http ntri tamuk educellribosomes html 17 1 676

http: //ntri. tamuk. edu/cell/ribosomes. html

17. 1, 676 How does everything get to where it has to go?

First, how does a protein fold that stays in cytoplasm? 3. 14, 64 A very small percentage of proteins fold spontaneously into the right shape after being translated. C. Anfinsen showed reversible denaturation and renaturation with ribonuclease- protein goes through several intermediate steps before arriving at “energy minimized state”

3. 15, 65 Most proteins will fold with the assistance of heat shock proteins (chaperonins)this requires ATP and can take several minutes/protein -can also ‘rescue’ proteins that unfold due to a stress

17. 26, 708 Disulfide bonds form, reform break and reform with aid of protein disulfide isomerase (PDI)

17. 14, 695 Yeast mutants called SEC mutants – isolate one class for each stage in a secreted protein-used to isolate which proteins are involved

17. 16, 698 1) ribosome assembles and after about 70 aa translated, signal sequence emerges and signal recognition particle (SRP) binds to signal sequence 2) SRP, ribosome, and signal sequence bind to SRP receptor in ER 3) GTP splits, SRP leaves, gate in translocon (pore) opens, and ribosome translates into lumen of ER 4) Signal sequence is cleaved off in the ER lumen 5) HSPs bind to growing polypeptide chain as it is translated-sometimes carbs added 6) After translation ended, ATP split, HSPs come off and protein folds 7) HSPs may rebind and protein refold if misfolded

17. 17 -19, 699 -700

What about membrane-bound proteins? 17 -21, 702

17. 22, 703

Lots of GTP hydrolysis involved 17. 20, 701

17. 24, 706 As complicated as you want to get

Group Exercise # 7 In groups of five, try to answer these questions: 1) Your western blot, against HSP 70, showed a reaction for proteins bigger than 70 k. Da. How can this be? 2) Your western blot used a monoclonal antibody against HSP 70, and yet multiple bands, of different size reacted to the antibody. How can this be?