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USMLE Step 1 Biochemistry

Subjects : health-sciences, usmle-step-1

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Answer 50 questions in 15 minutes.
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1. The three steps of PCR
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
Glycerol and propionyl coA; lactate and alanine
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
Steroid synthesis and detoxification

2. What type of disease is MERRF? What is the clinical presentation?
1 for all three classes of RNA; Rifampin; TB
Myoclonus epilepsy
plasma membrane
Its When two acrocentric chromosomes combine their long arms (and short arms disappear); When the translocation is functional

3. How many stages are there in HMP shunt? Where do they occur? how much energy does HMP shunt use up?
Glycogen and FFA oxidation - glucose conserved for final sprinting!
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
Lysine and arginine; basic
2 oxidative and nonoxidative; cytoplasm (both); none (none produced either - you are simply switching carriers of energy- from glucose 6 phosphate to NADPH)

4. What is the RNA called before processing? and after?
HnRNA; mRNA
Tryptophan; niacin
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
fructose

5. What regulates Fructose 1 -6 bisphosphatase? What reaction is it found in?
Tyrosine; phenylaline
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
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
Exons

6. in What disease are there antibodies to snRNPs?
to ions
Lupus
Hypophosphatemia rickets and Alports
Steroid synthesis and detoxification

7. Do RNA polymerases have proofreading function? What does this mean for HIV?
COP II
Cystine kidney stones (cystine staghorn calculi)
No; increased mutation rate!
Limit dextrans

8. How is CF treated? How does it work?
Oral uridine administration; provides nucleosides and provides feedback inhibition
Nacetyl cysteine; breaks disulfide bridges of mucus plugs
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
Abs against type IV collagen; pulmonary and glomerular capillaries

9. Cysteine is one of two _____ connected by disulfide bond
Methionine; f Met (formyl methyl methionine)
Whether or not the patient is also hyperammonemia (if yes - then OTC def)
Homogentistic acid oxidase
dimers

10. Where does NADH2 enter ETC? FADH2
Complex I - Complex II (lower energy)
RER; free ribosomes
Folinic acid; does not require DHF
Hydroxurea; deoxygenates ribose

11. What kind of linkages does glycogen synthase make? branching enzyme?
An allosteric regulator; fructose 1 phosphate; phosphofructokinase 2
Alpha 1 -4 linkages; alpha 1 -6 linkages
Presence of normal and mutated mtDNA (like mosaicism except in mit)
Ortinithine transcarbamoylase - orotic acid phosphoribosyltransferase - and orotidine 5 phosphate decarboxylase; urea cycle; last two are involved in conversion of orotic acid to UMP (adding PRPP to orotic acid)

12. What explains the excess phenylketones in the urine in phenylketonuria?
Phenylalanine build up
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
Formation of a proton gradient that is then used to create ATP through ATP synthase
allosteric regulation

13. other than increase Parathyroid hormone What else increases 1 alpha hydroxylase activity in the kidney?
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
Catalase positive because they reduce their H2O2 and WBCs cant use that to make bleach; because the way they protect is by building a wall around the organisms with granulomas
Decreased serum phosphate
5' capping (with 7 methylguanosine) - 3' adenylation - splicing of introns; nucleus

14. What does arsenic do? How is this important?
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
Essential fructosuria and fructose intolerance; fructose intolerance
Inhibits lipoic acid; lipoic acid is a cofactor for pyruvate dehydrogenase
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait

15. What is the rate limiting step in glycolysis? What does it do? who activates it? inhibits it?
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP
Microcephaly - mental retardation - high pitched mewing/crying - epicanthal folds - cardiac abnormalities; microdeletion on short arm of chrom 5
Acetazolamide to alkalinize the urine
liver and muscle

16. Other than glycogenesis and glycolysis - What else is Fructose used for?
VMA
Neurologic lesions and cardiomyopathies (ox phos!)
Mannose
Biotin (vit B7) and Vit K

17. What ensures that during gluconeogenesis all the ATP wont be used in glycolysis as youre producing it?
10 - 9 - 7 - 2; protein C and S
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
Adrenal medulla
Its When two acrocentric chromosomes combine their long arms (and short arms disappear); When the translocation is functional

18. What is a positive allosteric regulator on pyruvate carboxylase? for What reaction is this?
Riboflavin makes up FAD and FMN both used in redox reactions; vegans
Block Electron transport
Acetyl coA; gluconeogenesis
Glutamine PRPP amidotransferase

19. What is the confirmation of Downs?
Creates nicks in DNA to prevent supercoiling; both!
low Vmax
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
Amniocentesis karyotyping

20. What are the mucopolysaccharidoses? Which one is XR? AR? What accumulates in them?
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products
Decrease AFP - increased BCHG - decreased estriol - increased inhibin A
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Marfans - homocystinuria - MEN 2B

21. What is fructose 2 -6 phosphate? Where does it come from? by What enzyme?
Hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)
pleiotropic
A trinucleotide repeat disorder results in faulty methylation and thus expression of the FMR1 gene on the X chromosome (x linked recessive mode of inheritance)
An allosteric regulator; fructose 1 phosphate; phosphofructokinase 2

22. Glycogenolysis ________ maintains blood sugar
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Tryptophan; melatonin
in hepatocytes

23. What 4 diseases specifically results with B1 deficiency?
1) Dry beriberi: peripheral neuropathy demyelination (symmetricul muscle wasting) 2) Wernicke: ataxia - confusion - nystagmus - mammilary body and medial dorsal nuc of thalamus hemorrhage 3) Korsakoff: anterograde and retrograde amnesia - demyelinati
Fructose bisphosphatase 2
S - adenosyl methionine
AD

24. _____________ prevents fluidity of plasma membrane
Aldolase B
TRNA wobble
high cholesterol
Liver and skeletal muscle

25. How is the nitrogen of amino acids transferred to the liver for the urea cycle? explain this process.
Respiratory - seminal fluid - pancreatic - gallbladder; very thick without NaCl to pull water
Citrulline is combined with aspartate to make arginosuccinate Which is then split into fumarate (which leaves to enter TCA) and arginine. Arginine is then converted to Ornithine (via arginase) giving off Urea Which then goes to the kidney and ornithi
As alanine; amino acids donate their amino group to alpha ketoglutarate making it glutamate and the aa then becomes an alpha ketoacid (joins TCA cycle); glutamate then converts pyruvate to alanine by donating its amino group to pyruvate (with ALT); a
As BUN (blood urea nitrogen)

26. Which intermediate is involved in both pyrimidine synthesis and the urea cycle?
Carbamoyl phosphate
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
show disease

27. How can hyperammonia be hereditary? acquired?

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28. Which TCA cycle enzyme is found in the inner mit membrane? Where are the rest found?
Microcephaly - mental retardation - high pitched mewing/crying - epicanthal folds - cardiac abnormalities; microdeletion on short arm of chrom 5
Citrulline is combined with aspartate to make arginosuccinate Which is then split into fumarate (which leaves to enter TCA) and arginine. Arginine is then converted to Ornithine (via arginase) giving off Urea Which then goes to the kidney and ornithi
Vit K; neonates have sterile intestine and can not synthesize vit K
Succinate hydrogenase; matrix

29. What negatively regulates dopamine to norepinephrine?
Prolonged Ab use
Carbidopa
glycogenolysis
Helps make Vit K and antioxidant

30. What are the clinical symptoms that result from I cell disease?
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
When one allele on a gene is only expressed and the other is methylated/inactivated; during gametogenesis one of the alleles is methylated because the gamete from the other sex will provide those characteristics for the child
Iatrogenic - granulomatous disease (sarcoidosis d/t epitheloid macrophage release of calcitriol); hypercalcemia - hypercalciuria (renal calculi!) - loss of appetite - stupor
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes

31. why is there decreased immunity in kwashiokor and marasmus?
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
No protein!
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash
Trimethroprim inhibits bacterial dihyrofolate reductase

32. What is the end of anaerobic glycolysis?
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
Pyruvate! (not lactate - that is generate just in order to produce more NAD+)
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
Prevents neural tube defects in 1st trimester

33. list three uncoupling agents
show disease
Lactose (glucose and galactose)
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)
Dopamine beta hydroxylase; vit C

34. What is the metabolism of galactose like?
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
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover
Branche aa alpha ketoacid dehydrogenase; thiamine; Isoleucine - leucine - valine
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells

35. Which catecholamine has inhibitory action against acetylcholine?
AD
Dopamine
They increase the permeability of the inner mit membrane resulting in a loss of gradient and loss of ATP production BUT electron transport continues! heat is generated instead
Orotic aciduria megaloblastic anemia can not be corrected with folic acid or vit B12

36. What are rotenon - CN - antimycin A - CO?
Carbomyl phoshpate synthetase I
Block Electron transport
Creates nicks in DNA to prevent supercoiling; both!
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

37. From What aa does histamine come from? with What vitamin cofactors help?
Histidine; B6
This depends on if phosphofructokinase 1 is active and this depends on whether or not fructose 2.6 bisphophate is activating it or not - this can only occur if PFK 2 is on and not FBPase 2. then fructose 6 phosphate will participate in glycolysis. Ot
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA
Riboflavin; dairy and meat

38. What is the inheritance of Von Hippel Lindau disease?
Neurons and RBCs
AD
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Immediately after replication - DNA is unmethylated and so it is a signal to be double checked; HNPCC; heterochromatin

39. How do WBCs of CGD patients do some damage?
Hemolytic anemia; jaundice in newborn if mom gets too much vit K
Adrenal cells (steroid synthesis) - hepatocytes (p450 detox)
When different combination of exons get combined together; in Beta thallasemia
They use the H2O2 produced by some bacteria to produce bleach with myeloperoxidase Which they still have

40. What are the clinical symptoms of hyperammonemia?
linked recessive
Ehler Danlos; type III collagen def; joint dislocation - berry aneurysm - ecchymoses - organ rupture
Glycerol and propionyl coA; lactate and alanine
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits

41. Where does a majority of galactose in our diet come from?
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -
They can enter G1 from G0 and replicate if they like; hepatocytes - lymphocytes - fibroblasts
Lactose (glucose and galactose)
Whether or not the patient is also hyperammonemia (if yes - then OTC def)

42. What is the exception to degeneracy in the genetic code?
Branched alpha ketoacid dehydrogenase
Schilling test
Methionine is only encoded by AUG
Liver mit and liver cytosol

43. What are the key intermediates in the TCA?
Triacylglycerols in adipose tissue broken down into glycerol and free fatty acids; growth hormone and epinephrine
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
Fructose bisphosphatase 2

44. Is PRPP added later or first in pyrimidine synthesis?
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol
Vitamin C; facilitates iron absorption by making sure its in its reduced state (Fe2+) - hydroxylation for lysine and proline Which is necessary for crosslinking; necessary for dopamine Beta hydroxylase for conversion of dopamine to NE; keeps FH4 in i
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Later

45. What are the clinical symptoms associated with fragile X syndrome?
Carbomyl phosphate synthetase II
Macroorchitism - big ears - big jaw - mental retardation (2nd mcc!) - mitral valve prolapse - long face
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
AD

46. Where does catecholamine synthesis take place?
Pataus
Alpha amanitin; mushroom caps
Neural tissue and adrenal medulla
A 16C FA! the product in FA synthesis; saturated; no double bonds

47. Which intermediate filament is found connective tissue? muscle? epithelial cells? neuroglia? neurons? What can intermediate filaments be used for?
Vimentin - desmin - cytokeratin - glial fibrillary acidic protein (GFAP) - neurofilaments; to differentiate between different cells
Hydroxurea; deoxygenates ribose
A piece of glass or silicon chip with thousands of grids with different nucleic acid sequences and DNA or RNA probes are hybridized to the chip and a scanner detects the complementary binding; used to study a persons genome and to detect snps (single
kidney

48. What drug blocks acetaldehyde dehyrogenase? What are its side effects?
Homogentistic acid oxidase
O2 consumption (last electron acceptor) gets consumed also
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover
Fruits and vegetables

49. What disease is associated with chromosome 13?
Rb
activator
Bendy bones seen in children due to decreased Vit D; craniotabes - skeletal deformities - growth retardation - rosary
acetyl coA

50. Heterozygous females in X linked recessive disease...
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine
can be d/t lyonization
Methionine is only encoded by AUG
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP

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USMLE Step 1 Biochemistry

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