribosome associates with a TRANSLOCON of the ER membrane.
  3. The signal sequence binds to the interior of the translocon.
  4. The remainder of the polypeptide translocates through the membrane COTRANSLATIONLLY.
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34
Q

What kind of proteins are needed for the release of SRP from the SRP-ribosome-nascent polypeptide chain complex?

A

GTP-binding proteins (G proteins)

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35
Q

What occurs once the nascent (newly formed or in the process of being synthesized) polypeptide passes into the lumen of the ER?

A

the signal peptide is CLEAVED by a SIGNAL PEPTIDASE.

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36
Q

What is the translocon?

A

the translocon is a protein-lined channel embedded in the ER membrane through which the nascent polypetide can move from the ribosome to the ER lumen.

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37
Q

Carbohydrates are added to the nascent protein in the lumen of the ER by the enzyme __________

A

oligosaccharyltransferase

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38
Q

T/F: both oligosaccharyltransferase and signal peptidase are peripheral membrane proteins.

A

FASLE. Both oligosaccharyltransferase and signal peptidase are INTEGRAL membrane proteins associated with the translocon.

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39
Q

Function of protein disulfide isomerase (PDI)?

A

adds disulfide bonds to cystein.

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40
Q

hydrophobic proteins contain _____ transmembrane segments that interfere transfer into RER lumen.

A

HYDROPHOBIC

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41
Q

T/F: Membranes arise from preexsting membranes

A

True. Lipids are inserted into existing membranes.

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42
Q

T/F: cellular membranes are symmetric.

A

False. Cellular membranes are ASYMMETRIC. The two leaflets of a membrane have different compositions.

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43
Q

Newly synthesized phospholipids are inserted into half of the bilayer facing the _______, and then flipped into the opposite leaflet by __________

A

Newly synthesized phospholipids are inserted into half of the bilayer facing the CYTOSOL, and then flipped into the opposite leaflet by FLIPPASES.

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44
Q

Addition of sugars to an olygosaccharide chain is catalyzed by _________

A

glycosyltransferase

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45
Q

Name of the lipid carrier on which the basal segment of each carbohydrate is assembled and then transferred to specific asparagine residues of the polypeptide.

A

Dolichol Phosphate

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46
Q

Where is the dolichol phosphate located?

A

embedded in the ER membrane

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47
Q

Core segment of each carbohydrate chain is put together on __________ and then transferred to a ________

A

Core segment of each carbohydrate chain is put together on THE LIPID CARRIER, DOLICHOL PHOSPHATE and then transferred to a POLYPEPTIDE

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48
Q

The core carbohydrate is modified by ________ as the polypeptide is transferred into the ER lumen.

A

oligosaccharyltransferase

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49
Q

What does NAG stand for in glycosylation?

A

N-acetylglucosamine

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50
Q

Steps of glycosylation in the RER

A
  1. The first 7 sugars (2 NAG and 5 Mannose residues) are transferred one at a time to the dolichol phosphate on the CYTOSOLIC SIDE of the ER membrane.
  2. Dolichol with its attached oligosaccharide is then FLIPPED across the membrane.
  3. The remaining sugars (4 mannose and 3 glucose residues) are attached on the cytosolic side of the membrane to a dolichol phosphate molecule which then flips across the membrane and donates its sugar to the growing end of the oligosaccharide chain.
  4. Once the oligosaccharide is fully assembled, it is transferred enzymatically to an ASPARAGINE RESIDUE of the NASCENT POLYPEPTIDE.
  5. The dolichol phoshate is flipped back across the membrane and is ready to begin accepting sugars again.
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51
Q

The glycoprotein goes through a system of __________ to determine its fitness for a specific compartment.

A

QUALITY CONTROL

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52
Q

What happens to misfolded proteins?

A

they are tagged by a terminal glucose and recognized by CHAPERONES for refolding.

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53
Q

What does glucosyltransferase do to a misfolded protein?

A

adds a glucose to the end of the olygosaccharide chains. Glycoproteins containing MONOGLUCOSYLATED OLIGOSACCHARIDES are recognized by membrane-bound CHAPERONE CALNEXIN and given an opportunity to achieve their correctly folded (native) state. If they can’t, they are destroyed.

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54
Q

Where are misfolded proteins destroyed?

A

in PROTEASOMES in the cytosol

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55
Q

ER-associated degradation (ERAD)

A

process by which misfolded proteins and destroyed by proteasomes.
Ensures that misfolded proteins do not reach the cell surface.

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56
Q

What does the accumulation of misfolded proteins trigger?

A

UPR: unfolded protein response

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57
Q

Proteins that fail quality control are tagged with ____

A

UBIQUITIN

58
Q

What keeps the misfolded protein sensors inactive?

A

The molecular chaperone, BiP

59
Q

What causes BiP molecules to enter the ER lumen to act as chaperones for misfolded proteins? What does this influx result in?

A

accumulation of misfolded proteins. This results in the activation of sensors (PERK an ATF6) which monitor the concentration of misfolded proteins.

60
Q

What does the activation of [misfolded proteins] sensors do?

A

activated sensors (PERK and ATF6) send signals to trigger proteins involved in DESTRUCTION of misfolded proteins.

61
Q

What are PERK and ATF6?

A
  • Sensor proteins.
  • Sense accumulation of misfolded proteins.
  • Kept inactive by BiP.
62
Q

Explain what happens when sensor proteins are activated in UPR

A

1st strategy: Blocking translation of misfolded proteins.
-Once sensors are activated, DIMERIZATION takes place between PERK and ATF6. Once protein is DIMERIZED, it interacts with TRANSLATION FACTOR, eF2a, which gets phosphorylated.
This HALTS TRANSLATION of the misfolded protein.

2nd strategy: Increasing the transcription of chaperone mRNA and thus alleviating stress of the cell.

63
Q

ERGIC

A

“endoplasmic reticulum Golgi intermediate compartment.”

multiple transport vesicles fused together toward the Golgi complex.

64
Q

The ___ face of the Golgi complex faces the ER; the ____ face is on the opposite side of the stack.

A

The CIS face of the Golgi complex faces the ER; the TRANS face is on the opposite side of the stack.

65
Q

CGN function

A

“cis Golgi network” functions to sort proteins for the ER or the next Golgi station

66
Q

TGN function

A

‘trans Golgi network” functions in sorting proteins either to the membrane or various intracellular destinations.

67
Q

Assembly of carbohydrates found in glycolipids and glycoproteins takes place in the ____

A

Golgi

68
Q

Cisternal maturation model

A
  • model of movement of materials through Golgi complex.

- each cistern “matures” as it moves from the cis to the trans face.

69
Q

Vesicular transport model

A
  • model of movement of materials through Golgi complex.

- cargo is shipped from CGN to TGN in vesicles

70
Q

2 functions of protein coats on vesicles:

A
  1. cause membrane to curve to form a vesicle

2. select the components to be carried by vesicle

71
Q

Types of coated vesicles:

A
  1. COPII-coated vesicles
  2. COPI-coated vesicles
  3. Clathrin-coated vesicles
72
Q

COPII-coated vesicles:

A

move material from the ER “forward” to the ERGIC and Golgi complex

73
Q

COPI-coated vesicles

A

move materials from ERGIC and GOlgi “backwards” to ER, or from trans Golgi to cis Golgi cisternae.

74
Q

Clathrin-coated vesicles

A

move materials from the TGN to endosomes, lysosomes, and plant vacuoles

75
Q

Sar1

A

a small G protein which plays a regulatory role in vesicle assembly.
Sar1-GTP binds to the ER

76
Q

Vesicle disassembly is triggered by the hydrolysis of ______ which produces ________

A

Vesicle disassembly is triggered by the hydrolysis of GTP which produces Sar1-GDP

77
Q

Proteins are maintained in an organelle by two mechanisms:

A
  1. RETENTION of resident molecules that are excluded from transport vesicles.
  2. RETRIEVAL of “escaped” molecules back to compartment where they reside
78
Q

What type of coated vesicles are in charge of transporting escaped proteins BACK TO THE ER?

A

COPI-coated vesicles

79
Q

Resident proteins of the ER contain an amino acid sequence at the C-terminus serving as a _______ signal

A

retrieval signal

80
Q

LYSOSOMAL proteins are tagged with __________ and recognized/captured by __________

A

LYSOSOMAL proteins are tagged with PHOSPHORYLATED MANNOSE RESIDUES and recognized/captured by MPRs (mannose-6-phosphate receptors).

81
Q

Location: RER membrane
Tag: ?

A

SRP

82
Q

Location: ER resident proteins
Tag: ?

A

KDEL

83
Q

Location: ?
Tag: KKXX

A

membrane-bound proteins in RER

84
Q

Location: ?
Tag: Phosphorylated mannose residue

A

Lysosomes

85
Q

Location: peroxisome digestive enxyme
Tag: ?

A

PTS (peroxisomal targeting signal)

86
Q

Location: ?

Tag” presequence

A

Mitochondria

87
Q

Location: ?
Tag: internal targetting sequence

A

inner mitochondrial membrane proteins

88
Q

Location: Chloroplast stroma proteins
Tag: ?

A

stroma-targeting domain

89
Q

Location: Thylakoid membrane proteins
Tags: ?

A

stroma-targeting domain and thylakoid transfer domain

90
Q

Lysosomal enzymes are transported from the TGN in _____-coated vesicles by adaptor proteins, _____.

A

Lysosomal enzymes are transported from the TGN in CLATHRIN-coated vesicles by adaptor proteins, GGAs.

91
Q

The coats of clathrin-coated vesicles contain:

A
  1. outer lattice composed of clathrin

2. inner shell composed of PROTEIN ADAPTORS

92
Q

Funtion of ARF1

A

“adenosylation ribose factor 1” is a G PROTEIN required for vesicle transfer BETWEEN CISTERNAE.

93
Q

Role of tethering proteins

A

Different tethering proteins INITIATE FUSION between different types of membranes

94
Q

Role of Rab proteins

A

Rabs (G proteins) on the vesicle and target membrane are involved in RECRUITING TETHERING PROTEINS that mediate initial contact between two membranes.

95
Q

Interactions between the ______ and ________ pull the two lipid bilayers together during fusion of a vesicle to a target membrane.

A

t-SNAREs (located on the target) and v-SNAREs (incorporated into vesicle)

96
Q

Proteins going into the nucleus have an ___ sequence

A

NLS

97
Q

what is a “fusion pore”

A
  • point at which membranes are fused together.

- formed by interaction of v- and t-SNAREs

98
Q

How many a-helical proteins do v- and t-SNAREs each have? What do these a-helical strands do?

A
  • 2 each.

- a-helical strands interact and provide the mechanical force necessary to allow vesicle and target membrane to fuse.

99
Q

The process of exocytosis is triggered by an increase in concentration of what ion?

A

Ca2+ from cytoplasmic stores

100
Q

Contact between a vesicle and plasma membrane lead to the formation of

A

FUSION PORE

101
Q

When a cytoplasmic vesicle fuses with the plasma membrane, the _____ surface of the vesicle becomes part of the OUTER surface of the plasma membrane, whereas the ______ surface of the vesicle membrane becomes part of the INNER (cytosolic) surface of the plasma membrane.

A

When a cytoplasmic vescle fuses with the plasma membrane, the LUMINAL surface of the vesicle becomes part of the OUTER surface of the plasma membrane, whereas the CYTOSOLIC surface of the vesicle membrane becomes part of the INNER (cytosolic) surface of the plasma membrane.

102
Q

What are lysosomal enzymes called?

A

acid hydrolases

103
Q

The inside of lysosomes has a ____ pH (high or low?)

A

Low (acidic)

104
Q

What maintains the low pH optimum for acid hydrolases in lysosomes?

A

ATPase proton pumps on the membrane

105
Q

What does it “lysosomes play a key role in organelle turnover” mean?

A

it means that lysosomes play a role in the regulated DESTRUCTION of the cell’s OWN ORGANELLES and their replacement (ie. autophagy)

106
Q

Describe the general steps of autophagy

A

an organelle is surrounded by a double membrane structure (PHAGOPHORE) to produce a double-membrane sequestering vesicle called a AUTOPHAGOSOME.
The autophagosome outer membrane fuses with a lysosome, generating an AUTOLYSOSOME, in which both the inner membrane of the autophagosome and the enclosed contents are degraded.

107
Q

T/F: plant vacuoles contain acid hydrolases

A

true

108
Q

2 categories of endocytosis:

A
  • pinocytosis

- receptor-mediated endocytosis

109
Q

Endocytosis vs. phagocytosis

A

Endocytosis: uptake of cell surface receptors and BOUND extracellular ligands.
Phagocytosis: uptake of patriculate matter

110
Q

Pinocytosis:

A

NONSPECIFIC uptake of extracellular fluid or ions

111
Q

Receptor-mediated endocytosis

A

uptake of SPECIFIC extracellular ligands following their binding to receptors

112
Q

Substances that enter the cell through RME (receptor-mediated endocytosis) become bound to ____ on the plasma membrane

A

COATED PITS

113
Q

What shape do clathrin-coated pits resemble?

A

polygons (like a honeycomb)

114
Q

Clathrin contains ___ (number) chains that form a _____

A

Clathrin contains THREE chains that form a TRISKELION

115
Q

Clathrin-coated vesicles contain ____ between clathrin and membrane

A

adaptors

ex: AP2

116
Q

What is dynamin?

A

dynamin is a G protein required for the release of a clathrin-coated vesicle from the membrane where it forms.
Dynamin acts as an enzyme that uses energy from GTP to provide mechanical force.

117
Q

Explain dynamin’s role in the formation of clathrin-coated vesicles

A

Steps:
1. clathrin-coated vesicle forms connected to the plasma membrane by a stalk.
2. dynamin subunits undergo POLYMERIZATION to form a ring around the stalk.
3(a). GTP hydrolysis causes changes in ring conformation which leads to FISSION of the coated vesicle from the plasma membrane and DISASSEMBLY of the dynamin ring.
OR
3(b). If GTPγS is present, dynamin polymerization continues, producing a narrow tubule.

118
Q

Following internalization, vesicle-bound materials are transported in vesicles and tubules known as _______

A

endosomes

119
Q

Where are early endosomes located?

A

near the periphery of the cell, where materials are sorted and sent bound to the late endosomes

120
Q

Where are late endosomes located?

A

near the nucleus.

121
Q

LDLs stands for

A

low-density lipoproteins

122
Q

LDLs are a complex of ______ and _____

A

cholesterol and proteins

123
Q

LDL receptors are transported to the _____________ and bound to a ___________

A

LDL receptors are transported to the PLASMA MEMBRANE and bound to a COATED PIT

124
Q

How are LDLs taken up by the cell?

A

by Receptor-Mediated Endocytosis (RME)

125
Q

What do LDLs release?

A

cholesterol

126
Q

What is the role of HDLs?

A

“High-density lipoproteins” transport CHOLESTEROL from tissues to the LIVER for excretion.

127
Q

Which is associated with low blood cholesterol? HDLs or LDLs?

A

HDLs are associated with LOWERING cholesterol.

LDLs are associated with HIGH blood cholesterol

128
Q

What does the accumulation of LDLs lead to?

A

plaque formation on the inner walls of blood vessels.

Can lead to a HEART ATTACK

129
Q

In phagocytosis, the plasma membrane takes up large particles and pinches off to form a ____________

A

phagosome

130
Q

The phagosome fuses with a __________ and the material is digested within the ________

A

The phagosome fuses with a LYSOSOME and the material is digested within the PHAGOLYSOSOME

131
Q

The engulfment of particles by PHAGOCYTSIS is driven by _______________

A

actin-containing MICROFILAMENTS

132
Q

Uptake of proteins into a peroxisome requires a ________ _______ signal

A

peroxisomal targeting signal (PTS)

133
Q

Mitochondrial proteins are tagged with a

A

PRESEQUENCE

134
Q

Peroxisomes

A

membrane-bound organelles that contain enzymes which degrade hydrogen peroxide and free radicals

135
Q

T/F: movement of proteins into the mitochondria is voltage-dependent.

A

TRUE

136
Q

What is the name of the protein-import complex on the OUTER mitochondrial membrane?

A

TOM complex

137
Q

What is the name of the protein-import complex on the INNER mitochondrial membrane and what 2 major complexes does this complex include?

A

TIM complex: includes TIM22 and TIM23

138
Q

the protein containing a presequence interacts with a _____ protein which unfolds it and sends it into the mitochondria via a _____ complex on the outer mitochondrial membrane.

A

the protein containing a presequence interacts with a CHAPERONE protein which unfolds it and sends it into the mitochondria via a TOM complex on the outer mitochondrial membrane.

139
Q

Once inside the mitochondria, ____ proteins work to refold the protein

A

CHAPERONE

140
Q

Proteins headed to the chloroplast contain a sequence called:

A

TRANSIT PEPTIDE sequence

Cell Bio (4 decks)

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