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STEP1 > Metabolism Random > Flashcards

Metabolism Random Flashcards

1
Q

Disulfiram

A

inhibits ALDH (acetaldehyde dehydrogenase): this will cause buildup of acetaldehyde which causes the Sx of EtOH hangovers

used to discourage drinking

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2
Q

Fomepizole

A

inhibits ADH (alcohol dehydrogenase)

used as antidote For Overdoses of Methanol or Ethylene glycol

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3
Q

Ethanol metabolism pathway

A

Ethanol -> acetaldehyde (ADH) in cytosol -> acetate (ALDH) in mitochondria

Uses up a lot of NAD+ so you end up with a lot of NADH around

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4
Q

CYP2E1

A

used as overflow pathway when the regular ethanol metabolism system is overloaded in the MICROSOME

this enzyme also metabolizes a lot of other drugs (ex. Tylenol)

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5
Q

Consequences of ethanol metabolism

A
  1. increased NADH/NAD+ ratio
  2. energy depletion: TCA cycle is blocked, increased lactic acidosis
  3. Hypoglycemia: gluconeo. and glycolysis are blocked
  4. increased acetyl coA: FA synthesis accelerated, ketoacidosis
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6
Q

Rate limiting enzyme in glycolysis

A

PFK-1

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7
Q

Hexokinase vs. Glucokinase: location, Km, Vmax

A

Glucokinase: located in liver and beta cells of pancreas, has HIGH Km aka LOW affinity, has a HIGH Vmax aka works quickly

Hexokinase: located in most tissues except liver and beta cells of pancreas, has LOW Km aka HIGH affinity, has a LOW Vmax aka slower

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8
Q

End products of glycolysis

A

2 Pyruvate, 2 NADH, 2 ATP (4 total but 2 consumed)

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9
Q

Rate limiting enzyme for gluconeogenesis

A

Fructose 1,6 bisphosphatase

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10
Q

Pyruvate dehydrogenase complex function and cofactors

A

Links glycolysis and the TCA cycle

Requires TLC for Nancy:
Thiamine (B1)
Lipoic acid
CoA (B5)
FAD (B2)
NAD (B3)

Is activated when it is dephosphorylated by PDH phosphatase (ie during exercise)

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11
Q

Pyruvate dehydrogenase deficiency

A

Buildup of pyruvate that is shunted to lactate (via LDH) and alanine (via ALT)
X linked disorder
Lactic acidosis
Increase in serum alanine starting in infancy

Tx: increase ketogenic nutrients (fat, lysine, leucine)

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12
Q

HMP shunt purpose

A

provides a source of NADPH from glucose-6P
NADPH is required for glutathione reduction inside RBCs, fatty acid and cholesterol biosynth
Provides source of ribose (nucleotide synthesis; glycolytic intermediates
No ATP used OR produced

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13
Q

HMP reactions (oxidative and nonoxidative)

A

Oxidative is irreversible, uses G6PD, and produces NADPH

Non oxidative is reversible, uses transkelotases and phosphopentose isomerase, requires B1, and produces G3P and ribose

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14
Q

G6PD deficiency

A

X linked recessive
NADPH needed for glutathione reduction
Glutathione detoxifies free radicals in RBCs
Hemolytic anemia bc of poor RBC defense against oxidizing agents

Oxidizing agents: fava beans, sulfonamides, primaquine, antiTB drugs
Infection can ppt hemolysis bc inflamm response produces free radicals–>oxidative damage

Peripheral smear: heinz bodies (denatured Hb ppts within RBC), bite cells (phagocytic removal of heinz bodies by splenic macrophages)

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15
Q

Fructose metabolism pathway

A

Fructose–(fructokinase–>fructose 1 P–(adolase B)–>…met continues…

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16
Q

Essential fructosuria

A

Autosomal recessive
Defect in fructokinase
Benign, asymptomatic bc fructose is not trapped in cells
Fructose in blood and urine

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17
Q

Fructose intolerance

A

Autosomal recessive
Deficiency in adolase B
Fructose 1 P accumulates–>decrease in available phosphate–>inhibition of glycolysis and gluconeogenesis
Symptoms after consumption of fruit, juice, honey
Negative urine dipstick (tests for glucose only)
Reducing sugar can be detected in urine

Symptoms: hypoglycemia, jaundice, cirrhosis, vomiting

Tx: decrease fructose and sucrose intake

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18
Q

Galactose metabolism pathway

A

Galactose can either go:
Galactose–(galactokinase)–>galactose 1 P–(uridyltransferase)–>glucose 1 P–>glycolysis

OR

galactose –(aldose reductase)–>galactitol

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19
Q

Galactokinase deficiency

A

Galacitol accumulates if galactose is present in diet
Mild
Symptoms begin when infant breast/formula feeds
Galactosemia, galactosuria, infantile cataracts

Infant may have failure to track objects or to develop a social smile

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20
Q

Classic galactosemia

A

Severe
Absence of galactose-1-phosphate uridyltransferase
Aut recess
Damage due to accumulation of galacitol, which accum in the lens of the eye, and P depletion
Failure to thrive, jaundice, hepatomeg, cataracts, intellect disability
Can –> e coli sepsis in neonates

Tx: exclude galactose and lactose from diet

FAB GUT pneumonic:
fructose adolase B, galactose to uridyltransferase

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21
Q

Sorbitol

A

Alcohol counterpart of glucose

glucose–(aldose reductase)–>sorbitol–(sorbitol dehydrogenase)–>fructose

Traps glucose in the cell; tissues that do not have sorbitol dehydrogenase get intracell sorbitol accumulation
Schwann cells, retina, kidney, and lens (mostly) only have aldose reductase
–>cataracts, retinopathy, peripheral neuropathy
problem in chronic hyperglycemia DM pts

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22
Q

Lactase function and deficiency

A

–>dietary lactose intolerance
lactase functions on brush border to digest lactose–>glucose + galactose

Primary due to age dependent decline after childhood
Secondary due to losh of brush border (gastrienteritis from rotavirus, autoimmune)

Congenital deficiency is rare

Findings: bloating, cramps, flatulence, osmotic diarrhea

23
Q

Urea cycle function and important players

A

Nitrogen excretion; occurs in liver

Part in mitochondria, part in cytoplasm

Carbamoyl phosphate synthetase I is RLS; it requires N-acetylglutamate as an allosteric activator

Ornithine transcarbamylase converts ornithine–>citruline

Disorders–>hyperammonemia (confusion, vomiting, tachypnea)

24
Q

Cahill and Cori cycle

A

Transport ammonia between muscle and liver; uses alanine and glutamate
Uses alphaketoglutarate

25
Q

Hyperammonemia

A

Acquired (liver disease) or inherted
Excess NH3–>depletes alphaketoglutarate–>inhibition of TCA cycle
Tx with limited protein diet

Tremor, slurring of speech, vomiting, cerebral edema, blurred vision

Meds that lower ammonia levels:
lactulose (acidifies GI tract–>NH4 excreted)
Rifaximin (decreases ammoniagenic bacteria)
Benzoate, phenylacetate, phenylbutyrate (binds to NH4–>excretion)

26
Q

N-acetylglutamate synthase deficiency

A

Autosomal recessive
Required cofactor for CPS1
Hyperammonemia
Neonates: poorly regulated resp and body temp, poor feeding, developmental delay, intellect disability (same as CPS1 deficiency)

27
Q

Ornithine transcarbamylase deficiency

A

X linked recessive
most common urea cycle disorder
excess carbamoyl phosphate is converted to orotic acid (part of pyrimidine synthesis pathway)

Findings: increased orotic acid in blood and urine, low BUN, hyperammonemia,
No megaloblastic anemia (vs orotic aciduria, which is when there is low pyrimidine synthesis bc of megaloblastic anemia–>orotic acid accumulation)

28
Q

Phenylketonuria - what’s the etiology?

A

deficient phenylalanine hydroxylase or BH4 cofactor

29
Q

Phenylketonuria - what is the treatment?

A

Avoid phenylalanine (found in aspartame) and supplement tyrosine (becomes essential) and/or BH4 supplementation (depends on etiology)

30
Q

Phenylketonuria - symptoms/presentation

A

Musty Crusty: musty body odor, eczema
intellectual disability, growth delay, seizures
fair skin & eczema
musty body odor (specifically sweat and urine)
albinism (tyrosine needed to make melanin)
excretion of phenylketones in urine (causes smell)

Babies are all screened on day 2/3 of life

31
Q

What can happen to a pregnant woman with PKU?

A

If she is not keeping her PKU under control (following diet), the excess phenylalanine is teratogenic specifically to CNS development –> microcephaly, intellectual disability, growth retardation, congenital heart defects

32
Q

Phenylketonuria - inheritance

A

Autosomal recessive (enzyme deficiency)

33
Q

Maple syrup urine disease - etiology/pathogenesis

A

Deficient branched chain alpha ketoacid dehydrogenase (uses B1 as cofactor) - can’t degrade branched AA (Iso, Leu, Val)

34
Q

Maple syrup urine disease - inheritance

A

Autosomal recessive (enzyme deficiency)

35
Q

Maple syrup urine disease - sx/presentation

A

Urine that smells like maple syrup (duh!), vomiting, poor feeding - present in days 4-7 of life
Eventually –> CNS defects, intellectual disability, death (*Leucine crosses BBB and is responsible for the CNS effects)

36
Q

Maple syrup urine disease - treatment

A

Avoid branched AAs in diet (Iso, Leu, Val) and supplement thiamine

37
Q

Alkaptonuria - etiology/pathogenesis

A

Deficiency of homogentisate oxidase (tyrosine –> fumarate)

38
Q

Alkaptonuria - inheritance

A

autosomal recessive (enzyme deficiency)

39
Q

Alkaptonuria - symptoms/presentation

A

Blue-black coloration of cartilage (called ochronosis): connective tissue, ears, sclerae (brown pigment)
Urine will turn black when left out for a bit
Debilitating arthralgias, ankylosis, arthritis (toxic to cartilage)

*All due to effects of homogentisate build-up

40
Q

Cofactors of branched-chain alpha-ketoacid dehydrogenase

A

5: TPP, lipoic acid, CoA, NADH, FADH2

41
Q

Homocystinuria - etiology

A

3 types:
cystathione synthase deficiency
decreased affinity of cys synthase for B6 cofactor
methionine synthase deficiency

*All 3 lead to homocysteine build-up.

42
Q

Homocystinuria - inheritance

A

All 3 types are autosomal recessive (enzyme deficiencies).

43
Q

What reactions do cystathione synthase and methionine synthase catalyze?

A

CS: homocysteine + Ser –> Cystathione (*requires B6)

MS: Homocysteine –> Methionine (*req B9 + B12)

44
Q

Homocystinuria - treatment(s)

A

CS deficiency: Cys, B9, B6, B12 supplementation + reduced methionine consumption

CS decreased affinity for B6: Cys + B6 supplementation

MS deficiency: supplement Methionine

45
Q

Homocystinuria - sx/presentation

A

Marfanoid habitus but with down and in lens dislocation (Marfan’s is up and out)
Intellectual disability

46
Q

Cystinuria - etiology

A

Autosomal recessive deficiency of renal transporter (in PCT) for COLA: cysteine, ornithine, lysine, arginine

47
Q

Cystinuria - diagnostic test

A

Positive sodium cyanice-nitroprusside test:

Cyanide converts cystine to cysteine, cysteine binds nitroprusside, turning the solution purple.

48
Q

Cystinuria - sx/presentation

A

Typically presents as renal kidney stones in a child, possibly as staghorn calculi.
Stones are radiolucent on XR
Crystals are hexagonal

49
Q

Cystinuria - treatment

A

To prevent kidney stones:
alkalinization of urine (acetazolamide) and hydration/low salt diet are 1st line
chelation (penicillamine) if necessary

50
Q

Rate limiting enzyme glycogenesis

A

glycogen synthase

51
Q

Rate limiting enzyme glycogenolysis

A

glycogen phosphorylase

52
Q

Arsenic poisoning: how does it present? why is it important for metabolism?

A

Inhibits lipoic acid in pyruvate dehydrogenase complex

Presents as garlic breath with GI Sx (vomiting, rice water stools), QT prolongation

53
Q

End products of TCA cycle

A

3 NADH, 1 FADH2, 2 CO2, 1 GTP per acetyl CoA mc

10 ATP per acetyl CoA
20 ATP per glucose mc

STEP1 (11 decks)

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