Targetting in the Mitochondria

Question 1

How are proteins targetted to the matrix

Conservative sorting mechanism or Stop Start transfer?

Answer 1

proteins kept unfolded in matrix by chaperones
ampithatic helix hydrophobic +ve residues recognised by TOM20 pars it off to TOM22 respectively

Directs preprotein to GIP assisted by a 3rd receptor(TOM5)

Enters TOM40(pore) threaded through via help with hydrophobic and polar residues on the inside of the barrel, when energes it engages with TIM50, whihc brings TOM&TIM together

TIM 50 guides to TIM import channel (TIM23)
both
pulled in via PAM complex- power stroke via ATP cyles and HSC70,
and brownian ratchet model

SP is cleaved by mitochondrial processing enzyme

Question 2

How are carrier proteins transported into the innermembrane

Conservative sorting mechanism or Stop Start transfer

Answer 2

Carrier pathway to the inner mitochondrial
membrane. Cytosolic chaperones guide the precursor to the receptor Tom70. The precursor is transported through the translocase of the outer membrane in a loop formation and interacts with the Tim9-Tim10 chaperone complex. Tim9-Tim10 guides the precursor through the intermembrane space to the carrier translocase of the inner membrane (TIM22 complex with bound Tim9-10-12) (. The membrane potential (Δψ) promotes insertion of the precursor into the inner membrane via the TIM22 complex ++ve charges on matrix, followed by assembly into the mature form of the carrier protein (stage V).

Question 3

How do does the stop transfer mechanism work in intermembrane proteins
Stop transfer sequence(TMD) and SP

Answer 3

same pathway as matrix proteins
The sorting signal arrests translocation in the inner membrane and causes a lateral release into the lipid phase of the membrane . Although the details
of the mechanism are not understood, the release requires a lateral opening of the Tim23 channel and involves the activity of Tim17

Question 4

How does inter membrane protein processed
Tim 23 dependant
Conservative sorting mechanism or Stop Start transfer

Answer 4

SP -hydropboic sequence-protease site
when they diffuse laterally in TIM23 they come into contact with IMP1 protease which will cleave and release mature protein

Question 5

Cysteine dependant intermenbrane translocation

Conservative sorting mechanism or Stop Start transfer

Answer 5

Mia40 form disulphide bonds
pulls protein into IMS with help from ERV1 and trapping it inside(due to S-S). The reduced cysteines on Mi40 and protein are reoxided by ERV1 and the electron are transferred to cytochrome C then to O2(respiratory chain)

Question 6

Outermembrane protein formations TOM

Conservative sorting mechanism or Stop Start transfer

Answer 6

Sorting of ß-barrel proteins. The precursors of
ß-barrel proteins are initially transported via the translocase of the outer membrane (TOM complex) into the intermembrane space (IMS). IMS chaperone complexes transfer the precursors to the sorting and assembly machinery (SAM complex).
The two essential subunits, Sam50 and Sam35,
cooperate in insertion of the precursors into the
outer membrane pathway of the ß-barrel protein, Tom40. Mim1 supports integration of the Tom40 precursor into the outer membrane; Tom40 then associates with Tom5 and a further Tom40 molecule, followed by Mdm10-supported assembly of the oligomeric
TOM complex.

Question 7

How are mitocondrial genome encoded proteins targetted

Conservative sorting mechanism or Stop Start transfer

Answer 7

ancient conserved pathway- homologous bacteria and plants
co-translational insertion- mitochondrail sequences recognised by oxa1 and inserts into the membrane according to the charge distrubution of the protein
e.g++ve residues on the intermembrane space
helps to orientate the protein properly