CSGD Quiz 3 2007

1

Which ONE of the following is the principal mechanism for the inactivation of the neurotransmitter noradrenaline?


  Metabolism by Mono Amine Oxidase.

  Uptake into extraneuronal tissues.

  Metabolism by Catechol-O-Methyl Transferase.

  Reuptake into the nerve terminal.

  Diffusion away from the nerve terminal.


Noradrenaline synthesis is a multi-step process; it is more efficient to recapture it than to resynthesise it every time it is required.

2

With regard to the prostate gland, which ONE of the following statements is CORRECT?


  Nodular hyperplasia of the prostate occurs in 10 – 15% of the male population by age 80.

  Stromal proliferation is a characteristic feature of nodular hyperplasia of the prostate.

  Nodular hyperplasia of the prostate is associated with a significantly increased risk of carcinoma of the prostate.

  Squamous metaplasia is a characteristic feature of nodular hyperplasia of the prostate.

  "Back-to-back glandular acini" is a characteristic feature of nodular hyperplasia of the prostate.


A is incorrect: Almost 100% of males have developed BNH by age 80. B is correct: Stromal fibrous bands form around the nodules. C is incorrect: There is no associated increased risk of carcinoma. D is incorrect: The characteristic features of BNH are glandular proliferation, glandular dilatation and stromal proliferation. E is incorrect: This is a feature of prostate carcinoma.

3

Epilepsy can be treated with drugs that can target specific receptors or ion channels. Which ONE of the following is the molecular target for the anti-epileptic drug Phenytoin?


  NMDA receptors.

  GABA receptors.

  Calcium channels.

  Glutamate receptors.

  Sodium channels.


Epilepsy is though to occur because of excessive neuronal discharge. Phenytoin's anti-epileptic action occurs by reducing the excitatory activation of glutaminergic NEURONS. Phenytoin blocks open Na+ channels, inhibiting the propagation of action potentials. Note that this means that the Na+ channels must first be open before phenytoin can act (i.e. its effect is enhanced during high frequency firing - good for epilepsy).

4

Specific neurotransmitters, receptors, signalling molecules and gene expression mechanisms have been implicated in synaptic plasticity and thus cellular processes are thought to underlie learning and memory. Which ONE of the following has been most clearly associated with long-term potentiation (LTP) by experimental evidence?


  Activation of specific proteasomes and degradation pathways.

  Calcium influx through NMDA receptors and insertion of AMPA receptors into the postsynaptic membrane.

  Transcriptional activation of Hox genes.

  Zinc influx through ATP receptors and insertion of 5HT receptors in the presynaptic membrane.

  Signal transduction via Golgi proteins.


A is incorrect: LTP is associated with gene transcription and synaptic GROWTH. B is correct: Prolonged AMPA activity displaces Mg2+ blocking NMDA receptors, allowing Ca2+ influx. C is incorrect: Hox genes are involved in development, not LTP. D is incorrect: This statement is wrong at just about every point. The correct version might mention that more AMPA receptors are inserted post-synaptically in association with LTP. E is incorrect: What are Golgi proteins?

5

Which ONE of the following statements regarding oxygen free radicals (or reactive oxygen species) is CORRECT?


  In human cells they have almost entirely harmful effects.

  They are critical for mitochondrial function.

  They are enhanced by anti-oxidants.

  They are biochemical curiosities with little physiologic relevance in humans.

  They are responsible for telomere shortening during cell division.


A is incorrect: They are required for mitochondrial function. B is correct. C is incorrect: They are neutralised by anti-oxidants. D is incorrect: They are important in mitochondria and are implicated in carcinogenesis. E is incorrect: Telomere shortening is entirely mediated by DNA/RNA interaction.

6

Which ONE of the following pharmacological agents is least likely to cause delirium in older people?


  Nitrazepam.

  Motion sickness patches containing hyoscine.

  Cimetidine.

  Amoxycillin.

  Morphine.


A is incorrect: Confusion/delirium is a common adverse effect of benzodiazepines in elderly patients. B is incorrect: Hyoscine (scopolamine) has anti-cholinergic effects, which are strongly associated with delirium in the elderly. C is incorrect: Cimetidine notoriously interferes with the cytochrome P450 system, which may increase adverse effects for elderly people who are likely to be on a number of medications already. D is correct: Amoxycillin is an "ordinary" β-lactam antibiotic, and is therefore least likely to cause delirium. E is incorrect: Morphine is an opioid analgesic. Pain medication is commonly associated with delirium in hospitalised elderly patients.

7

Which ONE of the following classes of medication is most commonly under-prescribed in elderly patients?


  Diuretics.

  Bronchodilators.

  Antipsychotics.

  Gastric acid-suppressing medications.

  Bone preserving medications.


The most commonly underprescribed drugs are:

  • Osteoporosis drugs in postmenopausal women with a fracture (80%)
  • Warfarin for stroke prevention in AF (50%)
  • ACE inhibitors in heart failure (20-30%)
  • Low-dose aspirin in ischaemic heart disease (20%)
  • Anti-depressants and analgesics

8

Which ONE of the following statements is CORRECT?


  Monosomy of an autosomal chromosome is incompatible with fetal development because all of the genes on the chromosome are haploinsufficient.

  The major problem with chromosome translocations for normal cell growth and development is that the longer chromosomes can never be replicated accurately.

  Having an extra copy of any autosomal chromosome can cause growth and developmental abnormalities.

  Because of genomic imprinting some genes inherited from the father will only be expressed in his sons and not his daughters.

  Genomic imprinting is an epigenetic mechanism for gene inactivation that is inherited in a Mendelian fashion.


A is incorrect: Some of the genes may require monoallelic expression, so will not necessarily be haploinsufficient. B is incorrect: Longer chromosomes may show higher incidence of replication errors, but are often copied correctly. C is correct: Down syndrome (trisomy 21) is a common example. D is incorrect: Genomic imprinting is not associated with sex chromosomes and is therefore unrelated to offspring gender. E is incorrect: Genomic imprinting inheritance is not Mendelian - see inheritance trees of Prader-Willi/Angelman syndromes for examples.

9

Which ONE of the following best explains the main cause of standard trisomy 21?


  Non-disjunction of chromosome 21 in meiosis during paternal gametogenesis.

  Non-disjunction of chromosome 21 in meiosis I during maternal gametogenesis.

  Non-disjunction of chromosome 21 in meiosis II during maternal gametogenesis.

  Non-disjunction in mitosis during early embryogenesis.

  Inheritance of a balanced translocation.


A is incorrect: This statement is true but B is more precise. B is correct. C is incorrect: Non-disjunction during meiosis II would involve chromatids, not chromosomes. D is incorrect: This would produce a "mosaic" Down Syndrome. E is incorrect: Balanced translocation is usually benign.

10

Which ONE of the following statements about gene dosage is CORRECT?


  Fetuses with trisomies 13, 18 and 21 will typically reach full term gestation.

  Genetic conditions showing autosomal recessive inheritance are evidence of haploinsufficiency.

  All human genes require biallelic expression.

  Familial adenomatous polyposis is an autosomal recessive condition.

  The lethality of monosomies suggests that the majority of genes must be present in 2 copies.


A is incorrect: Spontaneous abortions are common with chromosomally abnormal fetuses. B is incorrect: Haploinsufficiency refers to when expression of a single normal gene copy is insufficient for normal function. Autosomal recessive inheritance requires two abnormal genes for a change in phenotype. C is incorrect: There are a small number of genes that require monoallelic expression. D is incorrect: FAP is an example of haploinsufficiency and is inherited in an autosomal dominant fashion (mutations have 100% penetrance). E is correct.