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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. Where is type IV collagen found? to What protein is bound? What is special about this type? How do the different types of collagen differ?
Respiratory burst - P450 - and glutathione reductase
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
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash
BM; laminins; most flexible; different aa composition

2. Other than glycogenesis and glycolysis - What else is Fructose used for?
Encode enzymes for oxphos mit reactions
An AP (apyrimidinic) endonuclease to cut the DNA - exonuclease then removes and then filled and sealed by enzymes
Mannose
Block Electron transport

3. What is the signal for adenylation? What enzyme does? does it require a template?
By addition of mannose 6 phosphate to proteins in the Golgi
AAUAAA; Poly A polymerase; no
No
Lyonization; nondisjunction in mitotic divisions during embryonic period

4. _______ is ubiquitous
the RER
hexokinase (glucokinase only found in liver and beta cells of pancreas)
Flourescent DNA/RNA In SITU hybridization; for visualization of anomalies (like microdeletions) that are too small to be seen on karyotype; Prader - Willi syndrome
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils

5. What is an example of a nonsense mutation?
Myotonic Dystrophy (CTG) - Huntington (CAG) Friedricks Ataxia (GAA) - Fragile (CGG)
Beta thalassemia
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
Vit D and K

6. Why do mitochondrial diseases exhibit variable expression?
Aminoglycosides and tetracyclines
Heteroplasmy
SER and mitochondria; NADPH
AST (mit damage) - and GGT (d/t SER hyperplasia d/t induction of p450 generation)

7. Where is anaerobic glycolysis used often?
Stored ATP - creatine phosphate - anaerobic glycolysis; as distances increase - ATP is obtained from additional resources; above plus ox phos
Prolonged Ab use
An AP (apyrimidinic) endonuclease to cut the DNA - exonuclease then removes and then filled and sealed by enzymes
RBCs - renal medulla - leukocytes - lens - testes - cornea

8. What does oligomycin do?
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
Block ATP synthase resulting in no ATP production and an increased proton gradient
Dry is just the symmetrical neuropathy with both motor and sensory symptoms; wet includes both the neuropathy and cardiac involvement of high output failure with peripheral edema - tachycardia - cardiomegaly
Edwards

9. Ocular albinism is...
Phenylaline
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers
linked recessive
Nitric Oxide - creatinine - Urea

10. What is SAM?
S - adenosyl methionine
Vitamin B1 (thiamine) - Vitamin B2 (riboflacin) - Vitamin B3 (niacin) - Vitamin B5 (pantothenate) - Vitamin B6 (pyridoxine) - Vitamin B7 (Biotin) - Vitamin B12 (cobalamin) - folate - Vit. C
Alkaptonuria; ochronosis
Developmental delay - gargoylism - airway obstruction (d/t short neck) - corneal clouding - CAD - hepatosplenomegaly

11. Give examples of the anabolic processes that NADPH participates in. From What process is NADPH produced?
Synthesis in liver and then hydrolysis of chylomicrons and VLDLs by capillary lipoprotein lipase in peripheral tissue; adipose tissue by lipases
Carbidopa
Oral uridine administration; provides nucleosides and provides feedback inhibition
Steroid - cholesterol FA synthesis; HMP shunt

12. What are the clinical findings in edwards syndrome?
Riboflavin makes up FAD and FMN both used in redox reactions; vegans
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage
Mental retardation - rocker bottom feet - micrognathia (small jaw) - low set ears - clenched hands with polydactyly - congenital heart disease
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)

13. What regulates Fructose 1 -6 bisphosphatase? What reaction is it found in?
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
liver
Metabolizes them with transferase enzymes to acetyl coA

14. What is the rate determining enzyme in glycogen synthesis?
Genotyping for mutant alleles (different sizes)
Phenylethanolamine N- methyl transferase; SAM
Glycogen synthase
allosteric regulation

15. Which anticancer drugs act on MT? how are they different?
DNA dependent RNA polymerase
By cyclin CDK complexes
Vincristine - vinblastine - and paclitaxel; the vinca alkaloids block formation of the spindle and paclitaxel prevents breakdown of the mT spindle
Type I collagen; AD

16. There are 2 GTP per...
glycogenolysis
Mit encephalopathy - lactic acidosis - stroke like episodes
Aldose reductase in the lens converts built up galactose to galactitol Which is osmotically active
tubulin dimer

17. From Where is alk phos release in the bone? What enzyme does it act on? What is the result?
III
Promoter binds RNA Pol II and is very close (25 bases) to initiation site and is AT rich; enhancer/silencers bind TFs only - can be located close or far and regulate gene expression but not specifically initiation; transcription
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
H1

18. What is hypophosphatemia rickets? Can it be treated with Vit D?
5'--> 3'; prokaryote only; for removing RNA primer and filling it with DNA
Collagen; fibroblasts; 4; ECM
Lens and neural tissue; converts galactose to osmotically active galactitol
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no

19. What are flagella made of?
Stored ATP - creatine phosphate - anaerobic glycolysis; as distances increase - ATP is obtained from additional resources; above plus ox phos
Carbomyl phosphate synthetase II
MT!
Structural (constitutively active)

20. From What aa does serotonin come from? What NT is serotonin a precursor for?
Tryptophan; melatonin
RER in nucleus (synthesize NTs)
Glutamate and aspartate; CO2 provides an ketone
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization

21. What is the result of arginase deficiency?
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)
Tyrosinase deficiency; defective tyrosine transporters; lack of migration of neural crest cells; skin cancer
Vit C
Chorea and spastic paresis

22. What is the pathogenesis of Goodpasteurs syndrome? What are the main targets?
Phenylaline
Release alk phos
Abs against type IV collagen; pulmonary and glomerular capillaries
Chromosomal imbalance (downs for ex)

23. What is used in a marathon?
Trimethroprim inhibits bacterial dihyrofolate reductase
Uracil; thymine
Aminoglycosides and tetracyclines
Glycogen and FFA oxidation - glucose conserved for final sprinting!

24. What is the impetus for ketoacidosis in starvation? alcoholism?
No protein!
A 16C FA! the product in FA synthesis; saturated; no double bonds
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate
Insertion or deletion of a number of nucleotides indivisible by 3; tay sachs - duchennes MD

25. For What three enzymes is arginine a precursor for?
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
golgi apparatus
Nitric Oxide - creatinine - Urea
Biotin

26. Which is the rate limiting step of the urea cycle?
Increased CPK and muscle biopsy
Tyrosine
Isocitrate dehydrogenase
Carbomyl phoshpate synthetase I

27. What are permanent cells? Which cells are permanent?
Galactocerebrosidase; Galactocerebroside
Cells that stay in G0 and cannot replicate - instead they regenerate from stem cells; neurons - skeletal and cardiac muscles - and RBCs
Arg
B12 and folate; B12; washed out

28. give an example of how phenylketonuria is pleiotropic.
Also have fair skin - blond hair - blue eyes - eczema
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
to ions
CNS defects - mental retardation - death - feeding difficulties - vomiting - hypoglycemia; thiamine

29. What is the precursor for both purines?
IMP
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
glucagon - insulin and epinephrine
Cells that are stable go in and out of the G1 to G0 Which is the stable/quiescent (can go into replication but dont) type of cells; cells that stay in G0 are permanent and can not enter G1

30. Which antifungal acts on MT?
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
Hexosaminidase A; GM2 ganglioside
Neurons and RBCs
Griseofulvin

31. What does SAM turn into after it loses a methyl? How does it get turned back to SAM?
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Carnitine shuttle
Homocysteine; homocysteine methyltransferase with B12 and tetrahydrofolate
pleiotropic

32. Where are secreted proteins synthesized? Where are cellular/organellar proteins synthesized?
Methionine; f Met (formyl methyl methionine)
RER; free ribosomes
ATP and biotin
Galactokinase deficiency and classic galactosemia; classic galactosemia

33. What are the findings with phenylketonuria?
Mental and growth retardation; seizures - fair skin - eczema - musty body odor; neurotoxic ketones and acids stimulate vomitting - can lead to pyloric stenosis
Dermatitis - glossitis - diarrhea
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Either salvage by HGPRT and PRPP or conversion to xanthine and then uric acid by xanthine oxidase

34. What Ab class blocks DNA gyrase?
Flouroquinolones
the RER
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
Hepatic glycogenolysis (mostly) - also hepatic gluconeogenesis - adipose release of FFA (minor)

35. What ensures that during gluconeogenesis all the ATP wont be used in glycolysis as youre producing it?
liver
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
Galactocerebrosidase; Galactocerebroside
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

36. What is the storage form of vit D? active form?
ATP is an allosteric inhibitor on both phosphofructokinase and pyruvate kinase and pyruvate hydrogenase; and fructose 2 -6 BP Which is an allosteric enhancer on phosphofructokinase is an allosteric downregulator on fructose 1 -6 bisphophatase
25 OH D3; 1 -25 (OH)2 D3 (Calcitriol)
NADPH oxidase; CGD
A topoisomerase II inhibitor; because cancer cells use II more so than healthy cells

37. What kind of DNA damage does ionizing radiation cause? What type of repair helps with this?
In the charging reaction! for this reason aminoacyl tRNA synthetase double checks
Cystic Fibrosis (CFTR gene)
Double strand breaks; nonhomologous end joining
the RER

38. From What aa does glutathione come from?
Glutamate
False; GTP hydrolysis
Retinol; Beta carotenes (dark and yellow vegetables)
Zero order; increased production of NADH no matter the amount of end products produced

39. What is the deficient enzyme in Krabbes disease? accumulated Substrate?
Galactocerebrosidase; Galactocerebroside
Acetyl coA; gluconeogenesis
Downs
Pulmonary - GI - reproductive (infertility in male due to absence of vas deferens and seminal fluid thickness)

40. in What organ is D3 converted from 25 OH D3? with What enzymes?
Chorea and spastic paresis
Arginne
Liver; P450 hydroxylation
high Vmax

41. 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?
Converts it to citrulline
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
Vit D levels
30S + 50S= 70S

42. Other than anabolic processes What else is NADPH used for?
Respiratory burst - P450 - and glutathione reductase
Inbit Na+K+ ATPase; Cardiac glycosides
Lesch Nyhan syndrome; X linked recessive
Hemolytic anemia; jaundice in newborn if mom gets too much vit K

43. What do statins inhibit?
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase
FA coA synthetase combines coA with FA to make acyl coA
HMG CoA reductase

44. Vit K in excess can cause _____ in newborns
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
jaundice
normal lactate levels
ATP synthase - ATP- ADP translocase - ETC

45. Which RNA polymerase synthesizes rRNA? where?
I; nucleolus
AD (trinucleotide expansion is not a mode of inheritance)
Cortisol; inhibits insulin action
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate

46. What is the source of Biotin?
Bacterial synthesis in the intestine
Fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio
Excreted from the kidney in the form of urea in hepatocytes
D2 (ergocalciferol) - D3 (cholecalciferol) - D3 (cholecalciferol)

47. What type of disease is MERRF? What is the clinical presentation?
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
False; GTP hydrolysis
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
Myoclonus epilepsy

48. What explains the fatty change in kwashiokor?
Abetalipoproteinemia and increased G3P production from all the carbs!
Phenylalanine
Bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating
25 OH D3; 1 -25 (OH)2 D3 (Calcitriol)

49. Which antihelminthic drugs act on microtubules?
Branched alpha ketoacid dehydrogenase
Vincristine - vinblastine - and paclitaxel; the vinca alkaloids block formation of the spindle and paclitaxel prevents breakdown of the mT spindle
Mebendazole and thiabendazole
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase

50. What is the other name of Vitamin B6? What is its function?
Arg - lys - his; positive except His has no charge at body pH
7 dehydrocholesterol
Pyridoxine; converted to pyridoxal phsophate used in transamination reaction - decarboxylations - heme synthesis - niacin synthesis from trp - glycogen phosphorylase - cystathionine synthesis - NT synthesis
Flouroquinolones

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USMLE Step 1 Biochemistry

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