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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. What is the end of anaerobic glycolysis?
A topoisomerase II
Chloramphenicol
Lupus
Pyruvate! (not lactate - that is generate just in order to produce more NAD+)

2. What is the rate determining enzyme in fatty acid oxidation?
By epoxide reductase in the liver; coumadin; intestinal flora and leafy vegetables
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
Branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa
Carnitine acyltransferase I

3. What does vit C excess cause?
Bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating
Alpha 1 -4 linkages; alpha 1 -6 linkages
Renal calculi of uric acid (replaces uric acid in excretion)
Phenylalanine

4. What is 'charging' of tRNA? What enzyme regulates this? What does this reaction require? in What process is this?
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
is active
liver and muscle
Mitochondria - archaebacteria - mycoplasma - and some yeasts

5. other than succinate dehydrogenase What other enzymes are found in the inner mit membrane?
ATP synthase - ATP- ADP translocase - ETC
UV nonionizing radiation causing thymidine dimers
Electron transport inhibitors - ATPase inhibitors - Uncoupling agents (increase permeability of the membrane - loss of hydrogen gradient)
Gets converted to pyruvate via the Cori cycle in the liver

6. What are the symptoms of infantile beriberi and When do they present?
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
AR
To amplify a specific desired fragment of DNA

7. Daughters of Xlinked recessive diseased fathers are...
allosteric regulation
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover
Ehler Danlos; type III collagen def; joint dislocation - berry aneurysm - ecchymoses - organ rupture
all carriers

8. name three glucogenic AA and how they enter gluconeogenesis. through What cycle do they enter gluconeogenesis?
Alanine (through pyruvate) - aspartate (through OXA) - glutamate (alpha ketoglutarase); TCA
Chediak Higashi Syndrome; decreased phagocytosis results in recurrent pyogenic infections - partial albinism - and peripheral neuropathy
Aldose reductase in the lens converts built up galactose to galactitol Which is osmotically active
Central and peripheral demyelination with ataxia and dementia

9. AD diseases are usually...
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
pleiotropic
Myotonic Dystrophy (CTG) - Huntington (CAG) Friedricks Ataxia (GAA) - Fragile (CGG)

10. Which amino acids are acidic? are they negatively or positively charged at body pH?
linked recessive
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance
Adrenal cells (steroid synthesis) - hepatocytes (p450 detox)
Asp and glu; negatively

11. ______________ interact with each other and decrease fluidity and increase melting temperature
Mental retardation - excessive laughter - seizures - ataxia - 'happy puppet'
long saturated fatty acids
AR
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan

12. What is the major cause of SCID? What does SCID stand for?
Adenosine deaminase deficiency; Severe combined immunodeficiency disease
TPP (from B1- pyrophosphate) - FAD (B2) - NADH2 (B3) - CoA (B5 - panothenate) - Lipoic Acid
Block Electron transport
glycogenolysis

13. What is the first step in the respiratory burst/oxidative burst? in What disease is this deficient?
Encode enzymes for oxphos mit reactions
ATP synthase - ATP- ADP translocase - ETC
NADPH oxidase; CGD
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50

14. Which vesicular trafficking protein takes vesicles from ER to the Golgi (anterograde)?
COP II
Steroid synthesis and detoxification
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate

15. What are the three mc autosomal trisomies in decreasing order?
Decreased would healing; microcytic anemia (d/t decreased iron [not absorbable]; macrocytic anemia (d/t Fh4 not reduced)
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes
Downs (21) - Edwards (18) - Pataus (13); also in increasing severity
Vomiting - rice water stools - garlic breath

16. IMP is degraded to inosine and then to hypoxanthine. What two options are next? by What enzymes?
glycogenolysis
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
Either salvage by HGPRT and PRPP or conversion to xanthine and then uric acid by xanthine oxidase
Alpha galactosidase A; ceramide trihexoside

17. What is Maternal PKU?

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18. Other than thymidylate synthase - What else is required to convert dUMP to dTMP?
N5N10 methylene THF
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
When child gets two chromosomes from one parent; imprinting dx
Acetyl coA activated pyruvate carboxylase in gluconeogenesis

19. Which cells have the most FA and thus are the most susceptible to FR injury?
Aromatic; musty body odor
CPSII
Neurons and RBCs
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils

20. With What type of inheritance is variable expression and incomplete penetrance associated with? Give an example of each.
Proprionyl coA; through methylmalonyl coA; B12
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances
By cyclin CDK complexes

21. What does the passage of electrons in the ETC result in?
Malabsorption problems (CF and sprue) and mineral oil intake
Methionine is only encoded by AUG
Defective neutral amino acid transporter on renal and intestinal cells; AR
Formation of a proton gradient that is then used to create ATP through ATP synthase

22. What converts dopa into melanin?
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no
Increased concentration of Cl ions in sweat test
Glutamate; glutamate decarboxylase; B6; gamma aminobutyrate
Tyrosinase

23. How does fructose enter glycolysis? galactose?
Carnitine shuttle
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Glutamine PRPP amidotransferase
Via fructose 1 P by fructokinase in the liver; as glucose 1 by being GALT- ed ;)

24. How is THF converted to N5N10 Methylene?
Gets converted to pyruvate via the Cori cycle in the liver
is active
Smoking (FR takes up all the antioxidants); diets lacking fruit
Using serine (which turns into glycine after reaction)

25. What are the clinical symptoms of duchennes muscular dystrophy?
Urea cycle enzyme deficiency (mc: ornithine transcarbamoylase); liver disease - alcoholic cirrhosis and reye's
Starts before age 5 with with pelvic girdle weakness with use of Gowers maneuver to stand up - it then progresses superiorly with muscle weakness (type 1 and 2!); waddling duck gait; hyporeflexia; pseudohypertrophy of calf muscles d/t fibrofatty repl
Leucine and lysine
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances

26. What experiment is chromosomes used for?
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
Karyotyping
I; nucleolus
S adenosyl homocysteine; homocysteine transferase; B12 and THF; M- THF

27. What enzyme is deficient in maple syrup disease? What does it result in?
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
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
Branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

28. What carries Acyl (as energy)?
Acetyl coA and NADH inhibit pyruvate dehyrogenase
It induces its action!
Coenzyme A and lipoamides
Cheilosis and corneal vascularization

29. Like mRNA has a poly A tail on the 3' end - What does tRNA have on its 3' end? What happens here?
Carnitine shuttle
HMG CoA reductase; converts HMG CoA to mevalonate
CCA and chemically modified bases Where amino acid is covalently bonded
Proprionyl coA; through methylmalonyl coA; B12

30. In protein translation - What is the 'A' site for? 'P' site? 'E' site? What is the exception to this?

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31. What is the order of cell cycle phases? What happens in each phase?
Mitosis then Interphase (G1 - S - G2); in G1 is presynthesis phase - S is synthesis phase (DNA rep. etc) - G2 is premitotic (making of MT spindle etc)
Phenylethanolamine N- methyl transferase; SAM
Peripheral neuropathy - developmental delay - optic atrophy - globoid cells
HMG CoA synthetase; HMG CoA reductase

32. __________ adds N linked oligosaccharides to proteins
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers
the RER
Vomiting - rice water stools - garlic breath
Aminoglycosides and tetracyclines

33. Findings for McArdle's disease? deficient enzyme?
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash
High glycogen in muscle - but cannot break it down - leading to painful muscle cramps - myoglobinuria with strenuous exercise - no increase in lactic acid after exercise; skeletal muscle glycogen phophorylase
FISH
They use the H2O2 produced by some bacteria to produce bleach with myeloperoxidase Which they still have

34. What is the deficient enzyme in Von Gierkes disease? What are the findings?
Glycine; proline and lysine
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Some viruses

35. What aa becomes essential with homocystinuria? phenylalaninuria?
Acidic
Do agarose gel eletrophoresis to separate the different sizes of the PCR products (sizes id the the fragment)
Cysteine; tyrosine
Glycogen phosphorylase; phosphorylation and dephosphorylation

36. What is the pathogenesis of fragile x syndrome?
pleiotropic
MT!
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)
tyrosine hydroxylase

37. other than Acetyl coA inhibiting pyruvate dehydrogenase complex - how else is it ensured that gluconeogenesis is occuring during FA oxidation and not glycolysis?
Pigmented iris hamartomas
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
Glutathione peroxidase (catalase) reduces H202 to H20 with glutathione; oxidized glutathione gets reduced by glutathione reductase with NADPH; NAP+ is regenerated to NADPH with Glucose 6 phosphate dehydrogenase; because H2O2 from the resp burts in th
Acetyl coA activated pyruvate carboxylase in gluconeogenesis

38. What is the mode of inheritance of phenyketonuria?
Pyruvate carboxylase (pyruvate to OXA) (mit) - PEP carboxykinase (OXA to PEP) (cyt) - Fructose 1 -6 bisphophatase (fructose 1 -6 bisphosphate to fructose 6 P) (cyt) and glucose 6 phosphatase (in ER); glucose 6 phosphatase
AR
To transfer methyls; a methionine and an ATP; norepinephrine plus a methyl makes epinephrine
Tyrosine

39. What enzyme is deficient in Essential fructosuria? What are the symptoms?
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)
Metabolizes them with transferase enzymes to acetyl coA
Fructokinase; benign - fructose in the blood and urine
Formation of the alpha chains out of glycine - lysine - proline in the RER to make preprocollagen; hydroxylation of the proline and lysine residues in the RER; glycosylation of the lysine residues to make procollagen Which is triple helix of alpha ch

40. What is the effect of defiiency of VIt E?
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
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait
plasma membrane

41. Other than anabolic processes What else is NADPH used for?
Increased CPK and muscle biopsy
Glucose 6 phosphatase
Respiratory burst - P450 - and glutathione reductase
COMT and MAO

42. What does alcohol do to the P450 system?
Downs (21) - Edwards (18) - Pataus (13); also in increasing severity
An anti cancer agent that is a topoisomerase II and creates nicks in DNA
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
hexokinase - glucokinase (its a glutton)

43. What is the rate limiting step in fatty acid synthesis? What four things inhibit this rate limiting step? What stimulates it?
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate
Phospholipids - sphingolipids - glycolipids
Ascites from liver damage
Acetyl coA activated pyruvate carboxylase in gluconeogenesis

44. What is the difference between methotrexate and trimethroprim?
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
Biotin; cofactor for carboxylation; pyruvate carboxylase (turning pyruvate to oxaloacetate) - acetyl coA carboxylase (acetyl coA to malonyl Co A) - and proprionyl coA caroboxylase for (propionyl CoA to methylmalonyl coA)
P53 and Rb; p53 activates BAX Which inhibits BCL2 When there is DNA damage - Rb phosphorylation allows progression into S phase
Trimethroprim inhibits bacterial dihyrofolate reductase

45. What disease is associated with chromosome 3?
Malabsorption problems (CF and sprue) and mineral oil intake
Glycogen and FFA oxidation - glucose conserved for final sprinting!
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash
VHL (Von Hippa Lindau)

46. 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?
BM; laminins; most flexible; different aa composition
is active
Vit C; Vit E
Osmotic diarrhea - bloating - cramps

47. From What aa does porphyrin come from? What is porphyrin the precursor of?
Ouabain
Chediak Higashi Syndrome; decreased phagocytosis results in recurrent pyogenic infections - partial albinism - and peripheral neuropathy
Glycine; heme
1) if it is stable/labile or permanent 2) intact BM and 3) intact ECM

48. Ca2+ is an ___________ on pyruvate deyhdrogenase - this links glycolysis with muscle contraction
VMA
Cu; hydroxylation
activator
Fat malabsorption (CF) and abetalipoproteinemia (damage takes up all antioxidants)

49. Where is glycogen mainly found?
Steroid - cholesterol FA synthesis; HMP shunt
Liver and skeletal muscle
glycogenolysis
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

50. From What aa do NAD+ and NADP+ come from?
Converts it to citrulline
Tryptophan
Myoclonus epilepsy
Def in Vit C; def in Vit D

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USMLE Step 1 Biochemistry

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