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17 Cards in this Set
- Front
- Back
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What tags proteins for degradation in the proteasome? |
Poly-ubiquitination
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What happens to peptide fragments in protein degradation? |
Proteolysis --> aa
Some: left intact for biosynthesis, aa - N disposal by urea cycle C skeleton - glucose/glycogen synthesis, cellular respiration, fatty acid synthesis |
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What is ubiquitin? |
Tag Has an extended C terminus - linked to other proteins Liked - poly-Ub >4 effective signals for protein destruction # |
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What are the enzymes involved in Ub conjugation? |
E1 - Ub activating enzyme E2 - Ub conjugating enzyme E3 - Ub-protein ligase |
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Explain the process of Ub conjugation |
E1 - terminal COO- group linked to Cys residue in E1 - thioester bond E2 - Ub shuttled to Cys residue in E2 E3 - Catalyses transfer of Ub from E2 to target protein |
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How is target specificity achieved? |
Some E1, more E2, more E3 E3 provides most specificity PEST sequence - aa sequence in several cell cycle proteins, targets degradation Interaction of E3 with target protein - regulated by phosphorylation of target protein |
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What is the major site of degradation? |
Liver |
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Is amino group or carbon skeleton removed first? |
Amino group |
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What is the point of release in amino acid degradation? |
Glutamate Oxidatively deaminated to yield NH4+ |
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What does aminotransferase do? |
Catalyses transfer of an α-amino group from an α-amino acid to an α-ketoacid. Asp + a-ketoglutarate <--> oxaloacetate + Glu Reversible so also used for synthesis |
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What does glutamate dehydrogenase do? |
Releases NH3 from glutamate Activated by ADP/GDP Eq favours glutamate |
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What is toxic NH3 converted into? |
Urea |
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What is the alanine cycle? |
Amino groups and carbons from muscle are transported to the liver Muscles degrade aa for energy, N transaminated to pyruvate to form alanine. Alanine is shuttled to the liver - Benters the urea cycle and pyruvate --> glucose |
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What is the result of defects in the urea cycle? |
Hyperammonemia - elevated NH4+ in blood Protein restricted diet |
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How are carbon skeletons in aa degraded? |
C skeletons to major metabolic intermediates that can be converted into glucose or oxidised by TCA cycle |
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What is the source of non-essential amino acids?
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a-keto acids by transfer of existing aa group by aminotransferase Or diet |
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How is protein absorbed and digested? |
Enzymes in pancreas. Enzyme in stomach - pepsin, pH 2 Specific transporters - take up aa and peptides in intestinal cells |
