Transport into mitochondria + peroxisomes Flashcards
Semester 1 year 1
What is the function of the mitochondria?
-energy production by making large amounts of ATP
-produces a H+ grad across the inner mito membrane, which drives ATPase
-plays a key role in apoptosis
Describe the outer membrane of mitochondria
-perforated with large channels (porins)
-allow entry of molecules < 5000 kDa
-contains enzymes involved in mitochondrial lipid synthesis
Describe the mitochondrial intermembrane space
-contains enzymes that use ATP to phosphorylate other nucleotides
-H+ pumped into this space to create proton grad to drive oxidative phosphorylation - impermeable to H+
Describe the inner membrane of mitochondria
-folded into cristae to maximise SA
-contains redox performing proteins of electron transport chain
-proteins for ATP synthesis
-transport proteins to move molecules in + out of matrix
Describe the mitochondrial matrix
-internal space containing enzymes of Krebs cycle
-contains: mitochondrial DNA, ribosomes, tRNAs, enzymes, metabolites
Do mitochondria contain their own genetic material?
-yes
-circular, double stranded chromosome
-DNA inherited from the mother
What are mitochondria always in a dynamic flux between?
Fusion and fission
What is quality controlled fission?
-mitochondria segregate debris to 1 side + undergo fission
-half without debris carries on as mitochondria
-half with debris undergoes mitophagy - destroyed by autophagosome
What are the translocator proteins embedded in the membranes of mitochondria?
-TOM complex - translocator of outer membrane
-SAM complex - sorting + assembling machinery
-TIM complex - translocator of inner membrane
-OXA complex - cytochrome oxidase activity
Describe how proteins enter the mitochondria
-precursor protein with signal sequence binds to receptors in TOM complex
-they’re then inserted into TIM23 complex, then pushed through into the matrix
-signal peptidase cleaves signal sequence off
-leaves mature mitochondrial protein in matrix
Are mitochondrial precursor proteins folded or unfolded?
Unfolded
What can the mitochondrial precursor proteins do before docking and how can this be stopped?
-fold before docking with TOM complex
-can be stopped by binding interacting proteins to the newly synthesised polypeptide chain e.g chaperones
What do chaperones need energy for?
To dissociate the chaperones from the polypeptide chain
What happens because the TOM complex can’t insert proteins into the bilayer?
Enter in intermembrane space + kept unfolded by chaperones
What is the most common route for proteins entering the inner mitochondrial membrane?
Use TOM + TIM 23 complex
What is the alternate route for proteins entering the inner mitochondrial membrane?
-protein completely enters the matrix
-signal sequence cleavage unmasks a 2nd signal
-signal causes insertion int OXA complex
What are multipass IMM proteins and what do they allow chaperones to do?
-they snake through TOM as a loop
-allow chaperones to bind to stop folding + guide towards TIM22
Describe peroxisomes
-only have a single membrane
-don’t contain DNA or ribosomes
-contain oxidative enzymes
What is the function of peroxisomes?
-carry out oxidative reactions
-remove H atoms from organic compounds
to produce H2O2
-H2O2 used by peroxidases in other reactions
-also involved in b-oxidation of fatty acids
What are the equations for the 2 reactions carried out in peroxisomes?
- RH2 + O2 –> R + H2O2
- H2O2 + R’H2 –> R’ + 2H2O
Why must the 2 reactions in peroxisomes be done together?
To prevent H2O2 from remaining in the body
Where are most peroxisomal proteins made?
-made in cytosol
-inserted into membrane of pre-existing peroxisomes
How do new peroxisomes arise?
From pre-existing ones by organelle growth + fission
How do proteins get into peroxisomes?
-Pex5 recognises signal sequence + accompanies cargo into peroxisome
-Pex5 then ubiquitylated + cycled back to cytosol
What does a mutation in Pex5 cause?
-Zellweger syndrome
-severe brain, liver + kidney abnormalities
