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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. Glucokinase is a...
Meiotic nondisjunction in mothers gametes during the first meiosis
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
tyrosine hydroxylase
glutton

2. What is the rate determining enzyme in glycolysis?
Glycogen phosphorylase
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
When child gets two chromosomes from one parent; imprinting dx
Phosphofructokinase 1

3. What is the point of having a gluttonous glucokinase in the liver?
By cyclin CDK complexes
Lens and neural tissue; converts galactose to osmotically active galactitol
Pellagra
So that excess glucose can be stored (phosphorylated glucose cant leave) in the liver and saved as a buffer

4. What is the effect of defiiency of VIt E?
Following gastroenteritis and kwashiokor (protein deficiency)
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
Decrease intake of fructose and sucrose (fructose and glucose)
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA

5. Which glycogen storage disease causes hypertriglyceridemia?
Ascites from liver damage
kidney
teratogenic
Von gierkes

6. What is the rate limiting step in fatty acid synthesis? What four things inhibit this rate limiting step? What stimulates it?
Do agarose gel eletrophoresis to separate the different sizes of the PCR products (sizes id the the fragment)
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate
Inability to taste

7. The three steps of PCR
SnRNPs; RNA polymerase III
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
HMG CoA reductase
To amplify a specific desired fragment of DNA

8. What are the main clinical symptoms of Lesch Nyhan syndrome?
In the charging reaction! for this reason aminoacyl tRNA synthetase double checks
Milder form of type 1 with normal blood lactate levels; debranching enzyme (alpha -1 -6 glucosidase)
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis
RER in nucleus (synthesize NTs)

9. What is the result of pyruvate dehydrogenase deficiency? What causes it?
Riboflavin; dairy and meat
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits
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

10. What is the net production of glycolysis from one glucose?
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
Retinol; Beta carotenes (dark and yellow vegetables)
Downs
Aldolase B

11. What are the clinical symptoms of NF1?
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
Synthesis in liver and then hydrolysis of chylomicrons and VLDLs by capillary lipoprotein lipase in peripheral tissue; adipose tissue by lipases
Peripheral neuropathy - developmental delay - optic atrophy - globoid cells
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors

12. The main hormonal regulation of glycogen is...
Glycine; heme
All and Alzheimers
glucagon - insulin and epinephrine
Kidney and intestinal epithelium

13. What does a def in folic acid cause? is it more or less common than cobalamin def? How do you differentiate it with cobalamin def?
HMG CoA reductase; converts HMG CoA to mevalonate
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
Calcium and calmodulin activate glycogen phosphorylase kinase
Macrocytic megaloblastic anemia; it is the most common vit def in the US; no neuro symptoms and no methylmalonyl coA in the urine

14. What does deficiency of Vit K cause?
Using serine (which turns into glycine after reaction)
A 16C FA! the product in FA synthesis; saturated; no double bonds
Hemorrhage with increased PT and PTT time but normal bleeding time
Oral uridine administration; provides nucleosides and provides feedback inhibition

15. What is the presentation for cystinuria?
Cystine kidney stones (cystine staghorn calculi)
glutton
Schilling test
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

16. Name two diseases that have to do with elastin; discuss their pathogenesis.
Marfans and emphysema; marfans is a fibrillin protein defect - fibrillin is a supporting protein in tropoelastin scaffolding and results in aorta - skeletal and eye defects; emphysema is due to a deficiency in the function of alpha 1 antitrypsin
Lack of lactase (brush border enzyme) so can not break down lactose (a dissaccharide of galactose and glucose); African Americans and Asians
An AP (apyrimidinic) endonuclease to cut the DNA - exonuclease then removes and then filled and sealed by enzymes
Inosine/IMP; adenosine deaminase

17. Where does catecholamine synthesis take place?
Neural tissue and adrenal medulla
Von gierkes
Glutamine - aspartate - glycine; aspartate
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)

18. What three enzymes lead to orotic acid accumulation? What reactions are they involved in?
Less; more
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)
Avidin in raw egg whites prevents their reabsorption; also antibiotic use; dermatitis - alopecia - glossitis - lactic acidosis - enteritis
NF2 - DiGeorge/Velocardiofacial syndromes

19. why is there hepatosplenomegaly in many of the lysosomal storage diseases?
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
S. aureus - Aspergillus
Because cells of mononuclear phagocytic are esp rich in lysosomes
Preprocollagen - procollagen - tropocollagen - collagen

20. What experiment is chromosomes used for?
adrenal medulla
Biotin
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance
Karyotyping

21. What is a positive allosteric regulator on pyruvate carboxylase? for What reaction is this?
Liver and skeletal muscle
Hepatic fatty change
Acetyl coA; gluconeogenesis
fat

22. What are the glucogenic and ketogenic amino acids?
Fructose bisphosphatase 2
Ile - Phe - Thr - Trp
Amniocentesis karyotyping
activator

23. What systems are affected by CF?
Pulmonary - GI - reproductive (infertility in male due to absence of vas deferens and seminal fluid thickness)
X linked recessive; deletion of the dystrophin gene (connects actin to the membrane glycoprotein) due to frame shift mutation - lack of dystrophin results in muscle breakdown Which gets replaced by fibrofatty tissue and collagen
Pyruvate to lactate (results in lactic acidosis and decreased pyruvate for oxaloacetate for gluconeogenesis) - increased production of glycerol 3 phosphate from DHAP for TG synthesis; and increased betahydroxybutyrate ketoacid production from increas
Cartilage (including hyaline) - vitreous body - nucleus pulposus

24. Which vesicular trafficking protein takes vesicles from the Golgi to the ER (retrograde)?
Pompes
COP I
SAM
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)

25. What enzyme is deficient in classic galactosemia? symptoms? treatment?
Kidney and intestinal epithelium
Galactose 1 phosphate uridyltransferase (GALT) results in an accumulation of toxic substances; failure to thrive - jaundice - hepatomegaly - infantile cataracts - mental retardation; exclude galactose and lactose from diet
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Hydroxurea; deoxygenates ribose

26. What are the clinical symptoms of hyperammonemia?
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
Mitochondria - archaebacteria - mycoplasma - and some yeasts
osteosarcomas (Rb mutation is in all cells)
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits

27. With hypervitaminosis D you will see increased ______ - it causes bone turnover - and stimulates osteoblasts also
alk phos
Hemolytic anemia due to heinz bodies Which are oxidized hemoglobin precipitating within the RBCs
Vit C
By giving high amounts of pyridoxal phosphate in the diet

28. What are two clinical symptoms of newborns with CF? and whats a lab value of a newborn with CF?
Acidic
Retinol; Beta carotenes (dark and yellow vegetables)
Acetazolamide to alkalinize the urine
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin

29. What causes fruity odor in ketoacidosis?
GALT
Acetone
G6PD; provides malarial resistance; X linked recessive
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)

30. Where is glycogen mainly found?
Fructose 1 -6 bisphosphatase
Met - arg - val - his
Liver and skeletal muscle
Excreted from the kidney in the form of urea in hepatocytes

31. Is PRPP added later or first in pyrimidine synthesis?
Later
activation of PFK1
Carnitine shuttle
Actin/myosin - MT - intermediate filaments

32. What is the degradation product of Norepinephrine?
Kidney and intestinal epithelium
Thick mucus plugs lungs recurrent pulmonary infections (pseudomonas and aureus) - chronic bronchitis - bronchiectasis (which can lead to cor pulmonale!); biofilms form on resp tract
Proteolytic processing (of water soluble parts to less soluble) to turn into troprocollagen and then crosslinking between hydroxylated lysine residues by lysyl oxidase to make collagen fibrils
VMA

33. What are the common symptoms of B vitamin deficiencies?
Tyrosinase
Decrease AFP - increased BCHG - decreased estriol - increased inhibin A
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
Dermatitis - glossitis - diarrhea

34. What are the clinical symptoms of Huntingtons disease? When does it present?
Carbomyl phoshpate synthetase I
AAUAAA; Poly A polymerase; no
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
Hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)

35. What are two examples of X linked Autosomal Dominant disease?
Decrease intake of fructose and sucrose (fructose and glucose)
By giving high amounts of pyridoxal phosphate in the diet
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes
Hypophosphatemia rickets and Alports

36. 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
Zero order; increased production of NADH no matter the amount of end products produced
N5N10 methylene THF
pleiotropic

37. Which oxidant is most attributable to damage of RBCs?
Galactose
be anorexic
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
LDL; LDL oxidize atherosclerosis

38. The result of dephosphorylation of PFK2 is...
activation of PFK1
To amplify a specific desired fragment of DNA
Uracil; thymine
Increased nuchal translucency

39. What happens in an aminotransferase reaction
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
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
Dihydrofolate reductase; vitamin B12; homocysteine

40. What two def. most commonly cause phenylketonuria?
Neurons and RBCs
Phenylalanine hydroxylase or tetrahydrobiopterin factor
Osmotic diarrhea - bloating - cramps
The products of FA oxidation (Acetyl CoA and NADH) phosphorylate pyruvate deyhdrogenase Which inactivates it

41. What are the three results that come from increased NADH in alcohol metabolism?
Dihydrofolate reductase; vitamin B12; homocysteine
usually present late
all carriers
Pyruvate to lactate (results in lactic acidosis and decreased pyruvate for oxaloacetate for gluconeogenesis) - increased production of glycerol 3 phosphate from DHAP for TG synthesis; and increased betahydroxybutyrate ketoacid production from increas

42. From What aa do NAD+ and NADP+ come from?
Decreased would healing; microcytic anemia (d/t decreased iron [not absorbable]; macrocytic anemia (d/t Fh4 not reduced)
Tryptophan
Exons
Phosphoenolpyruvate; pyruvate kinase; fructose 1 - 6 BP; ATP - alanine

43. What is carnitine deficiency and What does it result in?
AR
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
III
Carbamoyl phosphate to orotic acid

44. What aa is the precursor for creatinine?
Urine turns black on standing
Arginne
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP
Lysine and leucine

45. What is acyl coA dehydrogenase used in? What does a deficiency in this enzyme produce?
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis
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!!
Later
Fatty acid (acyl coA) oxidation to acetyl coA; increase in dicarboxylic acids - and decreased glucose and ketones

46. Which amino acid is the most basic?
Fomepizole; antidote for methanol or ethylene glycol poisoning
Tyrosine hydroxylase; tetrahydrobiopterin factor; NADP+
Arg
Exons

47. What does guanine have on it?
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
Using serine (which turns into glycine after reaction)
A ketone
glutton

48. What is the mode of inheritance of Marfans?
AD
Pyruvate (through OXA); lactate - alanine - malate (and all other TCA intermediates through OXA) - glycerol - odd chain fatty acids yield propionyl coA Which can be converted to succinyl coA and enter as TCA cycle
Isoleucine - valine - leucine
reabsorbs

49. What cofactor is required for lysyl oxidase cross linking? What reaction is required beforehand for crosslinking to occur?
Kidney and intestinal epithelium
Structural (constitutively active)
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances
Cu; hydroxylation

50. With What type of inheritance is variable expression and incomplete penetrance associated with? Give an example of each.
Less; more
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
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
Phosphoenolpyruvate; pyruvate kinase; fructose 1 - 6 BP; ATP - alanine

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USMLE Step 1 Biochemistry

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