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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 are the common symptoms of B vitamin deficiencies?
Asp and glu; negatively
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding
Dermatitis - glossitis - diarrhea

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

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3. HMG coA synthase; cholesterol synthesis
Uses HMG coA reductase
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Glycogen phosphorylase

4. What is the precursor for both purines?
Adipose tissue for brain and heart (ketone bodies) and then go to vital protein degradation (organ failure)
Neurons and RBCs
To supply sufficient glucose to the brain and the RBCs and to preserve protein
IMP

5. What can cause Biotin deficiency? What are the symptoms?
Von gierkes
Avidin in raw egg whites prevents their reabsorption; also antibiotic use; dermatitis - alopecia - glossitis - lactic acidosis - enteritis
1 for all three classes of RNA; Rifampin; TB
AAUAAA; Poly A polymerase; no

6. What are three ketone bodies? Which is not detected in urine? Which do you see most in alcoholic ketoacidosis?
TPP (thiamine pyrophosphate)
X linked recessive; deletion of the dystrophin gene (connects actin to the membrane glycoprotein) due to frame shift mutation - lack of dystrophin results in muscle breakdown Which gets replaced by fibrofatty tissue and collagen
Electron transport inhibitors - ATPase inhibitors - Uncoupling agents (increase permeability of the membrane - loss of hydrogen gradient)
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate

7. High blood levels of fructose - galactose - glucose can result in conversion to osmotically active alcohol forms by...
aldose reductase
ATP and biotin
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Macrocytic megaloblastic anemia; it is the most common vit def in the US; no neuro symptoms and no methylmalonyl coA in the urine

8. Sporadic Retinoblastoma results is unilateral - but only familial is associated with...
Respiratory - seminal fluid - pancreatic - gallbladder; very thick without NaCl to pull water
Tyrosine
osteosarcomas (Rb mutation is in all cells)
Glycogen phosphorylase

9. From What aa does porphyrin come from? What is porphyrin the precursor of?
Glycine; heme
Fructose gets phosphorylated into fructose 1- P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B
The products of FA oxidation (Acetyl CoA and NADH) phosphorylate pyruvate deyhdrogenase Which inactivates it
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)

10. How do digoxin and digitoxin work? What class of drugs are they?
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
Shiga toxin and ricin (protein in castor beans)
Branche aa alpha ketoacid dehydrogenase; thiamine; Isoleucine - leucine - valine
Inbit Na+K+ ATPase; Cardiac glycosides

11. Name two antineoplastic drugs that work by inhibiting the mitotic spindle by MT blocking.
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
Vincrstine (vinca alkaloids) and paclitaxel
Myotonic Dystrophy (CTG) - Huntington (CAG) Friedricks Ataxia (GAA) - Fragile (CGG)
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine

12. What disease is associated with chromosome 13?
HVA
Rb
ATP depletion and highly aerobic tissues (heart and brain) are affected first; false - glucose infusion worsens
Citrate shuttle in the inner mitochondrial membrane transports acetyl coA into the cytoplasm; liver; liver and adipose tissue

13. Which antioxidant does cigarette smoke injury eat up? Which antioxidant does LDL injury eat up?
Vit C; Vit E
succinyl coA (and then to OXA)
Glutamate
Presence of normal and mutated mtDNA (like mosaicism except in mit)

14. How does glycerol from triacylglycerols in adipose tissue used for gluconeogenesis?
Central and peripheral demyelination with ataxia and dementia
hexokinase - glucokinase (its a glutton)
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
Von gierkes

15. other than increase Parathyroid hormone What else increases 1 alpha hydroxylase activity in the kidney?
No protein!
A methyl
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
Decreased serum phosphate

16. Vit A is ________ - causes cardiac problems and cleft palate in newborns
Neural tissue and adrenal medulla
Biotin; rate limiting step in fA synthesis - acetyl coA into malonyl coA
Decreased serum phosphate
teratogenic

17. What is the rate determining enzyme in TCA cycle?
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
tyrosine hydroxylase
Isocitrate dehydrogenase
NADH - NADPH - FADH2

18. What is carnitine deficiency and What does it result in?
Carbomyl phosphate synthetase I turns N acetyl glutamate into carbomyl phosphate and then ornithine transcarbomyalse turns carbomyl phosphate into citrulline (using ornithine)
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
Cytosine to uracil
Cancers (rapidly synthesizing); MTX (blocks dihyrdofolate reductase); phenytoin (prevent conjugase from breaking down polyglutamate form to monoglutamate form; reabsorption in jejunum is blocked by alcohol and OCPs; also blocked by sulfonamides

19. What is the other name of Vitamin A? What is its source?
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
glycogen
Mit encephalopathy - lactic acidosis - stroke like episodes
Retinol; Beta carotenes (dark and yellow vegetables)

20. What is the confirmation of Downs?
Amniocentesis karyotyping
Thick mucus plugs lungs recurrent pulmonary infections (pseudomonas and aureus) - chronic bronchitis - bronchiectasis (which can lead to cor pulmonale!); biofilms form on resp tract
Water soluble vitamin stored in liver; converted to THF by dihydrofolate reductase and is a coenzyme in 1 methyl transfers - impt for DNA synth
Aldolase B

21. What is the function of Vitamin B1?
FA coA synthetase combines coA with FA to make acyl coA
Lysine and arginine; basic
Converts it to citrulline
It is apart of thiamine pyrophosphate Which is a cofactor enzymes involved in ATP production: pyruvate dehydrogenase (glycolysis) - alpha ketoglutarate dehydrogenase (TCA cycle) - transketolase (HMP shunt) - branched chain AA dehydrogenase

22. What are the clinical symptoms of hyperammonemia?
Renal failure - decreased sun - fat malabsorption - chronic liver disease - p450 induction - hypoparathyroidism (activates 1 alpha hyrdoxylase)
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
With glucose 6 phosphatase; Von Gierkes disease
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits

23. What are the findings in maple syrup disease? What should be tried to be given as treatment?
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
AR
CNS defects - mental retardation - death - feeding difficulties - vomiting - hypoglycemia; thiamine
Abs against type IV collagen; pulmonary and glomerular capillaries

24. What are the lab findings see in hyperammonemia?
Lens and neural tissue; converts galactose to osmotically active galactitol
Increased blood levels of ammonia - decreased BUN
SAM
Cysteine; tyrosine

25. What is 'charging' of tRNA? What enzyme regulates this? What does this reaction require? in What process is this?
Nitric Oxide - creatinine - Urea
Night blindness - dry skin
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
Vomiting - rice water stools - garlic breath

26. What type of diseases exhibit anticipation?
hexokinase (glucokinase only found in liver and beta cells of pancreas)
Nucleoside is just the ribose plus the base; nucleotide is the ribose plus the base but the phosphate bond
Trinucleotide expansion diseases
Adrenal medulla

27. What can cause hypervitaminosis D?
Iatrogenic - granulomatous disease (sarcoidosis d/t epitheloid macrophage release of calcitriol); hypercalcemia - hypercalciuria (renal calculi!) - loss of appetite - stupor
Robertsonian translocations
Night blindness - dry skin
GTP: gluconeogenesis - OXA to phosphoenolpyruvate

28. What type of enyzmes are used in base excision repair?
HMG CoA reductase
Glycosylases (only remove the base - cut the bond between ribose and base)
Isoleucine - valine - leucine
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)

29. What is the rate determining enzyme in glycogenolysis?
Glycogen phosphorylase
AR; trinucleotide deletion results in loss of a Phe aa on CFTR gene on chrom 7- the result is a mutated CFTR channel that gets degraded in the ER before reaching the surface; the purpose of CFTR is to increase Cl secretion in luminal secretions and r
4 -4 -9
To transfer methyls; a methionine and an ATP; norepinephrine plus a methyl makes epinephrine

30. What is the main form of glycogenolysis after glycogen phosphorylase? What happens instead in some lysosomes? does this process use glycogen phosphorylase? in What disease is this enzyme deficient?
Debranching enzyme; alpha 1 - 4 glucosidase; no!; Pompes disease
Gain of function gene after expansion results in overproduction of huntingtin protein that in overproduction results in toxicity to neurons in the caudate --> caudate atrophy and decreased levels of GABA and Ach
Acetyl coA; gluconeogenesis
are AR

31. Glycogenolysis ________ maintains blood sugar
Abs against type IV collagen; pulmonary and glomerular capillaries
Cardiomegaly - cyanosis - tachycardia - dyspnea - vomitting; 2-3 months
in hepatocytes
Lysine and leucine

32. Which syndrome results from microtubule polymerization defect? What are the clinical features?
Lactic acidosis and ketoacidosis
Assist in spontaneous refolding of proteins
Some viruses
Chediak Higashi Syndrome; decreased phagocytosis results in recurrent pyogenic infections - partial albinism - and peripheral neuropathy

33. What contributes to the acidosis in alcoholism?
Schwann cells - lens - retina - kidneys because they only have aldose reductase and no sorbital dehydrogenase
Genotyping for mutant alleles (different sizes)
Lactic acidosis and ketoacidosis
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

34. From What aa does niacin come from? with What vitamin cofactor?
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting
Tryptophan; B6
Cheilosis and corneal vascularization
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)

35. Which antifungal acts on MT?
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!
Griseofulvin
Metaphase (all lined up); blood - bone marrow - amniotic fluid - placental tissue; used to diagnose chromosomal abnormalities (deletions - trisomies - sex chromosomal disorders)
Carbamoyl phosphate

36. On a 100 meter sprint What is used as energy? in general What is the rule with exercise? What is used in 1000 meter run?
show disease
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits
Stored ATP - creatine phosphate - anaerobic glycolysis; as distances increase - ATP is obtained from additional resources; above plus ox phos
Both AD

37. What converts dopamine to norepinephrine? using What cofactor?
CNS defects - mental retardation - death - feeding difficulties - vomiting - hypoglycemia; thiamine
NADH - Acetyl CoA - ATP; NAD+ - ADP and Ca2+
Alanine (through pyruvate) - aspartate (through OXA) - glutamate (alpha ketoglutarase); TCA
Dopamine beta hydroxylase; vit C

38. polymerase chain reaction (PCR)- Name an application for it
long saturated fatty acids
Genotyping for mutant alleles (different sizes)
Cycloheximide
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

39. 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)
Succinate hydrogenase; matrix
all are diseased!
LDL; LDL oxidize atherosclerosis

40. Which two lysosomal storage diseases findings are very similar? How do you differentiate them?
Niemann pick and Tay Sachs; hepatosplenomegaly or not
Yes! congenital simply means 'born with'- hereditary is familial
Cystine kidney stones (cystine staghorn calculi)
Alcohol dehyrogenase (alcohol to acetaldehyde); acetaldehyde dehydrogenase (acetaldehyde to acetate); NAD+; B3 (niacin)

41. What can cause an excees of vit A? What are the symptoms?
Consumption of bear liver - and overtreatment isoretinoin; constitutional symptoms and alopecia and skin changes
Glycogen synthase
Loss of subcutaneous fat - tissue and muscle wasting (somatic muscle); visceral - not somatic
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

42. How do hepatocytes release glucose 6 P from glycogenolysis into the blood ? in What disease is this enzyme deficient?
By activating protein phosphatase Which both dephosphorylates glycogen phosphorylase (deactivating) and dephosphorylates glycogen synthase (activating it )
With glucose 6 phosphatase; Von Gierkes disease
kidney
Liver and skeletal muscle

43. What type of exonuclease activity does DNA polymerase I have? in What organisms is it found? What is it used for?

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44. What aa becomes essential with homocystinuria? phenylalaninuria?
Cysteine; tyrosine
They can enter G1 from G0 and replicate if they like; hepatocytes - lymphocytes - fibroblasts
A methyl
Folinic acid; does not require DHF

45. What are the three types of blotting procedures ? What are blotting procedures used for? What are steps in a blotting procedure?
Pompes
Southern - DNA - Northern - RNA - Western - Protein; blotting procedures are used to detect a specific nucleic acid or aa sequence; the sample is electrophoresed and then transferred to a filter Which is then soaked in a denaturant and then a radiola
Both AD
1 for all three classes of RNA; Rifampin; TB

46. What amino acids are required in purine synthesis? Which of these does pyrimidine synthesis require also?
Prolonged Ab use
Nucleus
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
Glutamine - aspartate - glycine; aspartate

47. What liver enzymes are increased in alcoholism? why?
AST (mit damage) - and GGT (d/t SER hyperplasia d/t induction of p450 generation)
Damaged 'ubiquinated' cytokeratin intermediate filaments build up in hepatocytes - damaged neurofilaments in idiopathic parkinsons disease build up to form Lewy bodies - Neurofibrillary tangles are build up of neurofilaments in alzheimers
Tryptophan; B6
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)

48. How is Vit K activated? What drug blocks this? What is the source of Vit K?
Endonucleases - exonucleases - DNA polymerase - DNA ligase
A methyl
By epoxide reductase in the liver; coumadin; intestinal flora and leafy vegetables
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)

49. What are the mucopolysaccharidoses? Which one is XR? AR? What accumulates in them?
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Arginine
It is apart of thiamine pyrophosphate Which is a cofactor enzymes involved in ATP production: pyruvate dehydrogenase (glycolysis) - alpha ketoglutarate dehydrogenase (TCA cycle) - transketolase (HMP shunt) - branched chain AA dehydrogenase
Cheilosis and corneal vascularization

50. When is there high levels of cAMP? What does this result in?
Peripheral neuropathies of hands/feet; angiokeratomas between umbilicus and knees; cardiovascular/renal disease
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes
A methyl
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

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USMLE Step 1 Biochemistry

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