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Protein sorting Flashcards

1
Q

What is protein sorting?

A

The transport of proteins to their specific destination

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2
Q

What are the possible destinations of proteins synthesised by free ribosomes?

A

Cytosol

Nucleus

Mitochondria

Peroxisome

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3
Q

What are the possible destinations of proteins synthesised by ribosomes on the ER?

A

ER

Golgi apparatus

Lysosome

Plasma membrane

Secretory vesicle

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4
Q

What are the requirements of protein sorting?

A

Signal in the protein

Receptor for signal

Translocation machinary

Energy

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5
Q

What is the signal for peroxisome proteins?

A

Peroxisome targeting sequence (PTS)

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6
Q

What is the receptor for the signal in peroxisome proteins?

A

Pex5

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7
Q

Where does Pex5 bind to PTS in the cell?

A

In the cytoplasm

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8
Q

What is the translocation machinery for peroxisome proteins?

A

Pex proteins form channel

across peroxisomal membrane

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9
Q

How are peroxisome proteins transported into the peroxisomes?

A

Pex channel binds to Pex5-protein complex

peroxisome protein enters peroxisome

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10
Q

How is Pex5 recycled?

A

ATP hydrolysis releases energy for Pex5 to be released back into cytoplasm

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11
Q

What is the signal for mitochondrial proteins?

A

Mitochondrial targeting signal (MTS)

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12
Q

What happens to mitochondrial proteins in the cytoplasm?

A

Kept unfolded by chaperone proteins

using energy from ATP hydrolysis

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13
Q

What is the translocation machinery for mitochondrial proteins?

A

Transporter on outer membrane (TOM)

Transporter on inner membrane (TIM)

Chaperone proteins

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14
Q

How are mitochondrial proteins transported into the mitochondrial matrix?

A

Pulled through TOM and TIM by chaperone proteins in the mitochondrial matrix
using energy from ATP hydrolysis

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15
Q

What happens to mitochondrial proteins in the mitochondrial matrix?

A

MTS is cleaved off

protein folds up

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16
Q

What is the signal for nuclear proteins?

A

Nuclear targeting sequence (NTS)

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17
Q

What is the receptor for the signal in nuclear proteins?

A

Importin

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18
Q

What is the translocation machinery for nuclear proteins?

A

Importin

Ran-GTP

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19
Q

How are nuclear proteins transported into the nucleus?

A

Importin binds to NTS
complex moves through nulear pore into nucleus
Ran-GTP binds to importin
causes release of nuclear protein into nucleus

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20
Q

How is importin recycled?

A

Ran GTP-importin complex leaves nucleus through nuclear pore
Ran-GTPase hydrolyses Ran-GTP into Ran-GDP and Pi
causes release of importin

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21
Q

What is the molecular cause of Swyer syndrome?

A

Defect in NTS in SRY protein

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22
Q

What is the genotype and phenotype of Swyer syndrome?

A

Genotype - XY

Phenotype - female

23
Q

Why do individuals with Swyer syndrome appear female despite an XY sex chromosome combination?

A

SRY protein not transported to nucleus

doesn’t bind to promoter regions of genes to initiate male sex development

24
Q

What is the secretory pathway?

A

Proteins passing through ER, Golgi

then on to secretory vesicles, lysosomes, membrane proteins etc.

25
What is the signal for proteins in the secretory pathway?
Signal sequence
26
What is the signal sequence called in proteins?
Given prefix pre-
27
What is the receptor for the signal in secretory proteins?
Signal recognition particle (SRP)
28
What is the signal recognition particle made up of?
Proteins RNA
29
What does the signal recognition particle bind to?
Signal sequence Ribosome
30
What happens when SRP binds to the signal sequence and a ribosome for secretory proteins?
SRP-signal sequence-ribosome complex binds to SRP receptor in ER membrane
31
What happens when the SRP-signal sequence-ribosome complex binds to SRP receptor in ER membrane?
Ribosome synthesises the rest of the secretory protein into the ER lumen
32
What happens to secretory proteins inside the ER lumen?
Signal sequence is cleaved off by signal peptidase secretory protein is entirely produced secretory protein folds up
33
What happens to the membrane protein in the ER lumen and membrane?
Signal sequence is cleaved off by signal peptidase stop-transfer sequence of amino acids remains in ER membrane rest of protein synthesised remains outside of the ER membrane
34
What shape does the stop-transfer sequence in membrane proteins form?
Alpha helix
35
What part of the membrane protein does the stop-transfer sequence form?
The transmembrane spanning region
36
What happens to the ribosome when it has finished producing the secretory protein?
Dissociated from ER membrane
37
Where are secretory proteins transported to from the ER?
Golgi
38
How is SRP receptor recycled?
Dissociates using energy released from hydrolysis
39
What is the signal of ER proteins?
KDEL sequence
40
What is the receptor for the signal in ER proteins?
KDEL receptor
41
Where is the KDEL receptor located?
Golgi membrane
42
How are ER proteins transported from the Golgi back to the ER?
KDEL sequence binds to KDEL receptor in Golgi membrane | KDEL receptor is bound to COP1 coat outside of Golgi membrane
42
Where do vesicles with a COP1 coat from the Golgi | travel to?
Go back to the ER
44
How is the KDEL receptor recycled?
Change in pH in ER KDEL receptor loses affinity for KDEL sequence so it dissociates returns to the Golgi
45
What is the signal for lysosomal proteins?
Mannose-6-phosphate
46
When is the signal for lysosomal proteins formed?
Formed in the Golgi
47
How is the signal for lysosomal proteins formed?
Enzymes add phosphate to mannose residues in lysosomal protein using energy from hydrolysis
48
How are lysosomal proteins targeted for the formation of mannose-6-phosphate signal?
Have a signal patch - a group of amino acids forming a recognisable site
49
How are lysosomal proteins transported from the Golgi to lysosomes?
In Golgi, M6P binds to M6P receptors in membrane | vesicles which bud off here travel to lysosomes
50
How are M6P receptors recycled?
Acidic pH in lysosome causes dissociation of M6P and M6P receptors M6P receptors bud off in vesicles that travel back to the Golgi
51
What happens to lysosomal proteins in lysosomes? Why?
Phosphatase enzymes remove phosphate from M6P | To prevent it from binding to M6P receptors again
52
What is the molecular cause of I-cell disease?
Defect in enzyme that phosphorylates mannose residues in lysosomal proteins to form M6P signal
53
How are lysosomes affected in I-cell disease?
Lysosomes lack lysosomal proteins e.g. enzymes | become bloated with undigested material

Cell Biology and Genetics (32 decks)

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