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Foundations 1 > Nitrogen Metabolism I and II > Flashcards

Nitrogen Metabolism I and II Flashcards

1
Q

nitrogen balance

A

in a normal human adult N(in) = N(out)

in a growing child, adolescent, pregnancy N(in) > N(out)

eating too little protein or lacking essential amino acids N(in) < N(out)

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2
Q

three sources for the amino acid pool

A

degradation of body proteins

dietary proteins

synthesis of non-essential amino acids

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3
Q

three fates of amino acids in the amino acid pool

A

synthesis of body proteins

precursors for essential nitrogen-containing small molecules

conversion to clucose, glycogen, fatty acids, or CO2

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4
Q

two main routes for amin removal

A

alanine aminotransferase transfers amino group from alanine to a-KG to make glutamate

aspartate aminotransferase transfers amino groups from glutamate to oxaloacetate to form aspartate

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5
Q

What coenzyme is required for aminotransferase reactions?

A

pyridoxal phosphate, a derivative of vitamin B6

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6
Q

What are the main sources for the nitrogen cycle?

A
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7
Q

What amino acid undergoes rapid oxidative deamination, and what is the enzyme that catalyzes this?

A

glutamate, glutamate dehydrogenase

uses NAD+ or NADP+ as the coenzyme

GTP is an allosteric inhibitor and ADP is an allosteric activator

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8
Q

What happens to D-amino acids from plants?

A

metabolized by D-amino acid oxidase in a FAD-dependent reaction in peroxisomes

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9
Q

Which amino acids do not undergo transamination reactions?

A

lysine, threonine, proline, and HO-proline

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10
Q

alanine aminotransferase reaction

A
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11
Q

aspartate aminotransferase reaction

A
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12
Q

glutamate dehydrogenase reaction

A
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13
Q

Describe the glucose/alanine cycle.

A

transfers nitrogen to the liver, ammonia in the blood is toxic so adds it onto alanine for transport

done primarily in muscle tissue

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14
Q

Describe the process of transporting nitrogen through blood as glutamine.

A

primarily used by peripheral tissues, but if there is a lot of tissue breakdown, muscle will use this process as well

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15
Q

Describe the oxidative deamination process by amino acid oxidases in peroxisomes.

A

Flavoprotein and FAD are the same

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16
Q

Describe the urea cycle.

A

Ornithine is an amino acid not used in proteins and is recycled

fumarate is a byproduct, connecting this with the TCA cycle

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17
Q

three mechanisms that regulate the urea cycle

A

substrate availability in a feed-forward mechanism

allosteric activation of carbamoyl phosphate synthease I (CPSI) by N-acetylglutamate (NAG)

induction/repression of urea cycle enzyme synthesis during high protein diet or during starvation

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18
Q

regulation of CPSI

A

main method of regulation, senses how much amine is coming in

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19
Q

How are the urea and TCA cycles linked?

A
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20
Q

Name and describe how the glucogenic amino aicds contribute to the TCA cycle.

A

carbons of these amino acids can be used in gluconeogenesis:

Thr, Gly, Trp, Ala, Ser, Cys, Asp, Asn, Tyr, Phe, Val, Ile, Met, Arg, His, Gln, Pro

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21
Q

Identify and describe how the ketogenic amino acids feed into the TCA.

A

ketogenic amino acids made acetyl CoA or acetoacetate:

Trp, Thr, Lys, Ile, Leu, Tyr, Phe

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22
Q

asparagine to oxaloacetate

A
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23
Q

a-KG from glutamine

A
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24
Q

a-KG from proline

A

type I hyperprolinemia - defect in proline dehydrogenase

typw II hyperprolinemia - defect in glutamate semialdehyde dehydrogenase

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25
Q

a-KG from arginine

A

hyperarginemia - defect in arginase

gyrate atrophy of the choroid and retina - mutations in ornithine-aminotransferase

26
Q

a-KG from histidine

A

glutamate formimino transferase uses folate, so deficiency will cause high levels of Figlu

27
Q

pyruvate from alanine

A
28
Q

pyruvate from serine

A
29
Q

pyruvate from cystine and cysteine

A

cystine is a dimer of cysteine

PAPS is used as a sulfate donor for the synthesis of sulfated proteoglycans

30
Q

propionyl CoA from methionine and threonine

A

propionyl CoA can feed into the TCA cycle through conversion to succinyl CoA

S-adenosyl-L-methionine is important in single carbon transfer reactions

31
Q

propionyl CoA by valine and isoleucine

A

oxidative decarboxylation by branched-chain alpha-keto acid dehydrogenase complex

deficincies in this enzyme result in maple syrup urine disease caused by accumulatiuon of branched-chain alpha-keto acids in theurine, giving it a sweet odor

occurs primarily in peripheral tissues and not liver

32
Q

acetyl-CoA and acetoacetate from leucine

A

blockage of enzyme also causes maple syrup uring disease

also occurs primarily in peripheral tissues instead of liver

33
Q

acetyl-CoA from tryptophan

A

first step of the process requires vitamin B6

34
Q

fumarate, acetyl CoA and acetate from tyrosine

A

type II tyrosinemia, neonatal tyrosinemia, alkaptonuria, type I tyrosinemia

35
Q

lysine degradation

A

produces a dicarboxylic acid which can undergo beta-oxidation

36
Q

synthesis of non-essential amino acids

A

asparagine, aspartate, glycine, serine, cysteine, alanine, glutamate, glutamine, proline, arginine

37
Q

serine from glycolysis intermediates

A
38
Q

glycine from serine

A

folate as cofactor

major reaction is serine to glycine

39
Q

cysteine from serine and methionine

A
40
Q

proline from glutamate

A

glutamate semialdehyde dehydrogense is important

41
Q

synthesis and degradation of spartate and asparagine

A
42
Q

tyrosine from phenylalanine

A

phenylketonuria is a disease due to deficiency in phenylalanine hydroxylase

leads to alternative pathways which give urine particular odor

43
Q

nucleoside

A

base with sugar

44
Q

nucleotide

A

phosphorylated nucleoside

45
Q

purine biosynthesis frome ribose 5-phosphate

A

requires folic acid

first reaction is important

R5P comes from PPP

end result is inosine monophosphate

46
Q

AMP and GMP from IMP

A
47
Q

Describe the regulation of de novo purine nucleotide biosynthesis.

A

AMP, GMP, ADP, and GDP all regulate the intial steps of purine biosynthesis

48
Q

Describe the regulation involved in balancing ATP and GTP levels

A
49
Q

salvage of purine bases

A

Lesch-Nyhan syndrome - complete deficiency of HGPRT, unable to salvage hypoxanthine or guanine leads to productio of excess uric acid

HGPRT = hypoxanthine-guanine phosphoribosyl transferase

50
Q

biosynthesis of pyrimidines

A

starts from glutamine and CO2, ends up as UDP, which can be converted into TMP or CTP

folate is a carbon donor

51
Q

interregulation of nucleotides

A
52
Q

synthesis of deoxyribonucleotides

A

maintains a blance of deoxyribonucleotides for DNA synthesis

high ATP levels can cause problems if not regulated such as in immunodeficiency disease as the result of an adenine deaminase deficiency

53
Q

degradation of purines

A

occurs in cells of intestinal mucosal cells of the small intestine with uric acid as the final product

gout - caused by high levels of uric acid in the blood, resulting in the deposition of monosodium urate in the joints

allopurinol can be used to treat by decreasing rate of degradation

54
Q

degradation of pyrimidines

A

eventually converted to succinyl CoA

55
Q

tetrahydrofolate (FH4)

A

the main coenzyme in accepting one carbon groups, once one-carbon groups reduced to methyl, carbon cannot be re-oxidized

have to get folate from diet

56
Q

sources of one-carbon groups

A

serine, glycine, formaldehyde, histidine, formate

57
Q

dTMP from dUMP

A

transfer of a one-carbon unit, uses TH4

cancer treatment dugs 5-fluorocuracil and methotrexate interfere with this pathway to kill dividing cells

58
Q

viatmin B12 (cobalamin

A

involved in transfer of methyl group to homocysteine to form methionine

also involved in rearrangement of L-methylmalonyl CoA to form succinyl CoA

59
Q

S-adenosylmethionine (SAM) from methionine

A

SAM is a major methyl donor for formation of methylated histones

methionine obtained from diet or produced from homocysteine

60
Q

The Methyl-Trap Hypothesis

A

vitamin B12 is required to take methyl group from FH4, if deficient for vitamin B12 or if methionine synthase is defective, the N5-methyl-Fh4 will accumulate and most of the folate in the body becomes trapped there, creating a functional folate deficiency

Foundations 1 (39 decks)

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