Q.60 Given below are two statements:
Statement–I: Ammonia is produced during catabolism of amino acids in muscle cells.
Statement–II: In muscle cells, ammonia is converted to urea and then excreted through kidney.
In the light of the above statements, choose the most appropriate answer from the options given below.
- Both Statement–I and Statement–II are true
- Both Statement–I and Statement–II are false
- Statement–I is true but Statement–II is false
- Statement–I is false but Statement–II is true
Correct Answer: Statement–I is true but Statement–II is false.
Ammonia is indeed generated in muscle during amino acid catabolism, primarily via AMP deaminase and glutamate metabolism, but muscle cells lack the urea cycle enzymes and instead detoxify ammonia primarily to glutamine, which is transported to liver/kidney.
Statement–I Analysis
Ammonia production occurs in muscle cells during amino acid catabolism through: (1) AMP deaminase (purine nucleotide cycle) during exercise, generating NH₃ from AMP → IMP; (2) glutamate deamination via glutamate dehydrogenase (minor); (3) branched-chain amino acid transamination producing glutamate, which can release ammonia. Muscle ammonia levels rise significantly during intense activity.
Statement–II Analysis
False: Muscle cells cannot convert ammonia to urea. The urea cycle (ornithine transcarbamylase, arginase, etc.) is liver-specific. Muscle detoxifies ammonia via glutamine synthetase: Glu + NH₄⁺ + ATP → Gln + ADP + Pi. Glutamine releases ammonia in liver (urea synthesis) and kidney (excretion as NH₄⁺), forming the Cahill/glucose-alanine cycles.
Option Breakdown
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Both true: Incorrect; Statement–II misrepresents muscle nitrogen metabolism.
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Both false: Wrong; Statement–I correctly describes ammonia genesis.
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Statement–I true, Statement–II false: Correct; muscle produces ammonia (I true) but converts to glutamine, not urea (II false).
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Statement–I false, Statement–II true: Invalid; both ammonia production and urea cycle absence are established.
Introduction to Muscle Ammonia Amino Acid Catabolism Urea
Muscle ammonia amino acid catabolism urea metabolism clarifies critical biochemistry: amino acid breakdown generates ammonia (Statement I true), but muscle lacks urea cycle enzymes, detoxifying via glutamine instead (Statement II false). This distinction defines tissue-specific nitrogen handling.
Ammonia Production Pathways
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Purine nucleotide cycle: AMP → IMP + NH₃ (exercise-activated)
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Glutamate metabolism: Transamination → glutamate → glutamine synthetase
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BCAA catabolism: Leucine/valine oxidation produces glutamate/NH₃
Muscle Ammonia Detoxification Reality
textMuscle: NH₃ + Glu + ATP → Gln → Blood → Liver (urea) / Kidney (NH₄⁺)
NOT: NH₃ → Urea (urea cycle absent)
Hyperammonemia during exercise causes fatigue; cirrhosis exacerbates via impaired liver detoxification.
Exam Context for Biochemistry
GATE Life Sciences tests tissue-specific metabolism: liver (urea cycle), muscle (glutamine), kidney (NH₄⁺ excretion). Glucose-alanine cycle links muscle glycolysis to hepatic gluconeogenesis, relevant to your plant physiology studies where nitrate assimilation follows analogous compartmentation principles.
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