Unit 6: Mitochondria Flashcards
(23 cards)
Is the outer membrane permeable/impermeable to ions and small molecules?
permeable
Is the inner membrane permeable/impermeable to ions and small molecules?
impermeable
The outer mitochondrial membrane contains _____
porins: integral membrane protein with a large internal channel
The inner mitoch. membrane forms ____
folds called cristae to increase surface area
The matrix is the site of:
TCA cycle
ATP from oxidative phosphorylation
The matrix contains ____ and ____.
- mitochondrial genome (circular DNA)
- ribosomes (translation of proteins)
The mitochondrial proteins possess unique targeting sequences that mediate and target:
specific sequences of amino acids that target:
- from cytosol to surface of the mitochondrion
- specific / proper location of mitochondrial subcompartment
What sends matrix-destined proteins to the target?
- 15-50 amino acid long targeting signal = presequence
Where is the presequence located and what does it consist of?
- 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)
What is the first step of mitochondrial matrix protein targeting and import?
- nascent protein in cytosol
- ## recognized by cystolic chaperone Hsp70
What does cytosolic Hsp70 do?
- controls the overal conformation of the matrix destined protein
- maintains it in a partially unfolded and import competent state
Nascent mitochondrial proteins are enriched in the vicinity of the mitochondrial surface due to ___ and ____.
diffusion
mRNA localization
What is the second step of mitochondrial matrix protein targeting and import?
- TOM complex recognizes Nterm presequence of the matrix destined protein
- at the surface of the mitochondria
What is TOM?
translocase of the mitochondrial outer membrane
- a multi-complex protein
What integral membrane proteins does the TOM complex consist of?
- 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)
What is the third step of mitochondrial matrix protein targeting and import?
- matrix protein passed
TOM complex to TIM23
What does TIM23 stand for?
translocase of the mitochondrial inner membrane protein 23
How is the protein translocated in step 3?
- TOM and TIM23 physically connected / interact in intermembrane space
- driven by electrochemical potential
Briefly explain the electrochemical potential in the mitochondria.
- 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
What is the TIM22 complex responsible for?
- different pathway
- insertion and assembly of inner membrane proteins
- TOM to TIM22 (pass to lipid bilayer laterally)
What is the fourth step of mitochondrial matrix protein targeting and import?
- N-term presequence exits TIM23
- binds mitochondrial chaperone
- Nterm presequence clevaed
- cleaved, mature protein is folded
How does mtHsp70 play a role in import to the matrix?
- 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
What is the protease that cleaves the sequence from the matrix peptide called?
MPP
mitochondrial processing peptidase
