Unit 6: Mitochondria

Question 1

Is the outer membrane permeable/impermeable to ions and small molecules?

Answer 1

permeable

Question 2

Is the inner membrane permeable/impermeable to ions and small molecules?

Answer 2

impermeable

Question 3

The outer mitochondrial membrane contains _____

Answer 3

porins: integral membrane protein with a large internal channel

Question 4

The inner mitoch. membrane forms ____

Answer 4

folds called cristae to increase surface area

Question 5

The matrix is the site of:

Answer 5

TCA cycle

ATP from oxidative phosphorylation

Question 6

The matrix contains ____ and ____.

Answer 6

• mitochondrial genome (circular DNA)

- ribosomes (translation of proteins)

Question 7

The mitochondrial proteins possess unique targeting sequences that mediate and target:

Answer 7

specific sequences of amino acids that target:

• from cytosol to surface of the mitochondrion
• specific / proper location of mitochondrial subcompartment

Question 8

What sends matrix-destined proteins to the target?

Answer 8

• 15-50 amino acid long targeting signal = presequence

Question 9

Where is the presequence located and what does it consist of?

Answer 9

• N terminus of the protein
• amphipathic alpha helix enriched but one side has lots of positively charged amino acids (cleaved once imported to the matrix)

Question 10

What is the first step of mitochondrial matrix protein targeting and import?

Answer 10

• nascent protein in cytosol
• ## recognized by cystolic chaperone Hsp70

Question 11

What does cytosolic Hsp70 do?

Answer 11

• controls the overal conformation of the matrix destined protein
• maintains it in a partially unfolded and import competent state

Question 12

Nascent mitochondrial proteins are enriched in the vicinity of the mitochondrial surface due to ___ and ____.

Answer 12

diffusion

mRNA localization

Question 13

What is the second step of mitochondrial matrix protein targeting and import?

Answer 13

• TOM complex recognizes Nterm presequence of the matrix destined protein
• at the surface of the mitochondria

Question 14

What is TOM?

Answer 14

translocase of the mitochondrial outer membrane

- a multi-complex protein

Question 15

What integral membrane proteins does the TOM complex consist of?

Answer 15

• receptor (binds +ve charged presequence)
• channel (barrel shaped, mediates protein translocation across OM)
• accessory proteins (serve as scaffold for protein transfer from receptor to channel)

Question 16

What is the third step of mitochondrial matrix protein targeting and import?

Answer 16

• matrix protein passed

TOM complex to TIM23

Question 17

What does TIM23 stand for?

Answer 17

translocase of the mitochondrial inner membrane protein 23

Question 18

How is the protein translocated in step 3?

Answer 18

• TOM and TIM23 physically connected / interact in intermembrane space
• driven by electrochemical potential

Question 19

Briefly explain the electrochemical potential in the mitochondria.

Answer 19

• intermembrane space has high [H+] ions, impermeable to the inner membrane
• this is the site of oxidative phosphorylation and production of ATP
• therefore there is a gradient that drives the +ve presequence towards the less +ve matrix

Question 20

What is the TIM22 complex responsible for?

Answer 20

• different pathway
• insertion and assembly of inner membrane proteins
• TOM to TIM22 (pass to lipid bilayer laterally)

Question 21

What is the fourth step of mitochondrial matrix protein targeting and import?

Answer 21

• N-term presequence exits TIM23
• binds mitochondrial chaperone
• Nterm presequence clevaed
• cleaved, mature protein is folded

Question 22

How does mtHsp70 play a role in import to the matrix?

Answer 22

• mitochondrial chaperone
• undergoes ATP-dependent conformation
• acts as a ratchet and “pulls” the protein into the matrix
• prevents backsliding back to cytosol
• also… proper folding

Question 23

What is the protease that cleaves the sequence from the matrix peptide called?

Answer 23

MPP

mitochondrial processing peptidase