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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.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

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. Which end carries the triphosphate? Which end of DNA makes the hydoxyl attack?

2. No offspring of affected males with a mit disease can...
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Leucine and lysine
show disease
Fructokinase; benign - fructose in the blood and urine

3. From Where is alk phos release in the bone? What enzyme does it act on? What is the result?
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
Glycerol and propionyl coA; lactate and alanine
Carbidopa

4. Which glycogen storage disease causes hypertriglyceridemia?
Silent - misssense - nonsense
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
Von gierkes

5. Is DNA acidic or basic?
Acidic
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)
All clathrin

6. What type of disease is MELAS? What is the clinical presentation?
Nucleus
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
Mit encephalopathy - lactic acidosis - stroke like episodes
Downs

7. What does PEP carboxykinase require? and for What reaction is this?
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding
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
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
GTP: gluconeogenesis - OXA to phosphoenolpyruvate

8. What is the difference between a nucleotide and a nucleoside?
Nucleoside is just the ribose plus the base; nucleotide is the ribose plus the base but the phosphate bond
Glycolysis and aerobic respiration
Vit C
only L form

9. From What aa does thyroxine come from?
Chronic pancreatitis leads to type 1 diabetes - pancreatic insufficiency leads to ADEK deficiencies - malabsorption and steatorrhea - blocked gallbladder ducts leads to secondary biliary cirrhosis
Galactocerebrosidase; Galactocerebroside
Tyrosine
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

10. Is heterochromatic more accessible or less accessible to TF? euchromatin?
Abetalipoproteinemia and increased G3P production from all the carbs!
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
Lens and neural tissue; converts galactose to osmotically active galactitol
Less; more

11. What is the confirmation of Downs?
Increased G3P for TG synthesis - increased acetyl CoA (Fatty acid synthesis for TG synthesis) - and decreased oxidation of FA in the mitochondria due to alcohols toxicity on the mit
allosteric regulation
Amniocentesis karyotyping
NF1

12. What does the passage of electrons in the ETC result in?
Glycogen synthase
Formation of a proton gradient that is then used to create ATP through ATP synthase
Arg - lys - his; positive except His has no charge at body pH
TPP (thiamine pyrophosphate)

13. What aa is most accumulated in hartnup disease? What vitamin becomes deficient?
Asp and glu; negatively
Tryptophan; niacin
paternal
fat

14. What is the rate determining enzyme in glycolysis?
ATP synthase - ATP- ADP translocase - ETC
Lack of proper dietary therapy during pregnancy resulting in infant's microcephaly - mental retardation - growth retardation and congenital heart defects
Phenylalanine
Phosphofructokinase 1

15. What is the net production of glycolysis from one glucose?
Griseofulvin
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
degradation

16. What are the findings in Metachromatic leukodystrophy?
Glucose 6 phosphate dehydrogenase
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
Central and peripheral demyelination with ataxia and dementia
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA

17. What are three ketone bodies? Which is not detected in urine? Which do you see most in alcoholic ketoacidosis?
III
False; GTP hydrolysis
Also have fair skin - blond hair - blue eyes - eczema
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate

18. Which amino acid is the most basic?
Also have fair skin - blond hair - blue eyes - eczema
Arg
Hydroxurea; deoxygenates ribose
Acetone

19. Give an example of codominance.
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting
Blood group types
GALT
Fructose 1 -6 bisphosphatase

20. What are the findings in Niemann Pick disease?
Von gierkes
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
low Vmax
False; GTP hydrolysis

21. The plasma membrane...
is asymmetric
Carnitine acyltransferase I
Glycine; proline and lysine
Oxaloacetate gets shifted to malate d/t excess NADH

22. What is given to prevent side effects When methotrexate is given? why does this work?
Branche aa alpha ketoacid dehydrogenase; thiamine; Isoleucine - leucine - valine
Arylsulfatase A; cerebroside sulfate
Folinic acid; does not require DHF
Homogentistic acid oxidase

23. What type of polymerase is primase?
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
DNA dependent RNA polymerase
Following gastroenteritis and kwashiokor (protein deficiency)
Osteomalacia is vit D def seen in adults and causes bowed legs and results in increased fractures

24. What are the clinical findings in patau syndrome?
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
Trinucleotide expansion diseases
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Dermatitis - glossitis - diarrhea

25. Insulin receptor is not cAMP second receptor but rater tyrosine kinase...
Phenylethanolamine N- methyl transferase; SAM
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase
Respiratory - seminal fluid - pancreatic - gallbladder; very thick without NaCl to pull water
Succinyl coA

26. What does arsenic do? How is this important?
alk phos
Mental retardation - excessive laughter - seizures - ataxia - 'happy puppet'
Inhibits lipoic acid; lipoic acid is a cofactor for pyruvate dehydrogenase
cell cycle events

27. Which RNA polymerase synthesizes tRNAs and snRPs?
Alcoholism - RA - inflammatory disease - chronic diarrhea
III
Phenylaline
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding

28. What is the presentation for cystinuria?
= q
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
calorie deficient
Cystine kidney stones (cystine staghorn calculi)

29. Other than ragged red fibers and lactic acidosis - What else is common in mit myopathies?
Neurologic lesions and cardiomyopathies (ox phos!)
Dihydrofolate reductase; vitamin B12; homocysteine
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)
Immediately after replication - DNA is unmethylated and so it is a signal to be double checked; HNPCC; heterochromatin

30. After glucose 6 P is converted to glucose 1 P - What is the next step in glycogenesis? then what?
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )
Ehler Danlos; type III collagen def; joint dislocation - berry aneurysm - ecchymoses - organ rupture
Pellagra
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)

31. 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
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products
Uric acidemia; HGPRT; purine salvage
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA

32. What is the metabolism of fructose?
Fructose gets phosphorylated into fructose 1- P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
Fructose bisphosphatase 2
They can enter G1 from G0 and replicate if they like; hepatocytes - lymphocytes - fibroblasts

33. What luminal secretions are affected in CF? What is wrong with the secretions?
Respiratory - seminal fluid - pancreatic - gallbladder; very thick without NaCl to pull water
Liver; P450 hydroxylation
TPP (from B1- pyrophosphate) - FAD (B2) - NADH2 (B3) - CoA (B5 - panothenate) - Lipoic Acid
Oxygen!

34. What is the deficient enzyme in Niemann Pick disease? accumulated Substrate?
Decreased substrate for gluconeogenesis (pyruvate to lactate and not oxaloacetate); and pyruvate doing only lactic acidosis and not glycolysis
Branched alpha ketoacid dehydrogenase
In the reproductive tract and in the resp tract; infertility - bronchiectasis and recurrent sinusitis - associated with situs inversus
Sphingomyelinase; sphingomyelin

35. Which intermediate is involved in both pyrimidine synthesis and the urea cycle?
Either salvage by HGPRT and PRPP or converstion to xanthine and then to uric acid by xanthine oxidase
Carbamoyl phosphate
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
alk phos

36. What are the two different ways you can insert genes into transgenic mice for experiments?
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase
Do an RT PCR (reverse transcriptase)- RT the RNA first - then PCR the DNA
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Phenylalanine hydroxylase; tetrahydrobiopterin factor

37. What is methotrexate?
activator
Metanephrine
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
A folic acid analogue

38. What is the source of Vitamin B1? What is its other name? What causes a deficiency in B1?
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse
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

39. What three enzyme def. can cause homocysteinura? What is their mode of inheritance?
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR
Glycosylases (only remove the base - cut the bond between ribose and base)
Trinucleotide expansion diseases
Lack of lactase (brush border enzyme) so can not break down lactose (a dissaccharide of galactose and glucose); African Americans and Asians

40. Even chain fatty acids can not produce new glucose since they...
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism
Increased blood levels of ammonia - decreased BUN
HMP shunt (to NADPH) and glycogenolysis (as glucose 1 phosphate)
only yield acetyl coA

41. Which amino acids are required during periods of growth?
Antineoplastic agents; alkylate DNA!; cyclophosphamide and nitrosurea (aka lomustrine - a nitrosource)
fat
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Arg and his

42. What is the pathogenesis of Goodpasteurs syndrome? What are the main targets?
Abs against type IV collagen; pulmonary and glomerular capillaries
Acetazolamide to alkalinize the urine
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Folinic acid; does not require DHF

43. What type of diseases exhibit anticipation?
Robertsonian translocations
Ceramide trihexoside
Trinucleotide expansion diseases
Hemolytic anemia; jaundice in newborn if mom gets too much vit K

44. The three steps of PCR
Methionine; f Met (formyl methyl methionine)
Oral uridine administration; provides nucleosides and provides feedback inhibition
Vit D levels
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat

45. Which glycogen storage disease results in hepatomegaly?
Von gierkes
tyrosine hydroxylase
Glycogen and FFA oxidation - glucose conserved for final sprinting!
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth

46. What is the rate determining enzyme in fructose metabolism?
Defective neutral amino acid transporter on renal and intestinal cells; AR
Aldolase B
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding
hexokinase (glucokinase only found in liver and beta cells of pancreas)

47. How is Vit K activated? What drug blocks this? What is the source of Vit K?
By epoxide reductase in the liver; coumadin; intestinal flora and leafy vegetables
hexokinase (glucokinase only found in liver and beta cells of pancreas)
fatty acid degradation
No; increased mutation rate!

48. What does oligomycin do?
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
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
Block ATP synthase resulting in no ATP production and an increased proton gradient
Phenylketones that build up in phenylketonuria

49. Which is the rate limiting step of the urea cycle?
To amplify a specific desired fragment of DNA
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
Chorea and spastic paresis
Carbomyl phoshpate synthetase I

50. What is the mode of inheritance for the multiple endocrine neoplasias?
Cu; hydroxylation
Increased G3P for TG synthesis - increased acetyl CoA (Fatty acid synthesis for TG synthesis) - and decreased oxidation of FA in the mitochondria due to alcohols toxicity on the mit
AD
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )