unit 4 part 2 - protein sorting transport vesicles

Question 1

purpose of protein coats

Answer 1

• surround vesicles to shape the membrane into a bud by curving the membrane and forcing it to bubble out
• participate in the capture of specific proteins to be trapped inside the vesicle

Question 2

components of coated vesicles

Answer 2

cargo receptors in the membrane - bind to cargo protein inside the organelle, fish out and collect the cargo
adaptor proteins - link cargo receptor with coat proteins
coat proteins - surround the vesicle
dynamin - forms a ‘collar’ and uses GTP to change shape and pinch the membrane off into vesicles

Question 3

formation of vesicles

Answer 3

1. coat proteins start to assemble and bind to adaptor proteins
2. dynaminhydrolyzes GTP, spiraling around neck of the budding vesicle, making the membrane fuse and pinch off

Question 4

types of coat proteins

Answer 4

COP-II - anterograde (forward) movement
ER –> cis golgi.
COP-I - retrograde (backward) movement
trans –> cis golgi or
cis golgi –> ER
clathrin - movement beyond the golgi
golgi –> plasma membrane
golgi –> lysosomes
plasma membrane –> endosomes plasma membrane –> lysosomes

coat proteins disassemble + reassemble every time it changes membrane

Question 5

clathrin structure

Answer 5

3-legged triskeleton structure, come together to form a basket case structure that coats the vesicles

Question 6

proteins involved in vesicle fusing and docking

Answer 6

Rab GTP on the vesicle
tethering proteins on the target membrane
SNARE proteins on both the vesicle and target membrane

Question 7

Rab GTP

Answer 7

protein on surface of vesicle with GTP attached.
involved in:
- binding to motor proteins to travel on microtubules
- recognizing the right target membrane:
-specificity to the transport vesicle (different Rab correspond to different target membranes)
- Rab also participates in the fusion of the membranes (vesicle and target membranes)

Question 8

tethering proteins

Question 9

SNARE proteins

Answer 9

long fiborous proteins on both the vesicle and the target membrane

Question 10

true or false

mebrane fusion always occurs immeadiately after docking

Answer 10

false, sometimes there needs to be a molecular signal to trigger fusion

Question 11

how close do the two membranes need to be in order to fuse?

Answer 11

within 1.5 nanometers

Question 12

botulinum toxin

Answer 12

cleaves SNARE proteins so that membranes are unable to fuse. blocks release of neurotransmitters at the neuromuscular junction, prevents muscle contraction and causes paralysis. death by paralysis of the diaphram

Question 13

transport of vesicles

Answer 13

motor proteins, which are bound to the vesicle via Rab GTP, walk the vesicle along cytoskeletal microtubules until it docks at the target membrane