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Cell Biology > Lecture 12: Endomembrane System Part I > Flashcards

Lecture 12: Endomembrane System Part I Flashcards

1
Q

Transport vesicles

A

Transport vesicles with folded proteins pinch off ER membrane and fuse to target membrane (golgi, lysosome, plasma membrane) to deliver proteins and lipids
Transport vesicles bud off membrane of one organelle (donor) and fuse with membrane of another organelle (target)

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2
Q

Endomembrane System

A

Consists of nuclear envelope, ER, Golgi apparatus, endosomes, and lysosomes to be collectively called endomembrane system
Allows cells to communicate with outside world and respond to environmental changes
Organelles can also communicate with each other due to similar origin

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3
Q

Why are the organelles in endomembrane system grouped together and able to communicate with one another?

A

All formed by invagination of plasma membrane
Share ancestry

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4
Q

Why is mitochondria not included in endomembrane system?

A

Different origin
Did not come from invagination of plasma membrane, but endosymbiosis

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5
Q

Transport vesicles are used to deliver ______ to various organelles and the plasma membrane

A

specific proteins from ER

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6
Q

Receptors in transport vesicles

A

Receptors in vesicles selectively bind to specific cargo protein that will be delivered to different organelle

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7
Q

When transport vesicles bud off membrane of donor organelle they are ________

A

coated vesicles

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8
Q

Coated vesicles

A

proteins surround transport vesicle on cytosolic surface of membrane
not permanent installment as vesicles shed protein coat before fusion so membranes can directly interact

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9
Q

Protein coats on vesicles 2 functions

A
  1. Help package cargo in vesicle to aggregate in small area (do not select cargo)
  2. Causes membrane to curve and form vesicle
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10
Q

For formation of budding to occur for transport vesicle, what proteins are needed?

A
  1. Cargo receptors
  2. Adaptor proteins
  3. Coat proteins
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11
Q

Critical steps for Vesicular transport

A
  1. cargo receptor binds to cargo in organelle
  2. adaptor protein connect cargo receptor to coat protein (ex. clathrin)
  3. protein coat promotes vesicle formation as continue to cover bilayer with coat proteins
  4. vesicle released from donor organelle; coat and adaptor proteins released from vesicle to be left with naked transport vesicle
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12
Q

Different _____ are used to make transport vesicles go to different target organelles

A

coat proteins

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13
Q

COPII coated vesicles

A

move materials from ER to Golgi
involved in forward (anterograde) pathway

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14
Q

COPII

A

coat protein used to make the transport vesicle at the ER membrane (donor organelle)

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15
Q

Sar1

A

GTP binding protein that controls formation of COPII coated vesicles on ER membrane

Sar1-GDP: inactive as cytosolic protein
Sar1-GTP: active and will help budding and is on ER membrane

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15
Q

Process of Sar1 GTP binding protein (ER to Golgi)

A

When Sar1GDP (inactive) binds to Sar1 GEF on membrane
Sar1GEF: promotes exchange of Sar1GDP –> Sar1GTP
Sar1GTP (active) anchored to ER membrane
Transmembrane segment protrudes out and provides anchor to ER membrane
Sar1GP recruit adaptor proteins (Sec23/24) to promote formation of COPII coated vesicle

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16
Q

COPI coated vesicles

A

move materials from Golgi to ER; trans Golgi to cis Golgi
involved in retrieval (retrograde) pathway
Stimulated by Arf1 (GTP binding protein) on Golgi membrane

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16
Q

Once vesicle sheds COPII proteins and fuses with..

A

cis face of Golgi to transport selected proteins

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17
Q

Why is retrieval pathway for transport vesicles needed?

A

Since forward pathway from ER to golgi is imperfect
Proteins from ER can get accidently packaged to golgi and need to be sent back

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18
Q

Proteins in retrieval pathway need

A

ER retrieval signal: signal sequence for soluble ER protein in retrival pathway, often found on C terminus
KDEL signal sequence: ER retrieval sequence used for retrieval and retention of ER protein

19
Q

COP1 coat proteins

A

COP1 coat proteins bind to KDEL receptor/ ER protein complex and form vesicle

20
Q

KDEL receptors

A

KDEL receptors in Golgi bind to ER protein with KDEL retrieval signal
KDEL receptors cannot bind to KDEL retrieval signal in the ER
KDEl receptor has high affinity for KDEL sequence in Golgi apparatus due to low pH

21
Q

Why does KDEL receptor not bind to KDEL retrieval signal in ER

A

KDEL receptor has low affinity for KDEL sequence in ER due to high pH
ER protein is released

22
Q

How is KDEL receptor transported back to golgi?

A

KDEL receptor transported back to Golgi by COPII vesicle after cargo is delivered to ER

23
Q

Arf1

A

GTP binding protein
Arf1 GDP: inactive binds to Arf1 GEF on Golgi membrane
Arf1 GEF promotes exchange of Arf1 GDP –> Arf1GTP
Arf1 GTP: active, will help budding and is anchored to golgi membrane

24
Q

After shedding protein coat, all vesicles need to

A

fuse with target membrane

25
Q

Rab proteins

A

GTP binding proteins on surface of transport vesicle and target membrane direct vesicle to organelle
Work in pairs and different Rab proteins for different locations

26
Q

Rab-GDP

A

inactive; bound to inhibitor (GDI) in cytosol

27
Q

Rab-GTP

A

active; on membrane and binds to tethering protein (effector molecule)

28
Q

Tethering

A

tethering protein is connecting Rab proteins on different membranes
process of fusion has been initiated

29
Q

Tethering between vesicle and membrane promotes

A

docking: initial interaction between v-SNARE and t-SNARE proteins

30
Q

SNARE proteins

A

promote fusion using trans-SNARE complex (tight interaction of tangling of snare proteins)
t-SNARE: snare on target
v-SNARE: snare on vesicle
“finish the job”

31
Q

Membrane fusion requires energy as all sorting mechanism needs input of energy (increase in order is unfavorable) because

A

all water molecules must be displaced for membranes to fuse
v-SNARE/t-SNARE go from initially unstructured to stable in trans-SNARE complex (spontaneous)
energy is required to convert trans-SNARE back to unstructured v-SNARE and t-SNARE (nonspontaneous)

32
Q

Different golgi stacks are used as

A

they have different enzymes for different protein modifications

33
Q

O linked glycosylation:

A

sugar is linked to hydroxl (OH) on threonine or serine within Golgi (different that N linked glycosylation within ER)

34
Q

Glycosylation in Golgi helps with

A

protein folding, protein sorting, cell adhesion and cell signaling

35
Q

Once in Golgi, soluble proteins without retrieval signal (go back to ER) have 3 options:

A
  1. lysosome
  2. plasma membrane
  3. secretion
36
Q

For lysosomal proteins need 2 signals:

A
  1. ER sorting signal to be escorted to ER
  2. M6P signal to form transport vesicle and fuse into lysosome
36
Q

cis face vs trans face of Golgi

A

cis face: receives proteins from ER and can ship proteins back to ER (involved in forward and retrieval pathway)
trans face: involved with sorting to lysosome, plasma membrane, or secreted

37
Q

Lysosomes

A

are critical for digesting molecules taken up by cell through endocytosis and worn out cell parts
breaks down molecules by hydrolytic enzymes (acid hydrolase)

38
Q

Acid hydrolase

A

hydrolytic enzyme used in lysosome that are only active under acidic conditions

39
Q

How are enzymes transported to lysosome?

A

Golgi transports inactive hydrolase enzymes to lysosomes; hydrolases become active in acidic pH within lysosome

40
Q

Critical steps for Lysosomal transport

A
  1. lysosomal (inactive) enzyme glycosylated in ER (mannose sugar is added) enter cis Golgi
  2. Phosphate is added to mannose sugars in cis Golgi which created mannose 6 phosphate (going through stacks = modifications made)
  3. Mannose 6 phosphate receptor bind to lysosomal enzyme in trans-golgi
    (recognize protein with M6P signal, Clathrin coat and adaptor proteins used to form transport vesicle)
  4. Clathrin coated vesicles forms at trans face of golgi; cargo is released in endosome (premature lysosome) for enzyme to become active
41
Q

Lysosomal hydrolase precursor

A

referred to inactive enzyme as it enters cis Golgi

42
Q

Constitutive secretory pathway

A

“default pathway”
operates continuously and supplies plasma membrane with lipids and proteins; also allows for proteins to be secreted
Entry into constitutive pathway does not require a specific signal sequence (has ER sorting signal to be transported into ER, but no signal sequence after)

43
Q

Regulated exocytosis

A

Only present in cells that are specialized for secreting a specific product (hormone, mucus, digestive enzyme) stored in secretory vesicles

44
Q

Secretory vesicles

A

made by clathrin coat protein fuse with plasma membrane when stimulated by extracellular signal

45
Q

How are proteins secreted from ER?

A

If soluble protein in ER is not retained or transported to lysosomes

46
Q

Examples of regulated exocytosis

A
  1. Synaptic vesicles: only fuse with nerve terminal membrane if given appropriate signal
  2. Pancreas telling cells when to absorb glucose as blood glucose has gotten too high

Cell Biology (13 decks)

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