ER and vesicular transport

Question 1

ER structure

Answer 1

• flattened interconnected sacs
• lumen is enclosed space
• continuous with outer nuclear envelope
• ribosome on rough

Question 2

ER functions

Answer 2

1. protein synthesis
2. protein modification
3. protein quality control
4. lipid synthesis
5. steroid hormone synthesis
6. detox lipid soluble drugs
7. store Ca

Question 3

ER protein synthesis

Answer 3

• all protein synthesis begins in cytosol
• if peptide has ER sequence it will bind SRP, which will bind SRP receptor on ER membrane.
• protein translocator opens and protein enters CO TRANSLATIONALLY
• protein threaded through, forms loop and signal peptidase cleaves signal sequence off
• if going to stay in ER membrane, hydrophobic regions act as starters and stoppers for threading through and move laterally through membrane

Question 4

where proteins made in ER go

Answer 4

1. ER, golgi, lysosomes, endosomes
2. PM
3. to be secreted

Question 5

Protein modification in ER

Answer 5

• signal sequence cleaved by signal peptidase
• glycosylation - oligosaccharide transferase puts 14 sugar on NH2 of asparagine of protein and then modifies it to make glycoproteins
• hydroxylate proline and lysine in collagen to stabilize. enzyme is Vit C dependent and scurvy without
• protein folding by chaperones
• s-s bonds by protein disulfide isomerase
• multisubunit polypeptides formed
• retention: KDEL sequence makes protein return to ER after getting to golgi

Question 6

Protein quality control

Answer 6

• misfolded proteins cant leave bc of chaperones; eventually degraded by proteasomes if not corrected
• unfolded protein response: increase number of chaperones and amt of ER if necessary. trigger apoptosis if doesnt help.

Question 7

Vesicular Transport

Answer 7

• vesicles bud from protein coated regions of membrane and protein coat guides target
• clathrin protein coat - 3 heavy and 3 light chains
• adaptin binds clathrin to vesicle and picks cargo
• dynamin - GTP binding protein. pinches vesicle off when it hydrolyzes
• Rab - GTPase on vesicle binds tethering protein on target
• V SNARES binds T SNARES on target and coil and make fusion occur

Question 8

golgi

Answer 8

• cis: sort proteins that go back to ER
• trans: sort proteins for lysosomes or PM
• proteins go to cell surface unless signal tells otherwise
• may go to lysosome or secretory vesicle

other functions:

• modify N link oligosaccharides
• make o linked oligosaccharides on lipids and proteins
• make glycosaminoglycan on proteoglycans