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IUSM Biochemistry > Amino Acid Degradation/Urea Cycle > Flashcards

Amino Acid Degradation/Urea Cycle Flashcards

1
Q

What is secreted by parietal cells in the stomach?

A

HCl

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2
Q

What is secreted by chief cells in the stomach?

A

Pepsinogen

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3
Q

What class of enzyme is pepsinogen?

A

zymogen

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4
Q

What is the active form of pepsinogen?

A

pepsin

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5
Q

What changes pepsinogen into its active form pepsin?

A

low pH

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6
Q

What does pepsin do?

A

Acts as an endopeptidase, cleaving peptide bonds to form smaller peptides and some free aa

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7
Q

What side group does pepsin prefer?

A

CO group provided by an aromatic or acidic amino acid

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8
Q

Where are pancreatic zymogens activated??

A

small intestine

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9
Q

What cellular mechanism absorbs amino acids?

A

Na+ transport proteins

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10
Q

What disease is characterized by an inability to absorb amino acids in the kidney due to defective Na+ amino acid pumps?

A

Hartnup disease

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11
Q

Why do patients with hartnup disease often show symptoms of pellagra?

A

Because they can’t absorb normal amounts of tryptophan, which is a precursor for niacin synthesis.

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12
Q

Patients with Cystinuria have problems absorbing which amino acid?

A

Cystine

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13
Q

What molecule tags proteins for degradation intracellularly?

A

ubiquitin

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14
Q

What protein degrades proteins inside the cell tagged by ubiquitin?

A

26S proteasome

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15
Q

Besides in the cytosol with proteasomes, where can proteins be degraded in the cell?

A

lysosomes

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16
Q

What type of enzymes degrade proteins in lysosomes and what is their optimal pH?

A

acid hydrolases

pH 5

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17
Q

What are two examples of enzymes that degrade proteins extracellularly?

A 
Serine proteases
matrix metalloproteases (Ex collagenases)
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18
Q

Where does the urea cycle take place?

A

Liver

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19
Q

What is the only organ with all of the enzymes for urea synthesis?

A

Liver

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20
Q

Which is very toxic to the CNS, ammonia or ammonium ion?

A

ammonia (in equilibrium with ammonium ion)

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21
Q

What are the two nontoxic compounds that ammonia is converted to?

A

Urea and glutamine

22
Q

What are the two types of reactions used to remove the amino groups in amino acid catabolism?

A

Transamination and deamination

23
Q

What type of reaction moves amino groups into glutamate?

A

Transamination

24
Q

What type of reaction directly releases ammonium ions?

A

Deamination

25
Q

What type of enzymes catalyze the transfer of an alpha-amino group from an amino acid to an alpha-ketoacid during transamination?

A

Aminotransferases (transaminases)

26
Q

Serum levels of what two amino acid transferases are used to evaluate liver damage?

A 
Aspartate aminotransferase (AST)
Alanine aminotransferase (ALT)
27
Q

What cofactor is required for aminotransferase reactions?

A

pyridoxal phosphate (PLP)

28
Q

What vitamin is PLP derived from?

A

B6

29
Q

Are transamination reactions reversible?

A

Yes

30
Q

What are the three types of deamination reactions?

A

Oxidative Deamination
Hydrolytic Deamination
Nonoxidative deamination

31
Q

Which deamination reaction is PLP dependent?

A

nonoxidative deamination

32
Q

Oxidative deamination is a reaction in liver mitochondria and is catalyzed by what enzyme?

A

glutamate dehydrogenase

33
Q

What two side aa side chain groups are targeted by hydrolytic deamination?

A

glutamine and asparagine

34
Q

What is an important deamination reaction in the kidney?

A

hydrolytic damination of glutamine by glutaminase

35
Q

What two amino acid side chains undergo nonoxidative damination?

A

Serine

Threonine

36
Q

What are the enzymes of the two major nonoxidative damination reactions?

A

serine dehydratase
threonine dehydratase
both use PLP prosthetic group

37
Q

What molecules transport most nitrogen from other tissues to liver or kidney?

A

Alanine

Glutamine

38
Q

Glutamine synthetase is one of three human enzymes that can fix ____ in a carbon compound

A

NH4+

39
Q

Why do mutations in glutamine synthetase cause severe brain malformation is newborns?

A

Glutamate is a neural toxin, large amounts of it accumulate in the brain

40
Q

What conditions would produce a postive-nitrogen balance in a patient? Need to increase protein synthesis

A

Physical trauma
Growing child
excreted N < consumed N

41
Q

What conditions would produce a negative-nitrogen balance in a patient? Body protein degraded to synthesis essential proteins

A

protein malnutrition or starvation

excreted N > consumed N

42
Q

What is the expectation of most all urea cycle defects?

A

hyperammonemia

There is no other way to get rid of NH4+

43
Q

What enzyme is involved in the rate limiting step of the urea cycle?

A

Carbamoyl phosphate synthetase 1 (CPS 1)

44
Q

Where is CPS1 located?

A

mitochondria

45
Q

What does CPS require as a cofactor?

A

N-acetylglutamate (NAG)

allosteric activator

46
Q

Where is NAG synthesized?

A

Mitochondria by N-acetylglutamate synthase

47
Q

NAG synthase is positively regulated by the presence of?

A

Argenine

48
Q

Which form of CPS 1 is active? the dimer or the monomer?

A

monomer

49
Q

What does CPS1 reaction require?

A

2 ATP

NH3 from deamination rxns

50
Q

What molecule is the first and last step of urea synthesis?

A

Ornithine

IUSM Biochemistry (11 decks)

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