Protein Sorting II

Question 1

Where are most mitochondria proteins encoded?

Answer 1

in nuclear DNA

Question 2

What is protein movement called?

Answer 2

translocation

Question 3

What do signal sequences do?

Answer 3

direct proteins to correct compartment in mitochondria

Question 4

Mitochondrial signal sequences form an ______ alpha helix

Answer 4

amphiphilic

Question 5

True or False?

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

Answer 5

true

Question 6

Multi-subunit proteins complexes called ____ ____ mediate translocation

Answer 6

proteins translocators

Question 7

Do specific receptor proteins recognize a precise sequence?

Answer 7

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

Question 8

What is the mitochondrial signal sequence bound to?

Answer 8

import receptor

Question 9

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

Answer 9

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

Question 10

Where is the TIM complex located?

Answer 10

present in both outer and inner membrane

Question 11

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

Answer 11

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

Question 12

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

Answer 12

2 components:

receptors for mitochondrial precursor proteins; translocation channels

Question 13

What is the SAM complex and what does it do?

Answer 13

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

Question 14

What does the OXA complex do?

Answer 14

mediates insertion of proteins synthesized in mitochondria

Question 15

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

Answer 15

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

Question 16

True or False?

Precursor proteins entering mitochondria are folded

Answer 16

false; unfolded

Question 17

Unfolding of the proteins in maintained through interaction with what?

Answer 17

chaperone proteins (cytosolic Hsp 70 family)

Question 18

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

Answer 18

chaperone proteins are stripped off

Question 19

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

Answer 19

signal sequence first

Question 20

TOM transports protein across the outer membrane and into what?

Answer 20

inner membrane space

Question 21

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

Answer 21

matrix

Question 22

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

Answer 22

peptidase

Question 23

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

Answer 23

ATP hydrolysis outside mitochondria

Question 24

What does transport through TIM depend on?

Answer 24

membrane potential

Question 25

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

Answer 25

electrophoresis

Question 26

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

Answer 26

matrix side

Question 27

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

Answer 27

ATP dependent step

Question 28

Hsp60 helps with what?

Answer 28

folding of imported protein using ATP

Question 29

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?

Answer 29

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

Question 30

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

Answer 30

inserts; folds

Question 31

Is the ER membrane continuous with the nuclear membrane?

Answer 31

yes

Question 32

Do the ER signal sequences vary in amino acid sequence?

Answer 32

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

Question 33

What two components guide signal sequences to the ER?

Answer 33

signal recognition partical (SRP); SRP receptor

Question 34

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.

Answer 34

hydrophobic

Question 35

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?

Answer 35

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

Question 36

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?

Answer 36

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

Question 37

Translocator is present in ER membrane and has water filled ___

Answer 37

pore

Question 38

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

Answer 38

Sec61 complex; has 3 subunits

Question 39

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

Answer 39

short helix which opens and closes pore as needed

Question 40

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

Answer 40

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.

Question 41

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

Answer 41

specificity

Question 42

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

Answer 42

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

Question 43

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

Answer 43

translocation

Question 44

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

Answer 44

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

Question 45

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

Answer 45

before entire polypeptide is translocated note: this is called the stop transfer signal

Question 46

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

Answer 46

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

Question 47

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

Answer 47

topology