Intracellular Compartments and Protein Sorting II

Question 1

What type of gene makes up mitochondrial proteins?

Answer 1

Nuclear genes

Question 2

Where can the TOM take cargo in general?

Answer 2

From cytosol to IMS or Outer membrane

Question 3

Where can TIM take cargo in general?

Answer 3

From IMS to matrix or inner membrane

Question 4

Where is the receptor for the sorting sequence located in the mitochondria?

Answer 4

It is part of the translocase complex

Question 5

What are the four distinct compartments of the mitochondria?

Answer 5

OM, IMS, IM, Matrix

Question 6

How do proteins enter the mitochondria and what helps them?

Answer 6

Proteins enter the mitochondria unfolded with the help of HSP 40 and HSP70

Question 7

How are TOM supportive of the endosymbiosis theory?

Answer 7

The pore is a Beta barrel which is usually seen in prokaryotes

Question 8

What is the significance of SAM?

Answer 8

SAM or TOB inserts beta barrels into the outer membrane AFTER they go through TOM.

Question 9

What is the significance of MIM?

Answer 9

MIM can interact with SAM and inserts transmembrane alpha helical proteins after they go through TOM

Question 10

Where is the sorting sequence for B-barrel proteins and does it get cleaved?

Answer 10

The sorting signal is a B-Signal found on the first beta strand inserted into SAM, it does not get cleaved after insertion into Outer membrane.

Question 11

For alpha helices what are the sorting signals and do they get cleaved?

Answer 11

They are signal anchor domains with hydrophobic amino acids and a positive charge at the N terminus and they do not get cleaved after insertion into the outer membrane

Question 12

Where are signal anchor domains found on transmembrane alpha helices?

Answer 12

Can be on the N terminal or Internal.
     If N terminal MIM is used
     If internal SAM is used
Can be single pass or multi pass.
     Single=MIM or SAM depends on location of signal
      Multi= MIM and TOM70

Question 13

What are the chaperones in the IMS?

Answer 13

Small TIMs

Question 14

What does MIA do?

Answer 14

Reduces proteins rich in Cysteine

Question 15

Differentiate TIM23 and TIM22.

Answer 15

TIM23 is the workhorse it inserts most of the IM transmembrane proteins.
TIM22 inserts some metabolite carriers as well as TIM23

Question 16

What are the three pathways to get to the Inner Membrane?

Answer 16

1. TOM–> TIM23 the sequence is cleaved
2. TOM—> TIM22 uses small TIM chaperones
3. OXA for proteins made in the matrix to inner membrane

Question 17

What is the sorting sequence to get into the matrix of the mitochondria?

Answer 17

Amphipathic helix- also gets cleaved after import needs energy (ATP)

Question 18

What helps fold proteins inside the matrix?

Answer 18

HSP 60

Question 19

How are proteins entered into the ER from Cytosol?

Answer 19

Unfolded through Co-Translational insertion or Post-Translational insertion.

Question 20

What is Co-Translational insertion for Cytosol to ER?

Answer 20

Happens on the RER, Needs a SRP, SRP receptor, and Sec61 gated translocator

Question 21

What is Post-Translational insertion Cytosol to Er?

Answer 21

Happens on free ribosome, Needs Cytosolic chaperon proteins, Sec61 gated translocator, and BiP.

Question 22

Where is the sorting sequence for proteins entering the ER?

Answer 22

Located on the N terminus- cleaved by signal peptidase.
N domain is hydrophillic and charged
H domain is hydrophobic (most important)
C domain is polar

Question 23

Where does energy use occur during Co-Translational Insertion?

Answer 23

During SRP recycling and translation elongation

Question 24

Where does energy use occur during post translational insertion?

Answer 24

When the binding protein is pulling (BiP)

Question 25

What amino acid lines the SRP binding pocket?

Answer 25

Met- hydrophobic

Question 26

What does SRP binding do?

Answer 26

Pauses the ribosome by covering the entry and exit sites translocation then continues using the Sec61 translocator pushing the peptide into the ER lumen.

Question 27

Describe transmembrane proteins in the ER.

Answer 27

USe Sec61 translocator
N terminal has start transfer signal and a stop transfer sequence that is hydrophobic. Internal start transfer signals aren’t cleaved.