USMLE Biochem Flashcards
What explains the synchronous production of multiple enzymes by bacteria in response to lactose?
One mRNA coding for multiple enzymes (polycistrionic mRNA)
What forces determine the secondary structure of proteins?
H bonds
Activation of phospholipase C results in the increase of what intracellular substance?
Ca
What do you call a mutation on the B-globin gene three bases upstream of the AUG codon, and what does it lead to?
Kozak sequence, B-thalassemia intermedia b/c mRNA can’t bind the ribosome
What enzyme does insulin upregulate?
Protein phosphatase 1
What part of the lac operon does the repressor protein bind onto?
Operator locus
Hyperammonemia depletes levels of what intermediate?
Alpha-ketoglutarate
High concentration of proprionic acid in plasma and urine results from the metabolism of what amino acid?
Valine
What enzyme is responsible for creating what substance that results in cataract formation in galactokinase deficiency?
Aldose reductase, galactitol
What is the allosteric activator in the first step of the conversion of pyruvate to glucose?
Acetyl CoA (by inhibiting its own creation and encouraging pyruvate carboxylase to convert pyruvate to oxaloacetate for gluconeogenesis)
What is the most common cause of cystic fibrosis?
Phenylalanine deletion at F508
What is the role of the 16S rRNA subunit?
Contains a nucleotide sequence complementary to the Shine-Dalgarno sequence on mRNA, which is necessary for protein translation
Tall with long extremities, pectus excavatum, hypermobile joints, long tapering fingers. Dx?
Marfan syndrome
Subluxation of lenses upward and temporally vs medially and downwards
Marfans vs Homocysteinuria
Urine turns black after exposure to air, hyperpigmented skin, brown sclerae. Dx and mechanism?
Alkaptonuria, accumulation of homogentisic acid
What enzymes does insulin activate?
Protein phosphatase 1, Glycogen synthase (all others are glucagon!)
What does methylmalonic acidemia/aciduria result from?
Defect in isomerization that transforms methylmalonic acid to succinyl CoA for entry to the TCA cycle
HSM, pancytopenia, osteoporosis, aseptic necrosis of femur. Dx?
Gaucher disease, glucocerebridase deficiency
Progressive neurodegeneration, cherry-red spot on macula, HSM, foam cells
Niemann-Pick, sphingomyelinase deficiency
Progressive neurodegeneration, developmental delay, NO HSM, cherry-red spot on macula
Tay Sachs, hexosaminidase A deficiency
Developmental delay, gargoylism, airway obstruction, corneal clouding, HSM. Dx?
Hurler syndrome, accumulation of heparan and dermatan sulfate
Mild Hurler + aggressive behaviour, no corneal clouding
Hunter syndrome, accumulation of heparan and dermatan sulfate (XR)
Ragged red fibres with neuromuscular lesions, lactic acidosis. What kind of disease is this?
Mitochondrial
Creamy layer in supernatant
Hyperchylomicronemia (AR problem with LPL or CII, results in high CM, TG, cholesterol)
Less than 3 days of starvation?
Hepatic glycogenolysis switches over to FFA as main source of energy as glycogen runs out after 1 day
Major energy source in fasting state?
Hepatic glycogenolysis (FFA and gluconeogenesis = minor)
More than 3 days of starvation?
FFA for energy, run out of fat = vital protein degradation
Central and peripheral neuropathy with ataxia and dementia
Metachromatic leukodystrophy
Peripheral neuropathy with developmental delay and optic atrophy
Krabbe disease
High serum alanine since birth, lactic acidosis, neurologic defects. Dx?
Pyruvate dehydrogenase complex deficiency
Areas of gluconeogenesis in the body?
Liver (MAIN), kidney, intestinal epithelium
How do you treat a pyruvate dehydrogenase complex deficiency?
With lysine and leucine (purely ketogenic amino acids)
How much ATP do you produce with aerobic metabolism of glucose?
32 with malate/aspartate shuttle and 30 with G3P shuttle
What is the role of F26BP in regulating metabolism?
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.
What is NADPH used for?
CYP450
Respiratory burst
Anabolic processes
Glutathione reductase
Garlic breath with vomiting and rice-water stools. Dx?
Arsenic poisoning
ATP deficiency that’s worsened with glucose infusion?
B1 deficiency
