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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 do enhancers/silencers bind?
ATP
TFs
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)
When there is glucagon; protein kinase A activation and thus phosphorylation of the complex resulting in the activation of fructose 2 -6 BPase and no PFK2

2. What disease is associated with chromosome 5?
jaundice
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin
Familial Adenomatous Polyposis (APC gene)
By giving high amounts of pyridoxal phosphate in the diet

3. list three uncoupling agents
Glycerol goes to liver for gluconeogenesis; free fatty acids bind to albumin in blood and travel to cells to be used as for energy
Phosphofructokinase 1
Oral uridine administration; provides nucleosides and provides feedback inhibition
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)

4. What enzyme is deficient in Fructose intolerance? What is the result of the enzyme def? What are the symptoms?
A topoisomerase II inhibitor; because cancer cells use II more so than healthy cells
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting
Colchine

5. Where does the HMP (pentose phosphate pathway) occur other than in the liver?
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
Cysteine; tyrosine
When child gets two chromosomes from one parent; imprinting dx
Carbomyl phoshpate synthetase I

6. What is the inheritance of Tuberous Sclerosis?
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
AD
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

7. Which is the rate limiting step of the urea cycle?
A lysosomal storage disease; mannose 6 phosphate can not be added to lysosomal proteins
Where there is insulin; low protein kinase A means dePhosphorylation of the complex Which results in increased PFK2 Which results in more fructose 2 -6 bp and thus more PFK1!!
Carbomyl phoshpate synthetase I
1 for all three classes of RNA; Rifampin; TB

8. What does alcohol do to the P450 system?
RER in nucleus (synthesize NTs)
AR
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
30S ribosomal RNA (small one)

9. What disease is associated with chromosome 13?
calorie deficient
Pataus
HMP shunt (to NADPH) and glycogenolysis (as glucose 1 phosphate)
Increased CPK and muscle biopsy

10. What is Pleiotropy? What is the opposite of Pleiotropy? Give an example of each.
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia
Glutamate
1 gene has greater than 1 phenotypic effect; locus heterogeneity (many different mutations can cause the same phenotype); PKU; albinism - deafness - Marfanoid habitus (Marfans - MEN 2B - homocystinuria)
Pompes

11. __________ adds N linked oligosaccharides to proteins
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
TRNA wobble
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
the RER

12. What are the titles of the two types of fructose disorders? Which is more serious>
Essential fructosuria and fructose intolerance; fructose intolerance
AST (mit damage) - and GGT (d/t SER hyperplasia d/t induction of p450 generation)
Type I collagen; AD
Excess ATP and dATP has negative feedback inhibition on ribonucleotide reductase Which results in decreased DNA synthesis and thus decreased lymphocyte count

13. What aa is the ultimate precursor of catecholamine synthesis?
Myoclonus epilepsy
Phospholipids - sphingolipids - glycolipids
Phenylalanine
homocysteine transferase

14. What is the treatment for cystinuria?
Arginine
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
Acetazolamide to alkalinize the urine
Mental retardation - rocker bottom feet - micrognathia (small jaw) - low set ears - clenched hands with polydactyly - congenital heart disease

15. ____ soluble vitamins are more likely to result in toxicity
Lactose in mothers milk contains galactose
fat
Oral uridine administration; provides nucleosides and provides feedback inhibition
Less; more

16. What liver enzymes are increased in alcoholism? why?
Adenosine deaminase deficiency; Severe combined immunodeficiency disease
AST (mit damage) - and GGT (d/t SER hyperplasia d/t induction of p450 generation)
HMG CoA synthetase; HMG CoA reductase
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!

17. why does galactose def present in newborns>
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Fabrys Disease and Hunters Syndrome
Respiratory burst - P450 - and glutathione reductase
Lactose in mothers milk contains galactose

18. What are the two most common aminotransferase and What amino acids do they turn to What glycolytic intermediates?
adrenal medulla
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST); alanine to pyruvate and aspartate to oxaxloacetate
2/3; LCAT (lecithin cholesterol acyltransferase)
Lack of lactase (brush border enzyme) so can not break down lactose (a dissaccharide of galactose and glucose); African Americans and Asians

19. What is the most common cause of Osteogenesis Imperfecta? What is the inheritance pattern?
Adrenal medulla
Type I collagen; AD
RBCs - renal medulla - leukocytes - lens - testes - cornea
Von gierkes

20. Where is type 1 collagen found?
Carnitine shuttle
MT!
Dactinomycin - doxorubicin
Bone - Skin - Tendon - dentin - fascia - cornea - late wound repair

21. What is imprinting?
SER and mitochondria; NADPH
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
Heterochromatin; euchromatin
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

22. After N5N10 methylene THF donates a methyl for conversion of dUMP to dTMP What is it converted to?
DHF
Cysteine; tyrosine
Heterochromatin; euchromatin
NADPH oxidase; CGD

23. Do RNA polymerases have proofreading function? What does this mean for HIV?
No; increased mutation rate!
Hemolytic anemia; jaundice in newborn if mom gets too much vit K
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate

24. What enzyme is necessary for branched aa degradation? What cofactor? What are the branched aa?
Flouroquinolones
Glucose 6 phosphate dehydrogenase
Cells that stay in G0 and cannot replicate - instead they regenerate from stem cells; neurons - skeletal and cardiac muscles - and RBCs
Branche aa alpha ketoacid dehydrogenase; thiamine; Isoleucine - leucine - valine

25. What is used in a marathon?
Acetyl CoA carboxylase
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
linked recessive
Glycogen and FFA oxidation - glucose conserved for final sprinting!

26. What carries aldehydes as energry?
Vit D levels
Mental retardation - rocker bottom feet - micropthalmia - microcephaly - cleft lip/palate - holoprosoncephaly - polydactyly
TPP (thiamine pyrophosphate)
Pellagra

27. Name a few intermediate filament defects. hints: alcohol - 2 neuro dx

28. Which antigout drugs act on MT?
Colchine
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
Riboflavin; dairy and meat
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly

29. RER adds ___________ to asparagines
N linked oligosaccharides
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
All and Alzheimers
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia

30. What is the function of Vitamin A?
Excess ATP and dATP has negative feedback inhibition on ribonucleotide reductase Which results in decreased DNA synthesis and thus decreased lymphocyte count
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
HMG CoA reductase
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis

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

32. What is the deficient enzyme in Metachromatic leukodystrophy disease? accumulated Substrate?
'9+2' 9 pairs of microtubules connected by an axonemal dynein ATPase in a cylinder with 20 MTs in the center; the connecting ATPase allows bending and differential sliding
paternal
Colchine
Arylsulfatase A; cerebroside sulfate

33. What is the major cause of SCID? What does SCID stand for?
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
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
Adenosine deaminase deficiency; Severe combined immunodeficiency disease
Cystic Fibrosis (CFTR gene)

34. What are the GI clinical symptoms of CF?
Chronic pancreatitis leads to type 1 diabetes - pancreatic insufficiency leads to ADEK deficiencies - malabsorption and steatorrhea - blocked gallbladder ducts leads to secondary biliary cirrhosis
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
Dactinomycin - doxorubicin
Steroid - cholesterol FA synthesis; HMP shunt

35. What dose a deficiency in Vit B12 cause? What causes it?
tubulin dimer
Microvilli - muscle contraction - cytokinesis - adherens junctions
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
Arginine

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

37. What is cystinuria due to?
Hereditary defect of renal tubular amino acid transporter for cysteine - ornithine - lysine and arginine in the PCT of kidnyes
Conversion of pyruvate to Acetyl CoA; acetyl coA - CO2 - and NADH (one of each per pyruvate)
Excreted from the kidney in the form of urea in hepatocytes
Glycolysis and aerobic respiration

38. What are the clinical symptoms of Marfans?
osteosarcomas (Rb mutation is in all cells)
Adenosine deaminase deficiency; Severe combined immunodeficiency disease
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )
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

39. What causes fruity odor in ketoacidosis?
Acetone
False; GTP hydrolysis
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance
5'--> 3'; prokaryote only; for removing RNA primer and filling it with DNA

40. What are labile cells? Which cells are labile?
3'--> 5'; prokaryote only
catecholamine synthesis (dopamine to norepinephrine)
Cells that never got into G0 and divide rapidly with a short G1; bone marrow - gut epithelium - hair follicles - skin
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off

41. What is the first step in FA degradation in the cytosol?
Hungtington
CCA and chemically modified bases Where amino acid is covalently bonded
All clathrin
FA coA synthetase combines coA with FA to make acyl coA

42. What builds up in the urine in homogentistic acid oxidase deficiency? What does this result in ?
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)
Glutamate
Urine turns black on standing
long saturated fatty acids

43. The mode of inheritance for both NF disease is...
Both AD
Hereditary defect of renal tubular amino acid transporter for cysteine - ornithine - lysine and arginine in the PCT of kidnyes
NADH - NADPH - FADH2
TCA cycle - FA oxidation - acetyl coA production; ox phos

44. What happens to S adenosyl methionine after it donates a methyl? What enzyme regenerates methionine? What two factors are necessary to do this? who gives the methyl?
25 OH D3; 1 -25 (OH)2 D3 (Calcitriol)
S adenosyl homocysteine; homocysteine transferase; B12 and THF; M- THF
enzymatic
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption

45. What are the clinical symptoms of Huntingtons disease? When does it present?
SER and mitochondria; NADPH
fructose
By activating protein phosphatase Which both dephosphorylates glycogen phosphorylase (deactivating) and dephosphorylates glycogen synthase (activating it )
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50

46. What is the rate determining enzyme in HMP shunt?
Glucose 6 phosphate dehydrogenase
Cysteine; tyrosine
Cri du Chat
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP

47. How do you treat niacin deficiency do to corn based diet?
Prolonged deficiency of Vitamin C results in decreased tensile strength of collagen because lack of hydroxylated lysines to crosslink (hydroxylation required vit C); bleeding gums - bone pain - poor wound healing - hemarthroses - glossitis - hemorrha
Lime and CaCO3 to displace the niacin
Phosphofructokinase 1
Hemolytic anemia (fragility of RBCs) - muscle weakness and posterior column and spinocerebellar tract demyelination (neuron damage) resulting in decreased proprioception and vibration sensation - and peripheral neuropathy - and retinal degeneration

48. How many enzymes does the pyruvate dehydrogenase complex have? and How many cofactors? Where is it located? to What enzyme is it similar to?
Alcohol dehydrogenase; cytosol; mitochondria; NAD+
3; 5; mit matrix; alpha ketoglutarate dehydrogenase complex
Retinol; Beta carotenes (dark and yellow vegetables)
Decreased phenylalanine - increase tyrosine

49. What enzyme converts phenylalanine to tyrosine? What cofactor is used?
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Formation of a proton gradient that is then used to create ATP through ATP synthase
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
Phenylalanine hydroxylase; tetrahydrobiopterin factor

50. Which two lysosomal storage disease are XR and not AR?
Both AD
Fabrys Disease and Hunters Syndrome
Pyruvate! (not lactate - that is generate just in order to produce more NAD+)
Dopa decarboxylase; B6