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31 Cards in this Set
- Front
- Back
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Polypeptides are synthesized by _____?
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ribosomes
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Where are polypeptides bound for secretion synthesized?
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ribosomes ass. w/ RER
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What is transcription?
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DNA -> mRNA
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What is a codon?
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A sequence of 3 consecutive DNA bases: one amino acid
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What is translation?
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mRNA -> protein
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What does translation require?
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adaptor molecules (tRNA, ribosomes [ribosomal protein, rRNA])
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What are the subunits of the ribosome?
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Large (60s) and small (40s)
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What are they composed of
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rRNA and protein
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How many steps are involved in translation?
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3
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To which end of the previous A.A. is the new A.A. attached to?
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carboxyl end
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During the elongation phase, an __________ molecule binds with the codon at the ___ site of the ribosome?
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amino-acyl tRNA; A
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What does this pairing result in?
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GTP hydolysis of the elongation factor
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What ensures that the correct A.A. is being added to the chain (a translational proofreading)?
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A delay in the time from when the amino-acyl tRNA binds and the amino acid is added to the chain allows for assurance of the correct anticodon.
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What inactivates elongation factors?
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phosphorylation by kinases
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Therefore, protein synthesis is indirectly regulated by ______
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the kinases that inactivate elongation factors
1.insulin 2.IGF 3.angiotensin II 4.glutamate 5.AMP 6.intracellular free A.A.'s |
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What type of cells commonly have many free polysomes?
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erythroblasts; synth. lots of protein for internal use
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What type of cells have many ER-bound polysomes?
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cells that synthesize proteins for export
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What is the Signal Hypotesis?
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mRNA's of proteins destined for secretion have a sequence (approx. 20 A.A.'s) that directs the mRNA/ribosome complex to be translocated to the ER.
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What enzyme cleaves the signal sequence?
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signal peptidase
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What molecule recognizes the signal ER sequence?
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Signal-recognition particle (SRP)
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Why does translation pause after SRP binding to the signal sequence?
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To allow time for travel to ER membrane
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What is the complex that allows the polypeptide chain to be injected to the lumen of the ER?
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Sec61
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Once in the ER, what protein modifications can take place?
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1. Signal Sequence cleaved by signal peptidase
2. Disulfide bridge formation - cysteines bond. Maintains s(x) integrity of folded proteins 3.N-Linked Glycosylation |
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How does N-linked glycosylation occur?
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a precursor oligosaccharide is attached to Asn on the polypeptide chain.
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What catalyzes this reaction?
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Oligosaccharyl transferase
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What is the purpose of this transfer?
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Marks the state of protein folding. Chaperones will bind to incompletely folded proteins, prevents bad folding.
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What happens if the protein in the ER folds improperly?
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Translocated back into cytosol (via Sec61) for proteosomal proteolysis (death!)
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What post-translational modifications happen at the Golgi?
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1.Removal of precursor oligosaccharide
2.Addition of sugars 3.Proteolytic processing of pro-proteins 4.Addition of glycosaminoglycan (GAG) to proteoglycans |
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Where does protein sorting take place?
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Trans golgi network
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What are the two modes of secretion for proteins intended to be exported?
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Constitutive - not a response to signal; move straight to membrane
Regulated - restrained until a signal arrives (hormone, etc.) |
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What do lysosomal proteins bind to before leaving the golgi?
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mannose-6-phosphate receptors in trans-golgi network
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