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USMLE Step 1 Biochemistry

Subjects : health-sciences, usmle-step-1

Instructions:

Answer 50 questions in 15 minutes.
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Match each statement with the correct term.
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This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. What kind of linkages does glycogen synthase make? branching enzyme?
Alpha 1 -4 linkages; alpha 1 -6 linkages
Tryptophan
Liver mit and liver cytosol
All clathrin

2. What is the difference between exonucleases and endonucleases?
fructose
Endonucleases are specific and break specific linking phosphodiester bonds - exonucleases are not sequence specific and just remove the nucleoside
Block Electron transport
Succinyl coA

3. Where is type 1 collagen found?
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
high cholesterol
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)
Bone - Skin - Tendon - dentin - fascia - cornea - late wound repair

4. What type of aa are histones made of? are they acidic or basic?
Limit dextrans
Vit C
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
Lysine and arginine; basic

5. How is muscle activity and glycogenolysis coupled in muscle?
CPSII
Vit C; Vit E
Calcium and calmodulin activate glycogen phosphorylase kinase
Exons

6. What dictates whether a cell will regenerate or repair after inflammation?
Glycolysis - fatty acid synthesis - HMP shunt - protein synthesis (RER) - steroid synthesis (SER) - glycogenolysis - glycogenesis
Karyotyping
1) if it is stable/labile or permanent 2) intact BM and 3) intact ECM
Microcephaly - mental retardation - high pitched mewing/crying - epicanthal folds - cardiac abnormalities; microdeletion on short arm of chrom 5

7. What explains the excess phenylketones in the urine in phenylketonuria?
Block Electron transport
Phenylalanine build up
Succinate hydrogenase; matrix
alk phos

8. With What tool are Prader Willi and Angelman diagnosed?
Carnitine acyltransferase I
FISH
Hepatic glycogenolysis (mostly) - also hepatic gluconeogenesis - adipose release of FFA (minor)
Because cells of mononuclear phagocytic are esp rich in lysosomes

9. What happens in an aminotransferase reaction
Because cells of mononuclear phagocytic are esp rich in lysosomes
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
An aminotransferase enzyme transfers an amino group from an amino acid on to alpha ketoglutarate making it a glutamate (to join the urea cycle or excreted in the kidney) and the amino acid that lost the amino group is then turned into a glycolytic in
Central and peripheral demyelination with ataxia and dementia

10. AD diseases are usually...
pleiotropic
When the disease manifestation depends on from who the gene deletion was inherited from d/t methylation that occurs; Prader Willi and AngelMann
Ret
When the 2nd hit of the allele is What causes the disease; sporadic retinoblastoma

11. Can a disorder be congential but not hereditary?

12. What lysosomal storage diseases are seen more in Ashkenazi Jew?
Lesch Nyhan syndrome; X linked recessive
Tay Sachs - Niemann Picks - Gauchers
Block ATP synthase resulting in no ATP production and an increased proton gradient
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate

13. What is the order of collagen synthesis - just the terms of the intermediate forms?
Mental retardation - obesity - short stature - hypogonadism - hypotonia - hyperphagia; father
NADH - Acetyl CoA - ATP; NAD+ - ADP and Ca2+
Exons
Preprocollagen - procollagen - tropocollagen - collagen

14. What does oligomycin do?
AD (trinucleotide expansion is not a mode of inheritance)
Macrocytic megaloblastic anemia - hypersegmented PMNs - subacute combined degeneration myelopathy Which results in degeneration of the dorsal and lateral columns (loss of position and vibration sense - spastic paresis and ataxia) due to abnormal myel
Ret
Block ATP synthase resulting in no ATP production and an increased proton gradient

15. After the PCR reaction - How do you actually visualize the DNA?
Southern - DNA - Northern - RNA - Western - Protein; blotting procedures are used to detect a specific nucleic acid or aa sequence; the sample is electrophoresed and then transferred to a filter Which is then soaked in a denaturant and then a radiola
Fomepizole; antidote for methanol or ethylene glycol poisoning
Do agarose gel eletrophoresis to separate the different sizes of the PCR products (sizes id the the fragment)
Phenylalanine hydroxylase or tetrahydrobiopterin factor

16. From What aa does thyroxine come from?
Tyrosine
Glucose 6 phosphate dehydrogenase
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)

17. What are some catalase positive bugs?
S. aureus - Aspergillus
When different combination of exons get combined together; in Beta thallasemia
Galactokinase; galactose appears in blood and urine - sometimes infantile cataracts may present as failure to track objects or lack of a social smile
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate

18. What does a pyridoxine deficiency look like? What causes it?
Decreased phenylalanine - increase tyrosine
Williams
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption
Liver and skeletal muscle

19. What builds up in the blood of patients with maple syrup urine disease? urine/poo? What does this cause?
Flouroquinolones
Cancers (rapidly synthesizing); MTX (blocks dihyrdofolate reductase); phenytoin (prevent conjugase from breaking down polyglutamate form to monoglutamate form; reabsorption in jejunum is blocked by alcohol and OCPs; also blocked by sulfonamides
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
Nucleoside is just the ribose plus the base; nucleotide is the ribose plus the base but the phosphate bond

20. What is the mc chromosomal disorder?
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes
Southern - DNA - Northern - RNA - Western - Protein; blotting procedures are used to detect a specific nucleic acid or aa sequence; the sample is electrophoresed and then transferred to a filter Which is then soaked in a denaturant and then a radiola
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate
Downs

21. Where does NADH2 enter ETC? FADH2
Complex I - Complex II (lower energy)
Increased CPK and muscle biopsy
all are diseased!
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months

22. What is the product of alpha ketoglutarate dehdrogenase?
Succinyl coA
Endonucleases are specific and break specific linking phosphodiester bonds - exonucleases are not sequence specific and just remove the nucleoside
Bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating
GTP: gluconeogenesis - OXA to phosphoenolpyruvate

23. HMG coA synthase; cholesterol synthesis
Tyrosinase
Uses HMG coA reductase
Beta glucocerebrosidase; glucocerebroside
Either salvage by HGPRT and PRPP or converstion to xanthine and then to uric acid by xanthine oxidase

24. In What genetic code is uracil found in? in replace of what?
Uracil; thymine
Hepatic fatty change
Inbit Na+K+ ATPase; Cardiac glycosides
Imprinting Dx's: prader Willi and Angelmann

25. What is hypophosphatemia rickets? Can it be treated with Vit D?
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no
Dactinomycin - doxorubicin
Converts it to citrulline
alk phos

26. What are phenylacetate - phenylactate - and phenylpyruvate?
XR - iduronate sulfatase
Phenylketones that build up in phenylketonuria
Limit protein in diet; give benzoate or phenylbutyrate Which bind amino acids and lead to excretion - lactulose (hydrogen ion binds to ammonia to make excretable ammonium) and neomycin (to kill bacteria that release ammonia from aa)
Becomes methionine

27. What is the degradation product of Norepinephrine?
No
AD
BM; laminins; most flexible; different aa composition
VMA

28. What causes the pathology in I- cell disease? What does I cell sidease
CPSII
The lack of lysosomal proteins (are secreted - default from RER!) results in macromolecules accumulating in lysosomes - inclusions cause pathology
Tyrosine
Mucus secreting goblet cells - ab secreting plasma cells - nt secreting neurons

29. Which is the rate limiting step of the urea cycle?
Galactose gets converted to galactose 1 Phosphate by galactokinase Which then gets turned into glucose 1 phosphate by Galactose 1 Uridyl Transferase (GALT) Which also produces UDP Gal Which is used for lactose production in the breast; the fate of gl
Carbomyl phoshpate synthetase I
32 or 30; malate aspartate shuttle or glycerol 3 phosphate shuttle; heart/liver and muscle
FA coA synthetase combines coA with FA to make acyl coA

30. What vesicular trafficking protein takes proteins from the Golgi to lysosomes? in between the golgi? from the plasma membrane to endosomes (receptor mediated endocytosis)?
Beta thalassemia
Shiga toxin and ricin (protein in castor beans)
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
All clathrin

31. What are the clinical symptoms of orotic aciduria?
Osmotic diarrhea - bloating - cramps
2-3 days after birth because maternal enzyme during fetal like might still be there
Whether or not the patient is also hyperammonemia (if yes - then OTC def)
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia

32. What is imprinting disease? Give 2 examples
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
SAM; Vit C
high cholesterol
When the disease manifestation depends on from who the gene deletion was inherited from d/t methylation that occurs; Prader Willi and AngelMann

33. What is the reason for blue sclerae in Osteogenesis Imperfecta?
Creates nicks in DNA to prevent supercoiling; both!
Thinned cornea from lack of connective tissue so see underlying choroidal lens
aldose reductase
Alpha amanitin; mushroom caps

34. What type of aa is phenylalanine? What implications does this have on the presentation of phenylketonuria?
Aromatic; musty body odor
B12 and folate; B12; washed out
fastest sugar
Glutamate and aspartate; CO2 provides an ketone

35. other than scurvy What else does vit C def cause? also - What kind of anemias and why?
Hemolytic anemia (fragility of RBCs) - muscle weakness and posterior column and spinocerebellar tract demyelination (neuron damage) resulting in decreased proprioception and vibration sensation - and peripheral neuropathy - and retinal degeneration
Decreased would healing; microcytic anemia (d/t decreased iron [not absorbable]; macrocytic anemia (d/t Fh4 not reduced)
Hydroxurea; deoxygenates ribose
Glycogen phosphorylase; phosphorylation and dephosphorylation

36. What is lebers hereditary optic neuropathy? What is the main clinical symptom? and What is its mode of inheritance?
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP
Liver mit and liver cytosol
Carnitine shuttle
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance

37. What is the mode of inheritance of phenyketonuria?
AR
AD
Limit dextrans
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)

38. What does guanine have on it?
A ketone
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)
UV nonionizing radiation causing thymidine dimers
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine

39. How does mismatch repair work? in What cancer is it mutated? What type of DNA is methylated?
Chronic pancreatitis leads to type 1 diabetes - pancreatic insufficiency leads to ADEK deficiencies - malabsorption and steatorrhea - blocked gallbladder ducts leads to secondary biliary cirrhosis
Immediately after replication - DNA is unmethylated and so it is a signal to be double checked; HNPCC; heterochromatin
Coenzyme A and lipoamides
Pyruvate! (not lactate - that is generate just in order to produce more NAD+)

40. What are the clinical symptoms of hyperammonemia?
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
only L form
Pyruvate! (not lactate - that is generate just in order to produce more NAD+)
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits

41. What are the findings in Tay Sachs disease?
Phospholipids - sphingolipids - glycolipids
degradation
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
dimers

42. In x linked - in males - prevalence is...
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover
Lesch Nyhan syndrome; X linked recessive
Cells that stay in G0 and cannot replicate - instead they regenerate from stem cells; neurons - skeletal and cardiac muscles - and RBCs
= q

43. What amino acids are required in purine synthesis? Which of these does pyrimidine synthesis require also?
is active
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
reabsorbs
Glutamine - aspartate - glycine; aspartate

44. Other than the H2O2 produced from the resp burst in infections - What other things does G6PD reproduce NADPH for glutathione reduction for? What cells are particularly vulnerable to these oxidizing agents?
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
Later
D2 (ergocalciferol) - D3 (cholecalciferol) - D3 (cholecalciferol)
tumor suppressor genes (p53 - Rb - BAX)

45. Phosphorylated glycogen phosphorylase...
Mental retardation - obesity - short stature - hypogonadism - hypotonia - hyperphagia; father
is active
DiGeorge and Velocardiofacial; deletion on chromosome 22q11 results in aberrant dev of 3rd and 4th branchial pouches; digeorge has thymic and parathyroid prob - velocardiofacial has palate and facial instead
Heme synthesis - urea cycle - gluconeogenesis

46. What disease is associated with chromosome 21?

47. What is elastin? How is it different from collagen? Where is it found? How is it broken down?
glucagon - insulin and epinephrine
Milder form of type 1 with normal blood lactate levels; debranching enzyme (alpha -1 -6 glucosidase)
Release alk phos
A fibrous protein (ie produced by fibroblasts); it has lysine and proline but nonglycosylated; arteries - lungs - elastic ligaments - vocal cords - ligamenta flava (connect vertebrae); broken down by elastase Which is inhibited by alpha 1 antitrypsin

48. Where is vit C found?
Def in Vit C; def in Vit D
A methyl
Hemolytic anemia due to heinz bodies Which are oxidized hemoglobin precipitating within the RBCs
Fruits and vegetables

49. What two enzymes are the apart of the same complex? What dictates What form they are in? and What dictates that?
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio
Galactose
Insertion or deletion of a number of nucleotides indivisible by 3; tay sachs - duchennes MD

50. Where is type III collagen found?
Fructose gets phosphorylated into fructose 1- P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B
False; GTP hydrolysis
Alcoholism - RA - inflammatory disease - chronic diarrhea
Reticulin - skin - blood vessels - uterus - fetal tissue - early phase of granulation tissue