BIOLOGY 2B03 Lecture Notes - Lecture 9: Protein Folding, Methotrexate, Alpha Helix
6 Jun 2018
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Protein Targeting: Post Translational Transport to Mitochondria
Characteristics of Mitochondria
1) bound by double membrane •
inner and outer ◦
2) involved in ATP production •
3) have their own DNA •
4) reproduction by fission •
ATP Synthesis Sites
nutrients are converted into cellular energy (ATP) •
most ATP is synthesized by proteins embedded in the inner membrane •
structure of mitochondria enables high level of ATP synthesis •
cells needing more ATP have more mitochondria •
i.e. muscles need ATP for muscle contraction ◦
Mitochondria Biogenesis
new mitochondria created via fission •
growth requires synthesis and import of new proteins •
two mitochondria can also under fusion - each daughter mitochondrion ends up with at least one mitochondrial •
genome during this process
if not, will die ◦
Where do Proteins in Mitochondria Come From?
some coded in mitochondrial genome - synthesized by ribosomes •
majority coded by nuclear genes - transported to mitochondria in post-translational pathway •
proteins transported into mitochondria go to 1 of 4 places: •
outer membrane ◦
inter membrane space ◦
inner membrane (including electron transport proteins and ATPase) ◦
matrix ◦
Post-Translational Transport to Mitochondria
Hypothesis: if fully translated proteins can be transported, then proteins •
in presence of mitochondria will move into mitochondria
Method: mitochondrial proteins followed in cell-free system - in one •
tube, energized mitochondria and protease added (degrades proteins in
solution)
in second tube, only protease added ◦
Observation: only proteins protected within mitochondria not digested •
by protease
this means fully translated protein can be transported into ◦
mitochondria
aka second tube had degraded protein, first did not due to mitochondria presence ◦
Conclusion: the proteins were fully translated prior to import •
*Recall 5 rules of protein transport: there must be a signal sequence, a receptor for that signal sequence, a
translocation channel across the membrane, a source of energy and a way of targeting proteins to go to different
locations within organelle
Document Summary
Characteristics of mitochondria: bound by double membrane inner and outer, involved in atp production, have their own dna, reproduction by fission. Hypothesis: if fully translated proteins can be transported, then proteins in presence of mitochondria will move into mitochondria. Method: mitochondrial proteins followed in cell-free system - in one tube, energized mitochondria and protease added (degrades proteins in solution) in second tube, only protease added. Observation: only proteins protected within mitochondria not digested by protease this means fully translated protein can be transported into mitochondria aka second tube had degraded protein, first did not due to mitochondria presence. Conclusion: the proteins were fully translated prior to import. Rule 1 - is there a signal peptide sequence? yes - matrix-targeting motif found at n terminus. Hypothesis: if matrix-targeting motif added to gfp, gfp will go to mitochondria. **note: tom = translocon of outer membrane, tim = translocon of inner membrane. Rule 2 - is there a signal receptor.
