General transamination

amino acid + α-ketoglutarate ⇌ α-keto acid + glutamate

Transamination enzyme class

Aminotransferases/transaminases

Transamination coenzyme

PLP, pyridoxal phosphate, a vitamin B6 derivative

Reversibility of transamination

Transamination reactions are reversible

Role of transamination

Used in both amino acid degradation and amino acid synthesis

Most amino acids and transamination

Most amino acids undergo transamination

alanine + α-ketoglutarate ⇌ pyruvate + glutamate

Nitrogen from amino acid catabolism is collected into alanine

Alanine transport role

Alanine travels from muscle to liver carrying nitrogen

Alanine gives nitrogen back to glutamate and pyruvate can be used for gluconeogenesis

Glucose-alanine cycle

Nitrogen is transported from muscle to liver as alanine while pyruvate supports hepatic gluconeogenesis

glutamate + oxaloacetate ⇌ α-ketoglutarate + aspartate

High-yield role of AST in liver

Aspartate donates the second nitrogen of urea

Metabolic connection made by AST

AST connects amino acid metabolism, the Krebs cycle, and the urea cycle

Major amino acid degradation route

Transamination followed by glutamate deamination

Oxidative deamination of glutamate reaction

glutamate + NAD(P)+ + H2O ⇌ α-ketoglutarate + NH4+ + NAD(P)H + H+

Free ammonium release

Glutamate dehydrogenase releases free NH4+

Central reaction in transdeamination

Oxidative deamination of glutamate by glutamate dehydrogenase

Most amino acid α-amino groups converted to ammonia by

Transaminases followed by glutamate dehydrogenase

Glutamine synthetase reaction

glutamate + NH4+ + ATP → glutamine + ADP + Pi

Glutamine synthetase role

Incorporates free ammonia into glutamine and detoxifies ammonia

Glutamine as nitrogen transport

Glutamine transports nitrogen safely in blood

Glutamine in nucleotide synthesis

Glutamine is a nitrogen donor in nucleotide synthesis

glutamine + H2O → glutamate + NH4+

Glutaminase role in liver

Provides NH4+ for urea synthesis

Glutaminase role in kidney

Provides NH4+ for urinary acid excretion

Official ammonia transport topics

Glutamine synthesis, glutaminase in liver and kidney, and ammonia transport by glutamine and alanine

Disposes of toxic ammonia as urea

Urea cycle compartmentation

First steps occur in mitochondria and later steps occur in cytosol

First nitrogen source of urea

Free NH4+ enters as carbamoyl phosphate

Second nitrogen source of urea

Aspartate donates the second nitrogen

NH4+ + HCO3− + 2 ATP → carbamoyl phosphate + 2 ADP + Pi

Carbamoyl phosphate synthetase I

Nitrogen entry into urea cycle

Nitrogen enters as carbamoyl phosphate and aspartate

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Midterm 4 Final Review

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Front
General transamination
Back
amino acid + α-ketoglutarate ⇌ α-keto acid + glutamate
Front
Usual amino group acceptor in transamination
Back
α-ketoglutarate
Front
Usual nitrogen-containing product of transamination
Back
Glutamate
Front
Transamination enzyme class
Back
Aminotransferases/transaminases
Front
Transamination coenzyme
Back
PLP, pyridoxal phosphate, a vitamin B6 derivative
Front
Reversibility of transamination
Back
Transamination reactions are reversible
Front
Role of transamination
Back
Used in both amino acid degradation and amino acid synthesis
Front
Most amino acids and transamination
Back
Most amino acids undergo transamination
Front
Classic amino acid exceptions to transamination
Back
Lysine and threonine
Front
ALT reaction
Back
alanine + α-ketoglutarate ⇌ pyruvate + glutamate
Front
ALT role in muscle
Back
Nitrogen from amino acid catabolism is collected into alanine
Front
Alanine transport role
Back
Alanine travels from muscle to liver carrying nitrogen
Front
ALT role in liver
Back
Alanine gives nitrogen back to glutamate and pyruvate can be used for gluconeogenesis
Front
Glucose-alanine cycle
Back
Nitrogen is transported from muscle to liver as alanine while pyruvate supports hepatic gluconeogenesis
Front
AST reaction
Back
glutamate + oxaloacetate ⇌ α-ketoglutarate + aspartate
Front
High-yield role of AST in liver
Back
Aspartate donates the second nitrogen of urea
Front
Metabolic connection made by AST
Back
AST connects amino acid metabolism, the Krebs cycle, and the urea cycle
Front
Major amino acid degradation route
Back
Transamination followed by glutamate deamination
Front
Vitamin required for transamination
Back
Vitamin B6 as PLP
Front
Oxidative deamination of glutamate reaction
Back
glutamate + NAD(P)+ + H2O ⇌ α-ketoglutarate + NH4+ + NAD(P)H + H+
Front
Oxidative deamination enzyme
Back
Glutamate dehydrogenase
Front
Oxidative deamination location
Back
Mitochondria
Front
Oxidative deamination reversibility
Back
Reversible
Front
Free ammonium release
Back
Glutamate dehydrogenase releases free NH4+
Front
Glutamate dehydrogenase cofactors
Back
NAD+ or NADP+
Front
Glutamate dehydrogenase activator
Back
ADP
Front
Glutamate dehydrogenase inhibitor
Back
GTP
Front
Central reaction in transdeamination
Back
Oxidative deamination of glutamate by glutamate dehydrogenase
Front
Most amino acid α-amino groups converted to ammonia by
Back
Transaminases followed by glutamate dehydrogenase
Front
Reason free ammonia is transported safely
Back
Free ammonia is toxic
Front
Main blood transport form of ammonia from most tissues
Back
Glutamine
Front
Main blood transport form of ammonia from muscle
Back
Alanine
Front
Glutamine synthetase reaction
Back
glutamate + NH4+ + ATP → glutamine + ADP + Pi
Front
Glutamine synthetase role
Back
Incorporates free ammonia into glutamine and detoxifies ammonia
Front
Glutamine as nitrogen transport
Back
Glutamine transports nitrogen safely in blood
Front
Glutamine in nucleotide synthesis
Back
Glutamine is a nitrogen donor in nucleotide synthesis
Front
Glutaminase reaction
Back
glutamine + H2O → glutamate + NH4+
Front
Glutaminase role in liver
Back
Provides NH4+ for urea synthesis
Front
Glutaminase role in kidney
Back
Provides NH4+ for urinary acid excretion
Front
Official ammonia transport topics
Back
Glutamine synthesis, glutaminase in liver and kidney, and ammonia transport by glutamine and alanine
Front
Urea cycle purpose
Back
Disposes of toxic ammonia as urea
Front
Urea cycle tissue
Back
Mainly liver
Front
Urea cycle compartmentation
Back
First steps occur in mitochondria and later steps occur in cytosol
Front
First nitrogen source of urea
Back
Free NH4+ enters as carbamoyl phosphate
Front
Second nitrogen source of urea
Back
Aspartate donates the second nitrogen
Front
CPS I reaction
Back
NH4+ + HCO3− + 2 ATP → carbamoyl phosphate + 2 ADP + Pi
Front
CPS I full name
Back
Carbamoyl phosphate synthetase I
Front
CPS I location
Back
Mitochondria
Front
CPS I activator
Back
N-acetylglutamate
Front
CPS I role
Back
Urea cycle
Front
Nitrogen entry into urea cycle
Back
Nitrogen enters as carbamoyl phosphate and aspartate
Front
Direct precursor of urea
Back
Arginine
Front
Urea cycle step 1
Back
CPS I converts NH4+ + HCO3− to carbamoyl phosphate
Front
Urea cycle step 2
Back
OTC converts ornithine + carbamoyl phosphate to citrulline
Front
Citrulline transport in urea cycle
Back
Citrulline exits the mitochondria
Front
Urea cycle step 3
Back
Argininosuccinate synthetase converts citrulline + aspartate + ATP to argininosuccinate
Front
Urea cycle step 4
Back
Argininosuccinate lyase converts argininosuccinate to arginine + fumarate
Front
Urea cycle step 5
Back
Arginase converts arginine to urea + ornithine
Front
Urea cycle connection to Krebs cycle
Back
Urea cycle produces fumarate
Front
Fumarate fate from urea cycle
Back
Fumarate → malate → oxaloacetate
Front
Aspartate regeneration for urea cycle
Back
Oxaloacetate + glutamate via AST → aspartate
Front
Most serious consequence of urea cycle failure
Back
Hyperammonemia
Front
CPS I pathway
Back
Urea cycle
Front
CPS II pathway
Back
Pyrimidine synthesis
Front
CPS I location
Back
Mitochondria
Front
CPS II location
Back
Cytosol
Front
CPS I tissue
Back
Liver
Front
CPS II tissue
Back
Many or all cells
Front
CPS I nitrogen donor
Back
NH4+
Front
CPS II nitrogen donor
Back
Glutamine amide nitrogen
Front
CPS I activator
Back
N-acetylglutamate
Front
CPS II activators
Back
PRPP and ATP
Front
CPS I inhibitor
Back
None emphasized
Front
CPS II inhibitor
Back
UTP
Front
CPS I versus CPS II high-yield distinction
Back
CPS I is mitochondrial, hepatic, uses NH4+, and functions in the urea cycle; CPS II is cytosolic, broadly expressed, uses glutamine, and functions in pyrimidine synthesis
Front
Only ketogenic amino acids
Back
Leucine and lysine
Front
Memory for only ketogenic amino acids
Back
Leu and Lys are lonely ketogenic
Front
Amino acids both glucogenic and ketogenic
Back
Isoleucine, phenylalanine, tyrosine, tryptophan, and threonine
Front
Glucogenic amino acids
Back
All amino acids except the only ketogenic amino acids and the amino acids that are both glucogenic and ketogenic
Front
Common past-test ketogenic amino acid answer
Back
Leucine
Front
Essential amino acid mnemonic
Back
PVT TIM HALL
Front
Phenylalanine essential status
Back
Essential amino acid
Front
Valine essential status
Back
Essential amino acid
Front
Threonine essential status
Back
Essential amino acid
Front
Tryptophan essential status
Back
Essential amino acid
Front
Isoleucine essential status
Back
Essential amino acid
Front
Methionine essential status
Back
Essential amino acid
Front
Histidine essential status
Back
Essential amino acid
Front
Arginine essential status
Back
Essential amino acid with conditional importance because synthesis may be insufficient in children or recovery
Front
Leucine essential status
Back
Essential amino acid
Front
Lysine essential status
Back
Essential amino acid
Front
Cysteine conditional nonessentiality
Back
Cysteine is nonessential only if methionine is supplied
Front
Tyrosine conditional nonessentiality
Back
Tyrosine is nonessential only if phenylalanine is supplied
Front
PLP identity
Back
PLP is pyridoxal phosphate, a vitamin B6 derivative
Front
PLP role in transamination
Back
PLP is required for transamination
Front
PLP role in amino acid decarboxylation
Back
PLP is required for amino acid decarboxylation
Front
PLP role in serine/threonine dehydratase
Back
PLP is required for serine/threonine dehydratase reactions
Front
PLP role in serine to glycine
Back
PLP is required for serine → glycine
Front
PLP role in cysteine synthesis
Back
PLP is required for cysteine synthesis from homocysteine + serine
Front
PLP role in heme synthesis
Back
PLP is required by ALA synthase
Front
PLP role in dopamine synthesis
Back
PLP is required for DOPA → dopamine
Front
PLP role in GABA synthesis
Back
PLP is required for glutamate → GABA
Front
PLP role in histamine synthesis
Back
PLP is required for histidine → histamine
Front
Phenylalanine to tyrosine cofactor trap
Back
Phenylalanine → tyrosine does not require PLP; it requires BH4
Front
Explicit PLP roles in outline
Back
Transamination, serine/threonine deamination, serine → glycine, and decarboxylations
Front
Serine synthesis precursor
Back
3-phosphoglycerate, a glycolysis intermediate
Front
Serine role in protein synthesis
Back
Serine is used for protein synthesis
Front
Serine as glycine precursor
Back
Serine is a precursor of glycine
Front
Serine as cysteine precursor
Back
Serine is a precursor of cysteine
Front
Serine in phospholipid synthesis
Back
Serine contributes to phospholipid synthesis
Front
Serine metabolic classification
Back
Glucogenic amino acid
Front
Serine to glycine reaction
Back
serine + THF ⇌ glycine + N5,N10-methylene-THF + H2O
Front
Serine to glycine enzyme
Back
Serine hydroxymethyltransferase
Front
Serine hydroxymethyltransferase coenzymes
Back
THF and PLP
Front
Major source of THF one-carbon groups
Back
Serine → glycine
Front
Glycine role in collagen/protein synthesis
Back
Glycine is needed for collagen and protein synthesis
Front
Glycine role in glutathione
Back
Glycine is needed for glutathione synthesis
Front
Glycine role in bile acids
Back
Glycine is needed for bile acids
Front
Glycine role in heme
Back
Glycine is needed for heme synthesis
Front
Glycine role in purines
Back
Glycine is needed for purine nucleotide synthesis
Front
Glycine role in creatine
Back
Glycine is needed for creatine synthesis
Front
Major non-dietary source of glycine
Back
Serine, requiring THF
Front
THF function
Back
Carries one-carbon units
Front
N5,N10-methylene-THF role
Back
dTMP synthesis
Front
N10-formyl-THF role
Back
Provides purine ring carbons C2 and C8
Front
N5-methyl-THF role
Back
Remethylation of homocysteine to methionine
Front
Folate deficiency effect on dTMP synthesis
Back
Impaired dTMP synthesis
Front
Folate deficiency effect on purine synthesis
Back
Impaired purine synthesis
Front
Folate deficiency effect on DNA synthesis
Back
Impaired DNA synthesis
Front
Folate deficiency effect on rapidly dividing cells
Back
Rapidly dividing cells are impaired
Front
Methotrexate target
Back
Dihydrofolate reductase
Front
Methotrexate effect on THF
Back
Prevents regeneration of THF
Front
Methotrexate effect on nucleotide synthesis
Back
Strongly slows dTMP, AMP, GMP, and IMP synthesis
Front
Methotrexate least direct nucleotide effect
Back
UMP synthesis is least directly affected because UMP synthesis does not need THF
Front
Explicit one-carbon metabolism outline topics
Back
THF, serine → glycine, folate effects on nucleotide synthesis, and B12/folate reactions
Front
SAM synthesis
Back
Methionine + ATP → S-adenosylmethionine/SAM
Front
SAM major role
Back
Major methyl donor
Front
SAM methylation example norepinephrine
Back
Norepinephrine → epinephrine
Front
SAM methylation example guanidinoacetate
Back
Guanidinoacetate → creatine
Front
SAM methylation example phosphatidylethanolamine
Back
Phosphatidylethanolamine → phosphatidylcholine/lecithin
Front
SAM methylation example N-acetylserotonin
Back
N-acetylserotonin → melatonin
Front
SAM methylation example nucleic acids
Back
DNA/RNA methylation
Front
SAM conversion after methyl donation
Back
SAM → S-adenosylhomocysteine → homocysteine
Front
Major fates of homocysteine
Back
Remethylation to methionine and transsulfuration to cysteine
Front
Homocysteine remethylation reaction
Back
homocysteine + N5-methyl-THF → methionine + THF
Front
Homocysteine remethylation requirements
Back
Vitamin B12 and N5-methyl-THF
Front
Homocysteine transsulfuration pathway
Back
Homocysteine + serine → cystathionine → cysteine
Front
Homocysteine transsulfuration requirement
Back
PLP/B6
Front
Carbon skeleton source for cysteine
Back
Serine
Front
Sulfur source for cysteine
Back
Methionine via homocysteine
Front
Cysteine conditional essentiality
Back
Cysteine is nonessential only if methionine is available
Front
B12-dependent homocysteine reaction
Back
Homocysteine → methionine
Front
B12-dependent methylmalonyl-CoA reaction
Back
Methylmalonyl-CoA → succinyl-CoA
Front
B12 deficiency effect on homocysteine
Back
Increased homocysteine
Front
B12 deficiency effect on methylmalonic acid
Back
Increased methylmalonic acid
Front
Folate deficiency effect on homocysteine
Back
Increased homocysteine
Front
Folate deficiency effect on methylmalonic acid
Back
Normal methylmalonic acid
Front
B12 versus folate deficiency distinction
Back
B12 deficiency increases homocysteine and methylmalonic acid; folate deficiency increases homocysteine with normal methylmalonic acid
Front
Amino acids producing propionyl-CoA
Back
Valine, isoleucine, methionine, and threonine
Front
Propionyl-CoA carboxylase reaction
Back
Propionyl-CoA → D-methylmalonyl-CoA
Front
Propionyl-CoA carboxylase cofactor
Back
Biotin
Front
Methylmalonyl-CoA racemase reaction
Back
D-methylmalonyl-CoA → L-methylmalonyl-CoA
Front
Methylmalonyl-CoA mutase reaction
Back
L-methylmalonyl-CoA → succinyl-CoA
Front
Methylmalonyl-CoA mutase cofactor
Back
B12
Front
Methylmalonic acidemia cause
Back
Defect in methylmalonyl-CoA mutase or B12 metabolism
Front
Phenylalanine to tyrosine reaction
Back
phenylalanine + O2 + BH4 → tyrosine + H2O + BH2
Front
Phenylalanine hydroxylase function
Back
Converts phenylalanine to tyrosine
Front
Phenylalanine hydroxylase cofactor
Back
Tetrahydrobiopterin/BH4
Front
Classical PKU defect
Back
Phenylalanine hydroxylase deficiency
Front
Classical PKU effect on phenylalanine
Back
Increased phenylalanine
Front
Classical PKU metabolites
Back
Increased phenylpyruvate, phenylacetate, and phenyllactate
Front
Tyrosine in classical PKU
Back
Tyrosine becomes essential
Front
Classical PKU treatment
Back
Low phenylalanine diet plus tyrosine
Front
Nonclassical hyperphenylalaninemia cause
Back
BH4 deficiency
Front
BH4 role in phenylalanine hydroxylase
Back
Required for phenylalanine hydroxylase
Front
BH4 role in tyrosine hydroxylase
Back
Required for tyrosine hydroxylase
Front
BH4 role in tryptophan hydroxylase
Back
Required for tryptophan hydroxylase
Front
BH4 role in nitric oxide synthase
Back
Required for nitric oxide synthase
Front
BH4 and transamination
Back
BH4 is not required for transamination
Front
Tyrosine to epinephrine pathway
Back
tyrosine → L-DOPA → dopamine → norepinephrine → epinephrine
Front
Tyrosine hydroxylase cofactor
Back
BH4
Front
DOPA decarboxylase cofactor
Back
PLP
Front
Dopamine β-hydroxylase cofactors
Back
Vitamin C and Cu
Front
PNMT cofactor
Back
SAM
Front
Tyrosine derivatives
Back
Catecholamines, melanin, and thyroid hormones
Front
Melanin synthesis enzyme
Back
Tyrosinase
Front
Tyrosinase cofactor
Back
Copper
Front
MSUD full name
Back
Maple syrup urine disease
Front
Amino acids affected in MSUD
Back
Leucine, isoleucine, and valine
Front
MSUD defective step
Back
Oxidative decarboxylation of branched-chain α-keto acids
Front
MSUD defective enzyme complex
Back
Branched-chain α-ketoacid dehydrogenase
Front
High-yield MSUD wording
Back
MSUD is inability to catabolize α-keto acids derived from valine, isoleucine, and leucine
Front
Glutamate derivatives
Back
GABA, glutathione, glutamine, proline, and arginine/ornithine family
Front
GABA synthesis reaction
Back
glutamate → GABA + CO2
Front
GABA synthesis enzyme
Back
Glutamate decarboxylase
Front
GABA synthesis cofactor
Back
PLP
Front
Histamine synthesis reaction
Back
histidine → histamine + CO2
Front
Histamine synthesis enzyme
Back
Histidine decarboxylase
Front
Histamine synthesis cofactor
Back
PLP
Front
Tryptophan to melatonin pathway
Back
Tryptophan → 5-hydroxytryptophan → serotonin → melatonin
Front
Tryptophan hydroxylase cofactor
Back
BH4
Front
5-HTP decarboxylase cofactor
Back
PLP
Front
Melatonin methylation cofactor
Back
SAM
Front
NOS reaction
Back
arginine + O2 + NADPH → citrulline + NO + NADP+
Front
NOS requirements
Back
Heme iron, FAD, FMN, BH4, and NADPH
Front
NO signaling
Back
NO activates guanylate cyclase → increased cGMP → smooth muscle relaxation
Front
Creatine precursors
Back
Arginine, glycine, and methionine/SAM methyl group
Front
Creatine synthesis in kidney
Back
Arginine + glycine → guanidinoacetate + ornithine
Front
Creatine synthesis in liver
Back
Guanidinoacetate + SAM → creatine
Front
Creatine in muscle
Back
Creatine ↔ creatine phosphate
Front
Creatinine excretion significance
Back
Reflects muscle mass and kidney function
Front
Heme metabolism high-yield topics
Back
Heme structure/role, heme synthesis, ALAS regulation, lead inhibition, porphyrias, heme oxygenase, bilirubin conjugation, jaundice patterns, and iron transport
Front
Main heme synthesis substrates
Back
Succinyl-CoA and glycine
Front
Highest heme synthesis activity
Back
Erythroid cells and liver
Front
Heme synthesis in mature erythrocytes
Back
Mature erythrocytes do not synthesize heme
Front
First and rate-limiting heme synthesis step
Back
succinyl-CoA + glycine → δ-aminolevulinate/ALA + CO2 + CoA
Front
ALA synthase function
Back
Catalyzes the first and rate-limiting step of heme synthesis
Front
ALA synthase cofactor
Back
PLP/B6
Front
ALA synthase location
Back
Mitochondria
Front
Major regulated step of heme synthesis
Back
ALA synthase reaction
Front
ALAS1 tissue
Back
Liver/nonerythroid isoform
Front
ALAS1 inhibitor
Back
Heme/hemin
Front
ALAS1 inducer
Back
Drugs that increase cytochrome P450 demand
Front
Fasting effect on porphyria
Back
Fasting or low-calorie states can worsen porphyria
Front
Glucose effect on hepatic ALAS1
Back
Glucose suppresses hepatic ALAS1
Front
ALAS2 tissue
Back
Erythroid isoform
Front
ALAS2 stimulation
Back
Stimulated by erythropoietin
Front
ALAS2 regulation
Back
Regulated by iron availability through IRE/IRP
Front
Heme and globin synthesis
Back
Heme coordinates globin synthesis
Front
Heme synthesis first sequence step
Back
Succinyl-CoA + glycine → ALA by ALA synthase with PLP in mitochondria
Front
Heme synthesis second sequence step
Back
2 ALA → porphobilinogen by ALA dehydratase/porphobilinogen synthase in cytosol
Front
ALA dehydratase inhibitor
Back
Lead
Front
Heme synthesis third sequence step
Back
4 porphobilinogen → hydroxymethylbilane by porphobilinogen deaminase/hydroxymethylbilane synthase
Front
Heme synthesis fourth sequence step
Back
Hydroxymethylbilane → uroporphyrinogen III by uroporphyrinogen III synthase
Front
Heme synthesis fifth sequence step
Back
Uroporphyrinogen III → coproporphyrinogen III by uroporphyrinogen decarboxylase
Front
Heme synthesis sixth sequence step
Back
Coproporphyrinogen III → protoporphyrinogen IX by coproporphyrinogen oxidase
Front
Heme synthesis seventh sequence step
Back
Protoporphyrinogen IX → protoporphyrin IX by protoporphyrinogen oxidase
Front
Heme synthesis final step
Back
Protoporphyrin IX + Fe2+ → heme by ferrochelatase
Front
Ferrochelatase inhibitor
Back
Lead
Front
Lead poisoning inhibited enzymes
Back
ALA dehydratase and ferrochelatase
Front
Porphyria general principle
Back
Enzyme block in heme synthesis causes upstream intermediates to accumulate
Front
Cause of photosensitivity in porphyrias
Back
Porphyrinogens/porphyrins cause photosensitivity because light exposure causes ROS formation
Front
Cause of neurovisceral symptoms in porphyrias
Back
ALA/PBG accumulation causes neurovisceral symptoms
Front
Acute intermittent porphyria defect
Back
Porphobilinogen deaminase/hydroxymethylbilane synthase
Front
Acute intermittent porphyria accumulation
Back
ALA and porphobilinogen
Front
Acute intermittent porphyria symptoms
Back
Abdominal pain, neuropsychiatric symptoms, constipation, and possible dark/red urine
Front
Acute intermittent porphyria photosensitivity
Back
No photosensitivity because accumulating compounds are precursors, not porphyrins
Front
Acute intermittent porphyria triggers
Back
P450-inducing drugs, barbiturates, alcohol, fasting/low-calorie diet, hormones, infection, and surgery
Front
Congenital erythropoietic porphyria defect
Back
Uroporphyrinogen III synthase
Front
Congenital erythropoietic porphyria inheritance
Back
Autosomal recessive
Front
Congenital erythropoietic porphyria accumulation
Back
Uroporphyrin I and coproporphyrin I
Front
Congenital erythropoietic porphyria symptoms
Back
Severe photosensitivity, red urine, erythrodontia, and hemolytic anemia
Front
Porphyria cutanea tarda defect
Back
Uroporphyrinogen decarboxylase
Front
Porphyria cutanea tarda frequency
Back
Most common porphyria
Front
Porphyria cutanea tarda features
Back
Photosensitivity/blistering, hepatic involvement, and red/brown urine
Front
Priority porphyrias for exam
Back
Acute intermittent porphyria, congenital erythropoietic porphyria, and porphyria cutanea tarda
Front
Heme oxygenase reaction
Back
heme + O2 + NADPH → biliverdin + Fe3+ + CO
Front
Heme oxygenase function
Back
Converts heme to biliverdin, Fe3+, and CO
Front
Biliverdin reductase reaction
Back
Biliverdin → bilirubin
Front
Unconjugated bilirubin solubility
Back
Water-insoluble and lipid-soluble
Front
Unconjugated bilirubin transport
Back
Transported in blood bound to albumin
Front
Bilirubin conjugation reaction
Back
bilirubin + 2 UDP-glucuronic acid → bilirubin diglucuronide
Front
Bilirubin conjugation enzyme
Back
UDP-glucuronosyltransferase
Front
Conjugated bilirubin identity
Back
Direct bilirubin
Front
Conjugated bilirubin solubility
Back
Water-soluble
Front
Conjugated bilirubin excretion
Back
Excreted in bile
Front
Intestinal bilirubin metabolism
Back
Bilirubin glucuronides enter intestine and bacteria convert them to urobilinogens
Front
Urobilinogen fate
Back
Some is reabsorbed, urinary urobilin is produced, and stool stercobilin is produced
Front
Hemolytic jaundice blood bilirubin
Back
Increased unconjugated bilirubin
Front
Hemolytic jaundice urine urobilinogen
Back
Increased urine urobilinogen
Front
Hemolytic jaundice feces
Back
Dark or normal feces with increased pigment
Front
Hepatocellular jaundice blood bilirubin
Back
Increased unconjugated and conjugated bilirubin
Front
Hepatocellular jaundice urine urobilinogen
Back
Increased urine urobilinogen
Front
Hepatocellular jaundice feces
Back
Pale/clay possible
Front
Obstructive/cholestatic jaundice blood bilirubin
Back
Increased conjugated bilirubin
Front
Obstructive/cholestatic jaundice urine urobilinogen
Back
Decreased or absent urine urobilinogen
Front
Obstructive/cholestatic jaundice feces
Back
Pale/clay feces
Front
Bile duct blockage bilirubin trap
Back
Conjugated bilirubin accumulates in blood because liver can conjugate bilirubin but bile cannot drain
Front
Newborn jaundice cause
Back
Low UDP-glucuronosyltransferase
Front
Newborn jaundice bilirubin pattern
Back
Increased unconjugated bilirubin
Front
Newborn jaundice major risk
Back
Kernicterus because unconjugated bilirubin can cross the blood-brain barrier
Front
Iron metabolism study focus
Back
Transport logic rather than obscure details
Front
Non-heme iron absorption
Back
Dietary Fe3+ is reduced to Fe2+
Front
Vitamin C effect on iron absorption
Back
Vitamin C helps non-heme iron reduction and absorption
Front
DMT1 function
Back
Fe2+ enters enterocyte via DMT1
Front
Heme iron absorption
Back
Heme iron is better absorbed and enters through a heme carrier pathway
Front
Iron release from heme in enterocyte
Back
Iron is released inside the enterocyte
Front
Intracellular iron storage
Back
Stored as ferritin
Front
Iron export from cells
Back
Fe2+ exits through ferroportin
Front
Hephaestin function
Back
Oxidizes Fe2+ to Fe3+ near enterocytes
Front
Ceruloplasmin function
Back
Oxidizes Fe2+ to Fe3+ in plasma/macrophage context
Front
Blood iron transport
Back
Fe3+ binds transferrin
Front
Hepcidin function
Back
Causes ferroportin degradation
Front
High hepcidin effect
Back
Decreased iron absorption and decreased iron release from macrophages
Front
Vitamin C iron absorption trap
Back
"Vitamin C inhibits iron absorption" is false; vitamin C helps non-heme iron absorption
Front
Nucleotide metabolism high-yield overview
Back
Purines are built on PRPP; IMP branches to AMP/GMP; pyrimidine ring comes from aspartate + carbamoyl phosphate; CTP comes from UTP + glutamine; RNR makes dNDPs; dTMP uses methylene-THF; salvage uses APRT/HGPRT; purine degradation ends in uric acid; allopurinol inhibits xanthine oxidase
Front
Purine de novo synthesis concept
Back
Purine ring is built on ribose
Front
PRPP synthesis reaction
Back
ribose-5-phosphate + ATP → PRPP
Front
PRPP synthetase function
Back
Converts ribose-5-phosphate to PRPP
Front
PRPP synthetase activator
Back
Pi
Front
PRPP synthetase inhibitor
Back
Purine ribonucleotides
Front
Committed step of purine synthesis
Back
PRPP + glutamine → 5-phosphoribosylamine + glutamate + PPi
Front
Committed purine synthesis enzyme
Back
Glutamine-PRPP amidotransferase
Front
Glutamine-PRPP amidotransferase activator
Back
PRPP
Front
Glutamine-PRPP amidotransferase inhibitors
Back
IMP, AMP, and GMP
Front
Purine ring N1 source
Back
Aspartate
Front
Purine ring N3 source
Back
Glutamine
Front
Purine ring N9 source
Back
Glutamine
Front
Purine ring C4 source
Back
Glycine
Front
Purine ring C5 source
Back
Glycine
Front
Purine ring N7 source
Back
Glycine
Front
Purine ring C6 source
Back
CO2/HCO3−
Front
Purine ring C2 source
Back
N10-formyl-THF
Front
Purine ring C8 source
Back
N10-formyl-THF
Front
Purine direct source trap
Back
N-methyl-THF or asparagine are not direct sources of purine ring atoms
Front
IMP role in purine synthesis
Back
Branch point for AMP and GMP synthesis
Front
IMP to AMP requirements
Back
Aspartate and GTP
Front
AMP synthesis fumarate production
Back
Fumarate is produced during the adenylosuccinate lyase step
Front
IMP to GMP requirements
Back
Glutamine, ATP, and NAD+ in the IMP dehydrogenase step
Front
Energy rule for AMP synthesis
Back
AMP synthesis uses GTP
Front
Energy rule for GMP synthesis
Back
GMP synthesis uses ATP
Front
Reciprocal energy balancing
Back
AMP synthesis uses GTP and GMP synthesis uses ATP
Front
Purine salvage purpose
Back
Saves energy
Front
Purine salvage tissue importance
Back
Important in brain and nonhepatic tissues
Front
Purine salvage ribose donor
Back
PRPP
Front
APRT reaction
Back
adenine + PRPP → AMP
Front
HGPRT hypoxanthine reaction
Back
hypoxanthine + PRPP → IMP
Front
HGPRT guanine reaction
Back
guanine + PRPP → GMP
Front
Lesch-Nyhan syndrome defect
Back
HGPRT deficiency
Front
Lesch-Nyhan syndrome features
Back
Hyperuricemia/gout, neurologic dysfunction, and self-mutilation
Front
HGPRT deficiency effect on purine synthesis
Back
Increased de novo purine synthesis because PRPP accumulates and salvage fails
Front
Conversion of hypoxanthine to IMP or guanine to GMP
Back
HGPRT
Front
Final product of purine degradation in humans
Back
Uric acid
Front
Important purine degradation enzymes
Back
Purine nucleoside phosphorylase, adenosine deaminase, and xanthine oxidase
Front
Xanthine oxidase reaction
Back
hypoxanthine → xanthine → uric acid
Front
Allopurinol target
Back
Xanthine oxidase
Front
Gout cause
Back
Hyperuricemia with sodium urate crystals
Front
Classic gout joint
Back
Big toe
Front
Adenosine deaminase deficiency
Back
Severe combined immunodeficiency pattern with decreased T cells, B cells, and antibodies
Front
Pyrimidine de novo synthesis concept
Back
Pyrimidine ring is built first, then attached to PRPP
Front
First step of pyrimidine synthesis
Back
glutamine + CO2 + 2 ATP → carbamoyl phosphate
Front
Pyrimidine first-step enzyme
Back
CPS II
Front
CPS II location
Back
Cytosol
Front
CPS II inhibitor
Back
UTP
Front
CPS II activators
Back
PRPP and ATP
Front
Pyrimidine ring aspartate contribution
Back
N1, C4, C5, and C6
Front
Pyrimidine ring carbamoyl phosphate contribution
Back
C2 and N3
Front
Ultimate source of pyrimidine N3
Back
Glutamine via CPS II
Front
Pyrimidine pathway first condensation
Back
Carbamoyl phosphate + aspartate → carbamoyl aspartate
Front
Pyrimidine pathway sequence
Back
Carbamoyl aspartate → dihydroorotate → orotate → OMP → UMP → UDP → UTP → CTP
Front
Orotate reaction
Back
Orotate + PRPP → OMP
Front
OMP reaction
Back
OMP → UMP
Front
UMP activation pathway
Back
UMP → UDP → UTP
Front
CTP synthesis reaction
Back
UTP + glutamine + ATP → CTP
Front
UTP to CTP enzyme
Back
CTP synthetase
Front
Direct precursor of CTP
Back
UTP
Front
Nitrogen donor for CTP synthesis
Back
Glutamine
Front
Ribonucleotide synthesis principle
Back
All ribonucleotides are first made as ribonucleotides
Front
Ribonucleotide reductase reaction
Back
NDP → dNDP
Front
Ribonucleotide reductase substrates
Back
ADP, GDP, CDP, and UDP
Front
Ribonucleotide reductase requirements
Back
Thioredoxin, NADPH, and ribonucleotide reductase
Front
Ribonucleotide reductase activator
Back
ATP
Front
Ribonucleotide reductase inhibitor
Back
dATP
Front
Ribonucleotide reductase substrate trap
Back
Substrate is NDP, not NMP or NTP
Front
dTMP synthesis reaction
Back
dUMP + N5,N10-methylene-THF → dTMP + DHF
Front
dTMP synthesis enzyme
Back
Thymidylate synthase
Front
Thymidylate synthase inhibitor
Back
5-fluorouracil converted to FdUMP
Front
THF regeneration reaction
Back
DHF → THF by dihydrofolate reductase
Front
Dihydrofolate reductase requirement
Back
NADPH
Front
Dihydrofolate reductase inhibitor
Back
Methotrexate
Front
Methotrexate consequence
Back
Blocks purine synthesis and dTMP synthesis
Front
5-FU consequence
Back
Directly blocks thymidylate synthase
Front
Folate deficiency nucleotide consequence
Back
Impairs DNA synthesis
Front
Xenobiotics/P450 study priority
Back
Not emphasized in the official outline but appeared in past questions enough to memorize a mini-block
Front
Cytochrome P450 identity
Back
Monooxygenase system
Front
Phase I metabolism
Back
Often introduces or exposes functional groups, often by hydroxylation
Front
Phase II metabolism
Back
Conjugation increases water solubility
Front
UDP-glucuronic acid role
Back
Used in glucuronidation
Front
Acetaminophen overdose toxic product
Back
NAPQI
Front
NAPQI detoxification
Back
Detoxified by glutathione
Front
Grapefruit juice effect
Back
Inhibits intestinal CYP3A4
Front
Grapefruit juice drug-level consequence
Back
Increases levels of some drugs such as statins
Front
Benzopyrene identity
Back
Polycyclic aromatic hydrocarbon activated by P450
Front
Benzopyrene detoxification
Back
Can involve glutathione conjugation

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