Lecture 10

Question 1

What is the cytoplasmic way of sorting proteins?

Answer 1

The cytoplasm has its own way to sort proteins, which includes the mitochondrion and the nucleus!

Question 2

Sorting signals are what kind of sequences?

Answer 2

Sorting sequences for protien translocation into organelles are linear signal sequences.

• N is synthesized first (N-terminus)
• COO is left at other end (C-terminus)

Question 3

What does the nuclear envelope include?

Answer 3

The nuclear envelope consists of two concentric membranes, which are
perforated by nuclear pore complexes

Question 4

What do nuclear pore complexes do?

Answer 4

nuclear pore complexes (NPCs) perforate the nuclear envelope in all
eukaryotes. Each NPC is composed of a set of approximately 30 different
proteins, or nucleoporins.

Question 5

What is able to pass through NPCs?

Answer 5

Large things are able to pass throuhg the nuclear pore complexes.

Question 6

What do unstructured proteins form?

Answer 6

Unstructured proteins at the inner ring form a mesh

Question 7

How does the mesh behave?

Answer 7

This mesh acts as a sieve that restricts the diffusion of large macromolecules while allowing smaller molecules to pass

Question 8

What do unstructures proteins lack?

Answer 8

Unstructured proteins regions lack a well-structured three-dimensional
fold. Some proteins are entirely unstructured..
- they aren’t fully folded - they tend to have a local disorder that remains unfolded

Question 9

Proteins with NLS directed to?

Answer 9

Proteins with a nuclear localization sequence (NLS) are directed into the
nucleus - they tell the protein to go into the nucleus.

Question 10

Adding an NLS?

Answer 10

Adding a NLS to a cytoplasmic protein moves it to the nucleus

Question 11

NLS’s have?

Answer 11

Nucklear localization signals have flanking basic clusters.

Question 12

NES proteins do what?

Answer 12

Proteins with a nuclear export sequence (NES) leave the nucleus.

Question 13

What are importins?

Answer 13

The import receptors (importins) are soluble cytosolic proteins that
contain multiple low-affinity binding sites for the FG repeats found in
the unstructured domains of several nucleoporins.

Question 14

Importins do what?

Answer 14

Importins recognize the nuclear localization signals (NLS) and moves the proteins.

Question 15

What does the low-affinity binding sites of importins mean?

Answer 15

The low-affinity binding sites for the FG receptors are there so that it can go through to the nucleus without getting stuck.

• FG binding sites are compsoed of amino acids

Question 16

Role of importin-cargo complex?

Answer 16

The importin–cargo complex locally dissolves the gel-like mesh and can diffuse into and within the NPC pore
- Doesn’t move without importin
- Moves fairly fast with importin there, interacting with the gel

Question 17

The concentration of Ran provides?

Answer 17

The concentration of Ran bound to GTP provides energy and directionality. The energy it provides is used to move items in and out of the cytoplasm.

Question 18

For importins, what does Rna-GTP do?

Answer 18

For importins, Ran-GTP in the nucleus promotes cargo dissociation

Question 19

Importins vs. Exportins?

Answer 19

Importins are the receptor for NLS containing proteins. Exportins are
the NES receptors.

Question 20

What does Ran-GTP promote for exportins?

Answer 20

For exportins, Ran-GTP in the nucleus promotes cargo binding, rather than
promoting cargo dissociation as in the case of importins

Question 21

What do GAPs do for Ran-GTP?

Answer 21

a cytosolic GTPase-activating protein (GAP) triggers GTP hydrolysis
to Ran-GDP, and a nuclear guanine nucleotide exchange factor (GEF) promotes the exchange of GDP for GTP.

Question 22

alpha subunit or importin?

Answer 22

The alpha subunit of importin binds the nuclear localization signal

Question 23

beta subunit of importin?

Answer 23

The beta subunit of the importin binds the unstructured chains.

Question 24

GTP molecule in Ran does what?

Answer 24

In the cytoplasm, a GTP molecule in Ran (shown in bright red) is
hydrolyzed and the Ran dissociates, leaving importin-beta ready to carry
the next cargo protein inside

Question 25

what do exportins bind to?

Answer 25

Exportins bind to both the export signal, either directly or via an adaptor, and to NPC proteins to guide their cargo to the cytosol.

Question 26

Many protiens have both ______ and _______?

Answer 26

Many proteins are known to have both NESs and NLSs and thus shuttle constantly between the nucleus and the cytosol

Question 27

Where are mitochondrial proteins made?

Answer 27

Most mitochondrial proteins are synthesized in the cytoplasm and then translocated into the mitochondria

Question 28

Sequence signals of mitochondrial?

Answer 28

Mitochondrial and plastid proteins have sequence signals

Question 29

TIM and TOM systems?

Answer 29

The TIM and TOM systems move polypeptide chains through the two membranes of the mitochondria

Question 30

TOM?

Answer 30

Translocase of the outer memrbane

Question 31

TIM?

Answer 31

Translocase of the inner membrane

Question 32

Chloroplasts have what?

Answer 32

Instead of TIM and TOM, chloroplasts have TIC and TOC.

Question 33

What do HSP-70 chaperones do?

Answer 33

HSP-70 chaperones interact with mitochondrial proteins at the cytoplasm and prevent them from folding