Endomembranes

Question 1

signal sequence

Answer 1

hydrophobic AA sequence that signals what organelle the cargo needs to go to, interacts with SRP which uses GTP to increase the SRP’s affinity for the SRP receptor on target organelle membrane, they bind, GTP hydrolyzed to GDP, cargo pulled through membrane

Question 2

2 methods of regulation on protein modification in the ER

Answer 2

1. ubiquitin degradation of misfolded proteins

2. UPR signaling pathway

Question 3

ubiquitin degradation

Answer 3

misfolded proteins are booted from the ER, tagged for degradation by ubiquitin, and degraded in spliceosome

uses protein translocator with an ATPase and ubiquitin ligase

Question 4

Unfolded protein response (UPR)

Answer 4

when there is an accumulation of too many unfolded proteins in the ER, this signaling pathway gets turned on, phosphorylates initation factors to decrease the overall protein production and then selectively increases production of chaperonins to fold the unfolded proteins

If UPR is left on too long, apoptosis.

Question 5

membrane fusion vesicle formation

Answer 5

not thermodynamically favored, must use coat proteins to form loop/vesicle

Question 6

coat proteins

Answer 6

have high affinity for themselves so overcomes the repel force of the lipid bilayer and allows vesicle formation

ex: clathrin, COPI, COPII

Question 7

membrane fusion docking

Answer 7

requires use of Rab-GTP

specific Rab protein active with GTP interacts with Rab-effector protein on target organelle, t-SNARES on target organelle interact with v-SNARES on vesicle, then fusion occurs

*Botox inhibits fusion by cleaving the snare proteins

Question 8

Golgi to ER and back

Answer 8

uses COPII, vesicles form at exit sites in the ER where it is devoid of ribosomes

Question 9

Golgi to lysosome

Answer 9

M6P (mannose 6-P) is the signal sequence

Question 10

Botox

Answer 10

cleaves snare proteins, blocks neurotransmitter release from vesicles in the synapse of muscle neurons thus causing paralysis

Question 11

lysosomal storage disorders

Answer 11

hydrolase enzymes are absent or low in lysosomes, can be due to issues with enzyme transport (I Cell disease)

Question 12

Hurler’s disease

Answer 12

defected GAG hydrolase in the lysosome, death by age 10

Question 13

I cell disease

Answer 13

almost all lysosomal hydrolases are absent due to defective M6P

causes backup of lysosomal machinery and death by age 6

Question 14

endocytosis

Answer 14

plasma membrane to golgi; ph decreases as you progress through the endocytic stages to the lysosome which allows receptor to be recycled

Question 15

clathrin-dependent endocytosis

Answer 15

clathrin dimers join to form triskelions which form a basket like coat on the membrane to help bend it into a vesicle (ex: LDL receptor)

Question 16

clathrin-independent endocytosis AKA phagocytosis

Answer 16

innate immune response, involves formation of pseudopod made of actin that warps around the target

Question 17

exocytosis

Answer 17

constituted or regulated, constituted is the default pathway, regulated is for hormones/neurotransmitters, etc.
Uses same docking/fusion process as endocytosis but backwards.