test #7 3/16 Flashcards Preview

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Flashcards in test #7 3/16 Deck (136)
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1

initiation of translation in prokaryotes requires..

N-formylated methionine-tRNA. initiation codon AUG (methionine) is 6-10 bases downstream Shine-Dalgarno element.

2

Shine-dalgarno element (prokaryotic translation)

6-10 bases upstream intiation codon AUG. recognizes complementary sequences in 16S rRNA and 30S small ribosomal subunit.

3

how do aminoglycosides affected prokaryotic translation?

bind to 30S, inhibit formation of initiation complex and protein synthesis.

4

which antibiotic blocks peptidyltransferase activity of prokaryotic ribosome (1)

chloramphenicol

5

which antibiotics block the translocation of ribosome along mRNA (2)

clindamycin and erythromycin

6

difference in p-values between studies suggests..

difference in sample size (i.e. underpowered)

7

Berkson's bias

selection bias created by selecting hospitalized patients as the control group

8

congenital torticollis

noted 2-4 wks of age, child prefers to hold head tilted to one side. usu result of malposition of head in utero (due to fetal macrosomia or oligohydramnios) or birth trauma (breech). sternocledomastoid injury and fibrosis. other musculoskeletal abnormalities: hip dysplasia, metatarsus adductus, talipes equinovarus (club foot)

resolve w/ conservative therapy / stretching

chin pointed away from contracted SCM. head tilted towards muscle.

9

maternal hypertension on intrauterine growth

intrauterine growth restriction w/ normal-almost normal headaize and reduced abdominal circumference

10

fragile X-syndrome characterestics

main: MR, facial dysmorphism, macroorchidsm. mild-severe mental retardation, long-thin face w/ prominent forehead and jaw, post-pubertal macroorchidism, large protruding ears, tooth crowding, arched palate

11

gene abnormality in fragile X syndrome

mutation in FMR1 gene, on long arm of chromosome X. normally has 5-55 CGG trinucleotide repeats. >200 repeats --> transcriptional instability. leads to hypermethylation --> gene inactivation.

12

chromosomal instability disorders (4)

related to mutations in DNA repair: xeroderma pigmentosum, ataxia-telangiectasia, fanconi's anemia, bloom syndrome

13

defective mismatch repair genes result in..

Lynch syndrome (increased risk of heriditary non-polyposis colorectal cancer) and extraintestinal malignancy

14

tay sach's deficiency & metabolite build-up

lysosomal storage disease. commonly seen in ashkenazi jews. deficiency in beta-hexosaminidase A. accumulation of cell membrane glycolipid GM2 ganglioside in lysosomes.

15

tay sach's clinical presentation

2-6 months -- progressive weakness, hypotonia, loss of motor skills, abnormal startle w/ acoustic stimuli, CHERRY-RED MACULA w/ NO hepatosplenomegaly. macrocephaly (accumulation of glycolipid in brain). eventually--> seizure, blindness, spasticity. life expectancy of 2-5 years.

16

histology of tay sach's (EM)

neurons w/ cytoplasmic distension and lysosomes w/ onion skin lamellar lipid rings

17

tay sach's vs. niemann-pick disease

both have cherry-red macular spot. niemann-pick has hepatosplenomegaly.

18

formula for NNH (number needed to harm)?

1/attributable risk.
attributable risk = adverse event rate in treatment group - adverse event rate in placebo group.

19

formula for NNT (number needed to treat)?

1/absolute risk reduction

20

combined OCP primary mode of action. secondary?

estrogen/progesterone suppress synthesis of FSH and LH (gonadotropins) in anterior pituitary (block LH spike needed for ovulation). also cause thickening of cervical mucus (prevent sperm from entering). also, prevents growth of endometrium, making it difficult for embryo implantation.

21

what is seen in periventricular plaques of MS? what is in CSF? on visual evoked potentials?

loss of myelin sheaths, depletion of oligodendrocytes, lipid-laden macrophages w/ myelin breakdown products. oligoclonal band on protein electrophoresis. slowed conduction velocity on visual evoked potentials.

22

PT and PTT and bleeding time in vWF deficiency?

both coagulopathy (factor VIII) and platelet deficiency. PTT and bleeding time elevated.

23

hemophilia C

very rare autosomal recessive, deficiency in factor XI

24

factor VIII deficiency

classic X-linked hemophilia. PTT prolonged.

25

which organ is least vulnerable to infarction? exception?

liver, has dual blood supply. portal vein and hepatic artery. also, retrograde arterial flow from accessory vessels (inferior phrenic, adrenal, intercostal). exception: transplanted liver --> hepatic artery thrombosis (collateral circulation severed during transplantation)

26

is the spleen vulnerable to infarction? why?

yes, bc perfusion via splenic artery = end-arterial. occurs in sickle-cell anemia, infective endocarditis, cardiac mural thrombosis

27

how long can the myocardium endure complete arterial ischemia

20-30min w/o severe consequence. briefer periods --> myocardial stunning.

28

organ susceptibility to infarction after occlusion of a feeding artery (greatest to least)

CNS, myocardium, kidney, spleen, liver.

29

what ions are responsible for -70mV resting potential?

high K+ conductance, low Na+ conductance (Cl- plays little if any role)

30

what role do the L-type Ca++ channels in myocyte T-tubules play in excitation-contraction.

NO significant flux of Ca++ from L-type Ca++ channels. Instead, they are triggered by depolarization and TETHERED to RyR1 channels in sarcoplasmic reticulum to release Ca++. skeletal muscles do NOT need extracellular Ca++ to contract!