Mitochondria- TIM

Question 1

Which type of proteins does TIM23 recognise

Answer 1

proteins with an internal amphipathic helical presequence- matrix soluble proteins

Question 2

Which Tim protein is responsible for sorting proteins with a matrix targeting signal followed by a hydrophobic sequence and where are these proteins destined for

Answer 2

tim23sort. these proteins are destined for IM integration

Question 3

what is the role of TIM22

Answer 3

translocates proteins with an internal presequence dedicated to metabolite carrier family proteins

Question 4

How do Tim23 and TIM17 work together

Answer 4

they form a cation selective voltage gated channel in the membrane. Tim17 regulates pore opening

Question 5

what is the role o TIM50

Answer 5

it has a domain which sticks into the inter membrane space and binds the prescience of proteins emerging from TOM22. it also helps to close the TIM23 channel

Question 6

what is the role of TIM21

Answer 6

links TIM and TOM by interacting with TOM22’s I’m space domain. It is also responsible for dissociating TIM23 from PAM

Question 7

what does the PAM complex stand for

Answer 7

presequence associated motor complex

Question 8

which subunits comprise PAM

Answer 8

Tim44, mtHSP70, Mge1, pam18, pam16 and pam17

Question 9

what is the role of tim44

Answer 9

binds to translocating polypeptide as it exits the TIM complex

Question 10

what is the role of mtHSP70

Answer 10

it binds TIM44 and the translocating peptide. it also hydrolyses ATP, energising translocation and aiding translocation through a pulling and trapping mechanism

Question 11

what is the role of mge1

Answer 11

it is a nucleotide exchange factor for Hsp70

Question 12

what is the role of Pam18

Answer 12

stimulates aptness activity of Hsp70

Question 13

what is the role of PAM16

Answer 13

controls pam18 mechanism

Question 14

what is the role of pam17

Answer 14

organises the PAM complex

Question 15

How does Tim23 optimise targeting of proteins to either the membrane or the matrix

Answer 15

interacts with partners for example recruits cytochrome bc1 and cytochrome oxidase complex leading to delta psi dependent integration of the protein into the inner membrane

Question 16

which Tim proteins comprise the Tim complex which translocates proteins with an internal presequences

Answer 16

Tim22, Tim54, Tim18, Tim12

Question 17

what is the role of Tim54

Answer 17

it is analogous to TIm50 and binds the proportion and other translocase proteins

Question 18

what is the role of tim18

Answer 18

involved in dynamics, assembly and interaction with other components

Question 19

what is the role of tim12

Answer 19

link between tim22 and small tim 9/10

Question 20

describe the stages of import of mitochondrial ATP/ADP related carrier proteins through the Tim22 complex

Answer 20

it is delivered to TOM70 receptor and passed onto TOM 20/22. interaction occurs between Tom70 and duplicated internal targeting sequences. the protein is released in an ATP dependent manner to GIP and inserted into the general insertion pore of which TOM40 is the main component. it then interacts with tim9/10. tim9/10 interacts with tim12 and tim22 and the protein is inserted into tim22 pore. under high membrane potential the protein exits tim22 and dimerises in the membrane to form the active functional protein

Question 21

describe the role/importance of delta psi in translocation of proteins that are inserted into the IM of the mitochondria

Answer 21

it;s electrophoretic effect on the presequence is required for import and insertion and it also regulates the opening of the channels

Question 22

describe the common structure of small time 8-13

Answer 22

they contain a conserved twin CXXXC motif and fold by forming 2 disulphide bonds between cysteine residues of 2 of these motifs and they assemble in 70da hecamers.

Question 23

what are the components of the small tim hexameter which chaperones carrier proteins

Answer 23

3xsmall tim 9 and 3x small tim 10

Question 24

what are the components of the small tim hexameter which chaperones proteins translocated through the Tim23 complex

Answer 24

3x 8 and 3 x13

Question 25

which small tim is membrane bound

Answer 25

tim12

Question 26

describe the import and folding of small tims into the mitochondrial IM space

Answer 26

they are imported via TOM40 complex then folded by a disulphide relay system catalysed by Mia40 and Erv1. Mia40 oxidises the imported protein and is itself reduced via disulphide bond exchange. Ev1 reoxidises Mia40 so cycle can repeat and Erv1 is deoxidised by donating electrons to cytC which donates electrons to the electron transport chain

Question 27

how are proteins with a C term presequence such as DNA helicase Hmi1 translocated

Answer 27

in the same manner however it occurs in Cterm to N term direction. this demonstrates polarity is not important

Question 28

how is fumarase dual targeted to the mitochondria and cytosol

Answer 28

transport is initiated into the mitochondria where the presequence is cleaved. some proportion of the protein is then released back into the cytosol

Question 29

how are mitochondrially encoded proteins inserted into the IM

Answer 29

via the Oxa pathway. Oxa1p interacts with ribosomes cotranslationally