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31 Cards in this Set
- Front
- Back
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Endoplasmic Reticulum |
network of membrane-enclosed tubules and sacs that extend from nuclear membrane throughout cytoplasm protein processing and sorting 1. Processing secreted and membrane proteins 2. Membrane lipids synthesized 3. Major site of synthesis or other membrane lipids - cholesterol and ceramide |
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Rough ER |
covered by ribosomes on its outer surface and is involved in protein metabolism |
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Transitional ER |
protein processing where vesicles exit to the Golgi membrane --> membrane Next Step: ER-Golgi Intermediate Complex |
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Smooth ER |
lipid metabolism no ribosomes steroid hormone in endocrine glands. Abundant in cell types active in lipid metabolism Detox organic chemicals --> safer water-soluble products of natural metabolism To detox excessive drinking --> can double surface area and then return to normal size |
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George Palade |
studied fate of newly synthesized proteins -labeled them with radioactive amino acids and then followed by autoradiography -3 min label: first in rough ER --> synthesis -7 min chase: cells then incubated in media containing nonradioactive aa ("chase"). Labeled proteins detected in Golgi -120 min chase: From Golgi --> cell surface --> plasma membrane to release outside of cell --> Not only for secretion, but also proteins destined to incorporate into the ER, Golgi, Lysosomes, or membrane. Otherwise, released into cytosol. |
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Signal for Ribosome Attachment |
Sabatini and Blobel (1971) --> Signal might be an aa sequence near amino terminus of growing polypeptide chain |
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microsomes |
small vesicles formed from the ER when cells are disrupted proteins are incorporated into it without the signal sequence --> cleaved by a microsomal protease |
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Signal recognition particle (SRP) |
Signal sequences are recognized and bound by SRPs on the ER Signal sequences are ~20 aa long and have stretch of hydrophobic residues Consisted of SRP proteins associated with small cytoplasmic RNA SRP receptors are proteins on membrane of the endoplasmic reticulum |
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Translocon |
membrane proteinous channel thru which polypeptide chains are transported into the ER |
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Signal Peptidase |
Cleaves signal sequence and releases it into lumen of ER Proteins destined for secretion form cell or residence within lumen of ER, Golgi, endosomes, or lysosomes are translocated across ER membrane and released into lumen of ER |
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Lumen of ER |
topologically equivalent to exterior of cell --> domains of plasma membrane that are exposed on cell surface correspond to regions of polypeptide chains translocated into ER lumen |
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Transport Vesicles |
deliver transmembrane proteins to other compartments in the secretory pathway Orientations of proteins are preserved |
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RER |
1. Protein folding 2. Assembly of multisubunit proteins 3. Disulfide bond formation 4. Initial stages of glycosylation 5. Addition of glycolipid anchors to some plasma membrane proteins |
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Chaperones |
catalysts that facilitate assembling stabilizing unfolded polypeptides --> 3D initially identified as heat shock proteins (hsp) that facilitate refolding of partially denatured proteins (when cells are stressed, misfold proteins) disulfide isomerase - facilitates oxidizing disulfide bond formation in ER (cytosol - reducing environment |
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Glycosylation |
modifying proteins by adding carbohydrates N-linked: in ER. To Asparagine. Happens on inside of cell membrane. Oligosaccharide (14 sugars) is assembled on the ER with dolichol. This part will later be on the cell surface. Then remove some residues in ER, and get changed up in Golgi. O-linked: add 1 sugar at a time, only a few residues, added in Golgi. Some proteins attached to plasma membrane with glycolipids added to C-terminus of protein in ER --> cell surface |
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Unfolded protein response |
Excess of unfolded proteins --> 1. General inhibition of protein synthesis 2. Increased activity of chaperones 3. Increased protease activity (--> degradation) Initiated when all chaperones (BiP) are deployed from their signal molecules which then set off the response |
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Membrane lipid synthesis |
Synthesized in association with already existing cellular membranes (rather than aqueous environment of cytosol) --> Allows hydrophobic fatty acid chains to remain buried in the membrane while membrane-bound enzymes catalyze reactions with water-soluble precursors in cytosol Phospholipid, glycolipids, and cholesterol |
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Glycerol Phospholipid Synthesis |
synthesis in ER membrane from the FA linked to co-A (to activate them) and Glycerol-3-phosphate to make phosphatic acid --> DAG (diacyglycerol) which are then attached to different polar groups in lumen |
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Flippases |
catalyze rapid translocation of phospholipids across ER --> even growth of both halves of the bilayer Newly synthesized lipids only added to cytosolic half of bilayer Flippase --> growth of both halves |
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ER Export Signals |
(di-acidic and di-hydrophobic aa sequences in cytoplasmic domain) recognized by cytoplasmic adaptor proteins which recruit them in secretory vesicle lumenal & glycolipid anchored proteins are recruited through interaction with transmembrane proteins |
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ER Resident Signals |
function within ER like KDEL or KKXX Cause ER resident proteins to be selectively retrieved from ER-Golgi Intermediate Complex compartment for Golgi --> return to ER via recycling pathway |
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Golgi Apparatus |
Also lipid metabolism and synthesis of glycolipids, and precursor in ER as ceramide and sphingomyelin functions as a factory in which proteins and lipids and polysaccharides are received from ER are further processed and sorted for transport to eventual destinations In plant cells, site where complex polysaccharides of cell walls are further synthesized Flattened membrane-enclosed sacs and associated vesicles - cis --> smaller, from ER - trans --> sorted and packaged to exit Stack: ERGIC; cis; stack: medial, trans; trans network --> out |
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Protein Glycosylation in Golgi |
Synthesizes and mediates carb part of glycoproteins O-linked: processed in Golgi in an ordered sequence of reactions N-linked: initiated in ER with some modifications in Golgi - Some things removed, some added - Different for lysosomal proteins vs secreted and plasma proteins. Lysosomes: phosphate to #6 on mannose, which directs via a receptor in trans Golgi to lysosomes |
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Glycosyltranserase |
enzyme that adds sugar residues to substrate |
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Glycosidase |
enzyme that removes sugar residues from its substrate |
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Constitutive secretory pathway |
operates in all cells continual - always active! - unregulated protein secretion When there is no specific targeting signals, proteins are carried to plasma membrane thusly There are also distinct regulatory secretory pathways in response to environmental signals (lysozyme) |
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Coated Vesicles |
Carry secretory proteins from ER to Golgi and from Golgi to other targets Coated within cytosolic coat proteins, and recognized by specific proteins on it Formation is regulated by small GTP-binding proteins like Ras, Ran, and Rab Bud off from selected regions of donor membrane. During transport, coat is dissembled, and transport vesicle docks and fuses with target membrane |
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COP I & COP II |
proteins that coat transport vesicles |
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Clathrin |
proteins that coat transport vesicles Coats cytoplasmic surface of cell membranes, and assembles into basket-like lattices that drive vesicles |
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SNARE Hypothesis |
Vesicle fusion is mediated by pairs of transmembrane proteins (v-SNARE on vesicle and t-SNARE on target membrane) Rab family can also help - facilitate formation of v/t-SNARE complexes Mark different organelles and transport vesicles, so their localization on the correct membrane is key to establishing specificity of vesicular transport |
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Lysosomes |
membrane-enclosed organelles that contain an array of enzymes to break down biological polymers Most helpful lysosymal enzymes are acid hydrolases, which are active at the acidic pH that is maintained within lysosomes but not at neutral pH at cytoplasm (so doesn't digest in ER) |
