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Biochemistry > Amino Acid Nitrogen And Urea Cycle > Flashcards

Amino Acid Nitrogen And Urea Cycle Flashcards

1
Q

Amino acid functions

A

. Protein synthesis

. Precursors for synthesis of specialized N-containing compounds

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2
Q

T/F there is long-term amino acid storage in body

A

F

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3
Q

Sources of amino acids

A

. Synthesis of nonessential amino acids
. Digestion and absorption of dietary protein
. Degradation (turnover) of body proteins

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4
Q

T/F most adults are in net nitrogen balance (N in = N out)

A

T

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5
Q

How do amino acids enter body pool?

A

. Cellular synthesis of nonessential amino acids
. Directions and absorption of dietary amino acids
. Degradation of body proteins

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6
Q

How are nonessential amino acids synthesized?

A

. Metabolism intermediates formed during glycolysis and TCA cycle

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7
Q

Essential amino acids

A 
. Phe
. Val
. Thr
. Trip
. Ile
. Met
. His
. Arg
. Leu
. Lys
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8
Q

Nonessential amino acids

A 
. Ser
. Gly
. Cys
. Ala
. Asp
. Asn
. Glu
. Gln
. Pro
. Tyr
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9
Q

Synthesis of Tyr from Phe

A

. Hydroxylation of Phe from diet via phenylalanine hydroxylase (PAH)
. Dependent on tetrahydrobiopterin (BH4)
. Rxn first step in catabolism of phe that forms fumarate and acetoacetate

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10
Q

What metabolic intermediate makes Ser

A

3-phosphoglycerate from glycolysis

. Gly and Cys made from Ser

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11
Q

What metabolic intermediate can form Ala

A

Pyruvate

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12
Q

What metabolic intermediate can form Aspartate?

A

Oxaloacetate

. Aspartate then can form asparagine

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13
Q

Aminotransferase enzymes

A

. Catalyze trans am inaction of alpha-Ketoacid intermediates to form Ala, Glu, and Asp
. Depends on vit. B6 (pyridoxal phosphate) for transfer of amino group

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14
Q

Amidation fo Aspartate

A

. Glutamine is nitrogen donor
. Done via Asparagine synthetase
. Needs ATP
. Forms asparagine

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15
Q

Amidation of glutamate

A

.done via glutamine synthetase
. Needs ATP
. Forms glutamine
. Ammonia is nitrogen donor

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16
Q

Synthesis of Pro and Arg from Glu

A

. Deamidation of Gln to Glu via glutaminase
. Glu then turns into Pro and Ornithine
. Ornithine turns into citrulline which then undergoes steps to form Arg

17
Q

Synthesis of Ser, Gly, and Cys from 3-phosphoglycerate

A

. 3-PG turns into Ser
. Ser dependent on THF and Vit. B6 forms Gly
. Ser dependent on Vit. B6 and homocysteine form cystathionine that forms Cys dependent on vit. B6 again

18
Q

Mechanism for transport of toxins ammonia w/in body

A

. Glu Gln conversation by glutamine synthetase/glutaminase

19
Q

Formation of homocysteine

A

. Formed during catabolism of Met

20
Q

Absorption of dietary protein in stomach

A

. HCL denatures proteins
. Pepsinogen is secreted, undergoes conformational change from low pH autoactivation via limited proteolytic to form active pepsin
. Pepsin further activates other pepsinogen
. Initiates breakdown of dietary protein to shorter polypeptides

21
Q

Digestion of dietary protein in small intestine

A

. Pancreatic enzymes activated via limited proteolysis initiated by enteropeptidase
. Each activated enzyme hydrolyzes specific peptide bonds of chains making oligopeptides
. Oligopeptides degraded to free amino acids via aminopeptidases in brush border

22
Q

Enteropeptidase

A

. Extracellular enzyme on luminal surface of intestinal epithelial cells
. Activates trypsinogen to trypsin
. Trypsin activates more trypsinogen and other zymogens

23
Q

Trypsin action

A

. Hydrolyzes internal peptide bonds where carboxylase group is provided by Arg or Lys

24
Q

Absorption of amino acids from small intestine

A

. Free amino acids and some di and tri-peptides absorbed
. Specific transporters on intestinal epithelial cell surface
. Di and tri-peptides absorbed and then hydrolyzed to free amino acids w/in cell
. Only free amino acids released into portal circulation

25
Q

Lab evaluation of exocrine pancreatic function

A

. Pancreatic elastase measured through fecal elastase

. Presence of this means exocrine dysfunction

26
Q

Degradation of body proteins

A

. Daily turnover of 300-400g protein
. Degraded via proteases in lysosome (ATP-independent) or via ubiquitin-proteasome system in cytosol (ATP-dependent)
. Amino acids enter body pool for utilization

27
Q

Removal of amino acid N from Glu

A

. Glu undergoes oxidative deamination to make Ketoglutarate and ammonia
. Done via glutamate dehydrogenase (GDH)
. Needs NADPH
. Reaction can go both ways

28
Q

Other than Glu, what are other sources of ammonia

A

. Bacterial breakdown of urea in intestine

29
Q

Role of Ala and Glu in transporting amino acid N to liver

A

. N removed during aminoa acid catabolism in peripheral tissues is brought to liver for detoxification
. Ala and Glu transport N from skeletal muscle

30
Q

What is major extrahepatic site for amino acid catabolism?

A

Skeletal muscle

31
Q

Besides transporting N, what else does Ala deliver to liver?

A

Carbon atoms for hepatic gluconeogenesis

32
Q

Detoxification of amino acid N in liver

A

. Done via urea cycle or Glu synthesis in perivenous hepatocytes

33
Q

Percentage of N detoxified through urea synthesis?

A

90%

34
Q

Number of reactions in urea cycle

A

5

35
Q

Urea cycle

A

. Low-affinity high capacity mechanism
. Found in periportal hepatocytes
. N from ammonia or Asp and carbon from bicarbonate are incorporated into urea
. ATP-dependent
. Irreversible
. Complete cycle only completed in liver (some reactions w/in cycle can be done in other tissues)
. Net rxn: NH4 + Asp + 3ATP + H2O -> Urea + Fumarate = 2ADP + AMP + 2Pi + 2 PPi
. Overall NH4 + Asp + 3ATP -> urea

36
Q

Where is glutamine transported to release ammonia?

A

From liver to kidney

37
Q

PH regulation w/ urea cycle during acidosis

A

. Drop in pH inhibits periportal urea synthesis via dec. transport of Glu into hepatocytes and inhibition of glutaminase
. Inc. in perivenous synthesis of Glu to prevent hyperammonemia
. Inhibition of urea cycle preserve bicarbonate

38
Q

PH regulation during alkalosis by urea cycle

A

. Urea synthesis inc. and Glu synthesis dec. causing inc. consumption of bicarbonate

Biochemistry (64 decks)

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