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Step 1 > Biochemistry - UWorld > Flashcards

Biochemistry - UWorld Flashcards

1
Q

Proteins transcribed by the lac operon

A

Lac Z = beta-galactosidase, hydrolyzes lactose to glucose and galactose

Lac Y = permease, allows lactose to enter the bacteria

Lac p = binding site of RNA polymerase

Lac I = constitutively produces Lac repressor protein, lactose binds this and prevents the repressor from binding to the operator site

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2
Q

Glucose’s effects on the lac operon

A

Glucose increases intracellular ATP levels, which deactivates adenylate cyclase, reduces cAMP levels and reduces CAP binding to the promotor region.

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3
Q

Consequence of the deltaF508 mutation that causes cystic fibrosis

A

This results in improper posttranslational folding and shunting of the improperly folded protein to the proteosomes instead of the epithelial membrane

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4
Q

Protein mutation in the Ras-MAP kinase pathway that commonly predisposes to cancer.

A

Mutation in Ras that makes it resistant to GTP hydrolysis or mutation in GAP that cannot hydrolyze GTP results in constitutive activation of Ras leading to overactivation of genes and cancer

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5
Q

Examples of molecules that use the PLC signalling pathway

A

alpha1, M1, M3, V1, H1, oxytocin, AT II, TRH, GnRH

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6
Q

How is NO synthesized?

A

Arginine + O2 is converted to NO by NO synthase

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7
Q

Proteins that can be labeled by a DNA probe

A

Proteins that can actually bind DNA: transcription factors (n-myc), steroids, thyroid proteins, vitamin D receptors, retinoic acid receptors, DNA replication and transcription proteins.

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8
Q

Clinical signs of OTC deficiency

A

Elevated carbamoyl phosphate, orotic aciduria (due to shunting of carbamoyl phosphate to thymine synthesis), neurological disorders and elevated serum NH3.

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9
Q

Components of telomerase

A

Reverse transcriptase component: TERT
RNA template: TERC
TERT repeatedly reads TERC TTAGGG to add telomeres to the end of DNA and does not need a template.

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10
Q

Why are cancer cells immortal?

A

They have high telomerase activity and do not undergo cell death initiated by shortening of their telomeres.

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11
Q

Consequence of vitamin A toxicity

A

Acute: nausea, vomiting, vertigo, blurred vision
Chronic: alopecia, dry skin, HLD, hepatoxicity, HSM and vision complaints
Teratogenic: microcephaly, cardiac abnormalities and 1st trimester fetal death

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12
Q

Riboflavin deficiency

A

Cheilosis, corneal vascularization

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13
Q

Vitamin C overdose

A

False negative stool guiac, bloating

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14
Q

Vitamin E overdose

A

Hemorrhagic stroke and infant NEC

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15
Q

Embryonic hemoglobin in the yolk sac

A

Two zeta and two epsilon chains (Hgb Gower)
Two alpha and two epsilon chains (Gower 2)
Two zeta and two gamma chains (Hgb Portland)

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16
Q

Fetal hemoglobin

A

Two alpha and two gamma chains. Replaces all embryonic Hgb by 14 weeks.

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17
Q

Hemoglobin A2

A

Two alpha and two delta chains

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18
Q

Factors that promote RBC sickling

A

Anoxia, acidity, 2,3-BPG binding and hypovolemia

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19
Q

What form of Hbg is stabilized by 2,3-BPG

A

Taut, this results in decreased Hgb affinity for O2 and increased peripheral O2 unloading

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20
Q

5 factors required by branched chain alpha-ketoacid dehydrogenase, pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase

A 
"Tender Loving Care For Nancy"
Thiamine
Lipoate
CoA
FAD
NAD
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21
Q

2-5 month old infant with irritability, developmental delay, poor muscle tone and liposomal galactocerebroside accumulation.

A

Krabbe disease due to autosomal recessive deficiency in galactocerebrosidase.

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22
Q

Homeobox genes code for…

A

DNA transcription factors that govern the proper placement of appendages

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23
Q

Adult with arthritis and blue-black deposits in the cornea and aricular cartilage. His urine sample turns black when exposed to air.

A

Alkoptonuria due to deficiency in the enzyme homogentistic acid dioxygenase. Accumulation of homogentistic acid results in these black-blue deposits.

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24
Q

18 month old who developed normally, but suddenly lost motor and language skills and constantly wrings her hands. Physical exam reveals decreased head size.

A

X-linked MECP2 mutation causing Rett syndrome.

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25
Q

Enzyme that increases use of PRPP in patients with Lesch-Nyhan syndrome

A

PRPP amidotransferase, this is because deficient HGPRT results in increased requirement for de novo purine synthesis, which goes through this enzyme.

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26
Q

A patient has acroparesthesia, acrokeratomas (dark red, non-blanching macules/papules between umbilicus and knees) and culture demonstrates failure to metabolize ceramide trihexose. What will likely result in this patient’s death?

A

Fabry disease due to inherited deficiency in alpha-galactosidase A. This results in accumulation of the globoside ceramide trihexose in tissue and patients die from renal failure if this enzyme is not supplemented.

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27
Q

How to tell failure of meiosis I vs. meiosis II on RFLP analysis for trisomy 21

A

Since you would inherit both sister chromatids in failure of meiosis II, there would be two bands with one band being thicker in the child. In failure of meiosis I, the child would have 3 different chromosomes.

28
Q

Principle forces stabilizing secondary protein structure

A

Hydrogen bonds

29
Q

Enzyme defect in a patient with early onset acute coronary syndrome, ocular lens displacement and intellectual disability with elevated methionine levels. Treatment?

A

Cystathione beta synthase. Patients cannot form cysteine from homocysteine, making cysteine an essential amino acid in their diet and homocysteine levels rise leading to hypercoaguability. Also, homocysteine buildup can result in hypermethioninemia. Treat with methionine restriction and pyridoxine (vitamin B6) supplementation to augment cystathione synthase’s activity.

30
Q

Type II glycogen storage disease

A

Pompe disease:

31
Q

Why do methylmalonyl CoA and methionine build up in patients with B12 deficiency

A

B12 is necessary for the enzymes methionine synthase and methylmalonyl-CoA mutase to synthesize methionine and succinyl-CoA, respectively. When these are absent, homocysteine builds up with reduced methionine synthase activity and methylmalonic acid builds up due to reduced methylmalonyl CoA mutase activity.

***Note that methylmalonic acid is disrupts myelin synthesis and results in subacute degeneration of the posterior column and lateral corticospinal tracts.

32
Q

Why does B2 deficiency result in normocytic anemia?

A

It is needed for RBC glutathione reductase. Deficiency can result in hemolysis secondary to increased RBC stress.

33
Q

Which monosaccharide is metabolized fastest through glycolysis

A

Fru-1P. This is because it reacts with aldolase B and splits to DHAP and glyceraldehyde. The glyceraldehyde can then enter glycolysis by conversion to glycerol-3P by triokinase. This allows it to bypass the rate limiting step of glycolysis, PFK-1.

34
Q

Metabolic intermediate that is deficient in the brain of a patient with hepatic encephalopathy

A

NH4+ causes increased conversion of Glu to Gln in the brain, depleting neurotransmitter stores. Increased Gln in the astrocytes increases cellular osmolarity and causes cellular swelling. Also, glutamate depletion results in shunting of alpha-ketoglutarate to glutamate by glutamate dehydrogenase, depleting the neurons of alpha-ketoglutarate for the TCA cycle.

35
Q

Site of oxidation of VL chain FAs and alpha oxidation

A

Peroxisomes

36
Q

How do you get niacin, serotonin and melanin if you never eat it?

A

Endogenous synthesis from tryptophan.

37
Q

Pyrimidine precursor molecule

A

Orotic acid

38
Q

How do RBCs sacrifice ATP in times of hypoxemia

A

RBCs need to produce 2,3-BPG from glycolysis and bypass the ATP generated from converting 1,3-BPG to 3-PG. They instead convert 1,3-BPG to 2,3-BPG, which decreases Hgb’s affinity for O2 and increases unloading.

39
Q

Cause of familial erythrocytosis

A

A beta-globin gene mutation results in decreased binding of 2,3-BPG. Normal Hgb has His and Lys residues that are positively charged and create a binding pocket for the negatively charged 2,3-BPG. Mutations in this binding site decrease affinity for 2,3-BPG, increase affinity for O2 and make the Hgb similar to HbF.

40
Q

HbC

A

Glu -> Lys mutation causing Hgb to form hexagonal crystals and mild chronic hemolytic anemia.

41
Q

Why is alpha-thalassemia so fatal?

A

Deficient alpha chain results in Hb Barts (4 gamma chains) and Hb H (4 beta chains), both which have very high affinities for O2 and do not deliver it to peripheral tissues.

42
Q

A child presents with photosensitivity and pellagra-like skin rash. She also has waxing and waning ataxia. Labs show amino aciduria restricted to neutral amino acids. Her symptoms improve significantly with niacin supplementation and a high protein diet. What is causing her symptoms?

A

Hartnup disease is due to defect apical enterocyte and renal transport of tryptophan, resulting in niacin deficiency because niacin is synthesized from tryptophan.

43
Q

HMP shunt rate limiting enzyme

A

Glc-6P DH. This converts Glc-6P to 6-phosphogluconolactone and one molecule of NADPH that can be used to reduce glutathione in RBCs. Remember, the next step is the conversion of 6-phosphogluconolactone to ribulose-5P + the second NADPH by 6-phosphogluconolactone dehydrogenase.

44
Q

t(15;17)

A

M3 AML due to fusion of the AML gene with the retinoic acid receptor that prevents myeloblasts from differentiating.

45
Q

Mutated cancer genes that result in EGF activation

A

ErbB1 small cell lung cancer and Her2/neu (erbB2)

46
Q

Friedrich’s ataxia pathophysiology

A

GAA repeats causes frataxin gene mutation, which codes for a mitochondrial protein imporatnt for respiration and iron hemostasis.

47
Q

t(9;22)

A

Philadelphia chromosome results in BCR-ABL fusion and CML.

48
Q

Mutation involved in classic galactosemia

A

AR mutation in galactose-1P uridyltransferase.

49
Q

Nucleus that holds the cell bodies of cholinergic neurons

A

Nucleus basalis of Meynert

50
Q

Xeroderma pigmentosa mutation

A

AR mutation in DNA excision repair.

51
Q

HNPCC mutation

A

Mutation in DNA mismatch repair enzymes

52
Q

Pyruvate carboxylase

A

Catalyzes the initial step of gluconeogenesis

53
Q

Location of pentose-phosphate pathway

A

Cytosol only

54
Q

Prokaryote vs. eukaryote DNA polymerase

A

Prokaryote: DNA polymerases I, II, and III
Eukaryote: DNA polymerase III does most of the work

55
Q

Mutations associated with early onset Parkinson’s disease

A

Parkin, PINK-1 and DJ-1 gene mutations result in malfunction of a protein that normally tags protein aggregates for degradation via the ubiquitin-proteosome pathway. This results in aggregation and formation of Lewy bodies seen in Parkinson patients.

56
Q

What causes skeletal muscle to increase glycogenolysis immediately upon contraction?

A

Muscle contraction releases Ca2+ which causes synchronized glycogen breakdown in muscle. EPI and glucagon bind Gs in the liver and increase cAMP levels. The elevated cAMP levels activate PKA, which activates phosphorylase kinase, which in turn phosphorylates and activates glycogen phosphorylase. In addition to Ca and EPI, reduced ATP and increasing AMP levels further activate glycogen phosphorylase, resulting in increased glycogenolysis.

57
Q

1 year old child of Ashkenazi Jewish descent has HSM, progressive hypotonia and mental retardation. Liver and spleen biopsy shows foamy histiocytes with accumulation of sphingomyelin. Physical exam reveals a cherry-red macula.

A

Niemann-Pick disease due to deficiency of sphingomyelinase.

58
Q

Genes commonly mutation in Ehlers-Danlos

A

Lysyl hydroxylase (presents with decreased hydroxyproline) or procollagen peptidase (presents with disulfide rich procollagen globular domains)…enzymes involved in the cytoplasmic processing of collagen

59
Q

What makes up neurofibrillary tangles?

A

Hyperphosphorylated tau proteins (microtubule component)

60
Q

Buspirone mechanism of action

A

5-HT1 receptor partial agonist

61
Q

Treatment of organophosphate poisoning

A

Organophosphate poisoning results in irreversible inhibition of AChE. Treat with muscarinic antagonist atropine or pralidoxime (decouples organophosphates from AChE).

62
Q

Huntington disease pathophysiology

A

Huntingtin gene mutation -> CAG repeats -> gain of histone deacetylation function in huntingtin protein -> silencing of genes necessary for neuronal survival

63
Q

Enzyme deficiency that can cause Ehlers-Danlos

A

Procollagen peptidase deficiency results in lack of cleavage of the N and C terminals of procollagen to make it less soluble tropocollagen.

64
Q

Cal per gram of protein, carbohydrate, fat and alcohol?

A

Protein and carbohydrate = 4
Fat = 9
Alcohol = 7

65
Q

Enzymes that correct thymidine dimerization

A

UV-specific endonuclease. This is the enzyme absent in xeroderma pigmentosum.

66
Q

Enzyme that corrects DNA mismatch

A

3’ -> 5’ exonuclease. This is deficient in HNPCC

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