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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 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)?
Collagen; fibroblasts; 4; ECM
Beckers is less severe (instead of deletion is either defect or deficiency) with later presentation
H1
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates

2. How do you treat homocystinuria due to decreased affinity of cystathionine reductase to B6?
By giving high amounts of pyridoxal phosphate in the diet
1 day; adipose release of FFA - hepatic gluconeogenesis from peripheral tissue lactate and alanine and from adipose tissue glycerol and propionyl coA
Sulfonamides - primaquine - dapsone - antiTB drugs - fava beans - LDL; RBCs
Bendy bones seen in children due to decreased Vit D; craniotabes - skeletal deformities - growth retardation - rosary

3. What does the excess NH4+ in hyperammonia eat up? What is the result?
Its the ribose; its made from PRPP synthetase using ribose 5 P from the HMP shunt
Osmotic diarrhea - bloating - cramps
Telomerase; an RNA polymerase that uses a RNA template to add DNA to the end of shortening 3' ends
Alpha ketoglutarate; no TCA cycle intermediates

4. What form of Vitamin D is in plants? milk fortified with vit D? formed in sun exposed skin?
D2 (ergocalciferol) - D3 (cholecalciferol) - D3 (cholecalciferol)
to ions
Helps make Vit K and antioxidant
Mucus secreting goblet cells - ab secreting plasma cells - nt secreting neurons

5. What causes scurvy? What are the symptoms of scurvy?
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -
Adrenal medulla
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
Liver; berry aneurysms (d/t hypertension!) - and mitral valve prolapse

6. What is the other name for Vitamin B5? What is its function?
Acetyl coA and NADH inhibit pyruvate dehyrogenase
Pantothenate; essential comp of CoA (needed for acyl transfers) and fatty acid synthase
Lesch Nyhan syndrome; X linked recessive
Vit C

7. Glucokinase is a...
pleiotropic
glutton
Lysine and arginine; basic
A ketone

8. why does branching occur in glycogenesis?
Branching increases the rate of synthesis and breakdown of glycogen by having more sites to add on to and break off
Liver; P450 hydroxylation
Mitosis then Interphase (G1 - S - G2); in G1 is presynthesis phase - S is synthesis phase (DNA rep. etc) - G2 is premitotic (making of MT spindle etc)
Hepatic glycogenolysis (mostly) - also hepatic gluconeogenesis - adipose release of FFA (minor)

9. What are the clinical symptoms of Marfans?
GTP: gluconeogenesis - OXA to phosphoenolpyruvate
Heart - SKELETON - and EYES: arachnodactyly - long limbs - cystic medial necrosis of aorta resulting in aneurysms (and eventual dissection) - floppy mitral valve (prolapse and regurg!) - subluxation of lens
Cri du Chat
tubulin dimer

10. Which oxidant is most attributable to damage of RBCs?
LDL; LDL oxidize atherosclerosis
Excreted from the kidney in the form of urea in hepatocytes
AD
Homogentistic acid oxidase

11. What is ascorbic acid? What is its 5 main function?
Peripheral neuropathies of hands/feet; angiokeratomas between umbilicus and knees; cardiovascular/renal disease
Niemann pick and Tay Sachs; hepatosplenomegaly or not
hexokinase - glucokinase (its a glutton)
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

12. In What syndrome is HGPRT deficient? What is the inheritance pattern?
Coenzyme A and lipoamides
Methionine is only encoded by AUG
Lesch Nyhan syndrome; X linked recessive
Neurons and RBCs

13. _______ is ubiquitous
Mitochondrial inheritance
A methyl
fat
hexokinase (glucokinase only found in liver and beta cells of pancreas)

14. What kind of kinetics does alcohol dehydrogenase work under? What are the implications of this?
Zero order; increased production of NADH no matter the amount of end products produced
An aminotransferase enzyme transfers an amino group from an amino acid on to alpha ketoglutarate making it a glutamate (to join the urea cycle or excreted in the kidney) and the amino acid that lost the amino group is then turned into a glycolytic in
Defective neutral amino acid transporter on renal and intestinal cells; AR
Tryptophan; niacin

15. What are the ketogenic amino acids?
Alpha ketoglutarate; no TCA cycle intermediates
AST (mit damage) - and GGT (d/t SER hyperplasia d/t induction of p450 generation)
Cytosine to uracil
Leucine and lysine

16. What three steps are included in RNA processing? Where does it occur?

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17. In What genetic code is uracil found in? in replace of what?
Lyonization; nondisjunction in mitotic divisions during embryonic period
Block ATP synthase resulting in no ATP production and an increased proton gradient
Uracil; thymine
NF1

18. What disease manifestations result in Prader Willi syndrome? is the deletion a result from the father or mothers chromosome?
Coenzyme A and lipoamides
Mental retardation - obesity - short stature - hypogonadism - hypotonia - hyperphagia; father
AD
fatty acid degradation

19. What causes the pathology in I- cell disease? What does I cell sidease
Liver and skeletal muscle
Acidic
The lack of lysosomal proteins (are secreted - default from RER!) results in macromolecules accumulating in lysosomes - inclusions cause pathology
Phospholipids - sphingolipids - glycolipids

20. In the genetic code - What does unambiguous mean?
Each codon specifies only one amino acid
Leucine and lysine
Beta thalassemia
Williams

21. What is the order of collagen synthesis - just the terms of the intermediate forms?
Neimann pick and tay sachs
Preprocollagen - procollagen - tropocollagen - collagen
So that excess glucose can be stored (phosphorylated glucose cant leave) in the liver and saved as a buffer
Von gierkes

22. 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?
Stored ATP - creatine phosphate - anaerobic glycolysis; as distances increase - ATP is obtained from additional resources; above plus ox phos
Downs (21) - Edwards (18) - Pataus (13); also in increasing severity
Von gierkes
Lactic acidosis and ketoacidosis

23. What are the findings of homocystinuria?
It contains the peptidyltransferase activity (for elongation of protein
hexokinase - glucokinase (its a glutton)
Increased homocysteine in the urine - mental retardation - osteoporosis - marfanoid habitus - and atherosclerosis
linked recessive

24. What are phenylacetate - phenylactate - and phenylpyruvate?
ATP depletion and highly aerobic tissues (heart and brain) are affected first; false - glucose infusion worsens
Prolonged Ab use
Phenylketones that build up in phenylketonuria
Isoleucine - valine - leucine

25. To What type of DNA damage are xeroderma pigmentation susceptible to?
Alpha ketoglutarate; no TCA cycle intermediates
UV nonionizing radiation causing thymidine dimers
Which dimerizes and activates a protein phosphatase Which de phosphorylates glycogen phosphorylase
Lysine and arginine; basic

26. From What aa does porphyrin come from? What is porphyrin the precursor of?
Endonucleases are specific and break specific linking phosphodiester bonds - exonucleases are not sequence specific and just remove the nucleoside
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
It contains the peptidyltransferase activity (for elongation of protein
Glycine; heme

27. There are 2 GTP per...
tubulin dimer
By cyclin CDK complexes
Coarse facial features - psychomotor retardation - clouded corneas - restricted joint movement - high plasma levels of lysosomal enzymes
Tyrosinase

28. What is the net production of glycolysis from one glucose?
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
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
Orotic aciduria megaloblastic anemia can not be corrected with folic acid or vit B12
2 NADH - 2 ATP - 2 pyruvate - 2H+ - 2H20

29. Breast milk has a little of...
Structural (constitutively active)
Glycine; heme
Malabsorption problems (CF and sprue) and mineral oil intake
Vit D and K

30. What aa is most accumulated in hartnup disease? What vitamin becomes deficient?
Tryptophan; niacin
Tremor (asterixis) - slurring of speech - decrease temperature - somnolence - vomitting - cerebral edema - blurring of vision - neural focal deficits
liver and muscle
Do agarose gel eletrophoresis to separate the different sizes of the PCR products (sizes id the the fragment)

31. 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?
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates
Acetone
Multiple bone fractures - blue sclerae - hearing loss (abdnormal middle ear bones!) - dental imperfections - retarded wound healing
Debranching enzyme; alpha 1 - 4 glucosidase; no!; Pompes disease

32. What are the two different ways you can insert genes into transgenic mice for experiments?
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
In ability to reabsorb phosphate from renal tubular cells results in osteomalacia due to defective bone mineralization; no
Decrease AFP - increased BCHG - decreased estriol - increased inhibin A
Constitutive - random insertion of gene into mouse genome; conditional - targeted through homologous recombination

33. We can't use even chain fatty acids for blood glucose or else we would all...
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
be anorexic
Back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)
Dermatitis - glossitis - diarrhea

34. What is the purpose of HMP shunt?
To provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates
By giving high amounts of pyridoxal phosphate in the diet
Autosomal Dominant; NF1 and mit. diseases (variable expression) - ?
Carnitine shuttle

35. What is scurvy caused by? rickets?
Def in Vit C; def in Vit D
NADH - NADPH - FADH2
Cheilosis and corneal vascularization
Release alk phos

36. What are the findings in Krabbes disease?
Peripheral neuropathy - developmental delay - optic atrophy - globoid cells
N linked oligosaccharides
Decreased serum phosphate
long saturated fatty acids

37. What is the rate determining enzyme in glycogen synthesis?
Glycogen synthase
Glycine; heme
HMG CoA synthetase; HMG CoA reductase
Hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)

38. Odd chain fatty acids yield one proprionyl coA which can enter the TCA cycle as...
Peripheral neuropathies of hands/feet; angiokeratomas between umbilicus and knees; cardiovascular/renal disease
succinyl coA (and then to OXA)
AD: yes! most common presentation; very rare (700 mg/dl cholesterol level!)
Flouroquinolones

39. What is the main use of glycogen?
Its When two acrocentric chromosomes combine their long arms (and short arms disappear); When the translocation is functional
Reserve supply of glucose in the fasting state - liver gives to the blood and skeletal muscle uses for itself
COP I
Succinate hydrogenase; matrix

40. What is the rate determining enzyme in glycogenolysis?
Glycogen phosphorylase
Decrease intake of fructose and sucrose (fructose and glucose)
Hungtington
A lysosomal storage disease; mannose 6 phosphate can not be added to lysosomal proteins

41. What is retinoic acid used for in treatments?
Wrinkles - acne and psoriasis topically - promyelocytic anemia - measles
Biotin
Glycolysis and aerobic respiration
Alcoholism - RA - inflammatory disease - chronic diarrhea

42. in Fabrys - What accumulates in tissue because fibroblasts express the def enzyme highly?
Dopamine beta hydroxylase; vit C
Glucose 6 phosphatase
Ceramide trihexoside
Liver mit and liver cytosol

43. What is the impetus for ketoacidosis in starvation? alcoholism?
Oxaloacetate depleted for gluconeogenesis; excess NADH shunts oxaloactetate towards malate
glutton
Peripheral neuropathy - developmental delay - optic atrophy - globoid cells
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

44. What is required to get Acyl coA in FA degradation into the mitochondria for beta oxidation to acetyl coA groups?
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST); alanine to pyruvate and aspartate to oxaxloacetate
Either salvage by HGPRT and PRPP or converstion to xanthine and then to uric acid by xanthine oxidase
Carnitine shuttle
CCA and chemically modified bases Where amino acid is covalently bonded

45. What is the difference between rickets and osteomalacia?
Ouabain
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
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
Osteomalacia is vit D def seen in adults and causes bowed legs and results in increased fractures

46. How does fructose enter glycolysis? galactose?
Increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)
glycogen
Via fructose 1 P by fructokinase in the liver; as glucose 1 by being GALT- ed ;)
Decreased substrate for gluconeogenesis (pyruvate to lactate and not oxaloacetate); and pyruvate doing only lactic acidosis and not glycolysis

47. What two substrates (other than pyruvate) does pyruvate carboxylase require?
Hepatic fatty change
Vit C deficiency; glossitis - anemia - weakened vessels - hemorrahges - hemarthroses - swollen gums - bruises -
ATP and biotin
fastest sugar

48. What is the function of Vitamin A?
Differentiation of cells - vision in reduced light (retinol makes up rhodopsin cells) - antioxidant
Alcohol dehyrogenase (alcohol to acetaldehyde); acetaldehyde dehydrogenase (acetaldehyde to acetate); NAD+; B3 (niacin)
Osmotic diarrhea - bloating - cramps
Heart - SKELETON - and EYES: arachnodactyly - long limbs - cystic medial necrosis of aorta resulting in aneurysms (and eventual dissection) - floppy mitral valve (prolapse and regurg!) - subluxation of lens

49. What is the rate determining enzyme in TCA cycle?
Phenylalanine
Hepatic fatty change
Isocitrate dehydrogenase
An allosteric regulator; fructose 1 phosphate; phosphofructokinase 2

50. What tissues contain aldose reductase? What does this enzyme do to what?
Alpha ketoacids in the blood; alpha keto acids in the urine/poo smells of maple syrup/burnt sugar
Lens and neural tissue; converts galactose to osmotically active galactitol
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
Fructokinase; benign - fructose in the blood and urine

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USMLE Step 1 Biochemistry

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