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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. What is the precursor for pyrimidines?
Increased acid production competes with uric acid for excretion
Malabsorption problems (CF and sprue) and mineral oil intake
Orotate
Aldose reductase in the lens converts built up galactose to galactitol Which is osmotically active

2. What carries activated Phosphate groups?
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait
anabolic processes
ATP
AAUAAA; Poly A polymerase; no

3. Which vesicular trafficking protein takes vesicles from ER to the Golgi (anterograde)?
Vit K; neonates have sterile intestine and can not synthesize vit K
Fructose bisphosphatase 2
COP II
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)

4. How does a kwashiokor patient present?
in hepatocytes
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
Ile - Phe - Thr - Trp
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol

5. The main hormonal regulation of glycogen is...
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
glucagon - insulin and epinephrine
Dermatitis - glossitis - diarrhea
When different combination of exons get combined together; in Beta thallasemia

6. why is there decreased immunity in kwashiokor and marasmus?
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)
Liver and skeletal muscle
Respiratory burst - P450 - and glutathione reductase
No protein!

7. What are the lab findings see in hyperammonemia?
3 hydrogen bonds; 2 hydrogen bonds
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
False; GTP hydrolysis
Increased blood levels of ammonia - decreased BUN

8. What is the result of lactase deficiency? in What nationalities is it seen the most?
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Lack of lactase (brush border enzyme) so can not break down lactose (a dissaccharide of galactose and glucose); African Americans and Asians
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off
Decrease intake of fructose and sucrose (fructose and glucose)

9. What causes fruity odor in ketoacidosis?
Acetone
5' capping (with 7 methylguanosine) - 3' adenylation - splicing of introns; nucleus
Cells that stay in G0 and cannot replicate - instead they regenerate from stem cells; neurons - skeletal and cardiac muscles - and RBCs
dimers

10. What does the passage of electrons in the ETC result in?
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia
Formation of a proton gradient that is then used to create ATP through ATP synthase
Glucosekinase to glucose 6 P

11. other than increase Parathyroid hormone What else increases 1 alpha hydroxylase activity in the kidney?
Decreased serum phosphate
Mitochondria - archaebacteria - mycoplasma - and some yeasts
XR - iduronate sulfatase
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis

12. What disease manifestations result in Prader Willi syndrome? is the deletion a result from the father or mothers chromosome?
Increased concentration of Cl ions in sweat test
Mental retardation - obesity - short stature - hypogonadism - hypotonia - hyperphagia; father
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase
Edwards

13. What are the clinical symptoms of hyperammonemia?
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits
Carbamoyl phosphate to orotic acid
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
Bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating

14. What explains the excess phenylketones in the urine in phenylketonuria?
Folinic acid; does not require DHF
It is apart of thiamine pyrophosphate Which is a cofactor enzymes involved in ATP production: pyruvate dehydrogenase (glycolysis) - alpha ketoglutarate dehydrogenase (TCA cycle) - transketolase (HMP shunt) - branched chain AA dehydrogenase
Phenylalanine build up
Glycogen phosphorylase; phosphorylation and dephosphorylation

15. 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
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth
It induces its action!
DHF

16. 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
Histidine; B6
Carnitine shuttle
In the charging reaction! for this reason aminoacyl tRNA synthetase double checks

17. In What syndrome are their immotile cilia? why?

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18. What are the mucopolysaccharidoses? Which one is XR? AR? What accumulates in them?
Lysine and leucine
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Inbit Na+K+ ATPase; Cardiac glycosides
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

19. What are the symptoms of infantile beriberi and When do they present?
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months
When the 2nd hit of the allele is What causes the disease; sporadic retinoblastoma
are AR
RBCs - renal medulla - leukocytes - lens - testes - cornea

20. What does 6 mercaptopurine do?
6MP blocks de novo purine synthesis
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
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
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

21. How does an enzyme know to go to lysosome?
By addition of mannose 6 phosphate to proteins in the Golgi
Collagen; fibroblasts; 4; ECM
Iatrogenic - granulomatous disease (sarcoidosis d/t epitheloid macrophage release of calcitriol); hypercalcemia - hypercalciuria (renal calculi!) - loss of appetite - stupor
Can inducibly manipulate genes at specific developmental points

22. What is RNAi? and How is it used in gene expression modification?
Double stranded RNA is created that is complementary to the mRNA of interest and When inserted into cells the strands separate and attach to the mRNA preventing it from being translated
1) if it is stable/labile or permanent 2) intact BM and 3) intact ECM
Genotyping for mutant alleles (different sizes)
Developmental delay - gargoylism - airway obstruction (d/t short neck) - corneal clouding - CAD - hepatosplenomegaly

23. What vit def occur from antibiotic use?
Essential fructosuria and fructose intolerance; fructose intolerance
Biotin (vit B7) and Vit K
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
Phosphoenolpyruvate; pyruvate kinase; fructose 1 - 6 BP; ATP - alanine

24. What does guanine have on it?
Matrix; intermembrane space
severe
Phosphorylation of glucose
A ketone

25. What are the two most common aminotransferase and What amino acids do they turn to What glycolytic intermediates?
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST); alanine to pyruvate and aspartate to oxaxloacetate
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes
Coenzyme A and lipoamides

26. Breast milk has a little of...
Increased concentration of Cl ions in sweat test
Vit D and K
Glucokinase
Branched alpha ketoacid dehydrogenase

27. Three causes of albinism. What does albinism increased risk of?
FA coA synthetase combines coA with FA to make acyl coA
Tyrosinase deficiency; defective tyrosine transporters; lack of migration of neural crest cells; skin cancer
RER; free ribosomes
Mannose

28. What is the impetus for ketoacidosis in starvation? alcoholism?
Pellagra (dermatitis - diarrhea - dementia); INH use - B6 deficiency - Hartnup disease - malignant carcinoid syndrome - and a corn based diet (lacks trp and niacin in corn cant be absorbed)
Vit K; neonates have sterile intestine and can not synthesize vit K
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate

29. What vitamin is given at birth to prevent hemorrhage? why?
Vit K; neonates have sterile intestine and can not synthesize vit K
Schwann cells - lens - retina - kidneys because they only have aldose reductase and no sorbital dehydrogenase
Galactocerebrosidase; Galactocerebroside
Macrocytic megaloblastic anemia - hypersegmented PMNs - subacute combined degeneration myelopathy Which results in degeneration of the dorsal and lateral columns (loss of position and vibration sense - spastic paresis and ataxia) due to abnormal myel

30. What tissues contain aldose reductase? What does this enzyme do to what?
Adipose tissue for brain and heart (ketone bodies) and then go to vital protein degradation (organ failure)
Metabolizes them with transferase enzymes to acetyl coA
Lens and neural tissue; converts galactose to osmotically active galactitol
HMG CoA reductase; converts HMG CoA to mevalonate

31. What is the rate determining enzyme in de novo pyrimidine synthesis?
Central and peripheral demyelination with ataxia and dementia
in hepatocytes
HMG CoA synthetase; HMG CoA reductase
Carbomyl phosphate synthetase II

32. What can cause a def in vit D?
be anorexic
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)
It is apart of thiamine pyrophosphate Which is a cofactor enzymes involved in ATP production: pyruvate dehydrogenase (glycolysis) - alpha ketoglutarate dehydrogenase (TCA cycle) - transketolase (HMP shunt) - branched chain AA dehydrogenase
FA coA synthetase combines coA with FA to make acyl coA

33. _______ is ubiquitous
Folinic acid; does not require DHF
III
Silent - misssense - nonsense
hexokinase (glucokinase only found in liver and beta cells of pancreas)

34. Fructose is the _______ metabolized - because fructokinase in the liver allows it to bypass the rate limiting step in glycolysis (PFK1) - and it enters through a different pathway (either through DHAP to glycogenolysis or to glyeraldehyde for glycoly
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
fastest sugar
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils

35. What is uniparental disomy? give an example of a disease it can cause.
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait
When child gets two chromosomes from one parent; imprinting dx
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
Vitamin C; facilitates iron absorption by making sure its in its reduced state (Fe2+) - hydroxylation for lysine and proline Which is necessary for crosslinking; necessary for dopamine Beta hydroxylase for conversion of dopamine to NE; keeps FH4 in i

36. What causes liver damage in kwashiokor?
tubulin dimer
Chorea and spastic paresis
Increased TG synthesis from increased Glycerol 3 P and abetalipoproteinemia
Steroid - cholesterol FA synthesis; HMP shunt

37. Which antifungal acts on MT?
Griseofulvin
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
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
DOPA

38. What cofactor is required of preprocollagen hydroxylation?
Carbamoyl phosphate
Orotate
Chediak Higashi Syndrome; decreased phagocytosis results in recurrent pyogenic infections - partial albinism - and peripheral neuropathy
Vit C

39. Phenylethanolamine N- methyl is only located in the...
Lactic acidosis and ketoacidosis
adrenal medulla
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
Methionine; f Met (formyl methyl methionine)

40. What does a deficiency cause?
Night blindness - dry skin
Neimann pick and tay sachs
Inbit Na+K+ ATPase; Cardiac glycosides
Endonucleases are specific and break specific linking phosphodiester bonds - exonucleases are not sequence specific and just remove the nucleoside

41. What else decreases production of oxaloacetate in alcoholism other than decreased pyruvate?
Downs (21) - Edwards (18) - Pataus (13); also in increasing severity
Oxaloacetate gets shifted to malate d/t excess NADH
Williams
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia

42. What are the clinical symptoms of duchennes muscular dystrophy?
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse
Aldolase B
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
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates

43. What type of exonuclease activity does DNA polymerase I have? in What organisms is it found? What is it used for?

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44. Only muscle and brain have transferase enzyme that converts ketone bodies to...
acetyl coA
Vit C
be anorexic
Vit K; neonates have sterile intestine and can not synthesize vit K

45. What are three ketone bodies? Which is not detected in urine? Which do you see most in alcoholic ketoacidosis?
Mental retardation - obesity - short stature - hypogonadism - hypotonia - hyperphagia; father
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)
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate
Tyrosinase

46. Phosphorylated glycogen phosphorylase...
Acetyl coA; gluconeogenesis
is active
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
usually present late

47. What two anti - neoplastic drugs work by blocking DNA and RNA polymerase?
Dactinomycin - doxorubicin
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
Proprionyl coA; through methylmalonyl coA; B12

48. What enzyme is necessary for branched aa degradation? What cofactor? What are the branched aa?
Rb
Branche aa alpha ketoacid dehydrogenase; thiamine; Isoleucine - leucine - valine
30S + 50S= 70S
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

49. What are the common symptoms of B vitamin deficiencies?
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse
GALT
Dermatitis - glossitis - diarrhea
Metanephrine

50. What are required for splicing? encoded by What polymerase?
Histidine; B6
Bilateral acoustic schwannomas - juvenile cataracts
SnRNPs; RNA polymerase III
No