Ran vs Rab

what turns Ran “ON”(GTP-bound)? describe the trigger /event, not a protein name

Ran only gets loaded with GTP when importin protein containing cargo enters the nuclear pore complex; once inside Ran-GTP binds the importin and drives a conformational change that releases the cargo into the nucleus.

what turns Rab “ON”(GTP-bound)?describe the trigger /event, not a protein name

A GEF loads a Rab protein with GTP on the surface of a newly budded vesicle, marking it as still in transit, GTP Rab is recognized by a matching tethering protein

what turns Tubulin (in a microtubule) “ON”(GTPbound)?describe the trigger /event, not a protein name

new dimers are added to the plus end of beta-tubulin already bound to GTP

what turns Ran “OFF”(GTP→GDP)? describe the trigger /event, not a protein name

As soon as the importin‑Ran‑GTP complex moves out of the nucleus, it runs into the GAP, and the GTP is hydrolyzed to GDP. Trigger/event: hydrolysis when it reaches the cytoplasmic face of the nuclear pore.

What turns Rab “OFF”(GTP→GDP)?describe the trigger /event, not a protein name

A GAP at the target membrane then stimulates Rab to hydrolyze its GTP to GDP. Trigger/event: hydrolysis at the target membrane.

What turns Tubulin(in a microtubule) “OFF”(GTP→GDP)?describe the trigger /event, not a protein name

It hydrolyzes GTP at a fairly steady, intrinsic rate once it’s incorporated into the lattice.” Trigger/event: intrinsic hydrolysis after incorporation into the lattice

Where is Ran concentrated in its ON state?

inside the nucleus

Where is Rab concentrated in its ON state?

surface of newly budded vesicle or target membrane

Where is Tubulin (in a microtubule) concentrated in its ON state?

the plus end where GTP-tubulin dimers are added to the growing end

Which of the three (Ran,Rab,Tubulin ) doesnt fit the same pattern as the other two? and why does that difference make sense given what each proteins job actually is?

Tubulin is a bit different than Ran and Rab, which need a GAP to assist in GTP hydrolysis; tubulin does this itself. makes sense because Ran and Rab are used in signaling events; while Tubulin builds a track

Locked-on Rab: Predict the Consequence:

Imagine a mutant Rab protein that binds GTP normally but can never hydrolyze it back to GDP-It’s permanently stuck in its “on”shape. A vesicle carrying this mutant Rab reaches its correct target membrane and fuses successfully. What happens next that wouldnt happen with a normal Rab? Think about what the GAP step normally accomplishes afterward, and what happens to the pool of free Rab and tethering protein available for the next vesicle.

When the Rab3‑GAP is mutated, vesicles are able to fuse to the membrane, but there is a major delay in the recycling.Therefore, for a Rab that can never hydrolyze GTP:

• Rab would remain stuck on the membrane because hydrolysis never happens.

• Rab would not be released:

  “That conformational change releases Rab from the tether.”
  (But the mutant cannot hydrolyze → cannot release.)

• The pool of free Rab and tethering protein would be depleted, because Rab never resets:The now GDP‑bound Rab is extracted… and recycled… resetting everything for next time.”
  (Mutant Rab never reaches GDP → never resets.)

So the next vesicle cannot use the tethering system normally.

A. Drug A locks every tubulin dimer in its GTP-bound state the instant it joins the lattice, so hydrolysis never happens. Predict what happens to catastrophe, and to the microtubule’s length over time.

More additions than hydrolysis → growth (GTP cap).”

Drug A prevents hydrolysis entirely → GTP cap never lost → catastrophe cannot occur.

Prediction

• Catastrophe stops (no hydrolysis → no curved GDP‑tubulin → no peeling).

• Microtubule length increases over time (continuous growth).

B. Drug B does the opposite of drug A- it forces GTP hydrolysis to happen the instant a new dimer joins the lattice, so a GTP cap can never form. Predict what happens to microtubule growth under this drug.

More hydrolysis than additions → collapse.”
“If the GTP cap is ever lost… the terminal‑most dimers… peel away… catastrophe.”

Prediction:

• GTP cap can never form → constant catastrophe → microtubules cannot grow

C. Real depolymerizing (like colchicine) work somewhat like Drug B. Given your answer to B, why would a drug like this be useful for stopping cell division, where microtubules must rapidly grow and shrink to build the mitotic spindle?

This growth/collapse switching = dynamic instability.”

Drug B‑like behavior → no growth, only collapse → spindle cannot form → cell division stops.

Material taken up by endocytosis at the plasma membrane needs to reach a lysosome near the cell’s center. Which motor protein carries it, and which end of the microtubule is it walking toward?

Dynein… moves towards the minus (–) end of microtubules.”
“Endocytosed material headed to lysosomes… [is carried by] Dynein.”
“Minus ends are anchored near the cell center.”

Answer:

Dynein, walking toward the minus end.

The Golgi lumen is mildly acidic (~pH 6) while the ER is near-neutral (~pH 7.2). If you

experimentally raised the Golgi's pH to match the ER's, what would you expect to

happen to KDEL retrieval?

B. The KDEL receptor would fail to bind escaped ER proteins in the Golgi

Ran-GTP is far more concentrated in the nucleus than in the cytoplasm. What's the direct

cause of that asymmetry?

A. Ran's GEF, RCC1, is physically bound to chromatin and thus only present in the nucleus

In the general GTPase switch cycle, which statement correctly pairs GEF and GAP with

their effects?

D. GEF loads GTP and turns the GTPase on; GAP stimulates hydrolysis and turns it off

A vesicle carrying a v-SNARE bumps into a membrane that has no matching t-SNARE and

no matching Rab tether. What happens?

The vesicle simply fails to dock or fuse there and moves on

A vesicle needs to travel from the Golgi (near the cell center) out to the plasma

membrane. Given that kinesin walks toward microtubule plus ends and plus ends

generally point toward the cell periphery, which motor most likely carries this vesicle?

Kinesin