Lecture 5 notes
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This 2 page Class Notes was uploaded by Brenna Eisenberg on Monday October 3, 2016. The Class Notes belongs to 327 at Syracuse University taught by erdman in Fall 2016. Since its upload, it has received 4 views. For similar materials see Cell Biology in Biology at Syracuse University.
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Date Created: 10/03/16
Lecture 5 Tuesday, September 20, 20110:48 AM Lecture 4 continued: • Prions- proteins that can produce proteinaceousinfectiousparticles ○ Cause mad cow disease ○ Transmissible, no nucleic acid component,species barriers ○ Protein present in normal cells ○ Nobel prize won by Stanley Pruisner ○ Ex- amyloid fibers associated with alzheimer's ○ Conversion of normal protein into abnormal form, ability to aggregate ○ Disturb formation of alpha helices ○ May help us understandalzheimer's, parkinson's, ALS • Spongiform encephalies: ○ Formation of protein aggregates/ plaques, leads to lysosomal lysis and holes in the tissue Lecture 5: • The steady state level/ concentration of a protein is a function of its synthesis and degradationfactors • The half-life of a protein is half the average of the time the protein spends in the cell. Half of the material has degraded ○ Determined by pulse chase experiment • Fine control of protein creation- add additional steps of regulation ○ Eukaryotes have more regulatory steps in making a protein than prokaryotes do • Proteins originate on the ribosome • Synthesis can be regulated before, during, and after translation • Protein degradation: ○ Proteasomes- multi-proteincomplexes that degrade damaged proteins or proteins marked with ubiquitin ○ Lysosomes- dedicated to degrading proteins found in membranes or soluble proteins imported into the cell • Other regulation mechanisms- ○ Sequestration-sequestering proteins bind and prevent assembly. Hold protein after their production in the cytoplasm. Common in actin. Localization- Ex- some transcription factors held in the cytosol until there are signals that modify, allow entry into nucleus where they can function ○ Assembly- proteins are typically not active until assembled into quaternarystructure. Ex- hemoglobin • ** study slide 7 clicker question • Many enzymatic reactions and pathways are self-regulatedby feedback inhibition mediated by the end products • An allosteric change due to bindingof a ligand can promote the bindingof a second ligand • Modifications: ○ Ubiquitin attached to lysine residues ○ Phosphorylation/dephosphorylationoccurs on polar non-charged residues: ser, thr, tyr ○ Nucleotide binding and hydrolysis. Ex- hydrolysis of ATP ○ Modification by lipid anchors • by modifying proteins, cells create at least 2 potential states of activity for any modified protein. Increases functionalityw/o synthesizing more proteins • If the modification or ligand bindingis reversible, the protein can run through many cycles of function • Combination of regulation of synthesis points and post translational modificationsare 1 way eukaryotes can make more complicated tissues without needing so many more genes. Combinatorial control • Phosphorylationof some substrates by kinases, dephosphorylationby phosphatases Cell Biology Page 1 • Phosphorylationcan also be inhibitory • Binding and hydrolysis of nucleotides (ATP/ADP,GTP/GDP) produces conformation changes that can control protein activities ○ Ex- in motorproteins such as myosins drive movements • Lipid addition- anchors or localizes proteins to different membranes • Modifications like N- and O- linked glycosylation can influence structure • Post translational modifications of histones controls nucleosome and chromatin structure Cell Biology Page 2
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