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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 3 genetic disorders can cause Marfanoid habitus?
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Marfans - homocystinuria - MEN 2B
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)

2. What is the other name for Vitamin B5? What is its function?
Dynein - retrograde - kinesin - anterograde
Lyonization; nondisjunction in mitotic divisions during embryonic period
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)
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase

3. What is acyl coA dehydrogenase used in? What does a deficiency in this enzyme produce?
Asp and glu; negatively
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
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
Fatty acid (acyl coA) oxidation to acetyl coA; increase in dicarboxylic acids - and decreased glucose and ketones

4. Ocular albinism is...
Cortisol; inhibits insulin action
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
linked recessive
Cysteine; tyrosine

5. ______________ interact with each other and decrease fluidity and increase melting temperature
long saturated fatty acids
Delayed wound healing - hypogonadism - decreased adult hair - dysgeusia - anosmia - and alcoholic cirrhosis - perioral rash
MT!
Consumption of bear liver - and overtreatment isoretinoin; constitutional symptoms and alopecia and skin changes

6. What are flagella made of?
Catalase positive because they reduce their H2O2 and WBCs cant use that to make bleach; because the way they protect is by building a wall around the organisms with granulomas
MT!
Tyrosine
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils

7. ______________ converts tyrosine to DOPA
Ehler Danlos; type III collagen def; joint dislocation - berry aneurysm - ecchymoses - organ rupture
Hungtington
tyrosine hydroxylase
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months

8. Phosphorylated glycogen phosphorylase...
Peripheral neuropathies of hands/feet; angiokeratomas between umbilicus and knees; cardiovascular/renal disease
Carnitine shuttle
Histidine; B6
is active

9. How is muscle activity and glycogenolysis coupled in muscle?
Fruits and vegetables
Calcium and calmodulin activate glycogen phosphorylase kinase
Citrate is positive on it - AMP and fructose 2 -6 bisphosphate is negative on it; gluconeogenesis
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 do enhancers/silencers bind?
TFs
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting
Cobalamin; cofactor for homocysteine methyltransferase (transfers SAM to THF to give to dUMP) and for methylmalonyl coA mutaseto make succinyl coA
Telomerase; an RNA polymerase that uses a RNA template to add DNA to the end of shortening 3' ends

11. Glucokinase is a...
glucagon - insulin and epinephrine
glutton
Tyrosine
Fe2+; Fe3+

12. From What aa does thyroxine come from?
SnRNPs; RNA polymerase III
Tyrosine
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
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers

13. What is Maternal PKU?

14. What type of diseases exhibit anticipation?
TCA cycle - FA oxidation - acetyl coA production; ox phos
Cycloheximide
Mitochondrial inheritance
Trinucleotide expansion diseases

15. What is the function of Vit K?
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Cells that never got into G0 and divide rapidly with a short G1; bone marrow - gut epithelium - hair follicles - skin
Dactinomycin - doxorubicin

16. What is the cilia structure? What provides fluidity and motility of the cilia structure?

17. How do hepatocytes release glucose 6 P from glycogenolysis into the blood ? in What disease is this enzyme deficient?
With glucose 6 phosphatase; Von Gierkes disease
Preprocollagen - procollagen - tropocollagen - collagen
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
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

18. What carries CO2 as energy?
Vit K; neonates have sterile intestine and can not synthesize vit K
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)
Orotic aciduria megaloblastic anemia can not be corrected with folic acid or vit B12
Biotin

19. What are the clinical findings in patau syndrome?
Becomes methionine
Adrenal cells (steroid synthesis) - hepatocytes (p450 detox)
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly

20. What are the findings in pyruvate dehydrogenase def? How do you treat it
Because cells of mononuclear phagocytic are esp rich in lysosomes
Glutamate
Cu; hydroxylation
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)

21. What enzyme converts norepinephrine to epinephrine? using What cofactor?
Can inducibly manipulate genes at specific developmental points
Phenylethanolamine N- methyl transferase; SAM
3'--> 5'; prokaryote only
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase

22. Which Hurlers is milder and presents with no corneal clouding?
FISH
Liver and skeletal muscle
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)
XR - iduronate sulfatase

23. What is the function of B2? What can cause deficiency?
Riboflavin makes up FAD and FMN both used in redox reactions; vegans
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate
Hungtington

24. How many RNA polymerases do prokaryotes have? What drug blocks prokaryotic RNA polymerase only? What is it used for?
1 for all three classes of RNA; Rifampin; TB
Multiple bone fractures - blue sclerae - hearing loss (abdnormal middle ear bones!) - dental imperfections - retarded wound healing
Fat soluble; either endogenous production or exogenous; D2 ergocalciferol is ingested from plants and D3 cholecalciferol is formed in sun exposed skin (and can be consumed in fortified milk)
Pataus

25. Phenylethanolamine N- methyl is only located in the...
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR
Metaphase (all lined up); blood - bone marrow - amniotic fluid - placental tissue; used to diagnose chromosomal abnormalities (deletions - trisomies - sex chromosomal disorders)
adrenal medulla
liver

26. Which antihelminthic drugs act on microtubules?
Mebendazole and thiabendazole
Yes! congenital simply means 'born with'- hereditary is familial
Using serine (which turns into glycine after reaction)
Tryptophan; B6

27. What inheritance pattern is Type IIA hypercholesterolemia? do heterozygotes present with disease? do homozygotes present?
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
No
adrenal medulla
Carbomyl phosphate synthetase I

28. What is the function of Vitamin A?
Blood group types
Fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio
Steroid synthesis and detoxification
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant

29. HMG coA synthase; cholesterol synthesis
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
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months
Uses HMG coA reductase

30. Where is antioxidant activity of Vit E most important?
Hungtington
2/3; LCAT (lecithin cholesterol acyltransferase)
Neurons and RBCs
Lyonization; nondisjunction in mitotic divisions during embryonic period

31. What is the defect that causes Alport's Syndrome? What is the most common inheritance pattern? What are the three mc clinical presentations?
Cytoplasmic side; active
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)
Glycine; proline and lysine
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances

32. Which vesicular trafficking protein takes vesicles from ER to the Golgi (anterograde)?
COP II
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
all are diseased!
HVA

33. What disease is associated with chromosome 3?
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
VHL (Von Hippa Lindau)
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
Acetyl coA; gluconeogenesis

34. What is the inheritance pattern of hereditary hemorrhagic telangiectasia or Olser Weber Rendu Syndrome? What is it?
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
Phenylalanine hydroxylase; tetrahydrobiopterin factor
Bacterial synthesis in the intestine
Inability to taste

35. What is needed for glycolysis to continue? How is this provided in aerobic glycolysis? anaerobic?
Oxygen!
low Vmax
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate
Uric acidemia; HGPRT; purine salvage

36. What is the rate limiting step in cholesterol synthesis? What does it do?
Trimethroprim inhibits bacterial dihyrofolate reductase
Ascites from liver damage
HMG CoA reductase; converts HMG CoA to mevalonate
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)

37. What are the findings in alkaptonuria? why do they occur?
TFs
Vit C; Vit E
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage
To transfer methyls; a methionine and an ATP; norepinephrine plus a methyl makes epinephrine

38. What contributes to the acidosis in alcoholism?
Lactic acidosis and ketoacidosis
Kartaganer's aka ciliar dyskinesia; lack of dynein arm ATPase
Downs
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR

39. From What aa does serotonin come from? What NT is serotonin a precursor for?
Phospholipids - sphingolipids - glycolipids
Tetrahydrofolates
2/3; LCAT (lecithin cholesterol acyltransferase)
Tryptophan; melatonin

40. What does ornithine transcarbamyolase do to carbamoyl phosphate?
No
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Converts it to citrulline
Beta thalassemia

41. What is a positive allosteric regulator on pyruvate carboxylase? for What reaction is this?
Converts it to citrulline
Von gierkes
Acetyl coA; gluconeogenesis
Following gastroenteritis and kwashiokor (protein deficiency)

42. What are the three branched aa?
Tay Sachs - Niemann Picks - Gauchers
Isoleucine - valine - leucine
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
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

43. What kind of DNA damage does ionizing radiation cause? What type of repair helps with this?
Double strand breaks; nonhomologous end joining
Cycloheximide
Abetalipoproteinemia and increased G3P production from all the carbs!
Adrenal cells (steroid synthesis) - hepatocytes (p450 detox)

44. What does alcohol do to the P450 system?
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
Matrix; intermembrane space
Mcardles disease
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

45. What is the rate determining enzyme in fructose metabolism?
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait
Galactokinase deficiency and classic galactosemia; classic galactosemia
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Aldolase B

46. What are the symptoms involved in lactase deficiency?
Osmotic diarrhea - bloating - cramps
Phosphoenolpyruvate; pyruvate kinase; fructose 1 - 6 BP; ATP - alanine
Heme synthesis - urea cycle - gluconeogenesis
Chromosomal imbalance (downs for ex)

47. How does lactate contribute to gluconeogenesis?
Coenzyme A and lipoamides
Gets converted to pyruvate via the Cori cycle in the liver
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar

48. Glucokinase has a LOW affinity (high Km) and...
Cleft palate - Abnormal faces - thymic aplasia (t cell def) - Cardiac defects - hypocalcemia (secondary to hypoparathyroid); 3rd and 4th branchial pouch aberrant development
Homocysteine; homocysteine methyltransferase with B12 and tetrahydrofolate
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
high Vmax

49. What happens outside the fibroblast to procollagen?
Defective neutral amino acid transporter on renal and intestinal cells; AR
Aminoglycosides and tetracyclines
Chorea and spastic paresis
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

50. What is the other name of Vitamine B2? In What foods can it be found?
Riboflavin; dairy and meat
Prolonged Ab use
Bone - Skin - Tendon - dentin - fascia - cornea - late wound repair
I; nucleolus