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33 Cards in this Set
- Front
- Back
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How can excess amion acids be stored or burned? |
By converstion into fats and sugars |
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Upon ingestion of food, hormones signal chief cells to secrete ______ and parietal cells to secrete _____ |
Chief cells secrete pepsinogen Partietal cells secrete HCl |
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What is the primary stomach protease? How is this protease excreted? At what pH does this protease have optimal activity |
Pepsin is the primary protease secreted as zymogen pepsinogen that unfolds in the stomach where it has maximal activity at pH=2 |
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The primary stomach protease preferentially cleaves at what amino acids? |
Phenyalanine Tyrosine Tryptophan Leucine |
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What organs secretes most intestinal proteases? |
Pancreas |
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What protein from the duodenum initiates proteolytic cascades activating pancreatic zymogens?
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Enteropeptidase |
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What pump is used to actively transport peptides from the lumen into the intestinal epithelium? |
Sodium/Potassium ATPase's |
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How is cellular protein degradation different from dietary protein degradation? |
Cellular proteins are degraded via the ubiquitin system |
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What is a Degron? Give examples |
Degrons are amino aciid sequences that signal degradation. They can be PEST sequences of N-terminal residues |
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Explain the Ub degradation mechanism |
1) Ubiquitins carboxyl end is conjugated to AMP at the expense of PPi 2) Activated Ub is transferred to E1 at the expense of AMP with formation of thioester bond to enzyme 3) E2 forms a thioester with activated Ub replacing E1 4) E2 transports Ub to E3 which has target bound 5) E3 catalyzes addition of activated Ub lysine of target forming a amide bond. Repeat |
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Describe the proteasome structure |
1 catalytic core (20S) + 2 regulatory subunits (19S) that resembles a barrel with caps on the ends |
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What is the function of the reglatory caps of the proteasome
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1) Recognition of the Ub chains 2) Cleavage of Ub by isopeptidase 3) Unfolding of target protein and feeding into the catalytic core |
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Why does the proteasome cap hydrolyze ATP? |
The regulatory cap hydrolyzes ATP to unfold the protein and to induce conformational changes needed to allow entry of unfolded protein into catalytic core |
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Processive degradation continues until only until what remains? |
Processive degradation continues until only amino acids and small peptides remain |
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What must occur in order to amino acids to be catabolized for energy? |
Alpha amino group needs to be removed |
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How do we remove a nitrogen as needed in phase 2 of amino acid degradation? |
1) Aminotransferase transfers the alpha-amino group of an amino acid to an alpha-ketoglutarate to form Glutamate 2) Glutamate is oxidized to (C=NH3+) Schiff-base intermediate 3) Schiff base is hydrolyzed to a ketone with release of NH4+ |
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What steps of the urea cycle that occur in the mitochondria. What does this achieve? How much energy is required? |
Step 1 which is the synthesis of Carbamoyl Phosphate from Bicarbonate Step 2 which is synthesis of Citrulline from ornithine Requires 2 ATP |
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Describe the synthesis of carbamonyl phosphate? What enzyme catalyzes this? |
1) Phosphorylation of bicarbonate's carboxylic acid by ATP 2) Attack of phosphoryl bond by NH3+, losing Pi 3) 2nd phosphorylation of hydroxyl by ATP Catalyzed by Carbamoyl Phosphate Synthetase |
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Descrie the synthesis of Ornithine transcarbamolyase. Why enzyme catalyzes this? |
1) Ornithine's lysine attacks phosphoester bond and binds Acyl unit of Carbamoly Phosphate by a amide bond with loss of inorganic phosphate Ornithine transcarbamolyase catalyzes this |
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What steps of the urea cycle occur in the cytoplasm. What do these steps achieve? How much energy is requires? |
Step 3 condenses citrulline and aspartate to Arginosuccinate at the expense of 1 ATP Step 4 cleaves arginosuccinate to Arginine and Fumarate with preservation of carbon skeleton in fumarate Step 5 hydrolyzes Arginine to ornithine and urea |
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Describe the synthesis Arginosuccinate. What enzyme catalyzes this? What step is this? |
Citrulline's acyl carbonyl forms a schiff base with aspartate's alpha-amino at the expense of ATP to yield arginosuccinate Catalyzed by Arginosuccinate synthetase Step 3 of the urea cycle |
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What is step 4 in the Urea cycle. Describe the mechanism. What enzyme catalyzes this? |
Arginosuccinate's terminal Schiff-base is cleaved to Arginine + Fumarate by Arginosuccinate |
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What is the final step of the urea cycle? Describe the mechanism. What enzyme catalyzes this? |
Arginine from step 4 is hydrolyzed to ornithine and urea by arginase |
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Why is the regeneration of ortnithine is the final step of the urea cycle significant? |
Ornithine is needed in step 2 to form citrulline |
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What is the overall reaction of the urea cycle? |
CO2 + NH4+ + 3 ATP + Asp + 2H2O -> Urea + 2 ADP + PPi + AMP + PPi + Fumarate |
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What organ catalyzes most of the removal of nitrogen and generation of urea? What organ excretes it? |
Liver removes the nitrogen Kidneys excrete it |
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What does high and low urine urea content suggest? What does high blood urea levels meam? |
Low urea content in urine suggests malnourishment or kidney failure High urea content in the the urine suggests protein overload High blood urea suggests that your liver is degrading protein but kidneys aren't excreting |
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Why would a cell use the urea cycle? |
If carbon is needed for fuel |
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What happens to the products of step 4 of the urea cycle? |
The arginine proceeds to hydrolysis yielding urea anf ornithine Fumarate is converted to malate and used in the krebs cycle to generate energy via gluconeogenesis |
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What is the role of glycolysis in amino acid synthesis? |
Pyruvate can be converted to Alanine, Serine, and Cysteine which can be further converted into other amino acids |
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How can the degradation of threonine lead to the generation of other amino acids? |
Threonine can be converted to pyruvate via a ketobutyrate intermediate which can then be used in the immediete synthesis of Alanine, Serine, and Cysteine and also contribute to further amino acids through more steps |
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AA carbon skeletons are ______genic and ______genic. Why do we refer to them as this? |
Gluconeogenic because AA's can be used to generate pyruvate or other glycotic intermediates and ketogenic because the amino acids can be used to generate Acetoacetyl CoA and Acetyl CoA |
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What glycotic intermediates can coem from amino acids? |
Oxaloacetate, Fumarate, Succinyl CoA, alpha-ketoglutarate, and pyruvate |
