Intracellular Compartments and Protein Sorting

Question 1

Name the 6 functions of Peroxisomes

Answer 1

1. Oxidation of long fatty acid chains
2. Oxidation of branched chain fatty acids
3. Oxidation of cholesterol to bile acids (liver)
4. Synthesis of plasmalogens (myelin membrane lipids)
5. Detox of metabolic intermediates and foreign substances for elimination via catalase and flavoprotein oxidases (EtOH)
6. Decomposition of hydrogen peroxide

Question 2

PTS1

Answer 2

tripeptide import signal (carboxyl terminal end) interacting with peroxisome translocators

Question 3

PTS2

Answer 3

nonapepetide import signal (amino terminal end) interacting with peroxisome translocators

Question 4

Process that occurs when peroxisomes accumulate many specific proteins from cytosol

Answer 4

fission=form daughter peroxisomes

Question 5

Properties of the RER

Answer 5

1. Continuous from the nuclear envelope
2. Made up of lipids
3. Contains attached ribosomes

Question 6

As proteins are translated, the _____ ______ signal sequence emerges and directs the engaged ribosome to the ___ where the _____ stays bound as synthesis continues

Answer 6

amino terminal, ER, mRNA

Question 7

SRP

Answer 7

signal recognition particles, they bind to the amino terminal signal sequence after it has been translated and then bind to the SRP receptor in the ER membrane (ribosome is now associated with the ER and the protein is pushed into the lumen)

Question 8

Sec61

Answer 8

a protein translocator complex on the ER membrane. In eukaryotes it associates with Sec 62/63/71/72 to form a complex that facilitates post-translational translocation

Question 9

BiP

Answer 9

an ER hsp70-like protein that drives post-translational translocation through bind and release (works with Sec 61)

Question 10

Protein stop-transfer sequence

Answer 10

a hydrophobic positively charges sequence of a protein, which when translocated through the ER, will open sec 61 and the start transfer sequence will be released=transmembrane protein

Question 11

What is the most common protein modification that occurs in the ER lumen?

Answer 11

Glycosylation of asparagine residues.

Question 12

List some functions of glycosylated Asn in the ER

Answer 12

1. The glycan protects the protein (glycocalyx)
2. Act as attachment sites for lectins
3. Allows for signaling
4. Guides folding
5. Stability/protein quality

Question 13

CDG glycosylation disorders are caused by…

Answer 13

Deficiency of one of 29 enzymes directed or indirected involved in N-linked glycosylation

Question 14

Calnexin (CNX)

Answer 14

integral membrane ER protein that retains the unfolded structure of glycosylated protein during trimming (glucosidases)

Question 15

Increased unfolded protein concentration in ER causes

Answer 15

ER stress response

1. Reduciton of synthesis of new proteins
2. Transcription of genes that encode ER chaperones (for folding)

Question 16

IRE1

Answer 16

an ER transmembrane protein kinase which senses misfolded proteins and regulates mRNA splicing to initiate translation of a gene regulatory protein

Question 17

PERK

Answer 17

an ER transmembrane protein kinase which senses misfolded proteins and inactivates translation initiation factor to reduce {protein}. It also translates a gene regulatory protein

Question 18

ATF6

Answer 18

a Golgi apparatus transmembrane protein which senses misfolded proteins and leads to regulated proteolysis that releases a gene regulatory protein

Question 19

Goal of the unfolded protein response

Answer 19

signal nucleus to make more chaperone proteins for the ER–> folding–> avoid apoptosis