Lect. 12 - intracell compartments and protein sorting 2

Question 1

mitochondrial proteins

Answer 1

encoded in nuclear DNA, synthesized on ribosomes and imported into mitochondria

Question 2

translocation

Answer 2

protein movement

Question 3

signal sequences

Answer 3

direct proteins to correct compartment in mitochondria

Question 4

Mitochondrial signa sequences

Answer 4

N terminal and internal sequences; form amphiphilic alpha helix; positively charged residues cluster on one end and hydrophobic on the other end of helix

Question 5

what mediates translocatoin?

Answer 5

multi-unit protein complexes called protein translocators

Question 6

what is recognized by the receptor proteins?

Answer 6

configuration of the amphiphilic alpha helix rather than a precise sequence

Question 7

Translocase of the outer membrane (TOM)

Answer 7

required for import of all nuclear encoded proteins; inserts them in outer membrane

Question 8

TIM 22

Answer 8

mediates the insertion of a specific subclass of proteins (e.g ATP, ADP, and Pi transport)

Question 9

TIM 23

Answer 9

transports soluble proteins into matrix and helps insert membrane proteins in inner membrane

Question 10

what are the 2 components of TOM and TIM?

Answer 10

receptors for mitchondrial precursor proteins and translocation channels

Question 11

Sorting and Assembly machinery complex (SAM)

Answer 11

translocates and inserts/folds beta barrel proteins in the outer membrane

Question 12

OXA complex

Answer 12

mediates insertion of proteins synthesized in mitchondria

Question 13

are precursor proteins entering the mitochondrial folded or unfolded?

Answer 13

unfolded

Question 14

how is the unfolding of precursor proteins maintained?

Answer 14

through interactions w/ chaperone proteins (cytosolic Hsp 70)

Question 15

what cleaves off the signal sequence once protein is in the mitochondrial matrix?

Answer 15

peptidase

Question 16

how does the bound Hsp 70 dissociate?

Answer 16

ATP hydrolysis outside mitochrondria

Question 17

what does the transport through TIM depend on?

Answer 17

membrane potential

Question 18

role of Hsp 60

Answer 18

helps in folding of imported protein using ATP

Question 19

mitochondrial Hsp 70

Answer 19

bound to TIM 23 on matrix side; pulls protein into matrix then releases protein in ATP dependent step

Question 20

import into outer membrane

Answer 20

pass through TOM and enter inter-membrane stpace; bind to chaperone then to SAM in outer membrane; SAM inserts and folds

Question 21

ER

Answer 21

organized into a network of branching tubules and sacs; its membrane is continuous w/ nuclear membrane; plays a central tole in protein and lipid synthesis

Question 22

ER signal sequence

Answer 22

vary in aa sequence; have 8 or more non-polar aas at center

Question 23

what 2 components guide the signal sequence to ER membrane?

Answer 23

signal recognition particle (SRP) and SRP receptor

Question 24

SRP (signal recognition particle)

Answer 24

made of 6 different polypeptides bound to a single small RNA molecule; it cycles b/w ER membrane and cytosol and binds to ER signal sequence

Question 25

SRP make up

Answer 25

rod shaped w/ large hydrophobic pocket lined by methionines; pocket can accomodate hydrophobic signal sequences of different size, shape and sequence

Question 26

Translocation across ER

Answer 26

SRP wraps around lg. ribosomal subunit. one end binds ER signal sequence and other to end of elongation factor binding site; blocks protein synthesis so protein can enter ER membrane;

Question 27

interaction of SRP-ribosome complex and SRP receptor during translocation across ER

Answer 27

SRP complex binds SRP receptor present in ER membrane; interaction brings the assembly to a translocator; SRP and receptor are released and protein translocated across ER membrane

Question 28

translocator in ER membrane

Answer 28

has water filled pore; 3 subunits; pore gated by short helix which opens and closes pore as needed

Question 29

what makes up the core of the translocator in the ER membrane?

Answer 29

Sec61 complex

Question 30

start-transfer signal

Answer 30

SRP binds to ER signal sequence on protein and brings it to ER membrane’ signal sequence triggers opening of translocator pore and sRP released; signal sequence interacts w/ a specific site w/i the pore which opens it - this is called the start-transfer signal

Question 31

what cleaves off the signal after protein translocation into ER?

Answer 31

signal peptidase