Mitochondria Flashcards
4 compartments
- outer membrane
- inner membrane
- intermembrane space
- matrix
outer membrane
-permeable to molecules up to 10 kDa
inner membrane
- impermeable
- molecules need a specific transporter/shuttle to pass through
- oxidative phosph proteins are located here
matrix
-contains TCA cycle enzymes and mitochondrial DNA
mtDNA
- size
- copies
- encodes
- different from genomic DNA
- small, circular (17kb)
- up to 10,000 copies per cell
- encodes 13 oxphos proteins, 2rRNAs and 22tRNAs
majority of mitochondrial proteins are…
- encoded for in genomic DNA
- synthesized in the cytosol
- have to be transported into the mitochondria
mitochondrial import of proteins is carried out by
- TOM (outer membrane)
- TIM (inner membrane)
targetting region of mitochondrial proteins
-typically N-terminal
energy requirement of proteins getting into the mitochondria
- energy dependent process
- proteins must be unfolded upon entry and refolded once inside
TOM proteins
transport proteins from the cytoplasm through the outer membrane
- TOM70: transports proteins that are destined to be integral membrane proteins in the inner membrane of the mitochondria
- TOM20: transports proteins that are destined to reside in the matrix
- TOM40: this is the actual channel protein which the mitochdria bound proteins pass through (lives in the outer membrane)
TIM proteins
-responsible for getting mitochondrial proteins through the inner membrane
Step 1 of oxidative phos
- called the respiratory chain
- a series of redox couples that transfer electrons from donors (NADH, succinate) to the final acceptor, oxygen
step 2
- transfer of protons from the matrix into the intermembrane space, creating a membrane potential between matrix and intermem space.
- this is called a proton gradient
- this is done via energy created from the respiratory chain
what complexes push electrons into intermembrane space
1,3,4
step 3
F0 complex
- part of complex 5 of oxphos
- proton channel in the mitochondrial inner membrane
F1 complex
-contains 3 ATP synthesizing active centers (faces mitochondrial matrix)
mechanics of F0F1 ATP synthesis
- F0 lets in protons creating a mechanical force that produces a confirmational change in active centers on F1
- these confirmational changes promote ATP synthesis
oligomycin
-inhibitor of ATP synthase
coupling
- interdependence of the rates of the respiratory chain (e transfer/oxygen consumption) and the rate of ATP synthesis
- this means that if one is inhibitted, it will directly inhibit the other
two main factors in the rate of ATP synthesis
- availibility of substrates of complexes 1 and 2 (NADH and succinate) (uncommon)
- availability of ADP for ATP synthase (very frequent)
uncoupling
- loss of coupling between respiratory chain and ATP synthase
- happens if protons are allowed back into the matrix without going through ATP synthase (through a different proton channel)
- membrane potential is abolished, respiratory chain is working at full steam, and ATP synthase isnt generating any ATP
- this will produce heat instead of ATP
how to test coupling
treat cells/mitochondria with oligomycin and measure oxygen consumption
-if it is decreased then mitochondria is coupled
uncouplers
- FCCP, dinitrophenols, UCP1/thermogenin
- brown fat contains mitochondria and burns calories at maximal rates
uncoupled mitochondria and obesity
- uncoupling forces respiratory chain to burn calories at a maximal rate without doing work
- this could be useful against obesity, however, heat production could be a harmful side affect
ANT
- adenine nucleotide translocase
- transports newly synthesized ATP from the mitochondrial matrix into the cytosol and ADP from cytosol into the mitochondrial matrix
inhibitors of ANT
- altractyloside
- bongkrekic acid
mitochondrial permeability transition
- loss of the impermeability of inner mitochondrial membrane
- caused by the permanent opening of the ANT pore caused by eg excess of calcium
- triggered through calcium dependent binding of matrix protein cyclophilin D to ANT
- can be inhibited by a non-specific CypD inhibitor (cyclosporine A)
- MPT happens in the cardia and neuronal cells during times of ischemia
- MPT causes collapse of the mitochondrial membrane potential (stopping ATP synthesis), destruction of the mitochondrial outer membrane and release of pro-apoptotic molecule from the intermembrane space
