Topic 6: Endoplasmic Reticulum Flashcards
what are the difference between the rough ER and the Smooth ER? What is made in each? Are these separate structures within the cell?
Rough ER is covered in Ribosomes while the smoother ER has no ribosomes. Continuous domains that perform different functions
What is the role of flipases and why are they needed?
Enzymes that help phospholipids flip from the cytosolic layer to the lumenal layer.
What types of proteins will be translated on the ER? Why would I want proteins to be translated there?
Membrane bound protein, lumenal proteins, or proteins that need ot leave the cell. Proteins are made in one location depending one where they end up.
What types of protein modifications can I perform inside the ER?
Can add sugars, protein glycosylation, happen on asparagine. Helps prevent protein aggregation, and promote protein folding, and helps with proteins sorting. Can also add lipid anchors
What determines if a protein will be translated on the ER or in the cytosol?
If where the protein needs to go is continuous with the ER.
Steps in cotranslation translocation. What proteins are involved? What do each of these proteins do?
A SRP binds to the signal sequence on the polypeptide chain. The SRP proteins binds to an SRP receptor that is attached to a translocon. Ribosome binds to the translocon which causes the SRP protein to unbind to the SRP receptor ribosomes binding to the translocon also causes the translcon to open. Translation resumes. Signal peptidase cleaves the signal sequence off the growing polypeptide chain. Coninued trnaslating causes the growing polypeptide chain to grow inot the lumen of the ER. The finished products spit out into the lumen of the ER.
What is BiP? Whi is it important that BiP stays inside the lumern of the ER?
Chaperone proteins. Important for it to stay in the lumen because helps aid in the folding process , and will not unbind till protein if properly folded.
What happens to proteins that are misfolded in the ER? What other proteins are involved in the process?
A chaperone sends misfolded protein to the ER membrean where it binds to ubiquitin ligase comples. Gets tagged with ubquitin, and then sets off inot cytosol to be broken down by Protesasome.
What indicated that a protein should be integrated into the membrane? How does this help the proteins become integrated into the membrane? What is the role of translocon in this?
When a ribosome translates a polypeptide chain of 20-25 consecutive hydrophobic amino acids = transmembrane sequence. Translocon read the sequence and inserts that segment into the membrane.
How can SRP help proteins become transmembrane proteins? What are 2 ways that SRP brings transmembrane proteins to the ER?
SRP binds to the transmembrane sequence which brings it to the SRP receptor translocon. Sequence is located in the middle of the polypeptide, allos for versatillity in the location in the N and C terminus.
If the protein is supposed to have multiple transmembrane domains how does this system integrates all of these domains?
Ribosome encounters multiple transmembrane sequences which will all be read by the translocon and inserted into the membrane. Every new transmembrane sequence changes where the polypeptide chain is growing.
How id cotranslation translocation different from post translation translocation?
Post translocation relocation has integral protein facing outside of the cell, facing ER lumen because signal sequence comes at the end after proteins is done.
