Transmembrane transport

Question 1

when would you use transmembrane transport

Answer 1

mitochondria and chloroplasts

Question 2

trans. mem. transport into mitochondria

Answer 2

proteins which are fully synthesises by the ribosomes in the cytoplasm - are unfolded and kept unfolded by chaperones
signal sequence made of amphiphilic a helices which have positive cluster on one side allow entry into the matrix by binding to the protein translators TIM and TOM

Question 3

protein translocators

Answer 3

TIM and TOM

Question 4

TOM complex

Answer 4

• binds signal sequence
• transports across ouster membrane (ATP hydrolysis)
• histones dissociate -HSP70 family

Question 5

TIM complex

Answer 5

• binds the signal sequence
• mitochondrial membrane potential - drives the initial translocation to +ve charged residue through to the matrix
• immediately bound to Hsp70 - release from this drives the completion of import
• Hsp 60 helps to fold the protein properly

Question 6

which proteins helps to form the protein properly after import through TIM into mitchondira

Answer 6

Hsp60 chaperone

Question 7

different end point for the mitochondrial import into inner membrane space

Answer 7

• hydrophobic residue following the +ve charged residue - TIM23 won’t translocate it through
• 2nd signal sequence - OXA translator - matrix to IMS
• metabolite transporter - pulled through TOM as look and bound by chaperones - TIM22 inserts them into the membrane

Question 8

TIM22 and 23

Answer 8

are structurally related

Question 9

TIM23

Answer 9

hydrophobic alpha helical extension - inserted into the ouster mitochondrial membrane - spans both membranes

• Mitochondrial side - TIM23 bound to Hsp70 (mitochondrial) which acts as an ATPase using ATP hydrolysis to pull proteins through the pore

Question 10

TOM complex

Answer 10

is required for import of all mitochondrial - nucleus encoded proteins

Question 11

SAM complex

Answer 11

helps to fold the B barrel proteins which are particularly abundant in the outer membrane

Question 12

what drives protein import into the matrix space

Answer 12

ATP hydrolysis and membrane potential

Question 13

unfolded proteins and chaperones bind and associate with import receptor

Answer 13

TOM - bind and release of Hsp70 requires ATP

Question 14

once a proteins has passed through the TOM complex and is bound to the TIM complex further translocation through the TIM complex requires

Answer 14

the membrane potential which is the electrochemical gradient across the inner membrane from pumping H+ from the matrix space to the inter membrane space driven by electron transport

Question 15

the electrochemical gradient in mitochondria

Answer 15

drives most of the ATP synthesis and also translocation of positively charged signal sequences through the TIM complex

Question 16

the OXA complex

Answer 16

mediates the insertion of those inner membrane proteins that are synthesised within the mitochondria

also helps to insert some imported inner membrane proteins that are initially transported into the matrix space by other complexes

Question 17

transport into the chloroplast

Answer 17

similar to the mitochondria however the transport into the thylakoid requires an extra step

• 2nd hydrophobic sequence - unmasked when it is cleaved in the stroma

Question 18

in chloroplast where does the energy come from

Answer 18

GTP and ATP - photosystem across a double membrane - H+ gradient across the thylakoid

Question 19

difference between mitochondria and chloroplasts harnessing their electrochemical gradient

Answer 19

The chloroplast has the H+ gradient across the thylakoid membrane rather than over the inner membrane as in the mitochondria

Question 20

Transport into the chloroplast sequence

Answer 20

• receptor proteins interact with the translator
• GTP/ATP dependent translocation into the storm
• cleavage chloroplast signal
• exposed thylakoid signal
• 4 pathway to get into the thylakoid

Question 21

4 pathways to get into the thylakoid membrane

Answer 21

Sec pathway - which has Sec homologues
SRPlike pathway
TAT pathway - twin arginine location - depends on the H+ gradient across the thylakoid membrane
spontaneous insertion pathway - this seems not to require protein translator