Lecture #2 Flashcards
what is mitochondrial DNA transcribed as?
a polycistronic unit
what do miRNAs act as?
post-transcriptional regulators and translational repressors
describe the expression of miRNAs
tissue-specific
describe the overall roles of miRNA:
both pathological and physiological
what are miRNAs coded from and processed by?
coded from nuclear DNA and processed by DNA polymerase II
what shape is pre-miRNA characterized by?
a hairpin loop
besides the cytosol, where is it proposed that miRNAs can also be found?
in mitochondria
what are the 6 potential ways that miRNAs can enter into the mitochondria?
through a specific motif at the 3’ terminal, through post-transcriptional modifications, with the help of PNPase, with the help of AGO2, through import inside of P bodies when in complex with AGO2, or by PUMILIO1 and AGO2 working in tandem
what was found to be associated with micromiRNAs when isolated from WT mouse cerebellum?
an interaction between mitomiRNA and AGO2
what cells have been shown to rely the most on mitochondria?
in neural cells
what are the three levels of mitochondrial quality control?
molecular, organelles, and cellular
what is a mirnome?
a library of all miRNAs present inside mitochondria of cerebella
what cells rely the most on mitochondria?
neurons
what two things are linked to transport across neurons?
both energy production and ion balance
what does ion balance directly control in neurons?
movement
what two areas of the body do mitochondrial dysfunctions affect?
neurons and muscles
what is mitophagy?
the fusion and fission events together with transport coupled with degredation of mitochondria
if mitophagy fails to recover damage, what occurs?
apoptosis is triggered via the release of cytochrome C
when apoptosis is triggered, where is the cytochrome C released from?
released from the inner membrane space to the cytosol
list the three ways in which the control of the mitochondrial proteome is not exerted in an autonomous way:
or proteins located on the outer mm, proteins containing disulphide bonds, and translocons that are engulfed and cannot import proteins from the outside
what is the degredation of proteins located on the omm called that is an exception from the typical autonomous degredation referred to as?
mitochondrial associated degradation
what is mitochondrial associated degredation of proteins located on the omm reminiscent of?
ER associated degredation (ERAD)
what is unique about each sub-compartment inside of mitochondria?
there is a specific quality control system for each compartment
what do proteases in the matrix always have?
presequences that travel by TOM40 -> TIM23 motor pathway, then cleaved and folded by Hsp60
if proteins brought into the matrix are folded improperly, what two proteases are involved in degredation?,
LON protease (LONP) and CLPXP protease
what is LONP?
a highly conserved serine-protease that degrades unfolded, damaged, or oxidized proteins
due to the leakage of electrons from the respiratory chain, what are abundant in the mitochondria?
reactive oxygen species (ROS)
what is the function of PTRM1 peptidase?
digests dipeptides into aa that are then transported outside to be recycled
what are the two specific proteases located in the inner mitochondrial membrane?
m-triple A and i-triple A
describe m-triple A and its position:
a hexameric complex arranged in which the catalytic chamber is directed towards the matrix space
describe the i-triple A protease:
hexameric complex in which the proteolytic chamber is directed towards the intermembrane space
m-triple A and i-triple A are integral to the membrane as well as their target proteins, so how can they decide what to degrade?
the presence of a hydrophobic domain outside the membrane
what specifically are recognized by m-triple A and i-triple A on proteins tagged for degredation?
solvent exposed domains - if there is a mutation that alters the folding of the state of these proteins
how do AAA proteases handle proteins that need to be degraded?
they exert a retrograde translocation of the protein - cut it and insert it in the proteolytic chamber for degredation
what does AAA stand for?
ATPase Associated with different cellular Activities
Describe the two roles of AAAs?
act like chaperones and proteases together - they can sense the protein folding state but can also degrade proteins
when are subunits of AAAs generally mutated?
in neuron degenerative diseases
what are the two key proteases of the intermembrane space?
HTRA2 and ATP23
what is the function of HTRA2?
highly conserved and forms a trimeric complex - important for the degredation of oxidized proteins
what is ATP23?
a metalloprotease
what is organellar quality control based on?
mitochondrial dynamics
what is molecular quality control based on?
control of proteostasis
what are the three different states of mitochondrial network?
tubular, intermediate, and fragmented
describe the tubular mitochondrial network:
mitochondria are elongated and highly interconnected
describe an intermediate mitochondrial network:
mitochondria are still tubular however the tubulars are shorter and not as connected
describe a fragmented mitochondrial network:
there isnt a network anymore and there are many individual structures
In order to be healthy, what must mitochondria balance?
fusion and fission events - cells need to shift their mitochondrial network depending on cellular needs
what is most often the cause of disease when mitochondria are involved?
excessive fusion or fission events
primary defects in fusion and fission events are related to what diseases in children?
neurological diseases of early childhood
in terms of generation, what makes mitochondria different than other organelles?
they are not generated de novo
what happens in autophagy?
autophagosome engults organelles that are not functioning properly and by fusing with lysosomes, degrades them
what is the final aim of autophagy?
to recycyle organelles and proteins
what is the triggering event for mitophagy?
depolarization
deploarization triggers a pathway in which what specifically happens?
specific proteins are exposed on the omm in order to recruit the the machinery for autophagy degredation
before autophagy is triggered, what do mitochonria try to use instead?
the salvage pathway such as fusion / fission events or the reverse activity of the ATPsintase in order to prevent depolarization
besides depolarization, what is another prerequisite for mitophagy?
fragmentation - autophagosome cannot englulf an entire network
how does the reversal of ATPsynthase work to promote degredation of miotchondria?
ATPsynthase is able to comsume ATP in order to pump the protons back into the intermembrane space in order to re-establish the mitochondrial membrane potential
what is the fastest way to assess the mitochondrial membrane potential?
TMRM
what happens if ATPsynthase is blocked in healthy cells?
the amount of protons in the ims are increased and there is a high polarization
what happens if ATPsynthase is blocked in unhealthy mitochondria?
the mitochondrial membrane potential goes down
what are the two main players in fision and fussion events?
MFN1 and MFN2
what mediates the fusion of the omm?
MFN1 and MFN2
what complex mediates the fusion of the imm?
OPA1 (optic atrohpy 1)
what disease is MFN2 mutated in?
Charcot-Marie-Tooth disease (peripheral neuropathy)
