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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. Can a disorder be congential but not hereditary?

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2. What are two examples of X linked Autosomal Dominant disease?
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
XR - iduronate sulfatase
Hypophosphatemia rickets and Alports
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

3. Prokaryotes have What ribosomal units?
Hexosaminidase A; GM2 ganglioside
30S + 50S= 70S
Arg
Oral uridine administration; provides nucleosides and provides feedback inhibition

4. What experiment is chromosomes used for?
adrenal medulla
Mcardles disease
Karyotyping
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

5. What two processes maintain the plasma glucose levels?
32 or 30; malate aspartate shuttle or glycerol 3 phosphate shuttle; heart/liver and muscle
Mitochondrial inheritance
Zero order; increased production of NADH no matter the amount of end products produced
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis

6. What is the most common human enzyme deficiency? why? What is the mode of inheritance of this deficiency?
Vomiting - rice water stools - garlic breath
AR; trinucleotide deletion results in loss of a Phe aa on CFTR gene on chrom 7- the result is a mutated CFTR channel that gets degraded in the ER before reaching the surface; the purpose of CFTR is to increase Cl secretion in luminal secretions and r
All clathrin
G6PD; provides malarial resistance; X linked recessive

7. Which intermediate filament is found connective tissue? muscle? epithelial cells? neuroglia? neurons? What can intermediate filaments be used for?
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
Tyrosine hydroxylase; tetrahydrobiopterin factor; NADP+
Chromosomal imbalance (downs for ex)
Vimentin - desmin - cytokeratin - glial fibrillary acidic protein (GFAP) - neurofilaments; to differentiate between different cells

8. Where is anaerobic glycolysis used often?
Dopa decarboxylase; B6
Silent - misssense - nonsense
RBCs - renal medulla - leukocytes - lens - testes - cornea
Malabsorption problems (CF and sprue) and mineral oil intake

9. What is the most common disorder of the urea cycle? What is the result? What is its mode of inheritance? What is the mode of inheritance of the other urea cycle enzyme def?
Ornithine transcarbomyalse; orotic aciduria; X linked recessive; autosomal recessive
Inability to taste
Vomiting - rice water stools - garlic breath
ATP

10. Breast milk has a little of...
Alcohol dehyrogenase (alcohol to acetaldehyde); acetaldehyde dehydrogenase (acetaldehyde to acetate); NAD+; B3 (niacin)
Vit D and K
Vit K; neonates have sterile intestine and can not synthesize vit K
ATP and dATP

11. What negatively regulates dopamine to norepinephrine?
Carbidopa
Cytoplasmic side; active
Because that is Where the products will be consumed; acetyl coA; TCA cycle of ketone body production
Renal calculi of uric acid (replaces uric acid in excretion)

12. The mode of inheritance for both NF disease is...
Galactokinase; galactose appears in blood and urine - sometimes infantile cataracts may present as failure to track objects or lack of a social smile
Adenosine deaminase deficiency; Severe combined immunodeficiency disease
Both AD
Riboflavin; dairy and meat

13. What are chromosomes? during What part of the cell cycle are they found? in What pathologic state would you see a lot of chromosomes?
Release alk phos
Carbomyl phosphate synthetase II
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )

14. What is type II collagen found?
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
Cartilage (including hyaline) - vitreous body - nucleus pulposus
Trimethroprim inhibits bacterial dihyrofolate reductase
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover

15. Which vitamin keeps Fh4 in its reduced form?
MT!
Because carbamaoyl phosphate is involved in both urea cycle and pyrimidine synthesis
To transfer methyls; a methionine and an ATP; norepinephrine plus a methyl makes epinephrine
Vit C

16. What is the precursor for pyrimidines?
Orotate
N linked oligosaccharides
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
= q

17. What are the two molecular proteins that are used on MT for transporting in neurons? Which direction do they go?
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)
Dynein - retrograde - kinesin - anterograde
SnRNPs; RNA polymerase III
Each codon specifies only one amino acid

18. Coris glycogen storage disease has...
Dactinomycin - doxorubicin
Glycerol and propionyl coA; lactate and alanine
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage
normal lactate levels

19. Which antioxidant does cigarette smoke injury eat up? Which antioxidant does LDL injury eat up?
Vit C; Vit E
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Incoming Aminoacyl tRNA; site Where peptidyltransferase bond is made between growing peptide aa's; the holds the empty tRNA as it exits; the initiator mRNA (met or f - met) starts off in E site rather than A site
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes

20. What is the exception to the universal aspect of the genetic code?
Lesch Nyhan syndrome; X linked recessive
Mitochondria - archaebacteria - mycoplasma - and some yeasts
Because that is Where the products will be consumed; acetyl coA; TCA cycle of ketone body production
Prevents neural tube defects in 1st trimester

21. Amino acids are found in...
10 - 9 - 7 - 2; protein C and S
Lesch Nyhan syndrome; X linked recessive
Retinol; Beta carotenes (dark and yellow vegetables)
only L form

22. HMG coA synthase; cholesterol synthesis
Fruits and vegetables
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth
Uses HMG coA reductase
Neurons and RBCs

23. in What disease are there antibodies to snRNPs?
Mebendazole and thiabendazole
A 16C FA! the product in FA synthesis; saturated; no double bonds
Lupus
plasma membrane

24. What are the clinical symptoms of NF1?
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
Mental and growth retardation; seizures - fair skin - eczema - musty body odor; neurotoxic ketones and acids stimulate vomitting - can lead to pyloric stenosis
To increase serum Ca and phosphate for bone deposition
30S ribosomal RNA (small one)

25. What type of polymerase is primase?
DNA dependent RNA polymerase
Mucus secreting goblet cells - ab secreting plasma cells - nt secreting neurons
When child gets two chromosomes from one parent; imprinting dx
Acetazolamide to alkalinize the urine

26. When are there low levels of cAMP? What does this result in?
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
Where there is insulin; low protein kinase A means dePhosphorylation of the complex Which results in increased PFK2 Which results in more fructose 2 -6 bp and thus more PFK1!!
Cheilosis and corneal vascularization
Mucus secreting goblet cells - ab secreting plasma cells - nt secreting neurons

27. If a cell has a hyperchromatic or condensed nucleus is it undergoing transcription etc?
No
25 OH D3; 1 -25 (OH)2 D3 (Calcitriol)
Dopamine beta hydroxylase; vit C
AD

28. How do you treat fructose intolerance?
Glycolysis and aerobic respiration
Vitamin B1 (thiamine) - Vitamin B2 (riboflacin) - Vitamin B3 (niacin) - Vitamin B5 (pantothenate) - Vitamin B6 (pyridoxine) - Vitamin B7 (Biotin) - Vitamin B12 (cobalamin) - folate - Vit. C
Decrease intake of fructose and sucrose (fructose and glucose)
30S ribosomal RNA (small one)

29. What are three ketone bodies? Which is not detected in urine? Which do you see most in alcoholic ketoacidosis?
Fructose gets phosphorylated into fructose 1- P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B
Becomes methionine
Blood group types
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate

30. Which catecholamine has inhibitory action against acetylcholine?
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR
Dopamine
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months
Folinic acid; does not require DHF

31. What contributes to the acidosis in alcoholism?
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
Neurons and RBCs
Lactic acidosis and ketoacidosis
Cardiomegaly and systemic findings leading to early death; lysosomal alpha -1 -4- glucosidase (acid maltase)

32. What aa does AUG mRNA code for in eukaryotes? prokaryotes?
Fe2+; Fe3+
Methionine; f Met (formyl methyl methionine)
Tyrosinase
Hungtington

33. Where does gluconeogenesis occur?
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)
By addition of mannose 6 phosphate to proteins in the Golgi
Liver mit and liver cytosol
fat

34. What form of Vitamin D is in plants? milk fortified with vit D? formed in sun exposed skin?
Carbamoyl phosphate
D2 (ergocalciferol) - D3 (cholecalciferol) - D3 (cholecalciferol)
SnRNPs; RNA polymerase III
DHF

35. What is the other name of B3? What is its function? Synthesis of B3 requires What other vitamin? What else?
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
In the reproductive tract and in the resp tract; infertility - bronchiectasis and recurrent sinusitis - associated with situs inversus
Alcohol dehydrogenase; cytosol; mitochondria; NAD+
Can inducibly manipulate genes at specific developmental points

36. What enzyme is involved in the degradation of tyrosine to fumarate?
Excreted from the kidney in the form of urea in hepatocytes
HVA
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Homogentistic acid oxidase

37. other than in the kidney - Where else are gluconeogenesis enzymes found?
Kidney and intestinal epithelium
2 oxidative and nonoxidative; cytoplasm (both); none (none produced either - you are simply switching carriers of energy- from glucose 6 phosphate to NADPH)
Genotyping for mutant alleles (different sizes)
Nitric Oxide - creatinine - Urea

38. What is the deficient enzyme in Tay Sachs disease? accumulated Substrate?
Fabrys Disease and Hunters Syndrome
Hexosaminidase A; GM2 ganglioside
All and Alzheimers
succinyl coA (and then to OXA)

39. What drug blocks alcohol dehydrogenase? What is it used for?
Ouabain
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Fomepizole; antidote for methanol or ethylene glycol poisoning
Lyonization; nondisjunction in mitotic divisions during embryonic period

40. What is hartnup disease? What is the mode of inheritance?
Tyrosine
Defective neutral amino acid transporter on renal and intestinal cells; AR
Cortisol; inhibits insulin action
Fat soluble; either endogenous production or exogenous; D2 ergocalciferol is ingested from plants and D3 cholecalciferol is formed in sun exposed skin (and can be consumed in fortified milk)

41. What enzyme converts norepinephrine to epinephrine? using What cofactor?
Arginine
Phenylethanolamine N- methyl transferase; SAM
Carnitine shuttle
Neurons and RBCs

42. Is heterochromatic more accessible or less accessible to TF? euchromatin?
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
Shiga toxin and ricin (protein in castor beans)
Amniocentesis karyotyping
Less; more

43. What is 'charging' of tRNA? What enzyme regulates this? What does this reaction require? in What process is this?
MT!
AR
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
Excreted from the kidney in the form of urea in hepatocytes

44. What disease is associated with chromosome 17?
Cytoplasmic side; active
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
NF1
Oxygen!

45. What is the treatment of hyperammonia?
10 - 9 - 7 - 2; protein C and S
Carbamoyl phosphate
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)
Alcohol dehydrogenase; cytosol; mitochondria; NAD+

46. What is the main hormonal regulation of glycogen?
Glucagon - insulin and epinephrine
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
Renal calculi of uric acid (replaces uric acid in excretion)
Glycogen phosphorylase

47. What is heteroplasmy?
Mitochondrial inheritance
Presence of normal and mutated mtDNA (like mosaicism except in mit)
Multiple bone fractures - blue sclerae - hearing loss (abdnormal middle ear bones!) - dental imperfections - retarded wound healing
Phosphorylation of glucose

48. From What aa does porphyrin come from? What is porphyrin the precursor of?
Exons
Glycine; heme
HnRNA; mRNA
HVA

49. What is the rate determining enzyme in urea cycle?
Glycogen phosphorylase; phosphorylation and dephosphorylation
Fructose bisphosphatase 2
Carbomyl phosphate synthetase I
The active form of Vit D (1 -25 (OH)2 D3)

50. What is the mcc of an autosomal trisomy?
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis
Meiotic nondisjunction in mothers gametes during the first meiosis
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)

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USMLE Step 1 Biochemistry

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