Test your basic knowledge |

USMLE Step 1 Biochemistry

Subjects : health-sciences, usmle-step-1

Instructions:

Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can study here.
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 aa is most accumulated in hartnup disease? What vitamin becomes deficient?
Prevents neural tube defects in 1st trimester
Carnitine shuttle
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits
Tryptophan; niacin

2. What aa does melanin come from? melatonin?
Acetyl coA; gluconeogenesis
Galactokinase deficiency and classic galactosemia; classic galactosemia
Hemolytic anemia; jaundice in newborn if mom gets too much vit K
Tyrosine; tryptophan

3. What enzyme converts norepinephrine to epinephrine? using What cofactor?
COP II
Bone - Skin - Tendon - dentin - fascia - cornea - late wound repair
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse
Phenylethanolamine N- methyl transferase; SAM

4. From What aa does dopa come from?
Uses HMG coA reductase
Tyrosine
Enriched whole grain cereals and other things; thiamine; malnutrition (nonenriched white processed bread and rice) and alcohol second to malnutrition
dimers

5. What is elastin? How is it different from collagen? Where is it found? How is it broken down?
1. denature by heating 2. during cooling anneal with DNA primers 3. elongation - add heat stable DNA polymerase 4. repeat
SAM
S - adenosyl methionine
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

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

7. What is the function of Vit D?
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)
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
To increase serum Ca and phosphate for bone deposition
Liver and skeletal muscle

8. What form of Vitamin D is in plants? milk fortified with vit D? formed in sun exposed skin?
D2 (ergocalciferol) - D3 (cholecalciferol) - D3 (cholecalciferol)
Niemann pick and Tay Sachs; hepatosplenomegaly or not
Electron transport inhibitors - ATPase inhibitors - Uncoupling agents (increase permeability of the membrane - loss of hydrogen gradient)
Carbidopa

9. Findings for Cori's disease? deficient enzyme?
Milder form of type 1 with normal blood lactate levels; debranching enzyme (alpha -1 -6 glucosidase)
Tyrosinase
Down's Syndrome
Creates nicks in DNA to prevent supercoiling; both!

10. What is the other name of B3? What is its function? Synthesis of B3 requires What other vitamin? What else?
Vincrstine (vinca alkaloids) and paclitaxel
Dopa decarboxylase; B6
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species

11. What does a pyridoxine deficiency look like? What causes it?
Marfans and emphysema; marfans is a fibrillin protein defect - fibrillin is a supporting protein in tropoelastin scaffolding and results in aorta - skeletal and eye defects; emphysema is due to a deficiency in the function of alpha 1 antitrypsin
Hepatic fatty change
glutton
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption

12. How is muscular dystrophies diagnosed?
Ehler Danlos; type III collagen def; joint dislocation - berry aneurysm - ecchymoses - organ rupture
Lime and CaCO3 to displace the niacin
Lack of proper dietary therapy during pregnancy resulting in infant's microcephaly - mental retardation - growth retardation and congenital heart defects
Increased CPK and muscle biopsy

13. What 4 diseases specifically results with B1 deficiency?
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase
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
enzymatic
Tryptophan; B6

14. What enzyme is deficient in classic galactosemia? symptoms? treatment?
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate
Sphingomyelinase; sphingomyelin
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
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting

15. What is the purpose of HMP shunt?
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Becomes methionine
activation of PFK1

16. What are permanent cells? Which cells are permanent?
Phenylalanine
Lens and neural tissue; converts galactose to osmotically active galactitol
Cells that stay in G0 and cannot replicate - instead they regenerate from stem cells; neurons - skeletal and cardiac muscles - and RBCs
Carnitine shuttle

17. In x linked - in males - prevalence is...
Galactose
Hereditary defect of renal tubular amino acid transporter for cysteine - ornithine - lysine and arginine in the PCT of kidnyes
= q
Pyridoxine; converted to pyridoxal phsophate used in transamination reaction - decarboxylations - heme synthesis - niacin synthesis from trp - glycogen phosphorylase - cystathionine synthesis - NT synthesis

18. ______________ interact with each other and decrease fluidity and increase melting temperature
Inbit Na+K+ ATPase; Cardiac glycosides
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
long saturated fatty acids
Cartilage (including hyaline) - vitreous body - nucleus pulposus

19. in What disease are there antibodies to snRNPs?
SnRNPs; RNA polymerase III
Lupus
Metanephrine
Hypophosphatemia rickets and Alports

20. Vit A is ________ - causes cardiac problems and cleft palate in newborns
teratogenic
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes
Heteroplasmy
Later

21. Which is the rate limiting enzyme in ethanol metabolism? Where is this enzyme located? Where is the other enzyme located? What is the limiting reagent?
Alcohol dehydrogenase; cytosol; mitochondria; NAD+
Abs against type IV collagen; pulmonary and glomerular capillaries
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
Beta glucocerebrosidase; glucocerebroside

22. What aa (other than glutamate) is a precursor for urea?
Exons
Fe2+; Fe3+
Arginine
7 dehydrocholesterol

23. How is urea measured
Glycosylases (only remove the base - cut the bond between ribose and base)
Phospholipids - sphingolipids - glycolipids
As BUN (blood urea nitrogen)
Chromosomal imbalance (downs for ex)

24. How do digoxin and digitoxin work? What class of drugs are they?
be anorexic
Pompes
Inbit Na+K+ ATPase; Cardiac glycosides
Codons may encode same amino acid since there are only ~20 aa

25. What converts dihydrobioterin back to tetrahydrobioterin factor? What energy carrier is used? in What reactions is this cofactor used?
Kidney and intestinal epithelium
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption
Dihydropterin reductase; NADP+; phenylalanine to tyrosine and tyrosine to DOP
Lack of proper dietary therapy during pregnancy resulting in infant's microcephaly - mental retardation - growth retardation and congenital heart defects

26. How does an enzyme know to go to lysosome?
Phenylalanine
Central and peripheral demyelination with ataxia and dementia
Pataus
By addition of mannose 6 phosphate to proteins in the Golgi

27. in What organ is D3 converted from 25 OH D3? with What enzymes?
No; increased mutation rate!
Hemolytic anemia; jaundice in newborn if mom gets too much vit K
Acetyl coA activated pyruvate carboxylase in gluconeogenesis
Liver; P450 hydroxylation

28. What is the findings in Fabrys disease?
Nucleoside is just the ribose plus the base; nucleotide is the ribose plus the base but the phosphate bond
Peripheral neuropathies of hands/feet; angiokeratomas between umbilicus and knees; cardiovascular/renal disease
Fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio
hexokinase (glucokinase only found in liver and beta cells of pancreas)

29. What is the first enzyme and step in ethanol metabolism? second step? What is a cofactor in both of these steps? What vitamin does this come from?
Glycolysis and aerobic respiration
Alcohol dehyrogenase (alcohol to acetaldehyde); acetaldehyde dehydrogenase (acetaldehyde to acetate); NAD+; B3 (niacin)
When child gets two chromosomes from one parent; imprinting dx
Down's Syndrome

30. What is the inheritance pattern of hereditary spherocytosis?
liver
AD
Oxygen!
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase

31. What kind of kinetics does alcohol dehydrogenase work under? What are the implications of this?
Pataus
Cheilosis and corneal vascularization
HMP shunt (to NADPH) and glycogenolysis (as glucose 1 phosphate)
Zero order; increased production of NADH no matter the amount of end products produced

32. What is a telangiectasia? Where can they be found?and What is a common result of them?
Metaphase (all lined up); blood - bone marrow - amniotic fluid - placental tissue; used to diagnose chromosomal abnormalities (deletions - trisomies - sex chromosomal disorders)
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding
Kidney and intestinal epithelium

33. What results in marasmus? What kind of muscle wasting? What kind of muscle wasting do you see in kwashiokor?
Loss of subcutaneous fat - tissue and muscle wasting (somatic muscle); visceral - not somatic
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)
Griseofulvin

34. What is the rate determining enzyme in glycolysis?
Hexosaminidase A; GM2 ganglioside
Phosphofructokinase 1
Later
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA

35. What is folic acid? What is its function?
GALT
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth
All clathrin
3 NADH - 1 FADH2 - 2 CO2 - 1 GTP = 12 ATP/acetyl CoA

36. polymerase chain reaction (PCR)- Name an application for it
Hereditary defect of renal tubular amino acid transporter for cysteine - ornithine - lysine and arginine in the PCT of kidnyes
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers
Genotyping for mutant alleles (different sizes)
6MP blocks de novo purine synthesis

37. other than bone resorption to release Ca and phosphate - What is the ultimate point of increasing the serum Ca2+ and phosphate?
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol
To increase serum Ca and phosphate for bone deposition
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
Mebendazole and thiabendazole

38. What converts pyruvate to Acetyl CoA ? What allosterically downregulates this enzyme?
In hepatocytes; B6
Glucose 6 phosphatase
When the disease manifestation depends on from who the gene deletion was inherited from d/t methylation that occurs; Prader Willi and AngelMann
Pyruvate dehydrogenase; ATP - NADH - acetyl CoA

39. What can cause an excees of vit A? What are the symptoms?
Intestine - renal - bone
fructose
Consumption of bear liver - and overtreatment isoretinoin; constitutional symptoms and alopecia and skin changes
Marfans - homocystinuria - MEN 2B

40. What is the function of Vitamin A?
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
Metanephrine
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
AR

41. What is the product of odd chain fatty acid synthesis? How does it return to TCA cycle? What cofactor is required?
As BUN (blood urea nitrogen)
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate
Proprionyl coA; through methylmalonyl coA; B12
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant

42. What is used in a marathon?
Oxaloacetate gets shifted to malate d/t excess NADH
= q
The active form of Vit D (1 -25 (OH)2 D3)
Glycogen and FFA oxidation - glucose conserved for final sprinting!

43. Where does the HMP (pentose phosphate pathway) occur other than in the liver?
acetyl coA
Lactating mammary glands - adrenal cortex (sites of fatty acid or steroid synthesis) - RBCS (for glutathione reduction for FR injury)
paternal
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes

44. How would one use a PCR to id an RNA virus?
Microvilli - muscle contraction - cytokinesis - adherens junctions
Do an RT PCR (reverse transcriptase)- RT the RNA first - then PCR the DNA
Electron transport inhibitors - ATPase inhibitors - Uncoupling agents (increase permeability of the membrane - loss of hydrogen gradient)
Dactinomycin - doxorubicin

45. What is the metabolism of galactose like?
Galactose gets converted to galactose 1 Phosphate by galactokinase Which then gets turned into glucose 1 phosphate by Galactose 1 Uridyl Transferase (GALT) Which also produces UDP Gal Which is used for lactose production in the breast; the fate of gl
allosteric regulation
Imprinting Dx's: prader Willi and Angelmann
NF1

46. What are causes of zinc deficiencies?
Exons
Assist in spontaneous refolding of proteins
Alcoholism - RA - inflammatory disease - chronic diarrhea
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA

47. What are the clinical symptoms associated with fragile X syndrome?
Heme synthesis - urea cycle - gluconeogenesis
Macroorchitism - big ears - big jaw - mental retardation (2nd mcc!) - mitral valve prolapse - long face
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
Increased G3P for TG synthesis - increased acetyl CoA (Fatty acid synthesis for TG synthesis) - and decreased oxidation of FA in the mitochondria due to alcohols toxicity on the mit

48. What are the four trinucleotide expansion disease and What are the expansions?
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)
Biotin; cofactor for carboxylation; pyruvate carboxylase (turning pyruvate to oxaloacetate) - acetyl coA carboxylase (acetyl coA to malonyl Co A) - and proprionyl coA caroboxylase for (propionyl CoA to methylmalonyl coA)
Myotonic Dystrophy (CTG) - Huntington (CAG) Friedricks Ataxia (GAA) - Fragile (CGG)
Kartaganer's aka ciliar dyskinesia; lack of dynein arm ATPase

49. fatty acid synthase requires ...
pleiotropic
Homocysteine; homocysteine methyltransferase with B12 and tetrahydrofolate
NADPH- reductive biosynthesis!
Reticulin - skin - blood vessels - uterus - fetal tissue - early phase of granulation tissue

50. Only muscle and brain have transferase enzyme that converts ketone bodies to...
Biotin (vit B7) and Vit K
Oxygen!
COP I
acetyl coA