Axonal Transport

Question 1

What are the two main functions of the axon?

Answer 1

1. AP conduction

2. Physical conduit for materials transport

Question 2

Which end of the axon is the one that grows? What is the growing tip called? What tells the axon where to grow towards?

Answer 2

Plus end has a growth cone that is guided by transmembrane axon guidance receptors that respond to growth signals in the environment.

Question 3

What are the basic steps involved in cargo vesicle formation and transport?

Answer 3

1. Cargo synthesized in ER.
2. Cargo is loaded into a vesicle and buds off from ER.
3. ER bud goes to cis-Golgi for processing.
4. Cargo buds off from trans-Golgi and goes to the mt for transport.

Question 4

What is required for clathrin to associate with cargo as the vesicle forms around the cargo?

Answer 4

Adapter proteins confer specificity and help clathrin associate with the cargo in the formation of the vesicle.

Question 5

What protein forms a three-pronged triskelia structure?

Answer 5

Clathrin

Question 6

In which two locations is clathrin involved?

Answer 6

1. Trans golgi

2. Plasma membrane for endocytosis

Question 7

Which GTPase is responsible for pinching off the clathrin-coated vesicle?

Answer 7

dynamin

Question 8

Coat proteins COPI helps traffic cargo from the _____ to the _____ while COPII helps traffic cargo from the _____ to the _____.

Answer 8

COPI: from golgi to the ER (retrograde)
COPII: from ER to the golgi (anterograde)

Question 9

SNARE proteins help with vesicle ______ and ______.

Answer 9

docking and fusion

Question 10

What is a t-SNARE? Name two t-SNAREs.

Answer 10

Target membrae SNAREs. SNAP-25 and syntaxin

Question 11

What is a v-SNARE? Name one.

Answer 11

Vesicle SNARE. Synaptobrevin.

Question 12

Describe the SNARE cycle.

Answer 12

1. Syntaptobrevin binds to the t-SNAREs, forming the trans-SNARE complex.
2. Action potential triggers fusion, cis-SNARE complex forms.
3. NSP and alpha-SNAP bind to SNARE complex to help disassemble.
4. Clathrin pit endocytoses the SNARE leftovers for re-use.

Question 13

What do Rab proteins do?

Answer 13

Regulate vesicle trafficking and fusion by hydrolyzing GTP.

Question 14

In the neuronal axon, on which end are mt “+” ends found?

Answer 14

Distal from the cell body.

Question 15

In neuronal dendrites, on which end are mt “+” ends found?

Answer 15

Polarity is mixed in dendrites.

Question 16

What are the two speeds of axonal transport?

Answer 16

Fast and slow!

Question 17

How is specificity enhanced by kinesin molecules?

Answer 17

Many kinesin tail domains exist. The tail domains interact with adapter proteins on cargo to confer specificity.

Question 18

Kinesin motor proteins move toward the _____ end of microtubules.

Answer 18

Trick question!

Most move towards the “+” end, but the KIFC family moves towards the “-“ end.

Question 19

Which direction does dynein move?

Answer 19

Towards the “-“ end.

Question 20

What is dynactin?

Answer 20

A large protein that interacts with dynein for activation. It includes p150 glued, Arp1 and dynamitin.

Question 21

Describe the movement mechanism of kinesin.

Answer 21

1. The kinesin globular head heavy chain binds to the mt and after binding releases ADP.
2. ATP fills the nucleotide-binding domain on the head, causing the linker protein to throw itself forward.
3. The other globular head is thrown forward due to the linker protein’s movement and attaches to the mt, releasing ADP, and starting the cycle over.

Question 22

Describe the movement mechanism of dynein.

Answer 22

1. ATP binding frees the dynein head from the microtubule.
2. ATP hydrolysis causes the head to re-attach to the mt 8nm further up.
3. The other head does the same and somehow this makes it walk.

Question 23

Synaptic vesicles are moved via ________. Most cytoskeletal elements are moved via _________.

Answer 23

fast anterograde transport

slow anterograde transport

Question 24

Name four diseases in which axonal transport may play a role.

Answer 24

1. ALS
2. Hereditary Spastic Paraplegia
3. Huntington’s
4. Charcot-Marie-Tooth Disease