Intracellular Compartments and Protein Sorting 2

Question 0

Where are mitochondrial proteins synthesized and then imported?

Answer 0

on ribosomes and imported into mitochondria

Question 1

Where are most mitochondrial proteins encoded?

Answer 1

In the nuclear DNA

Question 2

What do proteins need to cross to get in mitochondria?

Answer 2

Outer and/or inner mitochondrial membranes

Question 3

Protein movement is called what?

Answer 3

Translocation

Question 4

What directs proteins to correct compartments in mitochondria?

Answer 4

Signal sequences

Question 5

What are mitochondrial signal sequences?

Answer 5

N terminal and internal

Question 6

What do the mitochondrial signal sequences form?

Answer 6

amphiphilic alpha helix

Question 7

________ charged residues cluster on one end and _______ on the other end of the helix

Answer 7

Positively

Hydrophobic

Question 8

What recognizes the positively charged and hydrophobic configuration of mitochondrial signal sequences rather than precise sequence?

Answer 8

Specific receptor proteins

Question 9

What are multi-subunit protein complexes called that mediate translocation?

Answer 9

Protein translocators

Question 10

What is TOM

Answer 10

Translocase of the outer membrane

Question 11

Where is TOM present?

Answer 11

In the outer membrane of the mitochondria

Question 12

What is TOM required for?

Answer 12

For import of all nucleus encoded proteins and inserts them in outer membrane

Question 13

What is TIM?

Answer 13

Translocase of the inner membrane

Question 14

Where is TIM present?

Answer 14

inner membrane

Question 15

What are the two TIM complexes?

Answer 15

TIM 22 and TIM 23

Question 16

What does TIM 23 do?

Answer 16

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

Question 17

What does TIM 22 do?

Answer 17

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

Question 18

TOM and TIM complexes have ___ components

Answer 18

2

Question 19

What are the components of TOM and TIM responsible for?

Answer 19

Receptors for mitochondrial precursor proteins

Translocation channels

Question 20

What is SAM complex?

Answer 20

Sorting and assembly machinery: translocates and inserts/folds beta barrel proteins in the outer membrane

Question 21

What does the OXA complex do?

Answer 21

Mediates insertion of proteins synthesized in mitochondria

Question 22

Precursor proteins entering mitochondria are (folded/unfolded)

Answer 22

Unfolded

Question 23

Unfolding of mitochondrial proteins is maintained through what interactions?

Answer 23

With chaperone proteins: cytosolic Hsp 70 family

Question 24

What binds signal sequence of incoming mitochondrial protein?

Answer 24

Import receptors of TOM complex

Question 25

What are stripped off so that the unfolded protein is fed through TOM?

Answer 25

Chaperone proteins

Question 26

What enters first into translocation channel?

Answer 26

Signal sequence

Question 27

What does TOM transport?

Answer 27

Protein across the outer membrane to the inner membrane space

Question 28

What to proteins bind to in order to move through to the matrix?

Answer 28

TIM complex

Question 29

What are signal sequences of mitochondrial proteins cleaved off by?

Answer 29

Peptidase

Question 30

Bound Hsp ___ dissociated at expense of _________ outside mitochondria

Answer 30

70 | ATP hydrolysis

Question 31

After passing through TOM, what do proteins interact with?

Answer 31

TIM

Question 32

What does transport through TIM depend on?

Answer 32

Membrane potential

Question 33

What drives translocation of positively charged sequence through TIM

Answer 33

Energy in electrochemical gradient drives translocation by electrophoresis

Question 34

What is bound to TIM 23 on the matrix side?

Answer 34

Mitochondrial Hsp 70

Question 35

What pulls protein into matrix space?

Answer 35

Mitochondrial Hsp 70

Question 36

What releases the protein in the matrix in an ATP dependent step?

Answer 36

Hsp 70

Question 37

What helps folding of imported protein using ATP?

Answer 37

Hsp 60

Question 38

How are proteins imported into outer membrane?

Answer 38

Pass through TOM complex and enter intermembrane space Bind to chaperone proteins Then bind to SAM complex in outer membrane SAM inserts and folds them in outer membrane

Question 39

What is an example of proteins imported into outer membrane?

Answer 39

Porins (beta barrel proteins)

Question 40

What is the ER organized into?

Answer 40

A network of branching tubules and sacs

Question 41

What is the ER membrane continuous with?

Answer 41

The nuclear membrane

Question 42

What is the internal space of the ER called?

Answer 42

ER lumen

Question 43

What does the ER play a central role in ?

Answer 43

Proteins and lipid synthesis

Question 44

What is the site of production of all TM proteins?

Answer 44

ER | destined to other organelles and ER

Question 45

What do ER signal sequences vary in?

Answer 45

IN amino acid sequence

Question 46

What do ER signal sequences have at its center?

Answer 46

8 or more non-polar amino acids

Question 47

What are ER signal sequences guided to ER membrane by?

Answer 47

2 components: Signal recognition particle (SRP) SRP receptor

Question 48

What is the SRP made up of?

Answer 48

6 different polypeptides bound to a single small RNA molecule

Question 49

What do SRP cycle between?

Answer 49

ER membrane and cytosol

Question 50

What do SRP bind to?

Answer 50

ER signal sequence

Question 51

What is the shape of SRP?

Answer 51

Rod shaped with large hydrophobic pocket lined by methionines

Question 52

What can the pocket of SRP accommodate?

Answer 52

Hydrophobic signal sequences of different size, shape and sequence

Question 53

What does SRP wrap around and bind to?

Answer 53

Large ribosomal subunit | One end binds to ER signal sequence of emerging protein and other end to elongation factor binding site

Question 54

What does the SRP block?

Answer 54

Protein synthesis transiently giving enough time for protein to enter ER membrane

Question 55

What binds to SRP receptor present in ER membrane?

Answer 55

SRP-ribosome complex

Question 56

What does the interaction of SRP -ribosome complex and SRP receptor bring about?

Answer 56

The assembly to a translocator

Question 57

What is released and then the protein translocates across the ER membrane?

Answer 57

SRP and receptor

Question 58

Where is the translocator of the ER present?

Answer 58

In the ER membrane

Question 59

What type of pore does the translocator in the ER membrane have?

Answer 59

Water filled pore

Question 60

What is the core of the translocator made of?

Answer 60

Sec61 complex | Has 3 subunits with largest subunit surrounding the central lpore

Question 61

What is the pore of the translocator gated by?

Answer 61

Short helix which opens and closes pore as needed

Question 62

What triggers the opening of the translocator pore and SRP released?

Answer 62

Signal sequences that was brought to the ER membrane by SRP

Question 63

What does the signal sequence interact with, and thereby opening the pore?

Answer 63

Specific site within the pore called the start-transfer signal

Question 64

What ensures specificity of protein being translocated into ER?

Answer 64

Dual recognition

Question 65

What does the start-transfer signal also interact with?

Answer 65

Lipid core of ER membrane

Question 66

What cleaves off the ER signal?

Answer 66

Signal peptidase

Question 67

Where does the cleaved ER signal escape from?

Answer 67

Lateral opening in the pore

Question 68

What is the integration of trans-membrane proteins similar to?

Answer 68

The initial process is similar to soluble proteins

Question 69

What sequence initiates translocation of trans-membrane proteins?

Answer 69

N terminal sequence

Question 70

What does the integration of membrane proteins require?

Answer 70

Require that some portions of the proteins pass though membrane and some others do not

Question 71

What additional region in polypeptide stops transfer process before entire polypeptide is translocated?

Answer 71

Hydrophobic region called stop transfer signal

Question 72

What does the stop transfer signal anchor?

Answer 72

Protein in membrane after start-transer signal has been cleaved and released

Question 73

What helps to remove the cleaved start-transfer peptide and to integrate stop-transfer signal into bilayer?

Answer 73

Lateral gating

Question 74

What determines topology of the transmembrane proteins?

Answer 74

In multiple TM proteins several combinations of start-transfer and stop-transfer determines topology