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. ____ soluble vitamins are more likely to result in toxicity
By activating protein phosphatase Which both dephosphorylates glycogen phosphorylase (deactivating) and dephosphorylates glycogen synthase (activating it )
activation of PFK1
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
fat

2. What carries 1 carbon units as energy?
fat
Tetrahydrofolates
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Decrease AFP - increased BCHG - decreased estriol - increased inhibin A

3. why does branching occur in glycogenesis?
Glycosylases (only remove the base - cut the bond between ribose and base)
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off
Increased nuchal translucency
usually present late

4. What is the pathogenesis of fragile x syndrome?
No
golgi apparatus
Pigmented iris hamartomas
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)

5. Heterozygous females in X linked recessive disease...
DHF
Ascites from liver damage
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
can be d/t lyonization

6. What are the findings in Krabbes disease?
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
SAM
Peripheral neuropathy - developmental delay - optic atrophy - globoid cells
Karyotyping

7. What kind of bugs are CGD patients screwed with? why do they call it chronic granulamotous disease?
TRNA wobble
Catalase positive because they reduce their H2O2 and WBCs cant use that to make bleach; because the way they protect is by building a wall around the organisms with granulomas
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
Whether or not the patient is also hyperammonemia (if yes - then OTC def)

8. What is a common result of unbalanced robertsonian translocation?
HMG CoA reductase
Severe fasting hypoglycemia - very high levels glycogen in liver - high blood lactate - hepatomegaly
Ornithine transcarbomyalse; orotic aciduria; X linked recessive; autosomal recessive
Chromosomal imbalance (downs for ex)

9. What is the treatment of hyperammonia?
Phenylalanine
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)
When one allele on a gene is only expressed and the other is methylated/inactivated; during gametogenesis one of the alleles is methylated because the gamete from the other sex will provide those characteristics for the child
SAM

10. What step in pyrimidine synthesis requires aspartate?
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Carbamoyl phosphate to orotic acid
are AR
Genotyping for mutant alleles (different sizes)

11. The __________ adds O linked oligosaccharides to serine and threonine residues on proteins
Acetyl coA activated pyruvate carboxylase in gluconeogenesis
golgi apparatus
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

12. What is a clinical example of a missense mutation?
the RER
Galactose
Fructokinase; benign - fructose in the blood and urine
Sickle cell disease - conversion of hydroophillic glutamic acid to hyrdophobic valine

13. What disease is associated with chromosome 16?
Vincrstine (vinca alkaloids) and paclitaxel
Homogentistic acid oxidase
NF2 - DiGeorge/Velocardiofacial syndromes
APCKD

14. What is significant about 50S/60S ribosomal unit?
Heteroplasmy
NADH - Acetyl CoA - ATP; NAD+ - ADP and Ca2+
It contains the peptidyltransferase activity (for elongation of protein
SAM; Vit C

15. Ocular albinism is...
Asp and glu; negatively
Acetyl coA carboxylase converting Acetyl coA into malonyl coA; increased AMP - glucagon - epinephrine - palmitate; citrate
A ketone
linked recessive

16. What are the general symptoms of 22q11 chromosomal deletion? why is it that these occur?
Cleft palate - Abnormal faces - thymic aplasia (t cell def) - Cardiac defects - hypocalcemia (secondary to hypoparathyroid); 3rd and 4th branchial pouch aberrant development
RER in nucleus (synthesize NTs)
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
Branched alpha ketoacid dehydrogenase

17. What type of drug are alkylating agents? How do they work? give a couple examples
To transfer methyls; a methionine and an ATP; norepinephrine plus a methyl makes epinephrine
Antineoplastic agents; alkylate DNA!; cyclophosphamide and nitrosurea (aka lomustrine - a nitrosource)
Glucose 6 phosphatase
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

18. What antibiotic inhibits peptidyltransferase activity?
Chloramphenicol
Lactic acidosis and ketoacidosis
fructose
O2 consumption (last electron acceptor) gets consumed also

19. What does actin/myosin participate in?
Both AD
Inhibits lipoic acid; lipoic acid is a cofactor for pyruvate dehydrogenase
Microvilli - muscle contraction - cytokinesis - adherens junctions
Carnitine shuttle

20. What toxins prevent elongation in translation in humans (by binding 40s)?
Tryptophan
The products of FA oxidation (Acetyl CoA and NADH) phosphorylate pyruvate deyhdrogenase Which inactivates it
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Shiga toxin and ricin (protein in castor beans)

21. At What point is the amino acid correspondence to the mRNA code finalized?
Increased orotic acid in urine - megaloblastic anemia - +/- hyperammonemia
Beta thalassemia
Cortisol; inhibits insulin action
In the charging reaction! for this reason aminoacyl tRNA synthetase double checks

22. What are the first three enzymes in the first three steps in respiratory burst? Where do they occur? What do they result in? What does it do?
NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate
Increased homocysteine in the urine - mental retardation - osteoporosis - marfanoid habitus - and atherosclerosis
All clathrin
NADPH oxidase - superoxide dismutase - myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!

23. What is the other name for Vitamin B5? What is its function?
Essential fructosuria and fructose intolerance; fructose intolerance
Dactinomycin - doxorubicin
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)

24. What do statins inhibit?
Progressive neurodegeneration (spasticity d/t UMN disease) - NO hepatosplenomegaly - cherry red spot on macula - lysosomes with onion skin - muscle weakness
HMG CoA reductase
Phosphorylation of glucose
By epoxide reductase in the liver; coumadin; intestinal flora and leafy vegetables

25. What disease is associated with chromosome 15?

Warning: Invalid argument supplied for foreach() in /var/www/html/basicversity.com/show_quiz.php on line 183

26. What are the three types of point mutations?
Cheilosis and corneal vascularization
Silent - misssense - nonsense
When the 2nd hit of the allele is What causes the disease; sporadic retinoblastoma
AD

27. What causes gout in alcoholism?
Increased acid production competes with uric acid for excretion
Catalase positive because they reduce their H2O2 and WBCs cant use that to make bleach; because the way they protect is by building a wall around the organisms with granulomas
Nacetyl cysteine; breaks disulfide bridges of mucus plugs
MT!

28. What are the symptoms involved in lactase deficiency?
Osmotic diarrhea - bloating - cramps
Hemolytic anemia; jaundice in newborn if mom gets too much vit K
Liver and skeletal muscle
Increased concentration of Cl ions in sweat test

29. What are the clinical symptoms of NF1?
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
Cafe au lait spots - optic pathway gliomas - lisch nodules - scoliosis - neural tumors
'9+2' 9 pairs of microtubules connected by an axonemal dynein ATPase in a cylinder with 20 MTs in the center; the connecting ATPase allows bending and differential sliding
Biotin

30. What is the rate determining enzyme in HMP shunt?
Also have fair skin - blond hair - blue eyes - eczema
Liver; P450 hydroxylation
Glucose 6 phosphate dehydrogenase
HVA

31. What are the findings in Niemann Pick disease?
RER in nucleus (synthesize NTs)
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no
Arginine
Progressive neurodegeneration (spasticity d/t UMN disease) - hepatosplenomegaly - cherry red spot on macula - foam cells

32. What is the impetus for ketoacidosis in starvation? alcoholism?
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
Following gastroenteritis and kwashiokor (protein deficiency)
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate
Arginine

33. Other than being hereditary - What are two other ways you can have a lack of brush border enzymes?
Fat malabsorption (CF) and abetalipoproteinemia (damage takes up all antioxidants)
Codons may encode same amino acid since there are only ~20 aa
Following gastroenteritis and kwashiokor (protein deficiency)
Arg and his

34. Vitamin c is needed in...
Biotin; rate limiting step in fA synthesis - acetyl coA into malonyl coA
H1
catecholamine synthesis (dopamine to norepinephrine)
adrenal medulla

35. What are the titles of the two types of fructose disorders? Which is more serious>
Becomes methionine
Abnormal glycogen metabolism results in accumulation of glycogen in cells
Essential fructosuria and fructose intolerance; fructose intolerance
Blood group types

36. What are ragged red fibers?
Collections of abnormal mit collecting under sarcolemmal membranes and results in distortion of myofibrils
DOPA
Highly condensed forms of DNA; mitosis; neoplasia - highly dividing and thus hyperchromatic
Depression - progressive dementia - choreiform movements; between the ages of 20 and 50

37. How many enzymes does the pyruvate dehydrogenase complex have? and How many cofactors? Where is it located? to What enzyme is it similar to?
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates
3; 5; mit matrix; alpha ketoglutarate dehydrogenase complex
Indirect inhibtion of the Na+/Ca+2 exchange resulting in increased intracellular calcium Which increases cardiac contractility
Cleft palate - Abnormal faces - thymic aplasia (t cell def) - Cardiac defects - hypocalcemia (secondary to hypoparathyroid); 3rd and 4th branchial pouch aberrant development

38. What reactions occur in the mitochondrial matrix? mit inner membrane?
TCA cycle - FA oxidation - acetyl coA production; ox phos
Positive on phosphofructokinase 1 and negative on fructose 1 -6 bisphosphatase
Galactokinase; galactose appears in blood and urine - sometimes infantile cataracts may present as failure to track objects or lack of a social smile
DOPA

39. How is excess nitrogen taken care of?
Excreted from the kidney in the form of urea in hepatocytes
Cylindrical made up of a helical array of polymerized alpha and beta tubulin dimers - each dimer has 2 GTP bound
Niacin/Nicotinic acid; NAD+ and NADH used in redox reactions - and catabolic and anabolic reactions; B6; tryptophan
Tyrosine

40. What causes fat soluble vitamin deficiencies?
ATP synthase - ATP- ADP translocase - ETC
Coenzyme A and lipoamides
Malabsorption problems (CF and sprue) and mineral oil intake
Can inducibly manipulate genes at specific developmental points

41. What are two reasons why pyruvate would be pushed to lactate in an alcoholic?
4 -4 -9
Lupus
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)
is asymmetric

42. What are the findings in maple syrup disease? What should be tried to be given as treatment?
Phosphofructokinase 1; fructose 1 phosphate to fructose 1 -6 bisphosphate; enhancers: AMP - fructose 2 -6 Bisphosphate; downregulators: citrate - ATP
Glutamate
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
CNS defects - mental retardation - death - feeding difficulties - vomiting - hypoglycemia; thiamine

43. What vit def occur from antibiotic use?
Oxaloacetate gets shifted to malate d/t excess NADH
Arginne
Chromosomal imbalance (downs for ex)
Biotin (vit B7) and Vit K

44. All the glycogen storage diseases...
are AR
Carbidopa
fructose
A ketone

45. What is uniparental disomy? give an example of a disease it can cause.
When child gets two chromosomes from one parent; imprinting dx
Release alk phos
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -
fastest sugar

46. What is the degradation product of epinephrine?
In hepatocytes; B6
1) glycogenolysis (liver only contributes to plasma - muscle keeps it for itself) 2) gluconeogenesis
Orotic acid in blood and urine (from pyrimidine synthesis) - decreased BUN - and symptoms of hyperammonemia
Metanephrine

47. What type of vitamin is Vit D? Where do we get it? in What form?
Double strand breaks; nonhomologous end joining
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)
Vincristine - vinblastine - and paclitaxel; the vinca alkaloids block formation of the spindle and paclitaxel prevents breakdown of the mT spindle
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)

48. What has negative feedback inhibition on ribonucleoside reductase?
10 - 9 - 7 - 2; protein C and S
Loss of subcutaneous fat - tissue and muscle wasting (somatic muscle); visceral - not somatic
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
ATP and dATP

49. What is most often mutated in xeroderma pigmentosum? What is the inheritance pattern? What are the clinical symptoms?
UV specific endonucleases for excision repair; AR; dry skin - photosensitivity - poikiloderma - susceptibility to skin cancers
glutton
It induces its action!
Neural tissue and adrenal medulla

50. What is the source of Biotin?
Osteoblasts; de phosphorylates pyrophosphate Which inhibits bone mineralization; bone mineralization
Bacterial synthesis in the intestine
Hurlers Syndromes;Iduronate sulfatase deficiency; alpha L iduronidase def; heparan sulfate - dermatan sulfate
Osteomalacia is vit D def seen in adults and causes bowed legs and results in increased fractures