Chloroplasts Flashcards
describe the similarities between the Mit and chloroplast protein import system
protein is translated in the cytosol and contains an Nterm presequence. the proportion binds the TOC/TIC machinery which is analogous to TOM/TIM. Proteins import in the unfolded conformation. it requires chaperones
what is the main difference between the mist and chloroplast protein import system
requires GTP and ATP whereas mit just needs ATP. delta psi only needed for ATP synthesis and not for protein import
what is the presequence on proteins targeted to the stroma
lots of hydroxylated amino acids at the N term with overall positive charge
what is the presequence on proteins targeted to the thylakoid
helical section with an N term positive charge and C term small side chain amino acid
why do uncouplers inhibit transport in the light but not in the dark
because in the light they prevent ATP synthesis but in the dark, if ATP is added import can occur showing membrane potential is not necessary in chloroplasts
which proteins comprise the cytosol guidance complex
hsp70 and 14-3-3 protein
describe the process of import protein docking at TOC complex
hydroxyl containing presequence is phosphorylated co-translationally by protein kinase which is specific for transit peptides. It then can bind the hsp70/14-3-3 cytosol guidance complex. this then docks at TOC complex in the outer envelope. the precursor is then dephosphorylated before import
what is the role of TOC75
it is analogous to TOM44 and forms the voltage gated cation selective channel
what is the role of Toc34
receptor protein for protein docking in GTP dependent fashion. may have a role in regulating import
what is the role of toc64
it is the receptor for proteins which use hsp90 and proposed binding site for the guidance complex
what is the role of toc159
this is the major receptor which binds ATP and GTP. its N term is highly negative for binding positive presequence. this works with toc34
how does toc34/159 work
preprotein binds to phosphorylated toc34 which activates GTP hydrolysis to GDP. this drives conformational changes allowing toc159 to help deliver the proportion though the pore, acting as a motor
what are the components of the tic machinery
tic110,40,20,22,32,55 and 62
what is the role of tic110
associates with stroll chaperones and recruits them to drive translocation and folding
what is the role of tic40
it associates with tic110. the majority of it faces the storm with an n term membrane anchor has homology to hsp70 at the cterm
what is the role of of tic22
it is a peripheral membrane protein facing the IM space which may be a receptor or mediate association of tic and toc complexes
what is the role of tic20
could possible form the channel
what is the role of of tic 32, 55 and 62
they all have potential to regulate via redox potential. 32 and 55 bind NADPH and 62 binds FNR, linking ETC with translocation machinery
which chaperones are thought to be involved in outer envelope insertion of proteins
AKR2 and tok75
give an example of a protein which is dual targetted to the the chloroplast and mitochondira
tRNA synthetases
how can dual targeted proteins be sorted to 2 places
potentially as a result of different transcription start sites, alternative splicing or an ambiguous presequence which is recognised by both machinery
why is it thought that some chloroplast proteins go first to the ER
they have an ER signal sequence
how is carbonic anhydrase delivered to the chloroplast
it goes first to the ER, travels to the golgi then is glycosylated then reaches the chloroplast b vesicular trafficking
