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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 do hexokinase and glucokinase do? using what? What pathway is this in?
Ornithine transcarbomyalse; orotic aciduria; X linked recessive; autosomal recessive
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
Either salvage by HGPRT and PRPP or conversion to xanthine and then uric acid by xanthine oxidase
MT!

2. What metabolic reactions occur in the cytoplasm?
Mannose
Glycolysis - fatty acid synthesis - HMP shunt - protein synthesis (RER) - steroid synthesis (SER) - glycogenolysis - glycogenesis
Because cells of mononuclear phagocytic are esp rich in lysosomes
Lactose in mothers milk contains galactose

3. What does cross linking to collagen do? What does this have to do with age?
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption
Lesch Nyhan syndrome; X linked recessive
Central and peripheral demyelination with ataxia and dementia
Make it stiffer/more tensile; continues as we get older so gets less and less elastic

4. What is retinoic acid used for in treatments?
paternal
Wrinkles - acne and psoriasis topically - promyelocytic anemia - measles
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)
Via fructose 1 P by fructokinase in the liver; as glucose 1 by being GALT- ed ;)

5. Which intermediate is involved in both pyrimidine synthesis and the urea cycle?
3'--> 5'; prokaryote only
NADPH- reductive biosynthesis!
Carnitine acyltransferase I
Carbamoyl phosphate

6. What disease is associated with chromosome 5?
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no
NADH - Acetyl CoA - ATP; NAD+ - ADP and Ca2+
Cri du Chat
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover

7. Which amino acid is the most basic?
G6PD dehydrogenase; transketolases
BM; laminins; most flexible; different aa composition
The active form of Vit D (1 -25 (OH)2 D3)
Arg

8. On Which side of the cytoplasm is the ATP site in the Na+K+ ATPase pump? is a phosphorylated pump active or inactive?
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Cytoplasmic side; active
Pigmented iris hamartomas
Carbamoyl phosphate

9. From What aa does niacin come from? with What vitamin cofactor?
Zero order; increased production of NADH no matter the amount of end products produced
can be d/t lyonization
Tryptophan; B6
Mucus secreting goblet cells - ab secreting plasma cells - nt secreting neurons

10. What is heteroplasmy?
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
Presence of normal and mutated mtDNA (like mosaicism except in mit)
in hepatocytes
TFs

11. What is the inheritance pattern of hereditary spherocytosis?
Vincristine - vinblastine - and paclitaxel; the vinca alkaloids block formation of the spindle and paclitaxel prevents breakdown of the mT spindle
Arg and his
Whether or not the patient is also hyperammonemia (if yes - then OTC def)
AD

12. What happens in RBCs after their membranes get oxidized?
Mental retardation - excessive laughter - seizures - ataxia - 'happy puppet'
Hemolytic anemia due to heinz bodies Which are oxidized hemoglobin precipitating within the RBCs
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
AAUAAA; Poly A polymerase; no

13. What does ornithine transcarbamyolase do to carbamoyl phosphate?
Converts it to citrulline
Cytoplasmic side; active
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
Assist in spontaneous refolding of proteins

14. What are the two different ways you can insert genes into transgenic mice for experiments?
Vit C
Branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

15. Which metabolic reactions require both the mit and cytosol?
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase
Heme synthesis - urea cycle - gluconeogenesis
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate
30S + 50S= 70S

16. What is the difference between exonucleases and endonucleases?
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers
Endonucleases are specific and break specific linking phosphodiester bonds - exonucleases are not sequence specific and just remove the nucleoside
Branched alpha ketoacid dehydrogenase
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

17. What are the findings in ornthinie transcarbamoylase?
CPSII
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
fastest sugar
Arg and his

18. What aa (other than glutamate) is a precursor for urea?
Niacin treatment for hyperlipidemia; facial flushing
Block Electron transport
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Arginine

19. What aa does tyrosine come from?
Coenzyme A and lipoamides
Helps make Vit K and antioxidant
Phenylaline
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol

20. What are the clinical symptoms of NF1?
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
Galactocerebrosidase; Galactocerebroside
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism

21. Where does splicing occur?
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
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)
Nucleus
Metanephrine

22. What are the lab findings see in hyperammonemia?
Increased blood levels of ammonia - decreased BUN
kidney
Protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase
Formation of a proton gradient that is then used to create ATP through ATP synthase

23. What is the difference between the promoter and enhancer? in What process are they used for?
LDL; LDL oxidize atherosclerosis
Becomes methionine
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
normal lactate levels

24. What does a deficiency cause?
Night blindness - dry skin
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)
Karyotyping
Vit C

25. No offspring of affected males with a mit disease can...
Down's Syndrome
show disease
Glucagon - insulin and epinephrine
Carnitine shuttle

26. High blood levels of fructose - galactose - glucose can result in conversion to osmotically active alcohol forms by...
Cobalamin; cofactor for homocysteine methyltransferase (transfers SAM to THF to give to dUMP) and for methylmalonyl coA mutaseto make succinyl coA
NF1
glucagon - insulin and epinephrine
aldose reductase

27. What is the mcc of an autosomal trisomy?
Schwann cells - lens - retina - kidneys because they only have aldose reductase and no sorbital dehydrogenase
When water is pulled in; polyols (sugar alcohols); cataracts - retinopathy - peripheral neuropathy all seen in chronic hyperglycemia in diabetes
all carriers
Meiotic nondisjunction in mothers gametes during the first meiosis

28. What is ascorbic acid? What is its 5 main function?
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
Dynein - retrograde - kinesin - anterograde
Glucosekinase to glucose 6 P
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol

29. What is type II collagen found?
Lysine and arginine; basic
Fructokinase; benign - fructose in the blood and urine
NF1
Cartilage (including hyaline) - vitreous body - nucleus pulposus

30. What are the findings in alkaptonuria? why do they occur?
Telomerase; an RNA polymerase that uses a RNA template to add DNA to the end of shortening 3' ends
Karyotyping
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage

31. What aa does melanin come from? melatonin?
Tyrosine; tryptophan
It contains the peptidyltransferase activity (for elongation of protein
Lens and neural tissue; converts galactose to osmotically active galactitol
Alanine (through pyruvate) - aspartate (through OXA) - glutamate (alpha ketoglutarase); TCA

32. Increased levels of cAMP results in...
Nucleoside is just the ribose plus the base; nucleotide is the ribose plus the base but the phosphate bond
kidney
= q
glycogenolysis

33. Which Hurlers is milder and presents with no corneal clouding?
XR - iduronate sulfatase
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex
Schwann cells - lens - retina - kidneys because they only have aldose reductase and no sorbital dehydrogenase

34. In What tissues can sorbitol accumulate? why?
Familial Adenomatous Polyposis (APC gene)
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
Schwann cells - lens - retina - kidneys because they only have aldose reductase and no sorbital dehydrogenase
HnRNA; mRNA

35. What is carnitine deficiency and What does it result in?
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
Following gastroenteritis and kwashiokor (protein deficiency)
Microvilli - muscle contraction - cytokinesis - adherens junctions
Do an RT PCR (reverse transcriptase)- RT the RNA first - then PCR the DNA

36. What carries aldehydes as energry?
tyrosine hydroxylase
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
Tyrosine; phenylaline
TPP (thiamine pyrophosphate)

37. What is the most common disorder of the urea cycle? What is the result? What is its mode of inheritance? What is the mode of inheritance of the other urea cycle enzyme def?
Ornithine transcarbomyalse; orotic aciduria; X linked recessive; autosomal recessive
Rb
Reserve supply of glucose in the fasting state - liver gives to the blood and skeletal muscle uses for itself
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

38. Vit A is ________ - causes cardiac problems and cleft palate in newborns
Type IV collagen defect; X linked recessive; hereditary glomerulonephritis - deafness - ocular disturbances
teratogenic
HMG CoA synthetase; HMG CoA reductase
Converts it to citrulline

39. Which histone ties DNA- histone nucleosome beads into more condensed structures?
30S ribosomal RNA (small one)
Cortisol; inhibits insulin action
normal lactate levels
H1

40. What are the findings in pyruvate dehydrogenase def? How do you treat it
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
Galactose
Neurologic defects - myopathy - lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)
Heterochromatin; euchromatin

41. What is the first step in glycolysis?
Aldolase B
Heme synthesis - urea cycle - gluconeogenesis
Phosphorylation of glucose
Lesch Nyhan syndrome; X linked recessive

42. Because electron transport continues...
Some viruses
Iatrogenic - granulomatous disease (sarcoidosis d/t epitheloid macrophage release of calcitriol); hypercalcemia - hypercalciuria (renal calculi!) - loss of appetite - stupor
O2 consumption (last electron acceptor) gets consumed also
Myotonic Dystrophy (CTG) - Huntington (CAG) Friedricks Ataxia (GAA) - Fragile (CGG)

43. Achondroplasia is associated with advanced ________ age
Von gierkes
Succinyl coA
paternal
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate

44. What are the general symptoms of 22q11 chromosomal deletion? why is it that these occur?
Karyotyping
Abs against type IV collagen; pulmonary and glomerular capillaries
Cleft palate - Abnormal faces - thymic aplasia (t cell def) - Cardiac defects - hypocalcemia (secondary to hypoparathyroid); 3rd and 4th branchial pouch aberrant development
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)

45. What is the rate determining enzyme in gluconeogenesis?
Fructose 1 -6 bisphosphatase
Increased acid production competes with uric acid for excretion
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation

46. Where do aminotransferase reactions occur? and What vitamin cofactor do they require?
In hepatocytes; B6
Neurologic lesions and cardiomyopathies (ox phos!)
to ions
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin

47. What can cause a vit C deficiency?
Smoking (FR takes up all the antioxidants); diets lacking fruit
Retinol; Beta carotenes (dark and yellow vegetables)
Neurons and RBCs
Steroid synthesis and detoxification

48. From What aa does dopa come from?
A methyl
Acetyl coA activated pyruvate carboxylase in gluconeogenesis
Tyrosine
Multiple bone fractures - blue sclerae - hearing loss (abdnormal middle ear bones!) - dental imperfections - retarded wound healing

49. How does glycerol from triacylglycerols in adipose tissue used for gluconeogenesis?
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
Phenylketones that build up in phenylketonuria
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
Carbomyl phosphate synthetase II

50. Where are ketone bodies made? What is the rate limiting enzyme? What are they made from?
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA
Vincrstine (vinca alkaloids) and paclitaxel
Galactokinase; galactose appears in blood and urine - sometimes infantile cataracts may present as failure to track objects or lack of a social smile
Conversion of pyruvate to Acetyl CoA; acetyl coA - CO2 - and NADH (one of each per pyruvate)

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USMLE Step 1 Biochemistry

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