MCB 2050 Final: MCB Review

3 Pages
Unlock Document

University of Guelph
Molecular and Cellular Biology
MCB 2050
John Vessey

MCB Review - Lamina A not being anchored results in diseases (ex. Progeria) - Nuclear import and export o Proteins that go into the nucleus are genetically encoded with an NLS (classic and bipartite) o NLS are recognized by importin-alpha o Alpha binds to importin-beta and then can be translocated ▪ Beta associates with cytoplasmic filaments of the NPC o Complex pushes through NPC and sits in BASKET ▪ Beta associates with basket o Ran-GTP helps release protein from basket and is now in nucleus o Beta (associated with Ran-GTP in nucleus) diffuses through NPC back out into cytoplasm ▪ Ran-GTP is now converted to Ran-GDP o Alpha associates with exportin ▪ Exportin binds NES of alpha to let it leave nucleus ▪ Ran-GTP associates with complex to diffuse out o Exportin goes back into nucleus bc have NLS - ER and Co-Translational Translocation: o Signal sequence of protein going into ER is cleaved off o All translation starts on ribosomes o SRP recognizes signal sequence and binds to ribosome to PAUSE translation o SRP interacts with SRP receptor that is enriched at RER o SRP receptor is always in close proximity to a translocon o Ribosome sits on translocon, at same time, GTP hydrolysis occurs which releases the ribosome and the signal sequence – plug is released o As soon as the signal sequence reaches the lumen it is CLEAVED and now translation continues until your C-term EMERGES o If you’re an INTEGRAL MEMBRANE protein: ▪ Hydrophobic thus can’t emerge into lumen ▪ Alpha-helix of transmembrane domain pushes lateral gate of translocon open and protein slides out into bilayer ▪ Translation can be completed o To FLIP protein… ▪ Translocon = +ve at lumen and –ve at cytoplasmic side ▪ There will be +ve AA upstream of transmembrane domain and –ve AA downstream of domain ▪ charge repulsion causes FLIP of terminus in translocon and N-term emerges into the cytosol - Protein Processing in ER o Glycosylation happens AS the protein is being synthesized and emerging o N-X-S/T = signal for GLYCOSYLATION, detected by glycotransferase o The attached sugar is built on a lipid called dolochol phosphate ▪ 5 mannoses added on cytoplasmic side ▪ flippase flips complex from outer leaflet to inner leaflet ▪ now sugar is in lumen of ER ▪ now more sugars (mannose and 3 terminal glucoses) can be added - Protein folding in ER o 2 glucoses are released by glucosidase I and II, which allows the unfolded protein to bind to calnexin o calnexin sequesters unfolded proteins so they can fold ▪ unfolded proteins have hydrophobic domains that will aggregate with other unfolded proteins o now glucosidase comes and takes off the 3 glucose o UGGT comes along to assess the protein to see if it’s folded properly or glycosylated properly ▪ If not proper, UGGT can stick a glucose on the protein and calnexin sequesters it again to refold - BiP: binds to unfolded proteins and associates o BiP will dimerize and cross-phosphorylate which in turn activates it into a kinase o Kinase targets eIF2-alpha o ATF6: if lose access to BiP, it goes to the Golgi where it encounters a proteases that cleaves
More Less

Related notes for MCB 2050

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.