Zaidi: Protein sorting 1&2

Question 1

ER translocator structure

Answer 1

Has a water filled pore
Core of translocator made of Sec61 complex
3 subunits with the largest surrounding the central pore
Pore gated by short helix which opens and closes pore

Question 2

Protein transport to various compartments guided by

Answer 2

Sorting signals

Question 3

Nuclear pore complexes composed of

Answer 3

30 different proteins or nucleoporins

Question 4

Ran-GTP is hydrolyzed in the ______ which causes

Answer 4

Hydrolyzed in the cytoplasm, which causes release of receptor and Ran-GDP is ready for another cycle

Question 5

TOM

Answer 5

Translocase of the outer membrane
Required for import of all nuclear encoded proteins
Inserts them in the outer membrane

Question 6

ER signal sequence interacts with

Answer 6

Specific site within pore which opens it

Also interacts with lipid core of ER membrane

Question 7

Mitochondrial signal sequence location

Answer 7

N-terminal and internal signal sequences

Question 8

Binding of SRP to signal peptide causes

Answer 8

Pause in translation until peptide is relocated to ER membrane

Question 9

Each nuclear envelope has

Answer 9

3000-4000 pores

Question 10

ATP uses in mitochondrial transport

Answer 10

Dissociation of cytosolic Hsp 70 outside mitochondria
Dissociation of mitochondrial Hsp 70 inside matrix
Folding of imported protein by Hsp 60

Question 11

SRP wraps around the

Answer 11

Large ribosomal subunit

Question 12

Steps in import into outer membrane

Answer 12

Pass through TOM complex and enter inter-membrane space
Bind chaperone proteins
Bind SAM complex in outer membrane
SAM inserts and folds them in outer membrane

Question 13

OXA complex

Answer 13

Mediates insertion of proteins synthesized in the mitochondria

Question 14

Ran-GTP binds _____ which causes

Answer 14

Binds complex of import receptor and cargo, which causes release of cargo

Question 15

Nuclear localization signals (NLS)

Answer 15

Short sequences rich in positively charged amino acids lysine and argenine
Direct molecules to the nucleus

Question 16

Nuclear import receptors can bind to cargo both

Answer 16

Indirectly or directly

Question 17

What drives nuclear transport in the appropriate direction

Answer 17

Gradient of Ran conformational states

Question 18

Structure of mitochondrial signal sequence

Answer 18

Positively charged residues cluster on one end and uncharged hydrophobic on the other end to form an amphiphilic alpha helix

Question 19

Precursor proteins entering mitochondria are folded or unfolded

Answer 19

Unfolded, this is maintained through interactions with chaperone proteins (Hsp 70 family)

Question 20

2 components of TOM & TIM complexes

Answer 20

Receptors for mitochondrial precursor proteins

Translocation channels

Question 21

Transport through nuclear pores facilitated by

Answer 21

Binding of particles to fibrils extending from Nuclear pore complex (NPC)

Question 22

The signal sequence is fed into the translocation channel first or last

Answer 22

First

Question 23

TIM 23

Answer 23

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

Question 24

NPC have ______ repeats that serve as

Answer 24

Phenyalanine glycine repeats which serve as binding sites for import receptors

Question 25

Transport through TIM depends upon

Answer 25

Membrane potential

Question 26

Sorting signals are localized

Answer 26

On N or C terminus or within protein sequence

Question 27

Stop transfer signal

Answer 27

Additional hydrophobic region in polypeptide stops transfer process before entire polypeptide is translocated

Question 28

Shuttling proteins

Answer 28

Contain both NLS and NES, causing them to shuttle back and forth between nucleus and cytosol

Question 29

Signal sequences are ______ and _____ for

Answer 29

Signal sequences are necessary and sufficient for protein targeting

Question 30

NLS are recognized by

Answer 30

Nuclear import receptors (NIRs)

Question 31

SAM complex

Answer 31

Sorting and assembly machinery

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

Question 32

Gated transport occurs between

Answer 32

Nucleus and cytosol through nuclear pore complexes

Question 33

SRP made of

Answer 33

6 different polypeptides bound to a single small RNA molecule

Question 34

SRP shape/pocket

Answer 34

Rod shaped with large hydrophobic pocket lined by methionines

Question 35

ER signal sequences

Answer 35

Vary in amino acid sequence

Have 8+ non-polar AA at its center

Question 36

TIM 22

Answer 36

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

Question 37

Signal peptidase function

Answer 37

Removes signal after protein reaches final destination

Question 38

Nuclear pores are arranged in

Answer 38

Octagonal symmetry with one or more aqueous pores

Question 39

Most mitochondrial proteins are encoded in

Answer 39

Nuclear DNA (although some are made in mitochondria)

Question 40

NIRs puls cargo traverse NPC by

Answer 40

Binding, dissociating and rebinding FG (phenylalanine glycine) repeats

Question 41

Pores function in both x and y types of diffusion/transport

Answer 41

Passive diffusion

Facilitated transport

Question 42

ER signal sequence guided to ER membrane by what two components

Answer 42

Signal recognition particle (SRP)

SRP receptor

Question 43

NIRs are

Answer 43

Soluble cytosolic proteins that bind NLS on protein and NPC proteins on fibrils that extend into cytoplasm