Chapter 15 - Protein Sorting to Intracellular Compartments pt. 1

Question 1

Organelle duplication and growth requires a supply of what?

Answer 1

1) New lipids to make more membranes

2) New proteins, both membrane proteins and soluble proteins, that will occupy the interior of the organelle

Question 2

Proteins for organelle duplication and growth must be ___ and accurately ___ to their destined organelles.

Answer 2

sorted, delivered

Question 3

What instructs the correct delivery of proteins to their targeted organelles?

Answer 3

Amino acid sequence.

Similar to how a letter has a mailing address.

Question 4

What are the two types of protein synthesis?

Answer 4

1) Synthesis from free polyribosomes

2) Synthesis from membrane-bound polyribosomes

Question 5

What type of proteins does synthesis from free polyribosomes create?

Answer 5

Proteins floating freely in the cytosol.

Question 6

What type of proteins does synthesis from free polyribosomes NOT create?

Answer 6

Transmembrane proteins nor proteins that are going to be exoctyosed from the cell.

Question 7

(T/F) Synthesis from membrane-bound polyribosomes evolved along with internal membrane structures.

Answer 7

True

Question 8

Synthesis from membrane-bound polyribosomes creates what types of proteins?

Answer 8

Membrane associated proteins and proteins in endomembrane vesicles.

Question 9

Synthesis from membrane-bound polyribosomes are present only what kind of cells?

Answer 9

Eukaryotic

Question 10

A polyribosome is a messenger RNA that has multiple ribosomes on its progressing from its ___ to ___ end.

Answer 10

5’, 3”

Question 11

For both cases of protein synthesis, a polyribosome starts of as a what?

Answer 11

As a monoribosome (i.e., one ribosome).

Question 12

Which end of the messenger RNA does polyribosomes start?

Answer 12

The 5’ end in the cytosol.

Question 13

Where do sorting signals direct proteins?

Answer 13

To their target organelles

Question 14

The synthesis of virtually all proteins begins where? What are some exceptions?

Answer 14

On ribosomes inside the cytosol. Some exceptions are mitochondria and chloroplast proteins.

Question 15

What happens to proteins that lack sorting signals?

Answer 15

These proteins will remain in the cytosol.

Question 16

Where are some examples sorting signals will direct proteins?

Answer 16

The nucleus, mitochondria, chloroplast, and the ER.

Question 17

How can an organelle transport a protein across its membrane(s) which are normally impermeable to large and hydrophilic molecules?

Answer 17

Proteins from the cytosol move into:

1) Nucleus via nuclear pores
2) ER, mitochondria, or chloroplasts
3) Proteins move onward from ER

Question 18

For nucleus proteins what types of gates and transport do proteins rely on?

Answer 18

Selective gates which actively transport the proteins.

Question 19

How do proteins transverse across the membrane of the ER, mitochondria, or chloroplasts?

Answer 19

By protein translocation in the membrane. Protein must be unfolded and “snake” across the membrane.

Question 20

Proteins that move onward from one compartment of the endomembrane system to another are transported by what?

Answer 20

Transport vesicles

Question 21

How do proteins move onward from one compartment to the next?

Answer 21

They pinch off from one compartment and then fuse with the membrane of a second compartment.

Question 22

What do proteins usually deliver when being transported to another compartment?

Answer 22

Soluble cargo proteins and membrane proteins.

Question 23

How does the nuclear envelope get lipids and membrane proteins?

Answer 23

By backfilling along the appropriate lipid layer because the lipids themselves are not covalently linked and the membranes are contiguous.

Question 24

How are proteins transported through the nucleus?

Answer 24

Via nuclear pores

Question 25

The protein meshwork in the center of the nuclear envelope: each protein has a ___.

Answer 25

short repeated sequence; FGs.

Question 26

The protein meshwork in the center of the nuclear envelope and nuclear pores of repeated sequences that ___ to each other.

Answer 26

Bind

Question 27

The protein meshwork in the center of the nuclear envelope and nuclear pores form a mesh to prevent what?

Answer 27

Large molecules passing through.

Question 28

What are protruding both sides of the pore complex inside the nuclear envelope and nuclear pores?

Answer 28

Protein fibrils

Question 29

Protein fibrils ___ to form a basket-like structure on the nuclear side of nuclear pores.

Answer 29

converge

Question 30

Proteins destined to the nucleus must display what sorting signal?

Answer 30

Nuclear Localization Signal (NLS)

Question 31

What is the Nuclear Localization Signal (NLS)

Answer 31

It serves as both a mailing addresses and a ticket for protein transport.

Question 32

What signal is used when NSL is recognized by proteins?

Answer 32

Nuclear Import Receptor (NIR)

Question 33

Which signal directs the protein complex to a nuclear pore by grabbing the tentacle-like cytosolic fibrils?

Answer 33

Nuclear Import Receptor (NIR).

Question 34

Once in the pore, NIR grabs onto the ___ of the meshwork proteins, opening a ___ through the pore.

Answer 34

FG repeats, passage

Question 35

NIR bumps along the nuclear pore from one FG to another until what?

Answer 35

Enters the nucleus

Question 36

NIR and the cargo protein dissociates from each other thereby what?

Answer 36

Completing the delivery.

Question 37

Which cycle of active transport transports protein into, and out of, the nucleus?

Answer 37

Ran-GTP cycle

Question 38

In the nucleus, ___ protein encounters a ___ called Ran, which carries a GTP.

Answer 38

NIR-cargo, GTPase

Question 39

Ran binds to ___, causing the release of cargo protein.

Answer 39

NIR

Question 40

Which complex is transported back to the cytosol after the release of a cargo protein?

Answer 40

NIR-Ran-GTP

Question 41

Ran hydrolyzes what in the cytosol with the help of Ran GAP?

Answer 41

GTP

Question 42

What does GTP stand for?

Answer 42

GTPase Activating Protein

Question 43

NIR dissociates with ___, and ready to transport another nuclear protein.

Answer 43

Ran-GDP

Question 44

What type of conformation do proteins remain while being transported via nuclear pores?

Answer 44

Fully folded

Question 45

At what speed do proteins travel through nuclear pores?

Answer 45

Very high speeds - about 1000 translocations per second.

Question 46

Import and export of proteins via nuclear pores share what?

Answer 46

Similar mechanisms

Question 47

Which organelle(s) have their own genome, which can make some of their own proteins?

Answer 47

Mitochondria and Chloroplast

Question 48

Though they make some of their own proteins, most of Mitochondria and Chloroplasts's ___ are encoded by the nuclear genome and imported from the cytosol.

Answer 48

Protein

Question 49

How many membranes do mitochondria and chloroplasts have?

Answer 49

Two

Question 50

Do proteins pass through both membranes of mitochondria and chloroplasts?

Answer 50

Yes

Question 51

How do mitochondria and chloroplasts get proteins from the cytosol?

Answer 51

From proteins already synthesized on free polyribosomes. Hence, post-translational transport.

Question 52

How do mitochondria and chloroplast obtain lipids?

Answer 52

By lipid transporters

Question 53

By lipid transporters, mitochondria and chloroplasts extract ___ from the ER and deliver them to these organelles.

Answer 53

Phospholipids

Question 54

For protein transport into mitochondria and chloroplasts, the protein precursor protein is ___ and its ___ is recognized and bound by a specific ___ on the outer membrane, which is associated with a pore-forming ___ protein.

Answer 54

unfolded, signal sequence, receptor protein, translocator.

Question 55

For protein transport into mitochondria and chloroplasts, which precursor complex diffuses laterally until it meets a second translocator on the inner membrane?

Answer 55

protein-receptor-translocator complex

Question 56

For protein transport into mitochondria and chloroplasts, the two translocators transport the protein across both the ___ and ___ membrane.

Answer 56

outer, inner

Question 57

(T/F) For protein transport into mitochondria and chloroplasts, after translocator transport the protein across both the outer and inner membrane, the signal peptide is then cleaved off.

Answer 57

True

Question 58

For protein transport into mitochondria and chloroplasts, how do chaperones assist protein transport?

Answer 58

1) Keeping protein unfolded in the cytosol. 2) Pulling proteins across the membrane. 3) Promoting correct protein folding in the matrix

Question 59

For protein transport into chloroplasts, which proteins share the same transport mechanisms as mitochondria matrix protein?

Answer 59

Stroma proteins.

Question 60

For protein transport into chloroplasts, for proteins destined to the thylakoid lumen, what are the two signal peptides?

Answer 60

1) One for chloroplast stroma, which will be cleaved off in stroma. 2) This will expose the second signal peptide for thylakoid lumen.

Question 61

For protein transport into chloroplasts, the exposed thylakoid signal peptide will target the ___ to the ___ via a similar mechanisms as the one for stroma proteins.

Answer 61

protein, lumen

Question 62

How do you identify an unknown protein and study the function of this protein after identification?

Answer 62

Looking for a storing signal amino acid sequence.