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 does methotrexate do? What step is this enzyme involved in?
Some viruses
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase
Increased TG synthesis from increased Glycerol 3 P and abetalipoproteinemia
Mannose

2. What are the clinical symptoms of NF2?
Lesch Nyhan syndrome; X linked recessive
Uric acidemia; HGPRT; purine salvage
Bilateral acoustic schwannomas - juvenile cataracts
Block ATP synthase resulting in no ATP production and an increased proton gradient

3. What is the inheritance of CF? What is the pathogenesis of the disease?
Pyruvate carboxylase (pyruvate to OXA) (mit) - PEP carboxykinase (OXA to PEP) (cyt) - Fructose 1 -6 bisphophatase (fructose 1 -6 bisphosphate to fructose 6 P) (cyt) and glucose 6 phosphatase (in ER); glucose 6 phosphatase
Dark connective tissue - brown pigmented sclera - debilitating athralgias; homogentistic acid builds up and can be toxic to cartilage
Glutamate
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. What is dysgeusia?
Metabolizes them with transferase enzymes to acetyl coA
Marfans - homocystinuria - MEN 2B
fructose
Inability to taste

5. How does lactate contribute to gluconeogenesis?
Renal calculi of uric acid (replaces uric acid in excretion)
Iatrogenic - granulomatous disease (sarcoidosis d/t epitheloid macrophage release of calcitriol); hypercalcemia - hypercalciuria (renal calculi!) - loss of appetite - stupor
Homocysteine; homocysteine methyltransferase with B12 and tetrahydrofolate
Gets converted to pyruvate via the Cori cycle in the liver

6. 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?
Genotyping for mutant alleles (different sizes)
III
Dactinomycin - doxorubicin
Stored ATP - creatine phosphate - anaerobic glycolysis; as distances increase - ATP is obtained from additional resources; above plus ox phos

7. HMG coA synthase; cholesterol synthesis
A piece of glass or silicon chip with thousands of grids with different nucleic acid sequences and DNA or RNA probes are hybridized to the chip and a scanner detects the complementary binding; used to study a persons genome and to detect snps (single
Uses HMG coA reductase
Acetazolamide to alkalinize the urine
Catalyze gamma carboxylation of glutamic acid residues on coag factors so they can bind to Ca complex

8. What is the effect of defiiency of VIt E?
30S + 50S= 70S
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
Alpha amanitin; mushroom caps
Conversion to UDP glucose via UDP glucose pyrophosphorylase; glycogen synthase (rate limiting step )

9. Which is the rate limiting step of the urea cycle?
Cortisol; inhibits insulin action
Carbomyl phoshpate synthetase I
LDL; LDL oxidize atherosclerosis
Karyotyping

10. What does the brain do with ketone bodies?
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
calorie deficient
Coenzyme A and lipoamides
Metabolizes them with transferase enzymes to acetyl coA

11. Ocular albinism is...
Glycogen phosphorylase; phosphorylation and dephosphorylation
linked recessive
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
Can inducibly manipulate genes at specific developmental points

12. What is used in a marathon?
Pernicious anemia; older - mentally slow european woman who is anemic and icteric with a smooth shiny tongue and has broad based shuffling gait
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
Glycogen and FFA oxidation - glucose conserved for final sprinting!
Familial Adenomatous Polyposis (APC gene)

13. in What organ is the storage form of D3 converted to its active form? What enzyme? What hormone stimulates this action?
Kidney; 1 alpha hydroxylase; Parathyroid hormone
linked recessive
Mental retardation - excessive laughter - seizures - ataxia - 'happy puppet'
An anti cancer agent that is a topoisomerase II and creates nicks in DNA

14. What is the main aa composition of collagen? What other 2 aa are common?
Pyridoxine; converted to pyridoxal phsophate used in transamination reaction - decarboxylations - heme synthesis - niacin synthesis from trp - glycogen phosphorylase - cystathionine synthesis - NT synthesis
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Marfans - homocystinuria - MEN 2B
Glycine; proline and lysine

15. Which water soluble vitamins get stored in the liver with the fat soluble vitamins? Which has a greater pool of storage in the liver? Where do all the other water soluble vitamins go?
B12 and folate; B12; washed out
Glycogen phosphorylase
Met - arg - val - his
Edwards

16. other than scurvy What else does vit C def cause? also - What kind of anemias and why?
Tyrosine
Decreased would healing; microcytic anemia (d/t decreased iron [not absorbable]; macrocytic anemia (d/t Fh4 not reduced)
Formation of the alpha chains out of glycine - lysine - proline in the RER to make preprocollagen; hydroxylation of the proline and lysine residues in the RER; glycosylation of the lysine residues to make procollagen Which is triple helix of alpha ch
Isoleucine - valine - leucine

17. What is the rate limiting step in fatty acid synthesis? What four things inhibit this rate limiting step? What stimulates it?
Zero order; increased production of NADH no matter the amount of end products produced
Pigmented iris hamartomas
Fat malabsorption (CF) and abetalipoproteinemia (damage takes up all antioxidants)
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate

18. What is the treatment of hyperammonia?
activator
A folic acid analogue
Glycosylases (only remove the base - cut the bond between ribose and base)
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)

19. The __________ adds O linked oligosaccharides to serine and threonine residues on proteins
Aldolase B; Fructose 1 phosphate accumulates Which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia - jaundice - cirrhosis - vomitting
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
golgi apparatus
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

20. Heterozygous females in X linked recessive disease...
To increase serum Ca and phosphate for bone deposition
Tyrosine
Metanephrine
can be d/t lyonization

21. What builds up in the urine in homogentistic acid oxidase deficiency? What does this result in ?
Urine turns black on standing
Cells that never got into G0 and divide rapidly with a short G1; bone marrow - gut epithelium - hair follicles - skin
Induction in chronic alcoholism (increases tolerance); inhibition in acute alcoholism
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

22. What are the results of the pregnancy screen for Downs?
pleiotropic
Decrease AFP - increased BCHG - decreased estriol - increased inhibin A
A 16C FA! the product in FA synthesis; saturated; no double bonds
When child gets two chromosomes from one parent; imprinting dx

23. What is a common result of unbalanced robertsonian translocation?
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
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Chromosomal imbalance (downs for ex)

24. What goes on with G0 cell cycle phase?
succinyl coA (and then to OXA)
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
Phosphorylation of glucose
AD (trinucleotide expansion is not a mode of inheritance)

25. other than being returned to methionine - What else is the fate of homocysteine? through What enzyme? with What cofactor?
Cystathionine (which then goes to cysteine) via cystathionine reductase; B6
Sickle cell disease - conversion of hydroophillic glutamic acid to hyrdophobic valine
Vit C
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility

26. What are the two main function of Vit E?
Lack of proper dietary therapy during pregnancy resulting in infant's microcephaly - mental retardation - growth retardation and congenital heart defects
Helps make Vit K and antioxidant
Kidney; 1 alpha hydroxylase; Parathyroid hormone
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR

27. What is the rate limiting step in glycolysis? What does it do? who activates it? inhibits it?
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP
glycogen
Formation of a proton gradient that is then used to create ATP through ATP synthase
is asymmetric

28. IMP is degraded to inosine and then to hypoxanthine. What two options are next? by What enzymes?
Either salvage by HGPRT and PRPP or conversion to xanthine and then uric acid by xanthine oxidase
Starts before age 5 with with pelvic girdle weakness with use of Gowers maneuver to stand up - it then progresses superiorly with muscle weakness (type 1 and 2!); waddling duck gait; hyporeflexia; pseudohypertrophy of calf muscles d/t fibrofatty repl
Rb
Tyrosine

29. What are the priorities in fasting and starvation?
Dactinomycin - doxorubicin
To supply sufficient glucose to the brain and the RBCs and to preserve protein
acetyl coA
Genotyping for mutant alleles (different sizes)

30. Which Hurlers is milder and presents with no corneal clouding?
XR - iduronate sulfatase
reabsorbs
Cheilosis and corneal vascularization
Biotin; rate limiting step in fA synthesis - acetyl coA into malonyl coA

31. What disease is associated with chromosome 13?
Calcium and calmodulin activate glycogen phosphorylase kinase
Glutamate and aspartate; CO2 provides an ketone
Pataus
Fructokinase; benign - fructose in the blood and urine

32. What is the presentation of G6PD deficiency?
H1
APCKD
Lactose in mothers milk contains galactose
Hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)

33. What is lebers hereditary optic neuropathy? What is the main clinical symptom? and What is its mode of inheritance?
Ascites from liver damage
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance
Gets converted to glycerol 3 P Which is then converted to DHAP Which then can enter glycolyis
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan

34. What causes the lysosomal storage diseases?
Glycerol goes to liver for gluconeogenesis; free fatty acids bind to albumin in blood and travel to cells to be used as for energy
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST); alanine to pyruvate and aspartate to oxaxloacetate
25 OH D3; 1 -25 (OH)2 D3 (Calcitriol)
Deficiencies in one of the many lysosomal enzymes results in accumulation of abnormal metabolic products

35. What is this reaction dependent on?
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
Fat malabsorption (CF) and abetalipoproteinemia (damage takes up all antioxidants)
Isoleucine - valine - leucine
Oxygen!

36. What enzyme is involved in the degradation of tyrosine to fumarate?
= q
Homogentistic acid oxidase
Branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa
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

37. What are two clinical symptoms of newborns with CF? and whats a lab value of a newborn with CF?
Colchine
Meconium ileus and failure to thrive; negative serum immunoreactive trypsin
By activating adenylyl cylase Which increases cAMP Which increases levels of protein kinase A Which activates glycogen phosphorylase kinase; epinephrine
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

38. What carries 1 carbon units as energy?
Tetrahydrofolates
Night blindness - dry skin
Carnitine shuttle
When the disease manifestation depends on from who the gene deletion was inherited from d/t methylation that occurs; Prader Willi and AngelMann

39. From What aa does thyroxine come from?
Tyrosine
Vincrstine (vinca alkaloids) and paclitaxel
No protein!
Converts it to citrulline

40. What are the clinical symptoms of hyperammonemia?
A trinucleotide repeat disorder results in faulty methylation and thus expression of the FMR1 gene on the X chromosome (x linked recessive mode of inheritance)
Cardiomegaly and systemic findings leading to early death; lysosomal alpha -1 -4- glucosidase (acid maltase)
RER in nucleus (synthesize NTs)
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits

41. What does vit C excess cause?
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
hexokinase - glucokinase (its a glutton)
Renal calculi of uric acid (replaces uric acid in excretion)
Edwards

42. From What aa does GABA come from? with What enzyme? and What vit cofactor? What does GABA stand for?
Glutamate; glutamate decarboxylase; B6; gamma aminobutyrate
Inability to transport LCFA into mitochondria results in their build up and causes weakness - hypotonia And HYPOKETOTIC HYPOGLYCEMIA
hexokinase (glucokinase only found in liver and beta cells of pancreas)
Alpha ketoglutarate; no TCA cycle intermediates

43. in What disease are there antibodies to snRNPs?
5' end; 3' end
AR
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)
Lupus

44. What are the functions of zinc?
Microcephaly - mental retardation - high pitched mewing/crying - epicanthal folds - cardiac abnormalities; microdeletion on short arm of chrom 5
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
To amplify a specific desired fragment of DNA
(cofactor for 100+ enzymes!) needed for zinc fingers transcription motif - collagen synthesis - alcohol metabolism

45. What does a pyridoxine deficiency look like? What causes it?
Convulsions - hyperirritiability - peripheral neuropathy - sideroblastic anemias; alcoholics and INH and fortified goats milk consumption
Cell signaling defect in FGF receptor resulting in dwarfism and short limbs with normal head and trunk; AD
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)

46. Increased levels of cAMP results in...
Down's Syndrome
glycogenolysis
show disease
Microvilli - muscle contraction - cytokinesis - adherens junctions

47. AD diseases are usually...
Thymidylate synthase; 5- Flourouracil
pleiotropic
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Cortisol; inhibits insulin action

48. All glutamate goes to _______ d ammonia is used as a buffer in urine
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
kidney
3'--> 5'; prokaryote only

49. Which intermediate filament is found connective tissue? muscle? epithelial cells? neuroglia? neurons? What can intermediate filaments be used for?
As alanine; amino acids donate their amino group to alpha ketoglutarate making it glutamate and the aa then becomes an alpha ketoacid (joins TCA cycle); glutamate then converts pyruvate to alanine by donating its amino group to pyruvate (with ALT); a
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells
Malnutrition - edema (hypoalbuminemia) - anemia liver (fatty change) - diarrhea d/t no brush border enzymes (no protein!)
Vimentin - desmin - cytokeratin - glial fibrillary acidic protein (GFAP) - neurofilaments; to differentiate between different cells

50. What are the glycogen storage disease? What they result in?
TPP (thiamine pyrophosphate)
Decreased phenylalanine - increase tyrosine
Glycolysis - fatty acid synthesis - HMP shunt - protein synthesis (RER) - steroid synthesis (SER) - glycogenolysis - glycogenesis
Abnormal glycogen metabolism results in accumulation of glycogen in cells

Can you answer 50 questions in 15 minutes?

Major Subjects
Tests & Exams AP CLEP DSST GRE SAT GMAT	Certifications CISSP go to https://www.isc2.org/ PMP ITIL RHCE MCTS More...	IT Skills Android Programming Data Modeling Objective C Programming Basic Python Programming Adobe Illustrator More...	Business Skills Advertising Techniques Business Accounting Basics Business Strategy Human Resource Management Marketing Basics More...
Soft Skills Body Language People Skills Public Speaking Persuasion Job Hunting And Resumes More...	Vocabulary GRE Vocab SAT Vocab TOEFL Essential Vocab Basic English Words For All Global Words You Should Know Business English More...	Languages AP German Vocab AP Latin Vocab SAT Subject Test: French Italian Survival Norwegian Survival More...	Engineering Audio Engineering Computer Science Engineering Aerospace Engineering Chemical Engineering Structural Engineering More...
Health Sciences Basic Nursing Skills Health Science Language Fundamentals Veterinary Technology Medical Language Cardiology Clinical Surgery More...	English Grammar Fundamentals Literary And Rhetorical Vocab Elements Of Style Vocab Introduction To English Major Complete Advanced Sentences Literature Homonyms More...	Math Algebra Formulas Basic Arithmetic: Measurements Metric Conversions Geometric Properties Important Math Facts Number Sense Vocab Business Math More...	Other Major Subjects Science Economics History Law Performing-arts Cooking Logic & Reasoning Trivia

Test your basic knowledge |

USMLE Step 1 Biochemistry

Can you answer 50 questions in 15 minutes?

Let me suggest you:

Browse all subjects

Browse all tests

Most popular tests

Major Subjects

Tests & Exams

Certifications

IT Skills

Business Skills

Soft Skills

Vocabulary

Languages

Engineering

Health Sciences

English

Math

Other Major Subjects

Browse all subjects

Browse all tests

Most popular tests