Biogenesis of mitochondria and chloroplasts I Flashcards
% of mitochondrial/chloroplast proteins encoded by nuclear genes
90
why is it maybe good to have these proteins encoded in the nucleus?
isolation from the potential mutagenic effects of electron transfer systems
avoids Muller’s ratchet
allows reduction of organelle genome size, faster replication and lower metabolic maintenance for the cell
allows the cell more control over endosymbionts
why are protein localisation mechanisms so important?
need to target cytosol proteins to the right place, need them to be specific to the organelle and need to allow for control of how much/when protein is imported
sequences normally present on the proteins to be imported into mitochondria
N-terminal presequences, C-terminal tags
features of the N terminal presequence
amphipathic helix, with positive charged residues on one side, and hydrophobic ones on the other
cleavable
variable in length
example of chaperone proteins which keep proteins unfolded in the cytosol
Hsp70 and 90
key features of mitochondrial protein transport
mostly post-translational import- precursor proteins are fully synthesised in the cytosol
N terminus goes in first
ATP-dependent import, also dependent on the proton gradient
name given to the type of protein complex which protein precursors pass through
translocases
outer membrane translocase
TOM
inner membrane translocase
TIM
what recognises the presequence?
Tom20
import pore in the outer membrane
Tom40
how does the presequence get through the TIM channel
proton gradient drives it
what protein is required for import into the matrix?
mtHsp70, a chaperone
what cleaves off the presequence?
mitochondrial processing peptidase (MPP)
