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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 hepatocellular steatosis?
Mannose
Glycolysis - fatty acid synthesis - HMP shunt - protein synthesis (RER) - steroid synthesis (SER) - glycogenolysis - glycogenesis
RER; free ribosomes
Hepatic fatty change

2. Daughters of Xlinked recessive diseased fathers are...
CCA and chemically modified bases Where amino acid is covalently bonded
all carriers
SnRNPs; RNA polymerase III
When different combination of exons get combined together; in Beta thallasemia

3. What is the rate determining enzyme in glycogenolysis?
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
Glycogen phosphorylase
Aromatic; musty body odor
7 dehydrocholesterol

4. How many bonds does a G- C connection have? What type of bonds? how about a A- T?
3 hydrogen bonds; 2 hydrogen bonds
APCKD
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
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off

5. What are the findings in Niemann Pick disease?
Methionine is only encoded by AUG
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination
Respiratory burst - P450 - and glutathione reductase
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells

6. Vitamin c is needed in...
Vimentin - desmin - cytokeratin - glial fibrillary acidic protein (GFAP) - neurofilaments; to differentiate between different cells
Lime and CaCO3 to displace the niacin
catecholamine synthesis (dopamine to norepinephrine)
Both add phosphate; phosphorylase uses no ATP and inorganic phosphate

7. The mode of inheritance for both NF disease is...
Lesch Nyhan syndrome; X linked recessive
Also have fair skin - blond hair - blue eyes - eczema
Both AD
Alpha amanitin; mushroom caps

8. What causes an excess of B3? What are the symptoms?
Tyrosine; tryptophan
Niacin treatment for hyperlipidemia; facial flushing
S adenosyl homocysteine; homocysteine transferase; B12 and THF; M- THF
To increase serum Ca and Phosphate for ultimate bone deposition by: increase intestinal absorption of calcium and phosphate (also renal); and increase resorption of bone by stimulating macrophages (osteoclasts)

9. What are the two disorders of galactose metabolism? Which is worse?
Galactokinase deficiency and classic galactosemia; classic galactosemia
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
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
tubulin dimer

10. What are two clinical symptoms of newborns with CF? and whats a lab value of a newborn with CF?
Neurons and RBCs
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin
Increased concentration of Cl ions in sweat test
HMG CoA reductase; converts HMG CoA to mevalonate

11. What is the swollen belly from in a child with kwashiokor?
adrenal medulla
Acetyl CoA carboxylase
Ascites from liver damage
Methionine; f Met (formyl methyl methionine)

12. What luminal secretions are affected in CF? What is wrong with the secretions?
Phenylaline
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
Inosine/IMP; adenosine deaminase
Respiratory - seminal fluid - pancreatic - gallbladder; very thick without NaCl to pull water

13. What are the two different ways you can insert genes into transgenic mice for experiments?
3'--> 5'; prokaryote only
reabsorbs
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

14. What is the structure of Microtubules?
A ketone
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Flouroquinolones

15. What is an example of a nonsense mutation?
Beta thalassemia
Inosine/IMP; adenosine deaminase
Karyotyping
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

16. What is the precursor for pyrimidines?
Bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating
G6PD; provides malarial resistance; X linked recessive
Orotate
glycogen

17. With What tool are Prader Willi and Angelman diagnosed?
O2 consumption (last electron acceptor) gets consumed also
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
FISH
Phosphofructokinase 1

18. Where does gluconeogenesis occur?
Biotin; rate limiting step in fA synthesis - acetyl coA into malonyl coA
Liver mit and liver cytosol
By cyclin CDK complexes
ATP and biotin

19. What is the source of ATP When you are fasting (in between meals)?
Glucose 6 phosphate dehydrogenase
An allosteric regulator; fructose 1 phosphate; phosphofructokinase 2
7 dehydrocholesterol
Hepatic glycogenolysis (mostly) - also hepatic gluconeogenesis - adipose release of FFA (minor)

20. Where are cilia found? What symptoms are associated with kartageners syndrome?
be anorexic
Pigmented iris hamartomas
In the reproductive tract and in the resp tract; infertility - bronchiectasis and recurrent sinusitis - associated with situs inversus
Alpha amanitin; mushroom caps

21. What causes fruity odor in ketoacidosis?
AR
Phenylaline
Acetone
Vit D levels

22. Where does NADH2 enter ETC? FADH2
Shiga toxin and ricin (protein in castor beans)
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Complex I - Complex II (lower energy)
Exons

23. What does ultrasound show in Downs?
Increased nuchal translucency
Adrenal cells (steroid synthesis) - hepatocytes (p450 detox)
Carnitine shuttle
Cystic Fibrosis (CFTR gene)

24. What are the four fates of pyruvate metabolism?
Vit C
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
Calcium and calmodulin activate glycogen phosphorylase kinase
Pyruvate to alanine (to carry amino groups to liver) - pyruvate to OAA for gluconeogenesis (or replenish for TCA cycle) - acetyl coA (for TCA cycle transition or FA or chol. synthesis) - or the end of anaerobic glycolysis

25. What is the mode of inheritance of Marfans?
AD
Pigmented iris hamartomas
Cleft palate - Abnormal faces - thymic aplasia (t cell def) - Cardiac defects - hypocalcemia (secondary to hypoparathyroid); 3rd and 4th branchial pouch aberrant development
Thymidylate synthase; 5- Flourouracil

26. What aa becomes essential with homocystinuria? phenylalaninuria?
Cysteine; tyrosine
Do agarose gel eletrophoresis to separate the different sizes of the PCR products (sizes id the the fragment)
Steroid - cholesterol FA synthesis; HMP shunt
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

27. What type of disorders are associated with chromosomes 13 -14 -15 -21 -22?
FISH
AD
Robertsonian translocations
7 dehydrocholesterol

28. What enzyme is deficient in maple syrup disease? What does it result in?
Branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils
N5N10 methylene THF
As BUN (blood urea nitrogen)

29. What is the inheritance pattern of hereditary hemorrhagic telangiectasia or Olser Weber Rendu Syndrome? What is it?
Vit K; neonates have sterile intestine and can not synthesize vit K
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
Microcephaly - mental retardation - high pitched mewing/crying - epicanthal folds - cardiac abnormalities; microdeletion on short arm of chrom 5
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )

30. What aa does melanin come from? melatonin?
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase
A methyl
Tyrosine; tryptophan
Acetone

31. What is dysgeusia?
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage
Inability to taste
Mitochondrial inheritance
2-3 days after birth because maternal enzyme during fetal like might still be there

32. What reactions occur in the mitochondrial matrix? mit inner membrane?
TCA cycle - FA oxidation - acetyl coA production; ox phos
By cyclin CDK complexes
Increased homocysteine in the urine - mental retardation - osteoporosis - marfanoid habitus - and atherosclerosis
Dry is just the symmetrical neuropathy with both motor and sensory symptoms; wet includes both the neuropathy and cardiac involvement of high output failure with peripheral edema - tachycardia - cardiomegaly

33. Insulin receptor is not cAMP second receptor but rater tyrosine kinase...
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA
Glucose 6 phosphatase
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase
Vit D levels

34. What are two reasons why pyruvate would be pushed to lactate in an alcoholic?
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Mental retardation - rocker bottom feet - micrognathia (small jaw) - low set ears - clenched hands with polydactyly - congenital heart disease
Arginne

35. Where does splicing occur?
Nucleus
By giving high amounts of pyridoxal phosphate in the diet
calorie deficient
Beta glucocerebrosidase; glucocerebroside

36. Which is the most common lysosomal storage disease? What are its findings?
Metabolizes them with transferase enzymes to acetyl coA
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
Neurons and RBCs
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)

37. What does adipose tissue contribute for hepatic gluconeogenesis during starvation? muscle?
AD
Glycerol and propionyl coA; lactate and alanine
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate
Later

38. What is the order of cell cycle phases? What happens in each phase?
Dopamine beta hydroxylase; vit C
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)
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)
Double strand breaks; nonhomologous end joining

39. What is the exception to the universal aspect of the genetic code?
NADH - Acetyl CoA - ATP; NAD+ - ADP and Ca2+
fatty acid degradation
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Mitochondria - archaebacteria - mycoplasma - and some yeasts

40. Is heterochromatic more accessible or less accessible to TF? euchromatin?
6MP blocks de novo purine synthesis
Pulmonary - GI - reproductive (infertility in male due to absence of vas deferens and seminal fluid thickness)
Less; more
Succinate hydrogenase; matrix

41. What is the deficient enzyme in Fabry's disease? accumulated Substrate?
In the charging reaction! for this reason aminoacyl tRNA synthetase double checks
Alpha galactosidase A; ceramide trihexoside
Tyrosine
SAM

42. What are the findings in ornthinie transcarbamoylase?
Converts it to citrulline
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
HMG CoA synthetase; HMG CoA reductase
AD

43. What disease is associated with chromosome 17?
paternal
Vitamin B1 (thiamine) - Vitamin B2 (riboflacin) - Vitamin B3 (niacin) - Vitamin B5 (pantothenate) - Vitamin B6 (pyridoxine) - Vitamin B7 (Biotin) - Vitamin B12 (cobalamin) - folate - Vit. C
CCA and chemically modified bases Where amino acid is covalently bonded
NF1

44. What is the fate of the two products of lipolysis?
Glycerol goes to liver for gluconeogenesis; free fatty acids bind to albumin in blood and travel to cells to be used as for energy
Prevents neural tube defects in 1st trimester
LDL; LDL oxidize atherosclerosis
Bacterial synthesis in the intestine

45. What does a deficiency in homogentistic acid oxidase result in? What is this also known as?
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Alkaptonuria; ochronosis
Liver mit and liver cytosol
VMA

46. What creates a frameshift mutation? What are some clinical examples?
So that excess glucose can be stored (phosphorylated glucose cant leave) in the liver and saved as a buffer
Neurologic lesions and cardiomyopathies (ox phos!)
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
Insertion or deletion of a number of nucleotides indivisible by 3; tay sachs - duchennes MD

47. What does PEP carboxykinase require? and for What reaction is this?
To amplify a specific desired fragment of DNA
Vincrstine (vinca alkaloids) and paclitaxel
activation of PFK1
GTP: gluconeogenesis - OXA to phosphoenolpyruvate

48. name three glucogenic AA and how they enter gluconeogenesis. through What cycle do they enter gluconeogenesis?
reabsorbs
Alanine (through pyruvate) - aspartate (through OXA) - glutamate (alpha ketoglutarase); TCA
HnRNA; mRNA
5'--> 3'; prokaryote only; for removing RNA primer and filling it with DNA

49. list three uncoupling agents
Cu; hydroxylation
FISH
homocysteine transferase
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)

50. What is the mode of inheritance of Huntingtons?
AD (trinucleotide expansion is not a mode of inheritance)
AD
Loss of subcutaneous fat - tissue and muscle wasting (somatic muscle); visceral - not somatic
kidney

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USMLE Step 1 Biochemistry

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