Lecture 12

Question 1

Mitochondrial signal sequences

Answer 1

N-terminal and internal; form amphiphilic alpha helix; positively charged residues on one end and hydrophobic on other end

Question 2

TOM (translocase of outer membrane) complex

Answer 2

Present in outer membrane, required for import of all nuclear encoded proteins; inserts them in outer membrane

Question 3

TIM (translocase of inner membrane) complex

Answer 3

Present in both outer and inner membrane

Question 4

TIM23

Answer 4

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

Question 5

TIM22

Answer 5

Mediates insertion of specific subclass of proteins (ATP, ADP, Pi transporter)

Question 6

What are the 2 components of the TOM and TIM complexes?

Answer 6

1. Receptors for mitochondrial precursor proteins

2. Translocation channels

Question 7

SAM (Sorting and Assembly Machinery) complex

Answer 7

Translocates and inserts/folds beta barrel proteins in outer membrane

Question 8

OXA complex

Answer 8

Mediates insertion of proteins synthesized in mitochondria

Question 9

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

Answer 9

Peptidase

Question 10

Which 3 steps in import into the mitochondrial matrix require ATP?

Answer 10

1. Dissociation of bound cytosolic Hsp70 outside mitochondria
2. Mitochondrial Hsp70 releases protein inside matrix
3. Hsp60 helps folding of imported protein

Question 11

What energy dependent step in import into the mitochondrial matrix relies on the membrane potential?

Answer 11

Transport of the protein through the TIM complex

Question 12

ER signal sequence

Answer 12

8+ non-polar amino acids at center, otherwise varies

Question 13

Signal recognition particle (SRP)

Answer 13

Guides signal sequence to ER membrane; made of 6 polypeptides bound to small RNA molecule; rod shaped with large hydrophobic pocket to accommodate signal sequence

Question 14

SRP receptor

Answer 14

Sits in the ER membrane and is bound by SRP-ribosome complex, which brings assembly to a translocator and are released after protein translocated across ER membrane

Question 15

Translocator of ER membrane

Answer 15

Has a water filled pore and a core made of Sec61 complex; 3 subunits gated by short helix which opens and closes the pore as needed

Question 16

Start-transfer signal

Answer 16

Opens the pore of the translocator so that protein can pass into the ER

Question 17

Stop-transfer signal

Answer 17

Hydrophobic region in polypeptides that stops transfer process before entire polypeptide is translocated (for multiple TM proteins)