Chapter 23: Urea Cycle

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24 Terms

1
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What is the key reaction in the degradation of many amino acids?

transamination

2
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What are the two steps of transamination?

transaminase produces an alpha-keto acids

glutamate dehydrogenase regenerates alpha-ketoglutarate and produces ammonia

3
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What happens in aminotransferase?

the NH3+ and double bonded O "switch" places

4
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Glutamate dehydrogenase reaction

Major route for oxidative deamination

Regenerates the amino acceptor (α-ketoglutarate) and provides ammonia, either for re-utilization or disposal as urea

glutamate + NAD+ + H2O > α-ketoglutarate + NADH + NH3

5
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pyridoxal phosphate (PLP)

The active coenzyme form of vitamin B6 (6 forms)

6
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How is the pyridoxine cofactor bound to the enzyme? How is the binding spot displaced?

bound via lysine to the active site and is displaced by substrate binding

7
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What is the committed step of the urea cycle?

the formation of the carbamoyl phosphate

8
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What is the first step of the urea cycle?

coupling of ammonia with bicarbonate

9
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What is the second step of the urea cycle?

formation of citrulline

10
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What is the third step of the urea cycle?

process: formation of arginosuccinate (from citrulline + aspartate)

enzyme: arginosuccinate synthase

11
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What is the fourth step of the urea cycle?

arginosuccinate is cleaved into arginine and fumarate

12
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What is the fifth step in the urea cycle?

process: formation of ornithine + urea (from arginine)

enzyme: arginase

13
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Where does the urea cycle take place?

cytosol and mitochondrial matrix

14
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what is the key intermediate that links the urea cycle to the citric acid cycle?

arginosuccinate

converted to arg which is used in the urea cycle and fumarate which is converted to oxaloacetate in the citric acid cycle

15
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What is the "fate" of oxaloacetate?

transamination forms aspartate which is used in the urea cycle and biosynthesis

gluconeogenesis to form glucose

citric acid cycle to form ATP

16
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What are the glucogenic amino acids?

alanine, cysteine, glycine, serine, threonine, asparagine, aspartate, methionine, valine, arginine, glutamate, glutamine, histidine, proline

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What are the ketogenic amino acids?

leucine, lysine

18
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Which are both?

phenylalanine, isoleucine, tryptophan, tyrosine

19
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transamination of alanine and alpha-ketoglutarate produces what?

pyruvate and glutamate

20
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What are the two pathways of aspartate?

oxaloacetate via transamination or fumarate via the urea cycle

21
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What does glutaminase do?

converts glutamine to glutamate and NH4+ and then to alpha-ketoglutarate

22
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What are the metabolic intermediates if the ketogenic amino acids?

acetyl CoA and Acetoacetyl CoA

23
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What is an acceptor group for amino acids during catabolism?

alpha-ketoglutarate

24
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How is the urea cycle connected to gluconeogenesis?

fumarate and oxaloacetate