Protein trafficking 2

Question 1

How are proteins targeted to specific compartments?

Answer 1

Via the ER, Golgi, vesicles, or organelle-specific targeting signals.

Question 2

Where does protein synthesis occur?

Answer 2

At ER-attached ribosomes and free cytosolic ribosomes.

Question 3

What are the two compartments within mitochondria?

Answer 3

The intermembrane space and the matrix.

Question 4

Where are electron transport chain complexes located?

Answer 4

In the inner mitochondrial membrane.

Question 5

How do proteins enter mitochondria?

Answer 5

Post-translationally via N-terminal targeting sequences.

Question 6

What features do mitochondrial targeting sequences have?

Answer 6

Hydrophobic and positively charged amino acids.

Question 7

What keeps mitochondrial proteins unfolded before import?

Answer 7

Chaperones.

Question 8

What receptors do mitochondrial targeting sequences bind to?

Answer 8

TOM20/22 on the outer membrane.

Question 9

What is the general import pore in mitochondria?

Answer 9

Tom40.

Question 10

Which complex facilitates import across the inner membrane?

Answer 10

Tim23/17.

Question 11

What energy sources are required for mitochondrial import?

Answer 11

ATP hydrolysis and proton motive force.

Question 12

How are some proteins integrated into the inner mitochondrial membrane (Path A)?

Answer 12

Via stop-transfer anchor sequences.

Question 13

What is the role of Oxa1 in mitochondrial import (Path B)?

Answer 13

Inserts sequences into the inner membrane from the matrix.

Question 14

What is Path C for inner membrane targeting?

Answer 14

Internal targeting sequences use Tom70/22 and Tim22/18/54.

Question 15

What is the main pathway for intermembrane space targeting (Path A)?

Answer 15

Sequential targeting and cleavage through Tim23/17.

Question 16

What is rare Path B for intermembrane space targeting?

Answer 16

Diffusion through Tom40 and folding with disulfide bonds.

Question 17

What type of proteins dominate the outer mitochondrial membrane?

Answer 17

Beta-barrel proteins.

Question 18

What recognizes beta-barrel proteins for insertion?

Answer 18

The SAM complex.

Question 19

What complex is responsible for outer membrane integration?

Answer 19

The SAM complex.

Question 20

What do TOM and TIM stand for?

Answer 20

Translocase of the Outer/Inner Membrane.

Question 21

What encloses the nucleus?

Answer 21

The nuclear envelope (inner and outer membranes).

Question 22

What are nuclear pores?

Answer 22

Channels allowing exchange between nucleus and cytoplasm.

Question 23

What lines the inner nuclear membrane?

Answer 23

The nuclear lamina (made of lamins).

Question 24

What forms nuclear pores?

Answer 24

Nuclear pore complexes (NPCs).

Question 25

What are NPCs made of?

Answer 25

Over 30 proteins called nucleoporins.

Question 26

What are FG nucleoporins?

Answer 26

Nucleoporins with phenylalanine-glycine repeats forming a mesh.

Question 27

What is needed for import of proteins >40kDa into the nucleus?

Answer 27

A nuclear localization signal (NLS).

Question 28

What does Importin bind?

Answer 28

NLS and FG nucleoporins.

Question 29

What causes Importin to release cargo in the nucleus?

Answer 29

Binding of Ran·GTP.

Question 30

What regenerates Ran-GTP in the nucleus?

Answer 30

Ran-GEF (guanine nucleotide exchange factor).

Question 31

What processes Ran·GTP to Ran·GDP in the cytoplasm?

Answer 31

Ran-GAP (GTPase activating protein).

Question 32

What is the directionality of nuclear transport based on?

Answer 32

Localization of Ran-GEF and Ran-GAP.

Question 33

What is required for nuclear export?

Answer 33

A nuclear export signal (NES).

Question 34

What receptor is used for nuclear export?

Answer 34

Exportin 1.

Question 35

What removes mRNA transporters after export?

Answer 35

An ATP-dependent RNA helicase (Dbp5).

Question 36

What is the role of NXF1/NXT1?

Answer 36

Bind mRNPs and guide them through nuclear pores.

Question 37

What is the role of the nuclear lamina?

Answer 37

Provides stiffness and chromatin organization.

Question 38

How are nucleoporins organized?

Answer 38

Into membrane, structural, and FG types.

Question 39

How does Ran-GTP function in import vs export?

Answer 39

In import: releases cargo; in export: enables cargo binding.

Question 40

What determines the direction of nuclear transport?

Answer 40

Ran-GTP/GDP gradient from Ran-GEF/GAP distribution.