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 is 'charging' of tRNA? What enzyme regulates this? What does this reaction require? in What process is this?
2-3 days after birth because maternal enzyme during fetal like might still be there
Lysine and arginine; basic
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation
Collagen; fibroblasts; 4; ECM

2. What is lebers hereditary optic neuropathy? What is the main clinical symptom? and What is its mode of inheritance?
Degeneration of retinal ganglion cells and axons; acute loss of central vision; mit. inheritance
degradation
Galactokinase deficiency and classic galactosemia; classic galactosemia
Gauchers; hepatosplenomegaly - aseptic necrosis of the femur - bone crises - Gauchers cells - crumpled tissue paper looking (fibrillar appearing macrophages in liver - spleen - b.m.)

3. What is the first step in FA degradation in the cytosol?
Macroorchitism - big ears - big jaw - mental retardation (2nd mcc!) - mitral valve prolapse - long face
Beta glucocerebrosidase; glucocerebroside
FA coA synthetase combines coA with FA to make acyl coA
Homocysteine methyltransferase - cystathionine reductase - decreased affinity of cystathionine reductase for pyridoxal phosphate; AR

4. What is the precursor for both purines?
IMP
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
Calcium and calmodulin activate glycogen phosphorylase kinase
Cheilosis and corneal vascularization

5. Prokaryotes have What ribosomal units?
They can enter G1 from G0 and replicate if they like; hepatocytes - lymphocytes - fibroblasts
all are diseased!
30S + 50S= 70S
Dopamine beta hydroxylase; vit C

6. How many bonds does a G- C connection have? What type of bonds? how about a A- T?
Fructose 1 -6 bisphosphatase
3 hydrogen bonds; 2 hydrogen bonds
Vimentin - desmin - cytokeratin - glial fibrillary acidic protein (GFAP) - neurofilaments; to differentiate between different cells
Vit C; Vit E

7. What are the causes of folate def?
HnRNA; mRNA
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
1 for all three classes of RNA; Rifampin; TB
Mebendazole and thiabendazole

8. What are causes of zinc deficiencies?
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
Heterochromatin; euchromatin
Alcoholism - RA - inflammatory disease - chronic diarrhea

9. Where is type IV collagen found? to What protein is bound? What is special about this type? How do the different types of collagen differ?
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase
They increase the permeability of the inner mit membrane resulting in a loss of gradient and loss of ATP production BUT electron transport continues! heat is generated instead
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
BM; laminins; most flexible; different aa composition

10. What is a robertsonian translocation? What does it mean if its balanced?
paternal
Its When two acrocentric chromosomes combine their long arms (and short arms disappear); When the translocation is functional
Phenylethanolamine N- methyl transferase; SAM
HMG CoA reductase

11. What is the product of odd chain fatty acid synthesis? How does it return to TCA cycle? What cofactor is required?
Proprionyl coA; through methylmalonyl coA; B12
RER in nucleus (synthesize NTs)
Def in Vit C; def in Vit D
When different combination of exons get combined together; in Beta thallasemia

12. How do you differentiate causes of megaloblastic anemia?
Phenylalanine
Aromatic; musty body odor
Kidney and intestinal epithelium
Orotic aciduria megaloblastic anemia can not be corrected with folic acid or vit B12

13. What is another way to trap glucose in cells but not by phosphorylating it? What enzymes are used?
TPP (thiamine pyrophosphate)
Coenzyme A and lipoamides
By turning it into fructose - but sorbitol first; glucose to sorbitol via aldose reductase and sorbitol to fructose sorbital dehydrogenase
Malabsorption problems (CF and sprue) and mineral oil intake

14. What Abs block the binding between aminoacyl tRNA and rRNA by binding the 30S ribosome?
BM; laminins; most flexible; different aa composition
ATP synthase - ATP- ADP translocase - ETC
N linked oligosaccharides
Aminoglycosides and tetracyclines

15. other than increase Parathyroid hormone What else increases 1 alpha hydroxylase activity in the kidney?
Excess ATP and dATP has negative feedback inhibition on ribonucleotide reductase Which results in decreased DNA synthesis and thus decreased lymphocyte count
Milder form of type 1 with normal blood lactate levels; debranching enzyme (alpha -1 -6 glucosidase)
all carriers
Decreased serum phosphate

16. In x linked - in males - prevalence is...
= q
Triacylglycerols in adipose tissue broken down into glycerol and free fatty acids; growth hormone and epinephrine
Nacetyl cysteine; breaks disulfide bridges of mucus plugs
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -

17. RER adds ___________ to asparagines
Oral uridine administration; provides nucleosides and provides feedback inhibition
N linked oligosaccharides
Chediak Higashi Syndrome; decreased phagocytosis results in recurrent pyogenic infections - partial albinism - and peripheral neuropathy
All clathrin

18. What is type II collagen found?
Cartilage (including hyaline) - vitreous body - nucleus pulposus
Later
Via fructose 1 P by fructokinase in the liver; as glucose 1 by being GALT- ed ;)
Heterochromatin; euchromatin

19. What carries 1 carbon units as energy?
Liver and skeletal muscle
Lipoprotein lipases take FA from VLDL and chylomicrons Which are then combined with glycerol 3 P (a carb intermediate) to make triacylglycerol
Heteroplasmy
Tetrahydrofolates

20. After day 3 of starvation - What is the main source of energy?
Disulfiram (antabuse); acetaldehyde accumulate contributing to hangover
By activating protein phosphatase Which both dephosphorylates glycogen phosphorylase (deactivating) and dephosphorylates glycogen synthase (activating it )
Adipose tissue for brain and heart (ketone bodies) and then go to vital protein degradation (organ failure)
Pyruvate (through OXA); lactate - alanine - malate (and all other TCA intermediates through OXA) - glycerol - odd chain fatty acids yield propionyl coA Which can be converted to succinyl coA and enter as TCA cycle

21. What is needed after the glycosylase in base excision repair?
It inhibits conversion of DHF to THF by blocking dihyrdofolate reductase
Phenylalanine
An AP (apyrimidinic) endonuclease to cut the DNA - exonuclease then removes and then filled and sealed by enzymes
Ile - Phe - Thr - Trp

22. What type of enyzmes are used in base excision repair?
Glycosylases (only remove the base - cut the bond between ribose and base)
Carbomyl phosphate synthetase II
When the disease manifestation depends on from who the gene deletion was inherited from d/t methylation that occurs; Prader Willi and AngelMann
Calcium and calmodulin activate glycogen phosphorylase kinase

23. With What type of inheritance is variable expression and incomplete penetrance associated with? Give an example of each.
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
Milder form of type 1 with normal blood lactate levels; debranching enzyme (alpha -1 -6 glucosidase)
AD; disorder of blood vessels that results in telangietasias - skin discolorations - and AVMs (arteriovenous malformations)
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant

24. What builds up in the blood of patients with maple syrup urine disease? urine/poo? What does this cause?
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
MT!
Citrate - Isocitrate - alpha ketoglutarate - Succinyl CoA - Succinate - Fumarate - Malate - Oxaloacetate
Also have fair skin - blond hair - blue eyes - eczema

25. What are the findings in Metachromatic leukodystrophy?
ATP
Chromosomal imbalance (downs for ex)
CCA and chemically modified bases Where amino acid is covalently bonded
Central and peripheral demyelination with ataxia and dementia

26. What factors is Vit K responsible for the synthesis? and What else?
10 - 9 - 7 - 2; protein C and S
Mitochondria - archaebacteria - mycoplasma - and some yeasts
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
kidney

27. What can cause deficiency in Vit K?
Cycloheximide
Prolonged Ab use
GALT
Hemolytic anemia; jaundice in newborn if mom gets too much vit K

28. What happens in RBCs after their membranes get oxidized?
fructose
Methionine is only encoded by AUG
Hemolytic anemia due to heinz bodies Which are oxidized hemoglobin precipitating within the RBCs
Gets converted to pyruvate via the Cori cycle in the liver

29. What causes hypoglycemia in alcoholism?
Decreased substrate for gluconeogenesis (pyruvate to lactate and not oxaloacetate); and pyruvate doing only lactic acidosis and not glycolysis
Vomiting - rice water stools - garlic breath
Vit C; Vit E
Orotate

30. What else decreases production of oxaloacetate in alcoholism other than decreased pyruvate?
Very Poor Carb Metabolism (Von Gierke - Type 1 - Pompes - Type II - Cori's - Type III - McArdles disease - Type IV)
B hydroxybutyrate - acetone - acetoacetate; beta hydroxybutyrate; beta hydroxybutyrate
Oxaloacetate gets shifted to malate d/t excess NADH
cell cycle events

31. What carries Acyl (as energy)?
osteosarcomas (Rb mutation is in all cells)
Cobalamin; cofactor for homocysteine methyltransferase (transfers SAM to THF to give to dUMP) and for methylmalonyl coA mutaseto make succinyl coA
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
Coenzyme A and lipoamides

32. What does severe deficiency of B3 lead to? What are the causes?
Glycerol goes to liver for gluconeogenesis; free fatty acids bind to albumin in blood and travel to cells to be used as for energy
Calcium and calmodulin activate glycogen phosphorylase kinase
Encode enzymes for oxphos mit reactions
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)

33. What is palmitate? saturated or unsaturated? What does that meat?
A 16C FA! the product in FA synthesis; saturated; no double bonds
Trimethroprim inhibits bacterial dihyrofolate reductase
Carnitine shuttle
When the amino acid is covalently binded to its corresponding tRNA; Aminoacyl tRNA synthetase; ATP; translation

34. Vitamin c is needed in...
catecholamine synthesis (dopamine to norepinephrine)
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis
DHF

35. other than scurvy What else does vit C def cause? also - What kind of anemias and why?
Phenylalanine hydroxylase or tetrahydrobiopterin factor
Decreased would healing; microcytic anemia (d/t decreased iron [not absorbable]; macrocytic anemia (d/t Fh4 not reduced)
Urine turns black on standing
CPSII

36. What are the clinical symptoms of Down syndrome?
Biotin (vit B7) and Vit K
Dilated capillaries and veins; skin - mucous membranes - GI - resp - urinary tracts; rupture and can cause epistaxis - hemorrhage - GI bleeding
Mental retardation - flat faces - simean crease - epicanthal folds - ASD - duodenal atresia causing Hirshsprungs disease - redundant skin at the nape of neck - slanted palpebral fissures - hypotonia
Codons may encode same amino acid since there are only ~20 aa

37. What causes an excess of B3? What are the symptoms?
Mitochondria in liver; HmG CoA synthetase; amino acids and beta oxidation of FA
Because cells of mononuclear phagocytic are esp rich in lysosomes
SER and mitochondria; NADPH
Niacin treatment for hyperlipidemia; facial flushing

38. What two enzymes are in involved in catecholamine degradation?
Presence of normal and mutated mtDNA (like mosaicism except in mit)
COMT and MAO
Macrocytic megaloblastic anemia; it is the most common vit def in the US; no neuro symptoms and no methylmalonyl coA in the urine
Cobalamin; cofactor for homocysteine methyltransferase (transfers SAM to THF to give to dUMP) and for methylmalonyl coA mutaseto make succinyl coA

39. list three uncoupling agents
Fe2+; Fe3+
This depends on if phosphofructokinase 1 is active and this depends on whether or not fructose 2.6 bisphophate is activating it or not - this can only occur if PFK 2 is on and not FBPase 2. then fructose 6 phosphate will participate in glycolysis. Ot
2 -4 dinitrophenol - aspirin - and thermogenin (in brown fat)
Carbamoyl phosphate

40. What negatively regulates dopamine to norepinephrine?
Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species
Hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)
Carbamoyl phosphate
Carbidopa

41. What is the pathogenesis of skurvy? name some clinical symptoms.
Carbamoyl phosphate to orotic acid
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
Uracil; thymine
Fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio

42. What is the precursor for pyrimidines?
Orotate
Reserve supply of glucose in the fasting state - liver gives to the blood and skeletal muscle uses for itself
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
Sickle cell disease - conversion of hydroophillic glutamic acid to hyrdophobic valine

43. What is the most abundant protein in the body? From What cell type is it made? How many types are there? Where is it found (generally)?
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
golgi apparatus
Phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis
Collagen; fibroblasts; 4; ECM

44. What converts dopamine to norepinephrine? using What cofactor?
Uracil; thymine
Dopamine beta hydroxylase; vit C
Nucleus
Carbidopa

45. What type of vitamin is Vit D? Where do we get it? in What form?
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
Phenylalanine hydroxylase; tetrahydrobiopterin factor
Preprocollagen - procollagen - tropocollagen - collagen
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)

46. What is most often mutated in xeroderma pigmentosum? What is the inheritance pattern? What are the clinical symptoms?
Testing for antigen - antibody reactivity; can either add an antibody to a persons blood sample to see if there is binding or add an antigen to a persons blood sample to see if there immune system recognizes it; close to 100% for both; HIV eliza - an
Urea cycle enzyme deficiency (mc: ornithine transcarbamoylase); liver disease - alcoholic cirrhosis and reye's
Glycogen synthase
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers

47. For What three enzymes is arginine a precursor for?
Neurons and RBCs
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20
Nitric Oxide - creatinine - Urea
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis

48. What is dihydroxyphenylalanine ?
DOPA
Ortinithine transcarbamoylase - orotic acid phosphoribosyltransferase - and orotidine 5 phosphate decarboxylase; urea cycle; last two are involved in conversion of orotic acid to UMP (adding PRPP to orotic acid)
They increase the permeability of the inner mit membrane resulting in a loss of gradient and loss of ATP production BUT electron transport continues! heat is generated instead
Nitric Oxide - creatinine - Urea

49. Where does splicing occur?
AD
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates
Nucleus
Schilling test

50. What converts fructose 2 -6 phosphate back to fructose 2 phosphate?
Pellagra
Fructose bisphosphatase 2
Yes! congenital simply means 'born with'- hereditary is familial
Self mutilation - aggression - mental retardation - gout - hyperuricemia - choreathetosis

Sorry!:) No result found.

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

Sorry!:) No result found.

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