BSC 300 Lecture 18: 3-27-18
18 Apr 2018
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Document Summary
These selective gates actively transport specific macromolecules but also allow passive diffusion of smaller molecules. These pores are so large they allow proteins to pass without the need for modification (as in other organelles: proteins bound for the er, mitochondria/chloroplast and peroxisome are moved across the respective membranes via active protein translocators. Such translocation often requires the proteins to be unraveled as they are transported. Import mechanism experiment: cell-free system synthesis of mitochondrial precursor proteins containing uptake-targeting sequences, addition of respiring mitochondria to presynthesized mitochondrial precursor proteins: proteins taken up by mitochondria-- protected from added proteases, control-- proteins degraded when no mitochondria added. N-terminal organelle-specific signal sequence: protein import into the mitochondrial matrix. Amphipathic n-terminal targeting sequences target proteins to the mitochondrial matrix: n-terminal 20-50 amino acids-, amphipathic -helical conformation, positively charged and hydrophobic amino acids predominate on opposite sides of the helix. Signal sequence recognized by a receptor protein in the transporter outer membrane (tom) complex.
