Chat with AIExam 18: Amino Acid Oxidation and the Production of Urea
There are bacteria for which alanine can serve as the chief energy source; they oxidize the carbon skeleton of this amino acid, thereby generating ATP. Describe the first step in alanine degradation; show any cofactors that participate.
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Answered by Examlex AI CopilotThe first step in alanine degradation is the conversion of alanine to pyruvate through the action of the enzyme alanine transaminase. This reaction involves the transfer of an amino group from alanine to α-ketoglutarate, forming pyruvate and glutamate. The cofactor that participates in this reaction is pyridoxal phosphate (PLP), which is derived from vitamin B6. PLP acts as a coenzyme and is essential for the transamination reaction to occur. This step is crucial for the subsequent metabolism of pyruvate, which can enter the citric acid cycle to generate ATP through oxidative phosphorylation.
Describe the three different forms of nitrogen by which different organisms dispose of excess nitrogen obtained in the diet. Give examples of organisms that produce these different forms.
(86) Answered by Examlex AI CopilotThe three different forms of nitrogen by which different organisms dispose of excess nitrogen obtained in the diet are ammonia, urea, and uric acid.
Ammonia is the most toxic form of nitrogen and is produced by aquatic organisms such as fish and amphibians. These organisms excrete ammonia directly into the water through their gills or skin.
Urea is a less toxic form of nitrogen and is produced by mammals, including humans. It is excreted in urine and requires less water for disposal compared to ammonia.
Uric acid is the least toxic form of nitrogen and is produced by birds, reptiles, and insects. It is excreted as a paste or solid, which requires minimal water for disposal and is suitable for organisms living in arid environments.
Overall, different organisms have evolved different forms of nitrogen disposal to suit their specific environmental and physiological needs.
Which statement is FALSE regarding pyridoxal phosphate?
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VerifiedE
Both glutamine and alanine transport nitrogen in the bloodstream. Why might be it be considered an advantage to transport glutamine instead of alanine?
(81) Explain why one might provide high concentrations of the amino acid Arg to patients who have a deficiency in one of the first three enzymes of the urea cycle.
(83) Show the reaction in which ammonia is formed from glutamate; include any required cofactors and/or intermediates.
(78) Which substance directly donates a nitrogen atom for the formation of urea during the urea cycle?
(74) Which compound is used in single-carbon transfer reactions?
(82) Which statement is TRUE regarding the branched-chain -keto acid dehydrogenase complex?
(79) Carbamoyl phosphate synthase I is allosterically activated by what molecule?
(75) Which substance is NOT involved in the production of urea from NH4+ via the urea cycle?
(84) Deamination of most amino acids in the liver is accompanied by the conversion of:
(68) Which reaction involving an amino acid CANNOT be catalyzed via a PLP-dependent mechanism?
(79) Serotonin is produced from the metabolism of which amino acid?
(71) The human genetic disease phenylketonuria (PKU) can result from:
(69) Why does a mammal go to all of the trouble of making urea from ammonia rather than simply excreting ammonia as many bacteria do?
(69) The bacterium responsible for gastric ulcers, Helicobacter pylori, survives the acidic pH of the stomach surprisingly well. It does so in part by synthesizing and excreting large amounts of the enzyme urease, which hydrolyzes urea to bicarbonate and ammonia. Explain how these reaction products lead to a less acidic environment for H. pylori.
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