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USMLE > USMLE Biochem > Flashcards

USMLE Biochem Flashcards

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USMLE® Step 1 flashcards
1
Q

What explains the synchronous production of multiple enzymes by bacteria in response to lactose?

A

One mRNA coding for multiple enzymes (polycistrionic mRNA)

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2
Q

What forces determine the secondary structure of proteins?

A

H bonds

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3
Q

Activation of phospholipase C results in the increase of what intracellular substance?

A

Ca

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4
Q

What do you call a mutation on the B-globin gene three bases upstream of the AUG codon, and what does it lead to?

A

Kozak sequence, B-thalassemia intermedia b/c mRNA can’t bind the ribosome

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5
Q

What enzyme does insulin upregulate?

A

Protein phosphatase 1

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6
Q

What part of the lac operon does the repressor protein bind onto?

A

Operator locus

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7
Q

Hyperammonemia depletes levels of what intermediate?

A

Alpha-ketoglutarate

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8
Q

High concentration of proprionic acid in plasma and urine results from the metabolism of what amino acid?

A

Valine

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9
Q

What enzyme is responsible for creating what substance that results in cataract formation in galactokinase deficiency?

A

Aldose reductase, galactitol

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10
Q

What is the allosteric activator in the first step of the conversion of pyruvate to glucose?

A

Acetyl CoA (by inhibiting its own creation and encouraging pyruvate carboxylase to convert pyruvate to oxaloacetate for gluconeogenesis)

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11
Q

What is the most common cause of cystic fibrosis?

A

Phenylalanine deletion at F508

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12
Q

What is the role of the 16S rRNA subunit?

A

Contains a nucleotide sequence complementary to the Shine-Dalgarno sequence on mRNA, which is necessary for protein translation

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13
Q

Tall with long extremities, pectus excavatum, hypermobile joints, long tapering fingers. Dx?

A

Marfan syndrome

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14
Q

Subluxation of lenses upward and temporally vs medially and downwards

A

Marfans vs Homocysteinuria

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15
Q

Urine turns black after exposure to air, hyperpigmented skin, brown sclerae. Dx and mechanism?

A

Alkaptonuria, accumulation of homogentisic acid

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16
Q

What enzymes does insulin activate?

A

Protein phosphatase 1, Glycogen synthase (all others are glucagon!)

17
Q

What does methylmalonic acidemia/aciduria result from?

A

Defect in isomerization that transforms methylmalonic acid to succinyl CoA for entry to the TCA cycle

18
Q

HSM, pancytopenia, osteoporosis, aseptic necrosis of femur. Dx?

A

Gaucher disease, glucocerebridase deficiency

19
Q

Progressive neurodegeneration, cherry-red spot on macula, HSM, foam cells

A

Niemann-Pick, sphingomyelinase deficiency

20
Q

Progressive neurodegeneration, developmental delay, NO HSM, cherry-red spot on macula

A

Tay Sachs, hexosaminidase A deficiency

21
Q

Developmental delay, gargoylism, airway obstruction, corneal clouding, HSM. Dx?

A

Hurler syndrome, accumulation of heparan and dermatan sulfate

22
Q

Mild Hurler + aggressive behaviour, no corneal clouding

A

Hunter syndrome, accumulation of heparan and dermatan sulfate (XR)

23
Q

Ragged red fibres with neuromuscular lesions, lactic acidosis. What kind of disease is this?

A

Mitochondrial

24
Q

Creamy layer in supernatant

A

Hyperchylomicronemia (AR problem with LPL or CII, results in high CM, TG, cholesterol)

25
Q

Less than 3 days of starvation?

A

Hepatic glycogenolysis switches over to FFA as main source of energy as glycogen runs out after 1 day

26
Q

Major energy source in fasting state?

A

Hepatic glycogenolysis (FFA and gluconeogenesis = minor)

27
Q

More than 3 days of starvation?

A

FFA for energy, run out of fat = vital protein degradation

28
Q

Central and peripheral neuropathy with ataxia and dementia

A

Metachromatic leukodystrophy

29
Q

Peripheral neuropathy with developmental delay and optic atrophy

A

Krabbe disease

30
Q

High serum alanine since birth, lactic acidosis, neurologic defects. Dx?

A

Pyruvate dehydrogenase complex deficiency

31
Q

Areas of gluconeogenesis in the body?

A

Liver (MAIN), kidney, intestinal epithelium

32
Q

How do you treat a pyruvate dehydrogenase complex deficiency?

A

With lysine and leucine (purely ketogenic amino acids)

33
Q

How much ATP do you produce with aerobic metabolism of glucose?

A

32 with malate/aspartate shuttle and 30 with G3P shuttle

34
Q

What is the role of F26BP in regulating metabolism?

A

Shunts towards glycolysis (PFK-2, via insulin) or gluconeogenesis (FBPase 2, activated by PKA by glucagon) - bidirectional enzyme. FBPase2 when phosphorylated by PKA, PFK-2 when dephosphorylated.

35
Q

What is NADPH used for?

A

CYP450
Respiratory burst
Anabolic processes
Glutathione reductase

36
Q

Garlic breath with vomiting and rice-water stools. Dx?

A

Arsenic poisoning

37
Q

ATP deficiency that’s worsened with glucose infusion?

A

B1 deficiency

USMLE (23 decks)

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