L312/Spring 2007 Lecture 10 Drummond Feb 13

1. L312/Spring 2007 Lecture 10 Drummond Feb 13 Exams close, but not done! Back on Thursday (looking great so far!) • For today: Focus on Chapter 15, Ch. 16 497-511: Protein sorting • RTKs (receptor tyrosine kinases) were the focus of last lecture Ligand binding supports receptor dimerization. Dimerization supports intermolecular phosphorylation. Phosphorylated receptor is bound by adaptor proteins. Ras is a common target of RTKs. • Steroid hormone receptors are intracellular. Hormones pass through membranes Hormone/receptor complex enters nucleus to effect changes Today: how do you get a letter back home to your parents?

2. The multiple compartments in the cell General questions? What happens in each space? How do proteins get across membranes? How are proteins inserted in membranes? Makes you wonder… How is the sequence information distributed and translated?

3. The multiple compartments in the cell What happens to organelles when the cell divides? Where does new membrane come from? What is the relative surface area? LOOK CLOSELY AT ORGANIZATION Rough rule of sequence of events: Nucleus: DNA --> mRNA Rough ER: mRNA to proteins (into ER space!) lipids made here (Smooth ER: steroid synthesis et al) Golgi: modification of proteins and lipids Final destination (PM, lysosomes, etc)

4. How do proteins, made in the cytoplasm, get inside membrane-bound organelles? What targets them to the nucleus? How big a protein Can pass the pore? How is a protein specifically targeted to an organelle? How are they inserted Asymmetrically in membranes, Both facing inside and outside the cell?

5. What is it about a protein that targets it to a specific organelle? (KDEL) Key: Hydrophobic = Leu, Val, Phe, Met, Ile Positive charge = Lys, Arg Negative charge = Asp, Glu +H3N-Met… N-terminus; …XCOO- = C-terminus

6. Swapping protein localization. Can a protein go to two places? What might drive this process? What is the mechanism for import?

7. The membrane and ER lumen are contiguous (note double membrane) Note the enclosed ER space here How are proteins fed into the rough ER? Do they reach the ribosomes this way? (trafficking is an ENORMOUS Logistical problem)

8. Nuclear pores are really selective transporters for large cargo What are the Primary features Of this 100+ Subunit transporter? What materials Flow each way? LOOK AT size scales! How could this be isolated?

9. What are nuclear transport receptors, and how do they move? (really also ER--why?) What do you think might drive this process?

10. Nuclear import: the role of the Ran protein

11. How do proteins, made in the cytoplasm, get inside membrane-bound organelles? How is a protein specifically targeted to an organelle?

12. A simplified strategy for protein entry across two membranes (NOT traveling through a large (e.g. nuclear) pore!!!) How does a big folded protein cross a membrane? Where was this protein Synthesized? ER or cytosol? Where are most mitochondrial/chloroplast proteins made? What drives these Proteins across the membrane?

13. The ER is a complex network that can span the cell Why is this “ROUGH”? What is Crucial about this structural layout? How does the ER lumen relate to the perinuclear space? Look closely at SIZE scales and microscopy type

14. Proteins are made by ribosomes both free and attached to ER How do proteins Enter the ER Space? Is this Like Mitochondrial Import? What is the key Difference (and why?) Why is the rough ER ‘rough’?

15. How is translation coupled to ER insertion?

16. What is crucial about the signal sequence for ER insertion? (and how is it removed?)

17. How is a single pass transmembrane protein inserted in the membrane? What is a “stop transfer” sequence And how does it resemble the targeting sequence? Are there proteins with long hydrophobic stretches in the ER lumen?

18. Finally, how are multi-pass proteins (pores/receptors) inserted? Key is LATERAL exit from translocase