Biochemistry - Unit III - mitochondria genetics

  1. Essential functions of mitochondria
    • Biosynthesis of
    •     heme
    •     amino acids
    •     nucleotides
    •     steroid hormones
    • ATP synthesis
    • Oxidation of fatty acids
    • Apoptotic cell death
  2. Mitochondria proteins are encoded by 2 separate genomes and translated by 2 different protein synthesis machineries
    • 95% from chromosomes
    • synthesized/translated in cytosol
    • post-translationally imported into mitochondria (N-terminal locates mito outer membrane receptor) translocated across the membranes into the matrix

    • 13 proteins are encoded by the small circular mtDNA with multiple copies (all maternal)
    • directly synthesized inside mito
    • more affected by antibiotics
  3. mtDNA
    circular genome
    small in size ~16 kb in man
    5-10 copies of mtDNA / mitochondrion
    ~1,000 mitochondria / cell (depending on the cell type, myocyte 30% of volume is mito)
    ~1% of cellular DNA
    Compared to nuclear DNA/mRNA
    • 13 proteins
    • large and small rRNAs
    • tRNAs

    • NO introns- polycistronic mRNAs
    • different genetic code
  4. Proteins encoded by mtDNA
    • 13 proteins
    • some subunits of complexes I, III, IV, and V
    • I, III, IV pump H+ from matrix to inter-membrane space
    • V use the gradient to create ATP, ATPase
  5. Characteristics of mtDNA genetics
    • maternal inheritance (paternal mitochondria are actively excluded/degraded)
    • heteroplasmy
    • stochaistic (random) segregation
    • threshold effect
  6. Reactive oxygen species (ROS)
    • oxygen radicals
    • electrons leaked out from electron transport chain and react w/ O2 form O2- radical, superoxide
    • superoxide has short life and is quickly converted to H2O2 by enzyme MnSOD. H2O2 is more stable, lasts longer, and can diffuse out of the membrane, causes damage everywhere, major concern
    • H2O2 can be converted to H2O and O2 by catalase
    • H2O2 can also react w/ Fe2+, which is abundant in mitochondria (brown color), to form hydroxyl radical (⋅OH), which is highly reactive and dangerous, can cause damage to DNA, proteins, and lipids
  7. Why does electron transport chain generate ROS?
    • Double agent theory
    • In young and healthy cells, the mechanism is necessary for protection, transient oxidative stress is necessary for immune responses, part of the signaling, against pathogen,...
    • In aging cells, chronic oxidative stress leads to dysfunction and aging, arthritis, heart disease, cancer, ...
  8. mtDNA mutations and human disease
    • sometimes just single base mutation
    • can also be other types of mutations
  9. mtDNA replication starts with synthesis of ______, which requires ________ and _______.
    • RNA primer
    • mitochondrial RNA polymerase - single subunit
    • two accessory factors: TFAM and TFB2Mnic
  10. Continuation of RNA primer synthesis
    • remains hybridized to mtDNA
    • cleaved by RNase MRP (RNase mitochondrial RNA processing) to provide 3’OH for continuation
  11. mtDNA replication requires:
    • POLG (mtDNA polymerase γ)- consists of α and β subunits
    •     α- catalytic subunit
    •     β- accessory subunit, primer recognition
    •     polymerizing activity and 3’ to 5’ exonuclease activity.
    •     high fidelity, proofreading capability (1 error every 500,000 bases)
    • mtSSB - mtDNA single-strand DNA binding protein, binds to the displaced chain and protects it from being degraded
    • Twinkle - mtDNA helicase
  12. ________ have higher similarity with bacterial phage (viral) nucleic acid than eukaryonic DNA
    • Twinkle- mtDNA helicase
    • mitochondrial RNA polymerase
  13. Transgenic mice experiment suggested _____.
    a causal link between increased somatic mtDNA mutations and aging.
  14. Mitochondrial replacement therapy
    • AUGMENT (autologous mitochondrial treatment for in vitro fertilization)
    • Non-autologous Mitochondrial Replacement Treatmentfor IVF
    • Healthy mtDNA
Card Set
Biochemistry - Unit III - mitochondria genetics
Biochemistry - Unit III - mitochondria genetics - Suzuki