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Molecular Biology Test II - Jourdan > Intracellular Compartments and Protein Sorting 2 > Flashcards

Intracellular Compartments and Protein Sorting 2 Flashcards

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0
Q

Where are mitochondrial proteins synthesized and then imported?

A

on ribosomes and imported into mitochondria

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1
Q

Where are most mitochondrial proteins encoded?

A

In the nuclear DNA

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2
Q

What do proteins need to cross to get in mitochondria?

A

Outer and/or inner mitochondrial membranes

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3
Q

Protein movement is called what?

A

Translocation

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4
Q

What directs proteins to correct compartments in mitochondria?

A

Signal sequences

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5
Q

What are mitochondrial signal sequences?

A

N terminal and internal

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6
Q

What do the mitochondrial signal sequences form?

A

amphiphilic alpha helix

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7
Q

________ charged residues cluster on one end and _______ on the other end of the helix

A

Positively

Hydrophobic

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8
Q

What recognizes the positively charged and hydrophobic configuration of mitochondrial signal sequences rather than precise sequence?

A

Specific receptor proteins

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9
Q

What are multi-subunit protein complexes called that mediate translocation?

A

Protein translocators

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10
Q

What is TOM

A

Translocase of the outer membrane

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11
Q

Where is TOM present?

A

In the outer membrane of the mitochondria

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12
Q

What is TOM required for?

A

For import of all nucleus encoded proteins and inserts them in outer membrane

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13
Q

What is TIM?

A

Translocase of the inner membrane

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14
Q

Where is TIM present?

A

inner membrane

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15
Q

What are the two TIM complexes?

A

TIM 22 and TIM 23

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16
Q

What does TIM 23 do?

A

Transports soluble protein into matrix and helps insert membrane proteins in inner membrane

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17
Q

What does TIM 22 do?

A

Mediates the insertion of a specific subclass of proteins (e.g. ATP, ADP, and Pi transporter)

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18
Q

TOM and TIM complexes have ___ components

A

2

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19
Q

What are the components of TOM and TIM responsible for?

A

Receptors for mitochondrial precursor proteins

Translocation channels

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20
Q

What is SAM complex?

A

Sorting and assembly machinery: translocates and inserts/folds beta barrel proteins in the outer membrane

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21
Q

What does the OXA complex do?

A

Mediates insertion of proteins synthesized in mitochondria

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22
Q

Precursor proteins entering mitochondria are (folded/unfolded)

A

Unfolded

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23
Q

Unfolding of mitochondrial proteins is maintained through what interactions?

A

With chaperone proteins: cytosolic Hsp 70 family

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24
Q

What binds signal sequence of incoming mitochondrial protein?

A

Import receptors of TOM complex

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25
Q

What are stripped off so that the unfolded protein is fed through TOM?

A

Chaperone proteins

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26
Q

What enters first into translocation channel?

A

Signal sequence

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27
Q

What does TOM transport?

A

Protein across the outer membrane to the inner membrane space

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28
Q

What to proteins bind to in order to move through to the matrix?

A

TIM complex

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29
Q

What are signal sequences of mitochondrial proteins cleaved off by?

A

Peptidase

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30
Q

Bound Hsp ___ dissociated at expense of _________ outside mitochondria

A

70

ATP hydrolysis

31
Q

After passing through TOM, what do proteins interact with?

A

TIM

32
Q

What does transport through TIM depend on?

A

Membrane potential

33
Q

What drives translocation of positively charged sequence through TIM

A

Energy in electrochemical gradient drives translocation by electrophoresis

34
Q

What is bound to TIM 23 on the matrix side?

A

Mitochondrial Hsp 70

35
Q

What pulls protein into matrix space?

A

Mitochondrial Hsp 70

36
Q

What releases the protein in the matrix in an ATP dependent step?

A

Hsp 70

37
Q

What helps folding of imported protein using ATP?

A

Hsp 60

38
Q

How are proteins imported into outer membrane?

A

Pass through TOM complex and enter intermembrane space
Bind to chaperone proteins
Then bind to SAM complex in outer membrane
SAM inserts and folds them in outer membrane

39
Q

What is an example of proteins imported into outer membrane?

A

Porins (beta barrel proteins)

40
Q

What is the ER organized into?

A

A network of branching tubules and sacs

41
Q

What is the ER membrane continuous with?

A

The nuclear membrane

42
Q

What is the internal space of the ER called?

A

ER lumen

43
Q

What does the ER play a central role in ?

A

Proteins and lipid synthesis

44
Q

What is the site of production of all TM proteins?

A

ER

destined to other organelles and ER

45
Q

What do ER signal sequences vary in?

A

IN amino acid sequence

46
Q

What do ER signal sequences have at its center?

A

8 or more non-polar amino acids

47
Q

What are ER signal sequences guided to ER membrane by?

A

2 components:
Signal recognition particle (SRP)
SRP receptor

48
Q

What is the SRP made up of?

A

6 different polypeptides bound to a single small RNA molecule

49
Q

What do SRP cycle between?

A

ER membrane and cytosol

50
Q

What do SRP bind to?

A

ER signal sequence

51
Q

What is the shape of SRP?

A

Rod shaped with large hydrophobic pocket lined by methionines

52
Q

What can the pocket of SRP accommodate?

A

Hydrophobic signal sequences of different size, shape and sequence

53
Q

What does SRP wrap around and bind to?

A

Large ribosomal subunit

One end binds to ER signal sequence of emerging protein and other end to elongation factor binding site

54
Q

What does the SRP block?

A

Protein synthesis transiently giving enough time for protein to enter ER membrane

55
Q

What binds to SRP receptor present in ER membrane?

A

SRP-ribosome complex

56
Q

What does the interaction of SRP -ribosome complex and SRP receptor bring about?

A

The assembly to a translocator

57
Q

What is released and then the protein translocates across the ER membrane?

A

SRP and receptor

58
Q

Where is the translocator of the ER present?

A

In the ER membrane

59
Q

What type of pore does the translocator in the ER membrane have?

A

Water filled pore

60
Q

What is the core of the translocator made of?

A

Sec61 complex

Has 3 subunits with largest subunit surrounding the central lpore

61
Q

What is the pore of the translocator gated by?

A

Short helix which opens and closes pore as needed

62
Q

What triggers the opening of the translocator pore and SRP released?

A

Signal sequences that was brought to the ER membrane by SRP

63
Q

What does the signal sequence interact with, and thereby opening the pore?

A

Specific site within the pore called the start-transfer signal

64
Q

What ensures specificity of protein being translocated into ER?

A

Dual recognition

65
Q

What does the start-transfer signal also interact with?

A

Lipid core of ER membrane

66
Q

What cleaves off the ER signal?

A

Signal peptidase

67
Q

Where does the cleaved ER signal escape from?

A

Lateral opening in the pore

68
Q

What is the integration of trans-membrane proteins similar to?

A

The initial process is similar to soluble proteins

69
Q

What sequence initiates translocation of trans-membrane proteins?

A

N terminal sequence

70
Q

What does the integration of membrane proteins require?

A

Require that some portions of the proteins pass though membrane and some others do not

71
Q

What additional region in polypeptide stops transfer process before entire polypeptide is translocated?

A

Hydrophobic region called stop transfer signal

72
Q

What does the stop transfer signal anchor?

A

Protein in membrane after start-transer signal has been cleaved and released

73
Q

What helps to remove the cleaved start-transfer peptide and to integrate stop-transfer signal into bilayer?

A

Lateral gating

74
Q

What determines topology of the transmembrane proteins?

A

In multiple TM proteins several combinations of start-transfer and stop-transfer determines topology

Molecular Biology Test II - Jourdan (9 decks)

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