Term
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Definition
- Protein synthesis (ribosomes on the cytoplasmic side) transfer to lumen
- Oligosaccharide biosynthesis (cytoplasmic)
- Membrane lipid synthesis - where asymmetry of PM is 1st determined
- In the lumen of the RER, fully or partially luminal proteins may undergo the following modifications:
- Asparagine-linked glycosylation
- Folding (chaperone proteins)
- Vesicular transport to Golgi
- Transcriptional activation
- Retro-transport of unfolded proteins to cytoplasm
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Term
| differences between the environments of the cytoplasm and RER lumen |
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Definition
- Similar pHs
- Ca 2+ is 10,000 X higher in ER (some bound to proteins, some ions)
- Ionic composition, not determined
- The ER is much more oxidizing, and so intra and interchain disulfide bonds form, ex: insulin. In the cytoplasm, NADA, FADH2 and others keeps others reduced, so no disulfide bonds.
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Term
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Definition
| protein glycosylation (de), phosphorylation, sulfation, synthesis of glycosaminoglycans, O-linked glycosylation |
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Term
3 pathways through which proteins from Golgi are released to: |
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Definition
- Constitutive secretion – replenish plasma membrane proteins
- Regulated secretion- signals
- Transport of prelysomal enzymes to late endosomes or lysosomes
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Term
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Definition
- Cis – 1st compartments from RER
- Medial – glycosylation takes place
- Trans – sorting site for transport
- Trans-Golgi network (TGN) – secretory vesicles and prelysosomes (carrying enzymes to endosomes/lysosomes) come off
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Term
| Explain how a vesicle is formed at the RER-Golgi interface |
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Definition
- Transitional ER (TER) – this is where new proteins exit in vesicles that contain ER proteins that must be returned. There are no ribosomes.
- Anterograde – TER to Golgi (COPII)
- Retrograde – Golgi to TER (COP I)
- Coat proteins (COPs)- protein complexes which starts a vesicle – deforms the membrane, COP II is RER protein, transmembrane RER proteins provide binding sites for the COPs
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Term
Describe the roles of 2 small GTPases in vesicle formation and homing in the RER-Golgi trafficking
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Definition
- SAR 1 or ARF –Regulates vesicle trafficking by noncovalently binding to cytosolic face of furture vesicle. switches w/ 2 conformations- one which binds GDP and is inactive (floats around the cytoplasm), a NEF (regulator- nucleotide exchange factor) exchanges GTP for GDP and a lipid tail is exposed so that it can now insert itself into the membrane and become active. GAP (GTPase activating protein) then exposes the GTPase in the SAR 1 or ARF so that it hydrolyzes GTP to GDP.
- it recruits Coat complexes
- Rabs GTPasas- recognition proteins on the vesicles- binds when has ATP. There is a Rab receptor on the target membrane. GTP hydrolysis releases Rab. After it recognizes, a SNARE (v-SNARE on the vesicle and t-SNARE on the membrane) further recognizes and binds it.
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Term
| Describe functions of peroxisomes |
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Definition
- The peroxisomes metabolize long-chain fatty acids to acetyl-CoA
- Produce plasmalogens, major constituents of myelin, and cholesterol.
- Peroxisomes also metabolize ethanol to acetaldehyde. The acetaldehyde is further oxidized, but excess alcohol can allow some acetaldehyde to escape into tissues and circulation, which can cause hangovers and memory loss. Found genetic link.
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Term
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Definition
- They reduce O2 to H2O2- which is used to oxidize other substrates. Excess H2O2 is removed by catalase, a peroxidase, by converting it to water and oxygen. Catalase also oxidizes toxins- phenols, formic acid, formaldehyde and alcohols.
- They also can convert an acyl group into an ether group which creates ether lipids.
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Term
| Explain how peroxisomes acquire newly-synthesized proteins |
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Definition
- Free polyribosomes in the cytosol create peroxisomal proteins which contain a sm. AA sequence: Peroxisome Targeting Signal 1 (PTS-1).
- A PTS-1 receptor binds to the PTS-1 in the cytosol and escorts to the perioxisome. It is equivalent to importin proteins (Importin is a type of protein that moves other protein molecules into the nucleus by binding to a specific recognition sequence, called the nuclear localization signal (NLS).
- PTS1R Receptor on the peroxisome binds to the PTS1R
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Term
| Explain why pex 3 and pex 19 are different from other peroxisomal proteins |
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Definition
- These are in yeast cells, and are required to make a new (de novo/ de buddo) perosisome. Budding from the ER.
- Pex 3 (a RER protein) is a receptor on the ER for pex 19 (cytosolic protein) which appears to be a COP like protein (forces breakage/deformation of the membranes). Together they form a vesicle from the RER.
- The cytoplasm produces other peroxisome proteins (E1-E6) that are recognized and imported by the Pex receptor.
- Peroxisomes may also divide, and import membrane lipids using lipid transfer proteins
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Term
| Explain what a “peroxisome proliferator” is |
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Definition
- Many compounds, called peroxisomes proliferator activators =PPA - man-made and fatty acids, can stimulate proliferation.
- They bind to nuclear receptors, peroxisome proliferator-activated receptors (PPARs)
- The receptors, then, accelerate production of peroxisomal mRNAs and proteins, i.e. they stimulate gene expression for more peroxisome proteins
- An excess number of peroxisomes particularly in the liver and can lead to hepatic cancer, b/c peroxidase cannot be activated as much.
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Term
| Describe how newly-synthesized proteins enter mitochondria |
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Definition
- Most mitochondrial proteins result from nuclear DNA and are produced in the cytoplasm and then imported into the mitochondria.
- Newly synthesized proteins contain a mitochondrial localization signal and are bound by chaparones so that they remain unfolded.
- They pass through membrane translocator proteins and have their signals cleaved and are then bound to mitochondrial chaperones. Translocators of the inner and outer membranes come together where the membranes are close, translocase inner membrane #23 (TIM 23) and translocase, outer membrane (TOM).
- From here they are folded if they are to remain in the matrix or they may contain an additional signal for translocation to the inner membrane before folding.
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Term
| Describe the environment inside a lysosome and what controls it. |
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Definition
- Lysosomes – vesicle w/ hydrolytic enzymes so to hydrolyze macromolecules to their subunits and recycle via transmembrane transport to the cytoplasm. This is very imp. during postnatal starvation.
- cathepsins - a class of globular lysosomal proteases, most of which contain an active-site cysteine residue.
- Lysosomes have a H+ ATPase (proton pump) that make the lysosome the most acidic environment in the cell at pH 4.5 to 5.5.
- Other ions are allowed out of the lysosome to keep it electrically neutral (no voltage potential).
- The diff. pH’s in the cell are not from the conc. of proton-ATPases, but from rates of leakage of protons from ea. organelle.
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Term
| Describe four methods for uptake into lysosomes. |
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Definition
- Endocytotic vesicles of lipids from the PM
- plasma proteins and receptors
- phagocytosis brings in bacteria and other junk, PM-coated particle fuses w/ lysosomes
- autophagy is how the cell breaks down organelles and other cell particles
- in the case of protons they can enter the lysosome through an ATP dependent pump.
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