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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. What carries methyl groups as energy?
Lactic acidosis and ketoacidosis
SAM
teratogenic
Aldolase B

2. What is the order of collagen synthesis - just the terms of the intermediate forms?
long saturated fatty acids
Preprocollagen - procollagen - tropocollagen - collagen
Tyrosine; tryptophan
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash

3. Vitamin c is needed in...
catecholamine synthesis (dopamine to norepinephrine)
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism
Phenylaline
No protein!

4. What are the findings in pyruvate dehydrogenase def? How do you treat it
Acidic
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)
Inbit Na+K+ ATPase; Cardiac glycosides

5. What are the clinical symptoms of Huntingtons disease? When does it present?
Oxygen!
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
Heart - SKELETON - and EYES: arachnodactyly - long limbs - cystic medial necrosis of aorta resulting in aneurysms (and eventual dissection) - floppy mitral valve (prolapse and regurg!) - subluxation of lens

6. What is the difference between a kinase and a phophorylase?
Both add phosphate; phosphorylase uses no ATP and inorganic phosphate
Respiratory burst - P450 - and glutathione reductase
SER and mitochondria; NADPH
SAM; Vit C

7. How do hepatocytes release glucose 6 P from glycogenolysis into the blood ? in What disease is this enzyme deficient?
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Acetyl coA; gluconeogenesis
With glucose 6 phosphatase; Von Gierkes disease
Renal calculi of uric acid (replaces uric acid in excretion)

8. What does oligomycin do?
Block ATP synthase resulting in no ATP production and an increased proton gradient
Decreased serum phosphate
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes
Edwards

9. What type of disease is MELAS? What is the clinical presentation?
Oxaloacetate gets shifted to malate d/t excess NADH
Tyrosine; phenylaline
Mit encephalopathy - lactic acidosis - stroke like episodes
high Vmax

10. The three steps of PCR
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
Some viruses
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
Riboflavin; dairy and meat

11. Name two reasons why mosaicism might occur.
This depends on if phosphofructokinase 1 is active and this depends on whether or not fructose 2.6 bisphophate is activating it or not - this can only occur if PFK 2 is on and not FBPase 2. then fructose 6 phosphate will participate in glycolysis. Ot
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
Triacylglycerols in adipose tissue broken down into glycerol and free fatty acids; growth hormone and epinephrine
Lyonization; nondisjunction in mitotic divisions during embryonic period

12. What are ragged red fibers?
FA coA synthetase combines coA with FA to make acyl coA
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils
AD

13. What is the importance of folic acid?
Nacetyl cysteine; breaks disulfide bridges of mucus plugs
Mitochondrial inheritance
Prevents neural tube defects in 1st trimester
Galactose

14. What is the source of Vitamin B1? What is its other name? What causes a deficiency in B1?
Lime and CaCO3 to displace the niacin
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine
HVA

15. Where does synthesis of longer chain fatty acids occur? What does it require?
Neurologic lesions and cardiomyopathies (ox phos!)
Fructose gets phosphorylated into fructose 1- P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B
SER and mitochondria; NADPH
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA

16. What kind of kinetics does alcohol dehydrogenase work under? What are the implications of this?
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
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
Hemolytic anemia due to heinz bodies Which are oxidized hemoglobin precipitating within the RBCs
Zero order; increased production of NADH no matter the amount of end products produced

17. The mode of inheritance for both NF disease is...
Both AD
Increased homocysteine in the urine - mental retardation - osteoporosis - marfanoid habitus - and atherosclerosis
Meiotic nondisjunction in mothers gametes during the first meiosis
Isocitrate dehydrogenase

18. Daughters of Xlinked dominant diseased fathers are...
succinyl coA (and then to OXA)
Dopa decarboxylase; B6
all are diseased!
AD

19. What is Maternal PKU?

20. ______________ interact with each other and decrease fluidity and increase melting temperature
long saturated fatty acids
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
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)
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting

21. What causes the lysosomal storage diseases?
Orotic aciduria megaloblastic anemia can not be corrected with folic acid or vit B12
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products
Respiratory burst - P450 - and glutathione reductase
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism

22. What is loss of heterozygosity? Name an example.
When the 2nd hit of the allele is What causes the disease; sporadic retinoblastoma
Acetyl CoA carboxylase
Cycloheximide
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

23. What are the functions of zinc?
Fabrys Disease and Hunters Syndrome
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism
Downs
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers

24. Which RNA polymerase synthesizes tRNAs and snRPs?
III
Tyrosinase deficiency; defective tyrosine transporters; lack of migration of neural crest cells; skin cancer
Conversion of pyruvate to Acetyl CoA; acetyl coA - CO2 - and NADH (one of each per pyruvate)
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no

25. Odd chain fatty acids yield one proprionyl coA which can enter the TCA cycle as...
Succinyl coA
Also have fair skin - blond hair - blue eyes - eczema
2/3; LCAT (lecithin cholesterol acyltransferase)
succinyl coA (and then to OXA)

26. What is the swollen belly from in a child with kwashiokor?
Its When two acrocentric chromosomes combine their long arms (and short arms disappear); When the translocation is functional
Ascites from liver damage
Because carbamaoyl phosphate is involved in both urea cycle and pyrimidine synthesis
Biotin (vit B7) and Vit K

27. With What tool are Prader Willi and Angelman diagnosed?
Calcium and calmodulin activate glycogen phosphorylase kinase
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
Cycloheximide
FISH

28. What is the order of types of glycogen storage disease?

29. Glucokinase has a LOW affinity (high Km) and...
Steroid synthesis and detoxification
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
high Vmax
Citrate shuttle in the inner mitochondrial membrane transports acetyl coA into the cytoplasm; liver; liver and adipose tissue

30. What is the rate limiting step in glycolysis? What does it do? who activates it? inhibits it?
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
Riboflavin makes up FAD and FMN both used in redox reactions; vegans
be anorexic
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP

31. What glucose is stored as
Aromatic; musty body odor
glycogen
usually present late
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off

32. What is the purpose of the PCR?
ATP and biotin
G6PD; provides malarial resistance; X linked recessive
To amplify a specific desired fragment of DNA
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)

33. Which catecholamine has inhibitory action against acetylcholine?
Collagen; fibroblasts; 4; ECM
Dopamine
Von gierkes
Phosphoenolpyruvate; pyruvate kinase; fructose 1 - 6 BP; ATP - alanine

34. deamination of What pyrimidine makes what?
Galactokinase; galactose appears in blood and urine - sometimes infantile cataracts may present as failure to track objects or lack of a social smile
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)
Cytosine to uracil

35. What are lisch nodules?
Pigmented iris hamartomas
Glycerol and propionyl coA; lactate and alanine
Excreted from the kidney in the form of urea in hepatocytes
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)

36. How many RNA polymerases do prokaryotes have? What drug blocks prokaryotic RNA polymerase only? What is it used for?
Dermatitis - glossitis - diarrhea
Tyrosinase
1 for all three classes of RNA; Rifampin; TB
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)

37. Like mRNA has a poly A tail on the 3' end - What does tRNA have on its 3' end? What happens here?
CCA and chemically modified bases Where amino acid is covalently bonded
Schilling test
calorie deficient
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP

38. What is the first step in fatty acid synthesis? Where does it occur? Where does triacylglycerol synthesis occur?
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR
Citrate shuttle in the inner mitochondrial membrane transports acetyl coA into the cytoplasm; liver; liver and adipose tissue
S adenosyl homocysteine; homocysteine transferase; B12 and THF; M- THF
is asymmetric

39. What three enzymes lead to orotic acid accumulation? What reactions are they involved in?
Methionine is only encoded by AUG
SnRNPs; RNA polymerase III
Downs (21) - Edwards (18) - Pataus (13); also in increasing severity
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)

40. What is the function of Vitamin A?
Glycerol and propionyl coA; lactate and alanine
fat
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
Fat malabsorption (CF) and abetalipoproteinemia (damage takes up all antioxidants)

41. Amino acids are found in...
Hexosaminidase A; GM2 ganglioside
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
only L form
Promoter binds RNA Pol II and is very close (25 bases) to initiation site and is AT rich; enhancer/silencers bind TFs only - can be located close or far and regulate gene expression but not specifically initiation; transcription

42. What are the findings in Tay Sachs disease?
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
Silent - misssense - nonsense
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)
When different combination of exons get combined together; in Beta thallasemia

43. What causes fat soluble vitamin deficiencies?
Nitric Oxide - creatinine - Urea
Malabsorption problems (CF and sprue) and mineral oil intake
Encode enzymes for oxphos mit reactions
Lys and arg

44. What Ab class blocks DNA gyrase?
Mental retardation - flat faces - simean crease - epicanthal folds - ASD - duodenal atresia causing Hirshsprungs disease - redundant skin at the nape of neck - slanted palpebral fissures - hypotonia
aldose reductase
Flouroquinolones
MT!

45. What is achondroplasia? What type of inheritance?
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
10 - 9 - 7 - 2; protein C and S
show disease
HMG CoA reductase; converts HMG CoA to mevalonate

46. Where are receptors for Vit D? (think How does it increase serum Ca and Phosphate)
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products
P53 and Rb; p53 activates BAX Which inhibits BCL2 When there is DNA damage - Rb phosphorylation allows progression into S phase
severe
Intestine - renal - bone

47. What is folic acid? What is its function?
Ile - Phe - Thr - Trp
Heme synthesis - urea cycle - gluconeogenesis
Isoleucine - valine - leucine
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth

48. What is the mcc of an autosomal trisomy?
APCKD
UV nonionizing radiation causing thymidine dimers
Meiotic nondisjunction in mothers gametes during the first meiosis
Vincristine - vinblastine - and paclitaxel; the vinca alkaloids block formation of the spindle and paclitaxel prevents breakdown of the mT spindle

49. Which amino acids makes up histones?
Lys and arg
Mitochondrial inheritance
Phenylalanine
Fe2+; Fe3+

50. What is the rate determining enzyme in fructose metabolism?
Aldolase B
Make it stiffer/more tensile; continues as we get older so gets less and less elastic
Less; more
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization