Mitochondria and Peroxisomes Flashcards
(46 cards)
what is the appearance of mitochondria?
-2 membranes: outside with outer membrane and inside with inner membrane
-inner membrane is folded into structures called cristae to increase surface area and accommodate many protein complexes
-in between the 2 membranes = intermembrane space
-inner membrane inside is called the matrix with mitochondrial DNA
many mitochondria in the cell and mtDNA in each cell
-2 copies of nuclear DNA but more than 100s of copies of mtDNA
synthesis of ATP
-sugars, fats, and proteins are the first used in the TCA cycle or citric acid cycle in the matrix to create high energy compounds like NADH and FADH2
-used to create electrochemical gradient across the inner membrane using these pumps that pump protons from the matrix to enter membrane space –> force of energy created by mitochondria against the natural [] of the proton
-b/c of the gradient, the proton goes back to matrix using the F1/Fo ATPase and ATP synthase –> this energy creates ATP (complex five)
-in this energy production process, mitochondria use O2 to create ATP –> make smoke reactive oxygen species as a byproduct of electron transport
-taken care by enzymes which detox by reactive oxygen species (ROS)
-when you create a proton gradient, can be used to make ATP but also you can use for other purposes
mitochondrial ATP production
-import ADP to the matrix and also phosphate then after you make ATP, it gets transported out (many transporters)
-ATP is transported using a proton gradient and phosphate is also transported using this gradient
what happens since mitochondrial IM is impermeable?
many special carriers are needed to transport necessary small molecules into/out of the matrix
what are other functions of the mitochondria?
-metabolism of lipids, amino acids, and fatty acids (creates energy and urea degradation), and creates heme
-control our body temp by generating heat
-involved in signalling using Ca2+ and ROS
-controls apoptosis
mitochondria and disease
-general outcome of mitochondrial defect- tissues which are highly demanding for energy are mainly or predominantly affected
-muscle and heart, metabolic disorders, brain and neurons like neurodegeneration
-some types of cancer may be impacted like mutations in complex II that cause pheochromocytoma (neuroendocrine tumor)
what is a method to study mitochondria?
isolation of organelles
isolation of organelles
-break up the cells or tissues mechanically for homogenization –> make mixture of cytosol and broken organelles
-use differential centrifugation to spin down specific organelles based on size and density
-low speed: pellet with big structures like nuclei
-intermediate speed: mitochondria, lysosomes, peroxisomes, and intermediate size density structures
-really high speed: spin down pellet into smaller structures like fragments of ER (microsomes)
-use ultracentrifugation you can start pelleting big protein complexes like ribosomes
fractionations of mitochondria:
- OM- numerous ‘pores’, permeable to small molecules and ions
- IMS: a few proteins and enzymes (cytochrome C)
- IM: much of the OXPHOS machinery like cardiolipin
- Matrix: TCA cycle enzymes, mtDNA
outer membrane (OM)
-have many big pores that are permeable to many small structures
-forming the porin with big pores in OM –> small molecules like ATP or ADP can freely diffuse in and out across the OM
-beta-barrel protein- these types of proteins are found in the mitochondria of the membrane and bacterial membrane –> suggesting link between mitochondria and bacteria in origin
intermembrane space (IMS)
-cytochrome C- protein with 2 major functions: life and death of cells
-functions as a protein subunit of the ETC complex (complex four) –> oxidative phosphorylation machinery that creates proton gradient and ATP
-depending on the conditions cells are in or stimulation they receive, cytochrome C can function in ATP production or cell death
cytochrome C + apoptosis
when cells decide to die, cytochrome C is released from complex four and leads into the cytosol from IMS and binds to different regulators of apoptosis and stimulates or induces apoptosis
inner membrane (IM)
-huge membrane area with many proteins or transporters
-5 different complexes: complex 1-4 generate proton gradient by pumping out protons from the matrix side to the intermembrane space using NADH and FADH2 then complex 5 (ATP synthase) uses this gradient to create ATP from ADP and phosphate
-once ATP is generated in the matrix, the molecule is transported out to intermembrane space and eventually cytosol through porin
matrix (inside IM)
-T cell cycle uses pyruvate (product of glycolysis) as primary source to create high energy compound NADH and FADH2
-high energy compounds are used to create proton gradient across the IM by the ETC
the ‘code’ in mtDNA differs from that in nuclear DNA
-uses different codons from nuclear DNA Ex. AUA as Leucine in nuclear DNA but mitochondria use it for Methionine
-patterns similar to pattern of codons in bacteria- link between mitochondria and bacteria
what are some links between mitochondria and bacteria?
- presence of beta-barrel protein in the mitochondrial membrane and bacterial membrane
- codon patterns of mitochondria are similar to those of bacteria
- both have circular DNA structures
- CL and mitochondrial-specific lipids are also found in bacteria suggesting that precursor of mitochondria during evolution
- mitochondria have two membranes suggesting one from bacteria and one from the host cell plasma membrane
mitochondria have their own DNA (mtDNA) but it encodes only a few proteins
-13 proteins in humans –> all of them are subunits for different ETC complexes
-nuclear DNA is a linear structure but mtDNA is a circular structure
-mtDNA also encode ribosomal RNA and tRNA for protein synthesis in the matrix
-mtDNA tend to accumulate more mutations at increased rate compared to nuclear DNA –> due to inefficient repair and possibly ROS exposure, which can damage DNA
many diseases caused by mutations in mtDNA
-LHON- mutation in the subunit of complex I, ND1, 4, and 6
–> creates defects in protein synthesis, which affects muscles
-if you mutate the gene encoding F1 for ATPase five then that will lead to disease affecting nervous system
-many mitochondrial proteins are encoded by nuclear DNA
mtDNA is inherited differently from nuclear DNA
-mtDNA is only inherited from an oocyte but not sperm or father’s side
-mitochondria and mtDNA are degraded once fertilized and then fusion between oocyte and sperm happens –> only maintain mitochondria and mtDNA derived from the oocyte
-mutations in the oocyte can be inherited but mutation in mtDNA of sperm is not
-maternal inheritance and not 100% penetrance –> since we have many mtDNA with 100s of copies in cells, depending on ratio of mutant mtDNA to WT mtDNA the symptoms and defect outcome can be different
-people found that over 60% of mtDNA had to be mutated to actually start seeing the defects in the body
-WT mtDNA can dominate mutant mtDNA
how do you treat mitochondrial disease caused by a mutation in mtDNA?
-repress bad mitochondria with good mitochondria
-experiment showed you can replace affected mitochondria with healthy mitochondria using patient nuclear DNA –> remove the disease-causing mutation
can eukaryotic cells ever lose all of their mtDNA?
-yes- mtDNA encodes subunit of oxidative phosphorylation but you can generate ATP in other ways to bypass this requirement like through glycolysis
-cells can make mitochondria without mtDNA but cannot do oxidative phosphorylation
although mitochondria contain their own genome, the vast majority of mitochondrial proteins are encoded in the nucleus
-mammalian mitochondria have ~1500 proteins
-mitochondrial proteins are encoded in the nuclear genome and need to be imported into the mitochondria
multi-subunit complexes often contain subunits encoded in mtDNA and others encoded in the nucleus
-Complex I is a huge complex with 46 subunits
-some generated in the matrix and have to be transported to inner membrane
-some are synthesized in the cytosol and transported to the mitochondria and inserted into the inner membrane –> these proteins work together to make a functional complex
