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Medical Biochemistry > Ch. 15: Protein & a.a. Metabolism > Flashcards

Ch. 15: Protein & a.a. Metabolism Flashcards

1
Q

Why are His and Arg conditionally essential?

A

Required for optimal development & growth in infants

His essential for uremia pts (problem w/inflammation)

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2
Q

In liver dysfunction, which a.a. become essential?

A

Cys & Tyr

Cannot convert Met ➡️ Cys or Phe ➡️ Tyr

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3
Q

What is the metabolite of melamine? What problems can they cause?

A

Cyanuric acid

Form stones in kidneys ➡️ acute renal failure in infants

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4
Q

Why is it important to maintain nitrogen balance?

A

Absence of a.a. ➡️ pro synthesis stops, catabolism of unused a.a. ➡️ ⬆️ N loss in urine, ⬇️ growth

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5
Q

What is normal N balance? Negative? Positive?

A

Normal: Dietary intake of N = N loss
Negative: Dietary intake of N < N loss
Positive: Dietary intake of N > N loss

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6
Q

How are a.a. transported into cells?

A

Against concentration gradient

Semi-active process: coupled to Na+ dependent carrier system

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7
Q

What are the 5 a.a. transport systems in kidney & intestine?

A

1) Neutral
2) Acidic
3) Basic
4) Ornithine & cystine
5) Gly & Pro

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8
Q

Examples of inherited defects in a.a. transport?

A

1) Hartnup disease (neutral a.a.)
2) Cystinuria (cystine in urine)
3) Cystinosis (systemic cystine)

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9
Q

Effect of deficiency in GSH synthetase? (In gamma-glutamyl cycle for a.a. transport)

A

Accumulation of 5-oxoproline ➡️ excreted into urine ➡️ 5-oxoprolinuria

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10
Q

4 types of deamination reactions? Which is most important? Examples?

A

1) oxidative deamination (most important)
2) direct deamination: His
3) hydrolytic deamination: Asn, Gln
4) dehydrolytic deamination: Ser, Thr

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11
Q

4 examples of oxidative deamination? Which is major?

A

1) Glutamate dehydrogenase (major)
2) L-amino acid oxidase
3) D-amino acid oxidase
4) Monoamine oxidase (MAO)

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12
Q

Glutamate DH: metal ion cofactor? Requires what?

A

Zinc

NAD+ or NADP+

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13
Q

⬆️ [Glutamate DH] where?

A

Mitochondria of liver, heart, muscle, kidney

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14
Q

➕ modulators of glutamate DH?

A

ADP
GDP
some a.a.

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15
Q

➖ modulators of Glutamate DH?

A

ATP
GTP
NADH

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16
Q

Overall effect of transamination-deamination rxns depend on?

A

[substrate]

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17
Q

What is produced as by-product in transamination-deamination rxns? What happens to them?

A

1) NH3 (➡️ detoxified by: conversion to Gln & Asn or urea)
2) NADH (➡️ oxidized by ETC)

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18
Q

General steps of L-amino acid oxidase? Products?

A

Alpha a.a. ➡️ alpha-imino acid ➡️ alpha-keto acid
(Same enzyme at each step)

Alpha-keto acids, H2O2, NH4+

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19
Q

General steps of D-amino acid oxidase? Products? Where is this found?

A

Glycine ➡️ alpha-imino acid ➡️ glyoxylate
(Same enzyme each step)

Glyoxylate, H2O2, NH4+

Bacteria in gut (humans can’t have D-a.a. in body)

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20
Q

Steps of conversion from D-amino acids ➡️ L-amino acids? Enzymes?

A

D-a.a. ➡️ alpha-keto acid (D-a.a. Oxidase)

Alpha-keto acid ➡️ L-a.a. (Reamination via transaminase)

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21
Q

Norepinephrine (monoamine) ➡️ ? (via MAO)

Co-factors?

A

DOPGAL

FAD (➡️ FADH2)
H2O (➡️ NH4+)

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22
Q

2 possible products made from DOPGAL? Enzymes for each rxn?

A

1) DOPGAL ➡️ DOPEG (glycol) (aldehyde reductase)

2) DOPGAL ➡️ DOMA (acid) (aldehyde dehydrogenase)

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23
Q

General steps of dehydrolytic deamination?

Enzymes, co-factors?

A

Ser, Thr, or Homoserine ➡️ alpha-imino acid ➡️ alpha-keto acid

1) Uses specific dehydratase + pyridoxal P (H2O out)
2) NH3 out, H2O in

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24
Q

What is the most abundant a.a. in body? What synthesizes it?

A

Glutamine

Gln synthetase

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25
Q

Main steps of glu-gln cycle? (Using glu as neurotransmitter & recycle)

A

Signal ➡️ gln ➡️ glu (via glutaminase) ➡️ released ➡️ recycled back to gln (via gln synthetase)

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26
Q

What co-factor is important in transamination-aminotransfer rxns?

How is it bound to its apoenzyme?

A

Pyridoxal P

Carbonyl C reacts with epsilon-amino group of lysine residue ➡️ Schiff base

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27
Q

Important transamination-aminotransfer reaction?

A

a.a. + alpha-KG ➡️ alpha-keto acid + glu

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28
Q

All a.a. participate in transamination rxn EXCEPT?

A

Lys
Thr
Pro
OH-Pro

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29
Q

Alanine aminotransferase (ALT) same as? Substrates ➡️ products?

A

Glutamate pyruvate aminotransferase (GPT)

Ala + alpha-KG ➡️ pyruvate + glu

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30
Q

Aspartate aminotransferase (AST) same as? Substrates ➡️ products?

A

Glutamate oxaloacetate aminotransferase (GOT)

Asp + alpha-KG ➡️ oxaloacetate + Glu

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31
Q

Inhibitors of pyridoxal P? What do these cause?

A

Isonicotinic acid hydrazide
Hydralazine
Cycloserine

Inhibit transamination

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32
Q

Role of liver in a.a. metabolism?

A

1) Oxidize all a.a. EXCEPT BCAAs
2) a.a. Synthesis
3) urea synthesis

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33
Q

Role of skeletal muscle in a.a. metabolism?

A

1) metabolize ala, asp, glu, BCAAs

2) release ala, gln

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34
Q

Role of small intestine in a.a. metabolism?

A

1) metabolize dietary gln, glu, asn, asp ➡️ CO2 & H2O or lactate, ala, citrulline, NH3

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35
Q

Role of kidneys in a.a. metabolism?

A

1) release ser, ala
2) take up gln, pro, gly
3) acid/base regulation
4) alpha-KG ➡️ glucose or oxidized

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36
Q

Role of brain in a.a. metabolism?

A

1) take up BCAAs
2) glu-gln cycle
3) asp & gly = neurotransmitters
4) glu ➡️ GABA
5) tyr ➡️ dopamine, norepi, epi
6) trp ➡️ serotonin

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37
Q

How does brain use CHO, a.a., and lipids?

A

CHO: major fuel

a.a. & lipids: for major fxns

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38
Q

NH3 toxic to brain (not other tissues) ➡️ why?

A

1) Hydrophobic: interferes w/membrane integrity, signal transduction
2) Depletes glu (needed as neurotransmitter)
3) Depletes TCA cycle intermediates

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39
Q

How does NH3 cause anorexia, sleep disturbances, & pain insensitivity?

A

⬆️ trp transport across BBB & accumulation of its metabolites (serotonin, quinolinic acid)

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40
Q

Urea synthesis: where do the 2 N come from?

What is the precursor for both N?

A

1) free NH3
2) Asp

Glu: (1) by Glu DH, (2) by AST

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41
Q

How much ATP consumed in urea synthesis?

A

4 ATP

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42
Q

Where is urea formed? ➡️ urine?

A

Made in liver ➡️ kidneys ➡️ urine

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43
Q

What is the rate-limiting step of urea synthesis in hepatocytes?

Enzyme?

A

1st step: NH4+ + CO2 ➡️ carbamoyl P

Carbamoyl P synthase I (CPS I)

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44
Q

What substrate stimulates rate-limiting step of urea cycle?

How is it formed? What ➕ and ➖ this rxn?

A

N-acetylglutamate

Acetyl-CoA + glu (via N-acetylglutamate synthase)
➕: Arg
➖: N-acetylglutamate

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45
Q

Where in hepatocyte does urea cycle take place?

A

Mitochondrial matrix: carbamoyl P + ornithine ➡️ citrulline

Cytosol: citrulline moved out of MT ➡️ rest of cycle ➡️ ornithine moves into MT

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46
Q

Which enzyme in urea cycle is only found in liver? Fxn?

A

Arginase

Arginine + H2O ➡️ ornithine + urea

47
Q

CPS I: cellular location? Pathway involved? Source of nitrogen?

A

Mitochondria

Urea cycle

Ammonia

48
Q

CPS II: cellular location? Pathway involved? Source of nitrogen?

A

Cytosol

Pyrimidine synthesis

Gamma-amide group of gln

49
Q

3 fates of fumarate: to TCA cycle?

A

Fumarate ➡️ malate ➡️ MT ➡️ TCA cycle

50
Q

3 fates of fumarate: to urea cycle?

A

Fumarate ➡️ malate ➡️ OAA (via malate DH) ➡️ asp ➡️ urea cycle

51
Q

3 fates of fumarate: to glucose? (Major)

A

Fumarate ➡️ malate ➡️ OAA (via malate DH) ➡️ PEP ➡️ glucose

52
Q

3 causes of hyperammonemia?

A

1) inborn errors of ureagenesis & organic acidemias
2) liver immaturity (transient HA of newborn)
3) liver failure (hepatic encephalopathy)

53
Q

OCT enzyme deficiency: how is it diagnosed? What does it cause?

A

Allopurinol

Blocks pyrimidine synthesis ➡️ Orotidinuria (⬆️ orotidine in urine)

54
Q

Sodium benzoate: leads to? How many N lost?

A

Elimination of hippurate (benzoylglycine)

1 N

55
Q

Phenylacetate or phenylbutyrate: leads to? How many N lost?

A

⬆️ excretion of phenylacetylglutamine

2 N

56
Q

If NAGS enzyme deficiency, what can be given to activate CPS I?

A

N-carbamoylglutamate

57
Q

What is the most common cause of hyperammonemia in adults?

A

Liver disease (due to ethanol abuse, infection, cancer) ➡️ ⬇️ ability to detox NH3

58
Q

How are non-essential a.a. synthesized?

A

From carbon skeletons from lipid & CHO sources

From transformations involving essential a.a.

59
Q

Precursors of: glu, asp, ser, gly, tyr?

A 
Alpha-ketoglutaric acid
Oxalo-acetic acid
3-phospho-glyceric acid
Ser
Phe
60
Q

Precursors of: pro, ala, cys, arg, gln, asn?

A 
Glu
Pyruvic acid
Met &amp; Ser
Glutamate-gamma-semialdehyde
Glu
Asp
61
Q

Arg is a precursor for which metabolites?

A

NO
Phosphocreatine
Spermine
Ornithine

62
Q

Arg ➡️ citrulline

Enzyme? Co-factors?

A

NO synthase

FMN, FAD, BH4, Fe2+, heme complex

63
Q

How does NO cause vasodilation?

A

➕ modulator of guanylate cyclase (converts GTP ➡️ cGMP)

cGMP ➡️ smooth muscle relaxation

64
Q

Which a.a. is gly converted to?

What type of metabolism is this?

A

Ser

One carbon metabolism

65
Q

Disorders of glycine metabolism: nonketotic hyperglycinemia?

A

Inborn error due to defect in gly cleavage enzyme complex ➡️ ⬆️ gly in body fluids (CSF)

66
Q

Disorders of gly metabolism: ketotic hyperglycinemia?

A

Occurs in propionic acidemia (dysfxn of CoA metabolism ➡️ ketone bodies generated)

67
Q

Disorders of gly metabolism: primary hyperoxaluria type I?

A

Deficiency of cytosolic alpha-ketoglutarate-glyoxylate carboligase ➡️ ⬆️ glyoxylate ➡️ converted to oxalate (forms crystals)

68
Q

Creatine synthesis requires which 3 a.a.?

A

Arg, gly, SAM (S-adenosyl-homocysteine)

69
Q

3 diff products obtained from Ser?

A

3PG
Pyruvate
Gly

70
Q

Proline metabolism disorders: Ornithinemia?

A

Ornithine aminotransaminase deficiency

71
Q

Proline metabolism disorders: hyperprolinemia?

A

Proline oxidase deficiency

72
Q

Proline metabolism disorders: hydroxyprolinemia?

A

Hydroxyproline oxidase deficiency

73
Q

Folate deficiency ➡️ accumulation of? (Synthesized from which a.a. ?)

What other deficiencies cause this accumulation?

A

FiGlu (N-Formiminoglutamate)

His

Vit B12, Glu formimino-transferase deficiencies

74
Q

Important fxn of branch-chained a.a. metabolism?

A

Yield high energy (amino fats)

75
Q

What DH complex also similar to PDH and alpha-KG DH?

A

BCKADH (branched-chain alpha-ketoacid DH)

E1 diff, E2 & E3 same

76
Q

Products from Leu metabolism?

A

Acetoacetate

Acetyl CoA

77
Q

Products from Ile metabolism?

A

Propionyl CoA

Acetyl-CoA

78
Q

Product of Val metabolism? Requires which cofactor at which step?

A

Succinyl CoA

Vit B12 (methylmalonyl CoA ➡️ Succinyl CoA)

79
Q

Main fxn of SAM?

A

Methyl donor (in protein & cysteine synthesis)

80
Q

Which vit needed to methylated homocysteine ➡️ methionine?

A

Vit B12

Methyl donor is N5-methyl H4 folate

81
Q

CH3 transfer rxn w/SAM ➡️ SAH

acceptor: guanidinoacetic acid ➡️ ?

82
Q

CH3 transfer rxn w/SAM ➡️ SAH

acceptor: nicotinamide ➡️ ?

A

N-methylnicotinamide

83
Q

CH3 transfer rxn w/SAM ➡️ SAH

acceptor: norepi ➡️ ?

84
Q

CH3 transfer rxn w/SAM ➡️ SAH

acceptor: phosphatidylethanolamine ➡️ ?

A

Phosphatidylcholine (3 rounds of methylation)

85
Q

CH3 transfer rxn w/SAM ➡️ SAH

acceptor: N-acetyl-serotonin ➡️ ?

86
Q

How does Cys regulate its own formation?

A

Acts as allosteric ➖ of cysteine gamma lase (?)

87
Q

Cys required to form which products?

A

Glutathione

CoA-SH

88
Q

Major end products of Cys metabolism?

A

Taurine: conjugated w/bile in liver ➡️ excreted by kidneys

Sulfate: converted to PAPS (sulfate donor)

Pyruvate

89
Q

Abnormalities involving sulfur-containing a.a.:

Hypermethioninemia: which enzyme deficient?

A

Met adenosyltransferase

90
Q

Abnormalities involving sulfur-containing a.a.:

Hypermethioninemia, hyperhomocysteinemia, homocystinuria: which enzyme deficient?

A

Cystathionine beta-synthase

91
Q

Abnormalities involving sulfur-containing a.a.:

Homocystinuria: which vitamins are deficient?

A

Folate

Vit B12

92
Q

Abnormalities involving sulfur-containing a.a.:

Cystathioninuria: which enzyme deficient?

A

Cystathionine gamma-lyase

93
Q

Abnormalities involving sulfur-containing a.a.:

Cerebral atrophy, lens dislocation: which enzyme deficient?

A

Hereditary sulfate oxidase

94
Q

Abnormalities involving sulfur-containing a.a.:

Cystinuria: disorder with what transport?

A

Renal or GI a.a. transport disorder

95
Q

Abnormalities involving sulfur-containing a.a.:

Cystinosis: which transport defective? Causes what?

A

ATP-dependent cystine efflux from lysosomes ➡️ cystine crystals deposited in tissues

96
Q

Which 4 vitamins are required in homocysteine metabolism?

A

FH4
Vit B12
Pyridoxine
Riboflavin

97
Q

What causes hyperhomocysteinemia?

A

Def of enzymes in homocysteine remethylation / transsulfuration pathways

98
Q

What are clinical manifestations of severe hyperhomocysteinemia? (Due to genetic defect in which enzyme?)

A

cystathionine beta-synthase

Atherosclerosis, thromboembolic complications, skeletal abnormalities, ectopia lentis, mental retardation

99
Q

Metabolism of homocysteine: steps to enter FH4 into pathway?

Enzymes?

A

Folate ➡️ FH4 (dihydrofolate reductase, 2 NADPH)
FH4 + Ser➡️ methylene FH4 + gly (ser OHmethyl transferase, vit B6)
Methylene FH4 ➡️ Methyl FH4 (MTHFR)
Methyl FH4 + homocysteine ➡️ met

100
Q

What inhibits conversion of folate ➡️ FH4?

A

Methyltrexate

101
Q

Steps of methylation cycle of homocysteine metabolism?

Enzyme & co-factor needed in methylation of homocysteine?

A

Met + ATP ➡️ SAM ➡️ SAH ➡️ homocysteine + methyl FH4 ➡️ Met

Methyl transferase (methylcobalamin)

102
Q

Phe hydroxylase: where found? Requires what co-factors?

What other enzyme is needed in tyr & trp hydroxylation?

A

Liver, kidneys

BH4, NADPH

Dihydropteridine reductase

103
Q

PKU: deficiency of what enzymes/co-factors?

A

Phe hydroxylase, BH4, dihydropteridine reductase

104
Q

PKU: what accumulates in urine? How is it generated?

How many types of PKU are there?

A

Phenylpyruvate
Phe ➡️ phenylpyruvate (transaminase)

Types I, II, III

105
Q

Phe ➡️ Tyr: involves BH4 ➡️ quinonoid-dihydrobiopterin

Major path to regain BH4? Minor path?

A

Direct via Dihydropteridine reductase + NADPH

With intermediate (7,8-dihydrobiopterin) via dihydrofolate reductase

106
Q

Deficiency of what enzyme ➡️ alkaptonuria?

Involved in metabolism of what a.a.?

What builds up in urine ➡️ black pee

A

Homogentisic acid oxidase

Phe, Tyr

Homogentisic acid (oxidized w/air exposure)

107
Q

Phe & Tyr are precursors for what?

A

T4, melanin, norepi, epi

108
Q

Melanin is precursor to synthesize what?

A

Eumelanins

109
Q

Abnormalities of tyr metabolism: Tyrosinemia type II

Deficiency in which enzyme? Leads to what conditions?

A

Hepatic cytosolic tyr aminotransferase

Hypertyrosinemia, tyrosinuria

110
Q

Abnormalities of tyr metabolism: Tyrosinosis

Deficiency of what enzyme? Leads to what conditions?

A

Fumarylacetoacetate hydrolase

Abnormal liver fxn, renal tubular dysfxn, anemia, vit D-resistant rickets

111
Q

Abnormalities of tyr metabolism: Albinism

Cause? Some forms are from deficiency in what enzyme?

A

Lack of melanin production (hypomelanosis)

Tyrosinase

112
Q

Trp is involved in synthesis of what?

A

Nicotinic acid (amide): needed for NAD+ and NADP+ synthesis
5-hydroxytryptamine (serotonin)
Melatonin
Formate

113
Q

Abnormalities of Trp metabolism: carcinoid tumor?

A

⬆️ serotonin synthesis

114
Q

Abnormalities of Trp metabolism: Hartnup disease?

A

Disorder of renal tubular, intestinal absorption of Trp & other neutral a.a.

Medical Biochemistry (23 decks)

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