BIOL 225 Lecture 12.pdf - REMINDER EXAM 1(100 points...

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Unformatted text preview: 2/13/17 REMINDER: EXAM 1 (100 points) Wednesday, Feb. 15 Covering material in Lectures 1-­11 Format: Multiple-­choice & short answer For Students with Testing Accommodations • You need to reserve a desk at the Watson Lab at least 48 hours ahead of time (i.e. TODAY). REMINDER: MasteringBiology Homework udent s/servic es/studentaccessibilityservices/stude nts/service s/watsonlab/watsonlabres ponsibilities/index. php • Due TODAY at 11:59 pm Lecture 12 • Chapters 4, 5, 6, & 8 • 2.5 points each BioFlix: Tour of an animal cell Inside the Cell: The Dynamic Cell—Intracellular Transport BIOL 225 Prof. Liz Allison February 13, 2017 See Summary Table 7.1 (p. 153) for a “parts list” of structure and function Go over the parts of the cells because she ain't going to. 1 2/13/17 Problem for larger eukaryotic cells: Diffusion only allows for rapid movement across small distances Solution: Break up the large cell volume into several smaller membrane-­bound organelles Internal membranes divide eukaryotic cells into distinct compartments Diffusion can only get you so far- it tends to allow for rapid movement only over short distances. By breaking up the cell into organelles, it places necessary molecules closer to one another, thus organizing cells and reactions. Because there are now compartments there must be ways to move thigns between the compartments. How do proteins get targeted to their correct destination in the cell? They must have t he appropriate “molecular z ip code” Once these proteins are made they need to find their destinations- Protein synthesis occurs in the cytoplasm… How do mRNAs get out of the nucleus? How do nuclear proteins get into the nucleus? Protein synthesis occurs within the cytoplasm. The nucleus is pink, the endomembrane system is blue. The cytoplasm is packed with ribosomes, which are not organelles because they contain no membranes. 2 2/13/17 Nuclear Import and Export of Macromolecules • Occurs via the nuclear pore complexes (NPCs) Photo by Elena Kiseleva, Institute of C ytology and Genetics, Novosibirsk-­90, Russia Yeast cell nucleus The structures on the outside of the nucleus are nuclear pore complexes. Nuclear Pore Complex Cross section of nuclear pore complex. The lumen is the space between two membranes, the phospholipid bilayer. Nuclear Import of Proteins Nuclear Export of mRNA and Proteins • Molecular zip code for the nucleus • Molecular zip code for exiting the nucleus Nuclear localization signal (NLS): amino acid sequence within a protein that is rich in basic residues Nuclear export signal (NES): amino acid sequence within a protein, or nucleotide sequence within mRNA •NLS interacts with transport •NES interacts with transport proteins called importins They have an NLS. It is part of the primary sequence which contains a lot of basic amino residues, often. The transport proteins importins can recognize these signals and then direct them into the cell. proteins called exportins There are some proteins which also leave and come back, back and forth. These also have molecular zip codes: NES. For proteins, these too, have particular sections, usually leucine heavy and hydrophobic. There is also a nucleotide sequence for RNA. 3 2/13/17 Traffic Control between Cellular Compartments • Localization signals and mechanisms • Role in gene expression • Control of cell growth and differentiation This plays a role in regulation of gene expression. If a protein is mis localized this may cause disease states. The Endomembrane System: Manufacturing and Shipping Proteins GFP-­tagged thyroid hormone receptor NLS 22 23 24 25 26 27 28 29 P D G A R K R K -­ P D G K R K R K-­ 22 23 24 25 26 27 28 29 Mutagenesis studies: All the basic amino acids and the proline residue are required for efficient nuclear import. GFP does not localize, except when it has a nuclear localization signal from THS. The endomembrane system ships things out of the cells. 4 2/13/17 Gunter Blobel 1999 Nobel Prize RNA Ribosom e Signal sequence SRP Lum en of r ough ER SRP r eceptor Pr otein How does this differ from a nuclear localization signal? Cytosol and cytoplasm are not the same, cytosol refers only to the liquid potion of the cytoplasm. This differs from a NLS because the signal sequence is left behind. SRP is a protein complex present within the cytosol, it takes the messenger RNA and ribosome to the SRP receptor and docks it. The NLS is part of the proteins structure, it often has overlapping parts of functions. This signal sequence is degraded by other proteins. Example: Glycosylation What type of macromolecule? • Folds into 3-­D shape • Post-­translational modification This is like the SUMO signals we talked about in lab meeting. What type of macromolecule? Glycosylation is the addition of a carbohydrate. 5 2/13/17 What are tags composed of? Next stop… t he G olgi Lum en of Golgi appar atus “Tags” Receptor s Cytosol To other organelle Tr anspor t vesicles Proteins are transported from the ER to the Golgi in vesicles To pre-­lysosomal compartment To plasma membrane for s ecretion Lysosome tag: mannose-­6-­phosphate Golgi appa is just stacks of membranes. They are moving in vesicles and becoming further modified. The functional groups allow for a given post translational modification to occur. Recommended readings from the textbook Chapter 7: p. 142-­162 BioSkill 7: Separating Cell Components by Centrifugation BioSkill 9: Using Microscopy 6 ...
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