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Molecular Biology > Protein Sorting II > Flashcards

Protein Sorting II Flashcards

1
Q

Where are most mitochondria proteins encoded?

A

in nuclear DNA

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2
Q

What is protein movement called?

A

translocation

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3
Q

What do signal sequences do?

A

direct proteins to correct compartment in mitochondria

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4
Q

Mitochondrial signal sequences form an ______ alpha helix

A

amphiphilic

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5
Q

True or False?

Positively charged residues cluster on one end and hydrophobic residues cluster on the other end of the helix

A

true

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6
Q

Multi-subunit proteins complexes called ____ ____ mediate translocation

A

proteins translocators

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7
Q

Do specific receptor proteins recognize a precise sequence?

A

no, they recognize the configuration of pos and neg residues on opposite ends

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8
Q

What is the mitochondrial signal sequence bound to?

A

import receptor

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9
Q

Where is the TOM complex located and what is it required for?

A

present in the outer membrane; required for import of all nucleus encoded proteins - inserts them in outer membrane

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10
Q

Where is the TIM complex located?

A

present in both outer and inner membrane

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11
Q

What are the two types of TIM complexes and what do they do?

A

TIM 22 mediates the insertion of a specific subclass of proteins (ex: ATP)

TIM 23 transports soluble proteins into matrix and helps insert membrane proteins in inner membrane

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12
Q

How many components do TOM and TIM complexes have? What are they?

A

2 components:

receptors for mitochondrial precursor proteins; translocation channels

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13
Q

What is the SAM complex and what does it do?

A

Sorting and Assembly Machinery complex; translocates and inserts/folds beta barrel proteins in the outer membrane

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14
Q

What does the OXA complex do?

A

mediates insertion of proteins synthesized in mitochondria

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15
Q

What is the general pathway of protein import into the mitochondrial matrix?

A

Binding to import receptors; insertion into membrane TOM complex; translocation into matrix by TIM 23 complex; cleavage by signal peptidase

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16
Q

True or False?

Precursor proteins entering mitochondria are folded

A

false; unfolded

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17
Q

Unfolding of the proteins in maintained through interaction with what?

A

chaperone proteins (cytosolic Hsp 70 family)

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18
Q

After import receptors of TOM complex bind signal sequence of incoming proteins, what happens to chaperone proteins?

A

chaperone proteins are stripped off

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19
Q

How is the unfolded protein oriented as it is fed through the translocation channel?

A

signal sequence first

20
Q

TOM transports protein across the outer membrane and into what?

A

inner membrane space

21
Q

The protein in the inner membrane space binds to the TIM complex and moves through a channel to the ____

A

matrix

22
Q

What cleaves off the signal sequence once the protein is inside the matrix?

A

peptidase

23
Q

In regards to protein transport needs, bound Hsp 70 is dissociated at the expense of what?

A

ATP hydrolysis outside mitochondria

24
Q

What does transport through TIM depend on?

A

membrane potential

25
Q

Energy in electrochemical gradient drives translocation of positively charged sequence through TIM by what?

A

electrophoresis

26
Q

On what side of TIM 23 is mitochondrial Hsp 70 bound to?

A

matrix side

27
Q

After the protein is pulled into the matrix, Hsp 70 releases the proteins in what type of step?

A

ATP dependent step

28
Q

Hsp60 helps with what?

A

folding of imported protein using ATP

29
Q

In regards to import into the outer membrane, the protein passes through the TOM complex and enters what? What does it bind to when its here?

A

inter-membrane space; binds to chaperone proteins and then to SAM complex in outer membrane

30
Q

In regards to import into the outer membrane, Sam ___ and ___ the protein in the outer membrane.

A

inserts; folds

31
Q

Is the ER membrane continuous with the nuclear membrane?

A

yes

32
Q

Do the ER signal sequences vary in amino acid sequence?

A

yes; have 8 or more non-polar amino acids at center

33
Q

What two components guide signal sequences to the ER?

A

signal recognition partical (SRP); SRP receptor

34
Q

SRP cycles between ER membrane and cytosol and binds to the ER signal sequence. It is rod shaped with a large _____ pocket lined by methionines.

A

hydrophobic

35
Q

In regards to translocation across ER, SRP wraps around large ribosomal subunit. One end binds to ER signal sequence of emerging protein and other end to what? What does this do?

A

elongation factor binding site; this blocks protein synthesis transiently giving enough time for protein to enter ER membrane

36
Q

In regards to translocation across ER, after the SRP-ribosome complex binds to SRP receptor present in ER membrane, interaction brings the assembly to a ____. What happens after this?

A

translocator; SRP and receptor are released and protein is translocated across the ER membrane

37
Q

Translocator is present in ER membrane and has water filled ___

A

pore

38
Q

In regards to the translocator in the ER membrane, what is the core of the translocator made of?

A

Sec61 complex; has 3 subunits

39
Q

In regards to the translocator in the ER membrane, what is the pore gated by?

A

short helix which opens and closes pore as needed

40
Q

In regards to protein translocation across the ER, describe the sequence of events leading up to the start-transfer signal

A

SRP binds to ER signal sequence in protein and brings it to the ER membrane. Signal sequence triggers opening of translocator pore and SRP is released. Signal sequence interacts with a specific site within the pore, thereby opening the pore. This is called the start-transfer signal.

41
Q

In regards to protein translocation across the ER, dual recognition ensures what?

A

specificity

42
Q

In regards to protein translocation across the ER, what cleaves off the signal? And where does it go?

A

Signal peptidases; signal escapes from a lateral opening in the pore

43
Q

In regards to integration of Trans-membrane proteins, what does the N terminal sequence initiate?

A

translocation

44
Q

In regards to integration of Trans-membrane proteins, integration of membrane proteins require what?

A

that some portions of protein pass through membrane and others do not

45
Q

In regards to integration of Trans-membrane proteins, an additional hydrophobic region in polypeptide stops transfer process before what?

A

before entire polypeptide is translocated

note: this is called the stop transfer signal

46
Q

In regards to integration of Trans-membrane proteins, what does lateral gating help?

A

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

47
Q

In multiple trans-membrane proteins, several combinations of start-transfer and stop-transfer determine ____ of the protein

A

topology

Molecular Biology (17 decks)

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