Week 2 Protein trafficking

Question 1

why elks have so many complex organelles

Answer 1

once cells got bigger, they ran into a surface to volume problem
had to fold the membranes of the organelles to increase SA

Question 2

where do proteins go?

Answer 2

from ribosomes to:

cytosol, nucleus, mito, ER, golgy, lysosomes, PM, cell exterior, secretory vesicles

Question 3

signal sequence on protein

Answer 3

directs protein sorting- tells where the protein to go
receptors reads those sequences
can be a linear sequence at the end or an internal sequence that, when folded together, conglomerate that make a signal patch

Question 4

Nuclear envelope

Answer 4

IL2 impt TF
nuclear import occurs thru gated transport of nuclear pores- completely folded and functional
nuc envelope is contiguous with the ER

Question 5

Gated transport- nucleus

Answer 5

seen in transport thru nuclear pores
specific to nuclear location signals on the proteins
it only lets thru certain sized things (> 60 kDa needs active transport thru nucl. pore)

Question 6

active transport thru nuclear pores

Answer 6

nuc import recpetors bind to NLS on the proteins and to the nucleoporins on the nuclear pore complex
need GTP-Ran (monomeric GTPase) proteins to bind to the receptor, replacing the cargo protein and is recycled
hydrolyzed to remove the GTP-ran from the receptor
(don’t want proteins in the nucleus all the time, esp wrt TFs)

Question 7

Nuc import during T cell activation

Answer 7

dephosphorylation allows import signal to be recognized by the receptor (NF-AT)

Question 8

cytosporin

Answer 8

inhibits calcinurin
useful to prevent kidney rejection
prevents the dephos so T cells can’t be activated

Question 9

constitutive secretory pathway

Answer 9

direct path from golgi to the outer cell
the N terminal of the new peptide is the signal sequence
recognized by the signal recognition particle which sends it to the ER

Question 10

collagen- constitutive sec. pathway

Answer 10

16 types, mostly 1 2 and 3
makes fibrils
25% to 35% of whole body protein content
made of 3 alpha helices, translated on ribosomes, then directed to the default pathway for secretion to the extracellular matrix

Question 11

SRP/ SRP receptor

Answer 11

the N Terminal signal attracts SRP, that delivers the ribosome to the receptor, and the polypeptide is translated straight into the ER, SRP is removed

Question 12

embedding protein in PM

Answer 12

there is a stop transfer sequence within the transcript, which stalls the transcript (membrane spanning region)
hydrophobic

Question 13

transmembrane proteins

Answer 13

start and stop transfer sequences allow the proper construction of multi pass transmembrane proteins

Question 14

modifications that occur in the lumen of the ER

Answer 14

N terminal signal is dissolved ( now pro peptide)
hydroxylation of lysine’s and prolines to aid in cross linking, needs vitamin C
glyclosylation

Question 15

proteins from ER to golgi

Answer 15

membrane buds off with the contents for transport, membrane coat proteins direct it to the golgi, fuse to the correct target compartment as a transport
1. They must take up only the correct proteins from
the donor compartment.
2. Deliver itself to the correct target membrane
3. Fuse with the correct target membrane.

Question 16

coated vesicles

Answer 16

depending on the coat protein, the vesicles travel to different places
clathrin, COPI, COPII

Question 17

clathrin

Answer 17

brings from the PM to the lysosome and also from golgi to the PM

Question 18

golgi apparatus modification

Answer 18

oligosacch. are added and then pro collagen is packaged by COP I into a secretory vesiclesand then sent out to the extracellular space

absence of certain signals keep it in default secretory pathway (constitutive)

Question 19

signal mediated secretion

Answer 19

digestive enzymes- regulated exocytosis
assemble into vesicles that are coated with clathrin
sit there and wait for signal (neurotransmitter, hormone) and then it stimulates that vesicle and it releases the materials

Question 20

acinar cells- pancreas

Answer 20

signal mediated
secretes digestive enzymes for a meal digestion
exocrine to the small intestine

Question 21

pancreatic specific transcription factors

Answer 21

PTFs tells when and where these enzymes need to go

depending on diet type it affects the type of enzymes that are made and secreted

Question 22

clathrin- signal mediated

Answer 22

used in regulated secretion too even though signal isn’t known yet
1. In the trans-Golgi network: clathrin coats sort lysosomal proteins for transport to lysosomes

2. In the trans-Golgi network: clathrin coats sort the substances for storage in secretory vesicles
3. At the plasma membrane: clathrin coats are used for the uptake of extracellular material via
   receptor-mediated endocytosis

triskelion shape

Question 23

release of digestive enzyme

Answer 23

hormones 
gastrin releasing peptide
cholecystokinin
Ach
increase both calcium and cAMP simultaneously

Question 24

ER stress (ERAD)

Answer 24

quality control for proteins
degrades the misfiled proteins
makes sure they aren’t sent out to the cell

Question 25

unfolded protein response

Answer 25

results from stressors, mediates an adaptive reposne so the exocrine pancreas can adjust machinery to the effects of the stressors and proceed with normal synth and transport fxns

upregulate the expression and function of chaperones and foldases to augment the folding and export capacity of the ER

activate the ER-associated protein degradation (ERAD) system to rid the ER of accumulated unfolded and misfiled proteins

a global reduction in translation of mRNA to decrease the processing demand for newly synthesized proteins. Can’t do this for the demand for digestive enzymes.

Question 26

N linked glycosylation and protein folding

Answer 26

it helps fthe folding process
it sends misfolded protein to calnexin chaperone for refold, then it is sent out of the ER
if it doesnt refold, ubiquinated and sent to proteasome for degradation

Question 27

ERAD

Answer 27

misfolded, glycosylated protein is attached to chaperone, it is sent out to the cytosol, ubiquinated and sent to proteasome

Question 28

endocytosis

Answer 28

brings in things and sent to lysosome, usually

Question 29

receptor mediated endocytosis

Answer 29

take in material, not much ECfluid

allows specific things to be taken into the cell- clathrin coat

Question 30

receptor mediated endocytosis of LDL

Answer 30

removes cholesterol from the body by converting to bile salts
apolipoprotein B100 in the LDL complex rec. by the LDL receptor for removal from circulation
clathrin coated

Question 31

hypercholesterolemia

Answer 31

mutation in LDL receptor protein that didn’t bind/recognize clathrin, so it couldn’t be endocytosed

Question 32

lysosomes

Answer 32

contains nucleases, proteases, glycosidases, lipases, phosphatases, sulfatases, phospholipases, pH 5

Question 33

assembly of lysosome

Answer 33

needs mannose 6 p
assemble clathrin coats
endocytotic vessels coming from PM
H pump lowers the pH
take good stuff out and send to golgi, destroy bad stuff

Question 34

3 pathways to lysosomal degradation

Answer 34

1. endocytosis to late endosome to lysosome or mitochondria
2. autophagy- sends its own organelles to lysosome
3. phagocytosis- take in bacteria, make phagosome, send to lysosome