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Cell Biology and Genetics > Protein sorting > Flashcards

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
Q

What is the signal for proteins in the secretory pathway?

A

Signal sequence

26
Q

What is the signal sequence called in proteins?

A

Given prefix pre-

27
Q

What is the receptor for the signal in secretory proteins?

A

Signal recognition particle (SRP)

28
Q

What is the signal recognition particle made up of?

A

Proteins

RNA

29
Q

What does the signal recognition particle bind to?

A

Signal sequence

Ribosome

30
Q

What happens when SRP binds to the signal sequence and a ribosome for secretory proteins?

A

SRP-signal sequence-ribosome complex binds to SRP receptor in ER membrane

31
Q

What happens when the SRP-signal sequence-ribosome complex binds to SRP receptor in ER membrane?

A

Ribosome synthesises the rest of the secretory protein into the ER lumen

32
Q

What happens to secretory proteins inside the ER lumen?

A

Signal sequence is cleaved off by signal peptidase
secretory protein is entirely produced
secretory protein folds up

33
Q

What happens to the membrane protein in the ER lumen and membrane?

A

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
Q

What shape does the stop-transfer sequence in membrane proteins form?

A

Alpha helix

35
Q

What part of the membrane protein does the stop-transfer sequence form?

A

The transmembrane spanning region

36
Q

What happens to the ribosome when it has finished producing the secretory protein?

A

Dissociated from ER membrane

37
Q

Where are secretory proteins transported to from the ER?

A

Golgi

38
Q

How is SRP receptor recycled?

A

Dissociates using energy released from hydrolysis

39
Q

What is the signal of ER proteins?

A

KDEL sequence

40
Q

What is the receptor for the signal in ER proteins?

A

KDEL receptor

41
Q

Where is the KDEL receptor located?

A

Golgi membrane

42
Q

How are ER proteins transported from the Golgi back to the ER?

A

KDEL sequence binds to KDEL receptor in Golgi membrane

KDEL receptor is bound to COP1 coat outside of Golgi membrane

42
Q

Where do vesicles with a COP1 coat from the Golgi

travel to?

A

Go back to the ER

44
Q

How is the KDEL receptor recycled?

A

Change in pH in ER
KDEL receptor loses affinity for KDEL sequence
so it dissociates
returns to the Golgi

45
Q

What is the signal for lysosomal proteins?

A

Mannose-6-phosphate

46
Q

When is the signal for lysosomal proteins formed?

A

Formed in the Golgi

47
Q

How is the signal for lysosomal proteins formed?

A

Enzymes add phosphate to mannose residues in lysosomal protein
using energy from hydrolysis

48
Q

How are lysosomal proteins targeted for the formation of mannose-6-phosphate signal?

A

Have a signal patch - a group of amino acids forming a recognisable site

49
Q

How are lysosomal proteins transported from the Golgi to lysosomes?

A

In Golgi, M6P binds to M6P receptors in membrane

vesicles which bud off here travel to lysosomes

50
Q

How are M6P receptors recycled?

A

Acidic pH in lysosome causes dissociation of M6P and M6P receptors
M6P receptors bud off in vesicles that travel back to the Golgi

51
Q

What happens to lysosomal proteins in lysosomes? Why?

A

Phosphatase enzymes remove phosphate from M6P

To prevent it from binding to M6P receptors again

52
Q

What is the molecular cause of I-cell disease?

A

Defect in enzyme that phosphorylates mannose residues in lysosomal proteins to form M6P signal

53
Q

How are lysosomes affected in I-cell disease?

A

Lysosomes lack lysosomal proteins e.g. enzymes

become bloated with undigested material

Cell Biology and Genetics (32 decks)

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