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FA - Biochemistry > Biochem - Metabolism (Amino Acid Derivatives & Associated Disorders) > Flashcards

Biochem - Metabolism (Amino Acid Derivatives & Associated Disorders) Flashcards

Pg. 110-112 in First Aid 2014 Sections include: -Amino acid derivatives -Catecholamine synthesis/tyrosine catabolism -Phenylketonuria -Alkaptonuria (ochronosis) -Homocystinuria -Cystinuria -Maple syrup urine disease

1
Q

Draw the derivatives of phenylalanine in consecutive order, including the cofactors required to create them.

A

See p. 110 in First Aid 2014 for visual at top of page

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2
Q

Draw the derivatives of Tryptophan in consecutive order, including the cofactors required to create them.

A

See p. 110 in First Aid 2014 for visual at top of page

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3
Q

What substance is a derivative of Histidine? What cofactor is required for its synthesis?

A

Histamine; B6

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4
Q

What important substance is a derivative of Histidine? What cofactor is required in their synthesis?

A

Porphyrin => Heme; B6

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5
Q

What are 2 important derivatives of glutamate? Which requires B6 cofactor for its synthesis?

A

GABA, Glutathione; B6 for GABA synthesis

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6
Q

What are 3 important derivatives of arginine? Which of these requires BH4 cofactor for its synthesis?

A

Creatine, Urea, Nitric oxide; BH4 for Nitric oxide synthesis

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7
Q

What enzyme is affected in Alkaptonuria? What is the normal function of this enzyme?

A

Homogentisate oxidase: Homogentisic acid => Maleylacetoacetic acid; Note: Homogentistic acid is derived from Tyrosine (which is dervied from Phenylalanine) and Maleylacetoacetic acid feeds into the TCA cycle

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8
Q

What enzyme is affected in PKU? What is the normal function of this enzyme?

A

Phenylalanine hydroxylase: Phenylalanine => Tyrosine (using BH4 as cofactor)

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9
Q

What enzyme is affected in Albinism? What is the normal function of this enzyme?

A

Tyrosinase; DOPA (dihydroxyphenylalanine) => Melanine

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10
Q

What enzyme is inhibited by Carbidopa? What is the normal function of this enzyme?

A

DOPA decarboxylase: DOPA (dihydroxyphenylalanine) => Dopamine (using vitamin B6 as cofactor)

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11
Q

What factor in the catecholamine synthesis/tyrosine catabolism pathway is stimulated by cortisol? What effect does this have?

A

SAM (S-adenosylmethionine): Norepinephrine => Epinephrine

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12
Q

Draw the major products of the phenylalanine/tyrosine catabolism/catecholamine synthesis pathway.

A

See p. 110 in First Aid 2014 for visual near bottom of page

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13
Q

What are 2 causes of phenylketonuria? Which of these causes malignant PKU?

A

Due to decreased phenylalanine hydroxylase or decreased tetrahdrobiopterin cofactor (malignant PKU).

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14
Q

What amino acid becomes essential in patients with PKU?

A

Tyrosine becomes essential

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15
Q

What urine finding is associated with PKU, and what causes this?

A

Increased phenylalanine leads to excess phenylketones in urine

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16
Q

What are 6 clinical findings associated with phenylketonuria?

A

Findings: (1) Intellectual disability (2) Growth retardation (3) Seizures (4) Fair skin (5) Eczema (6) Musty body odor; Think: “disorder of AROMAtic amino acid metabolism => musty body ODOR”

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17
Q

What is the treatment of phenylketonuria?

A

Treatment: Low phenylalanine and High tyrosine in diet

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18
Q

What is of most concern with maternal PKU?

A

Lack of proper dietary therapy during PKU

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19
Q

What are 4 clinical findings in an infant affected by maternal PKU?

A

Findings in infant: (1) microcephaly (2) intellectual disability (3) growth retardation (4) congenital heart defects

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20
Q

What is the mode of inheritance of PKU? What is its incidence?

A

Autosomal recessive. Incidence ~ 1:10,000

21
Q

When is PUK screened for, and why?

A

Screened for 2-3 days after birth (normal at birth because of maternal enzyme during fetal life)

22
Q

What are 3 examples of phenylketones?

A

Phenylketones - (1) Phenylacetate, (2) Phenyllactate, and (3) Phenylpyruvate

23
Q

What substance must PKU patients avoid, and why?

A

PKU patients must avoid the artificial sweetener aspartame, which contains phenylalanine

24
Q

What is another name for Alkaptonuria?

A

Alkaptonuria (ochronosis)

25
Q

What is Alkaptonuria (ochronosis)?

A

Congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate

26
Q

What is the mode of inheritance of Alkaptonuria? Is it a benign or malignant disease?

A

Autosomal recessive. Benign disease.

27
Q

What are 4 clinical findings associated with Alkaptonuria?

A

Findings: (1) dark connective tissue, (2) brown pigmented sclerae, (3) urine turns black on prolonged exposure to air. May have (5) debilitating arthralgias (homogentisic acid toxic to cartilage).

28
Q

What musculoskeletal finding may be present in patients in Alkaptonuria, and why?

A

May have debilitating arthralgias (homogentisic acid toxic to cartilage).

29
Q

What is the mode of inheritance of all types of homocystinuria?

A

All autosomal recessive

30
Q

What are 3 forms of homocystinuria? What do all forms have in common?

A

Types (all autosomal recessive): (1) Cystathionine synthase deficiency (2) Decreased affinity of cystathionine synthase for pyridoxal phosphate (3) Homocysteine methyltransferase (methionine synthase) deficiency; All forms result in excess homocysteine

31
Q

What is the treatment for homocystinuria due to cystathionine synthase deficiency?

A

Treatment: low methionine, high cysteine, high B12 and folate in diet

32
Q

What is the treatment for homocystinuria due to low affinity of cystathionine synthase for pyridoxal phosphate?

A

Treatment: very high B6 and high cysteine in diet

33
Q

What is the treatment for homocystinuria due to homocysteine methyltransferase (methionine synthase) deficiency?

A

Treatment: High methionine in diet

34
Q

What are 8 clinical findings associated with homocystinuria?

A

Findings: (1) very high homocysteine in urine (2) intellectual disability (3) osteoporosis (4) tall stature (5) kyphosis (6) lens subluxation (downward and inward) (7) thrombosis and (8) atherosclerosis (stroke and MI)

35
Q

What ophthalmologic condition is associated with homocystinuria?

A

Lens subluxation (downward and inward)

36
Q

What vascular condition is associated with homocystinuria? What are 2 complications that may arise?

A

Atherosclerosis (stroke and MI)

37
Q

Draw the important reactions related to homocysteinuria, highlighting the 2 enzymes that may be affected to cause this disorder.

A

See p. 111 in First Aid 2014 for visual near bottom of page

38
Q

What is the defect in cystinuria?

A

Hereditary defect in renal PCT and intestinal amino acid transporter for Cysteine, Ornithine, Lysine, and Arginine; Think: “COLA”

39
Q

What urine finding occurs in cystinuria, and why?

A

Excess cysteine in urine can lead to precipitation of hexagonal cystine stones

40
Q

What is the mode of inheritance of cystinuria? What is its incidence like?

A

Autosomal recessive. Common (1:7000)

41
Q

What test is diagnostic for cystinuria?

A

Urinary cyanide-nitroprusside test

42
Q

What is the treatment for cystinuria?

A

Treatment: urinary alkalinization (e.g., potassium citrate, acetazolamide) and chelating agents increase solubility of cystine stones; good hydration

43
Q

Of what is cystine composed?

A

Cystine is made of 2 cysteines connected by a disulfide bond

44
Q

What is the defect and metabolic effects of maple syrup urine disease?

A

Blocked degradation of branched amino acids (Isoleucine, Leucine, Valine) due to decreased alpha-ketoacid dehydrogenase (B1). Causes increased alpha-ketoacids in the blood, especially those of leucine; Think: “I Love Vermont MAPLE SYRUP from maple trees (with BRANCHES)”

45
Q

What are 3 symptoms/conditions caused by maple syrup urine disease?

A

Causes severe CNS defects, intellectual disability, and death

46
Q

What is the mode of inheritance of maple syrup urine disease?

A

Autosomal recessive

47
Q

What describes the urine of patients with maple syrup urine disease?

A

Urine smells like maple syrup/burnt sugar

48
Q

What is the treatment for maple syrup urine disease?

A

Treatment: restriction of leucine, isoleucine, and valine in diet, and thiamine supplementation

FA - Biochemistry (31 decks)

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