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Flashcards in USMLE Biochem Deck (37):
1

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

One mRNA coding for multiple enzymes (polycistrionic mRNA)

2

What forces determine the secondary structure of proteins?

H bonds

3

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

Ca

4

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

5

What enzyme does insulin upregulate?

Protein phosphatase 1

6

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

Operator locus

7

Hyperammonemia depletes levels of what intermediate?

Alpha-ketoglutarate

8

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

Valine

9

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

Aldose reductase, galactitol

10

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)

11

What is the most common cause of cystic fibrosis?

Phenylalanine deletion at F508

12

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

13

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

Marfan syndrome

14

Subluxation of lenses upward and temporally vs medially and downwards

Marfans vs Homocysteinuria

15

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

Alkaptonuria, accumulation of homogentisic acid

16

What enzymes does insulin activate?

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

17

What does methylmalonic acidemia/aciduria result from?

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

18

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

Gaucher disease, glucocerebridase deficiency

19

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

Niemann-Pick, sphingomyelinase deficiency

20

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

Tay Sachs, hexosaminidase A deficiency

21

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

Hurler syndrome, accumulation of heparan and dermatan sulfate

22

Mild Hurler + aggressive behaviour, no corneal clouding

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

23

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

Mitochondrial

24

Creamy layer in supernatant

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

25

Less than 3 days of starvation?

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

26

Major energy source in fasting state?

Hepatic glycogenolysis (FFA and gluconeogenesis = minor)

27

More than 3 days of starvation?

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

28

Central and peripheral neuropathy with ataxia and dementia

Metachromatic leukodystrophy

29

Peripheral neuropathy with developmental delay and optic atrophy

Krabbe disease

30

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

Pyruvate dehydrogenase complex deficiency

31

Areas of gluconeogenesis in the body?

Liver (MAIN), kidney, intestinal epithelium

32

How do you treat a pyruvate dehydrogenase complex deficiency?

With lysine and leucine (purely ketogenic amino acids)

33

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

32 with malate/aspartate shuttle and 30 with G3P shuttle

34

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.

35

What is NADPH used for?

CYP450
Respiratory burst
Anabolic processes
Glutathione reductase

36

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

Arsenic poisoning

37

ATP deficiency that's worsened with glucose infusion?

B1 deficiency