Usmle Step 1 - May 1 (Biochem)

Front 1

What are phenylketones?

Back 1

Urine products that accumulate in PKU (phenylalanine hydroxylase or THB deficiency).

1) Phenyl-pyruvate
2) Phenyl-lactate
3) Phenyl-acetate

Front 2

What causes alkaptonuria? What are the findings?

Back 2

Deficiency of: HGA Oxidase
(Homogentisic acid oxidase)

1) Dark stuff:
- Dark CT
- Dark urine (turns black)
- Dark sclera (brown)
2) Arthralgias
- HGA is toxic to cartilage

Front 3

Causes of albinism (oculocutaneous)?

Back 3

1) Enzyme deficiency = Tyrosinase
2) Transport problem = defective tyrosine transporters
3) Migration problem = failure of neural crest cells

Front 4

What is the active form of vitamin B6?

Back 4

Pyridoxal phosphate.

Front 5

What are the causes and treatments of homocystinuria?

Back 5

1) Cystathionine synthase deficiency
- Tx = ↓Met; ↑Cys, ↑B12 & Folate (reduce homocysteine)

2) Cystathionine Synthase Affinity (↓ for B6)
- Tx = ↑↑B6!

3) Homocysteine methyltransferase deficiency

Front 6

What disorders are associated w/ lens subluxation?

Back 6

1) Marfan's syndrome
2) Homocystinuria

Front 7

What drug do you give to alkalinize the urine??

Back 7

Acetazolamide!

Front 8

What causes cystinuria and what does it lead to?

Back 8

Defective transporter in the PCT for COLA AA's:
- C - cysteine
- O - ornithine
- L - lysine
- A - arginine

Leads to Cystine (2 x cysteines connected by S-S bond) Kidney stones → Cystine Staghorn Calculi

Front 9

What causes maple syrup disease?

Back 9

↓α-ketoacid dehydrogenase → unable to degrade the branched amino acids:
- Ile = isoleucine
- Leu = leucine
- Val = valine

(I L-ove V-ermont maple syrup from maple trees [w/ BRANCHES])

Causes severe CNS defects, MR, and death

Front 10

What is Hartnup disease?

Back 10

Defective renal/intestinal transporter for NEUTRAL amino acids.

Tryptophan lost in urine and ↓ absorbed in gut.

Front 11

What is pellagra?

Back 11

Niacin (B3) deficiency.

D's of B3 Deficiency:
- Diarrhea
- Dementia
- Dermatitis
&.... DEATH

Front 12

What is the function of Apo E?

Back 12

mEdiates rEmnant uptakE

Found in ALL but LDL

Front 13

What is the function of Apo A-1?

Back 13

Activates lcAt
- Chylomicron
- HDL

Front 14

What is the function of Apo B-100?

Back 14

B-inds LDL receptor
- VLDL
- IDL
- LDL

Front 15

What is the function of Apo B-48?

Back 15

Medicates chylomicron secretion
- Chylomicron & remnant

Front 16

What is the function of Apo C-II?

Back 16

C-ofactor for LL (Lipoprotein Lipase = 2L's)
- C-hylomycron
- vLdL (=2L's)

Front 17

What is the function of Apo C-III?

Back 17

Inhibits LPL