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Question 1

What are the two primary structural components enabling intracellular trafficking?

Answer 1

Vesicles (membrane-bound carriers) and cytoskeleton (microtubules/actin filaments).

Question 2

How do motor proteins interact with the cytoskeleton for vesicle movement?

Answer 2

Kinesins (+ end movement) dyneins (- end movement)

Question 3

Describe the complete vesicle trafficking pathway from formation to fusion.

Answer 3

1) Coat proteins (COPII/clathrin) bud vesicles
2) Motor proteins transport along cytoskeleton

Question 4

What determines whether a vesicle moves anterograde or retrograde? COPII mediates anterograde (ER→Golgi)

Answer 4

COPI mediates retrograde (Golgi→ER); directional motors (kinesins/dyneins).

Question 5

What are the key features of an ER signal sequence?

Answer 5

N-terminal hydrophobic sequence (16-30 aa) recognized by SRP

Question 6

Compare and contrast KDEL and KKXX motifs

Answer 6

KDEL: Soluble ER retention (binds COPI) = LUMINAL proteins

KKXX: Transmembrane protein retrieval (ER retrieval signal). MEMBRANE BOUND proteins

Question 7

What happens to proteins lacking proper localization signals? Remain cytosolic

Answer 7

may aggregate or be degraded by proteasome.

Question 8

How does ER quality control work? Chaperones (BiP) retain misfolded proteins; UPR triggers degradation if folding fails.

Question 10

Experimental Applications

Question 12

What would happen if you mutated the KKXX motif to KXKX? Disrupts COPI binding → failure of retrograde trafficking → protein accumulates in Golgi.

Question 14

How could you test if a protein uses KDEL for ER retention? Fuse GFP to KDEL sequence → should localize to ER; mutate KDEL → should secrete.

Question 16

What technique would show vesicle movement in real-time? Live-cell imaging with fluorescently tagged cargo (e.g.

Answer 16

GFP-tagged VSVG).

Question 18

Critical Thinking

Question 20

Why do cells need both anterograde and retrograde trafficking? Anterograde: Deliver new material; Retrograde: Recycle components

Answer 20

maintain organelle identity.

Question 22

How does hydrophobicity determine membrane protein localization? Hydrophobic domains anchor in lipid bilayers; length/composition targets specific organelles.

Question 24

What would happen if all dynein motors were inhibited? Retrograde transport blocked → Golgi disperses

Answer 24

ER accumulates material.