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25 Cards in this Set
- Front
- Back
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There are two types of proteins synthesized in the ER:
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1. Transmembrane
2. Water soluble |
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50% of synthesized proteins are shuttled to:
The rest are shuttled to: |
Cytosol or ER
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What is the fate of proteins shuttled to the Cytosol?
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1. Retain in Cytosol
2. Mitochondria 3. Nucleus 4. Peroxisomes |
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What is the fate of proteins shuttled to the ER?
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1. Retain in ER or sent to golgi
2. Retain in golgi or: 3. To lysosomes or 4. Cell surface or 5. Secretory vesicles |
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Are there compartment specific (i.e. cytosolic vs ER) ribosomes?
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No
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What is SRP and what is its basic function?
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Signal Recognition Particle - it binds to a specific sequence on a growing peptide. When it does, the entire complex binds to the ER where protein synthesis is completed with the final product inside the ER
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SRP is composed of:
It binds to and causes: |
RNA and 6 proteins
Binds to signal sequence and ribosome and arrests translation (bc it'll fold otherwise and not make it through the pore to the ER |
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Define Tripartitie Domain Structure
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1. Hydrophilic amino-terminal domain which typically contains a net positive charge
2. A hydrophobic core domain with a minimum length of 7 residues 3. A polar carboxy-terminal domain of 4-6 residues |
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Where is the SRP receptor typically found?
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It is an integral membrane protein of the ER facing the cytoplasm.
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Does translocation of protein across ER membrane require energy?
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Yes, ATP
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Where are all integral proteins synthesized?
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In the ER
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In addition to a signal sequence, proteins destined to become integral proteins have this signal sequence:
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A stop transfer signal sequence
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What are stop-transfer sequences?
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They are hydrophobic alpha-helical sequences that function to anchor the protein in the membrane by forming helixes.
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What part of the Golgi separates nascent proteins according to their destination? (p451)
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The Trans Golgi Network
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Constitutive vs Regulated secretory pathway?
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The Constitutive pathway is common to all cells and continuously secretes its contents. The Regulated secretory pathway is only in certain cells and release contents only upon stimulation.
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What is a protein destined for the lysosome tagged with?
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Mannose-6-Phosphate
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How is Mannose-6-P added to a protein targeted to the lysosome?
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1. GlcNAc phosphotransferase enzyme addes GlcNAc to a mannose sugar.
2. GlcNAc glycosidase cleaves GlcNAc from the oligosaccharide - leaving behind the phosphate group. 3. Man-6-p is recognized by MPR receptors |
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Describe what happens in Lysosomal Storage Disorders (LSDs)
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Most often, its due to a single defective hydrolytic enzyme. Most often, this is due to the enzyme not being processed correctly and inserted into the lysosome. Material accumulates within enlarged lysosomes that are ultimately called inclusion bodies. Causes death
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What causes Mucolipidosis II (I-cell disease)? (p453)
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A deficiency in the enzyme GlcNAc phosphotransferase that generates the M6P tag on high mannose type N-linked oligosaccharides of proteins destined for the lysosome. Without the tag, they never make it lysosome and material that's supposed by degraded by this enzyme accumulates in the lysosome.
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Tetanus vs Botulism? (symptom-wise)
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Tetanus blocks release of inhibitory neurotransmiter GABA and causes spastic (T for Tight) paralysis or "lockjaw".
Botulinum blocks release of acetylcholine and causes flaccid paralysis. |
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What is the tetanus and botulism mechanism of action?
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The encode enzymes that cleave either the T-snare or V-snare to prevent vesicle/target binding.
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Define endocytosis:
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Internalization using plasma membrane and internalization.
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What does receptor-mediated endocytosis improve the efficiency of? (p456)
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It effectively increases the concentration of low concentration molecules via receptor mediated selective uptake of these compounds. Receptors bound to ligand tend to cluster too. Overall, its an efficient pathway for taking up specific macromolecules from the extracellular fluid.
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Which side of the bilayer does clathrin coat?
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The cytoplasmic side. So it actually forms a clathrin-coated vesicle.
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What must happen before a clathrin coated vesicle can fuse with an endosome?
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It must lose its clathrin coat.
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