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WVSOM - Molecular-3
Mutations
| Question | Answer |
|---|---|
| Congenital birth defects | Disorders present at birth; can be behavioral or metabolic defects or malformations |
| Teratogenesis | To produce a defect by interfering with a developmental process, without changing any DNA sequence (i.e. FAS) |
| Mutation | Any change in DNA sequence; these may or may not produce a birth defect |
| Mutant | An entity that possesses a mutation; entity could be a person or animal with a specific mutation, or a gene that's mutated |
| Wild type | Not mutated; standard form found in nature |
| Loss of function mutation | Decrease or inactive gene |
| Gain of function mutation | Increase gene activity |
| Spontaneous mutation | Mutations that arise with no known cause |
| Induced mutation | Mutations produced by intentional exposure to mutagenic agents |
| Types of mutations | Silent mutations, point mutations, chromosomal aberrations, aneuploidies, polyploidies |
| Silent mutation | Sequence change with no phenotypic affect (i.e. 3rd base of wobbly codon, intron spliced out of message, spacer region o/s of expresed gene, similar AA w/ same effect on protein function, region of protein not critical for function - linker) |
| Point mutation | Alteration of one codon, usually due to single base pair subsitution |
| Transition point mutation | Substitution of a pyrmidine for a pyrimidine (or purine for purine) |
| Transversion point mutation | Substitution of pyrimidine for purine (or purine for pyrimidine) |
| Missense mutation (point mutation) | Single base pair substitution altering one AA (i.e. sickle cell) |
| Nonsense mutation (point mutation) | Base pair substitution producing premature stop codon, resulting in truncated polypeptide |
| Frame shift mutation (point mutation) | Insertion or deletion of sequence that is not a multiple of 3, so that codon reading frame is altered & random AA sequence is produced beyond the change |
| Chromosomal aberrations | Any gross change in chromosome structure, large enough to be observed under light microscope; can occur at any level |
| Deletion | Mutation where sequence is lost |
| Insertion | Mutation where sequence is added |
| Duplication | Insertion where sequence is copied |
| Translocation | Misplacement of DNA fragment to different location of genome (different spot on same chromosome or on different chromosome) |
| Inversion | DNA fragment excised and inserted back into same chromosome in opposite orientation |
| Chromosome 3 duplication-deletion syndrome | Inversion of center of chromosome 3, including centromere; rare |
| Chromosome 3 duplication-deletion syndrome survival | No defects in first generation; 1/2 of second generation offspring died before birth |
| Chromosome 3 duplication-deletion syndrome symptoms | Few cases survived with general developmental delay; recurrent urinary, respiratory, eye infections; numerous head and facial abnormalities preventing children from sucking |
| Cri-du-chat syndrome | Deletion of part of the short arm of chromosome 5 |
| Cri-du-chat syndrome survival | Infant or early childhood fatality |
| Cri-du-chat syndrome symptoms | Plaintive catlike meowing cry, microcephaly, broad face, saddle nose, widely spaced eyes with epicanthic folds, mental retardation |
| Ploidy | Number of sets of parental chromosomes |
| Polyploidy | More than two sets (i.e. triploidy - 3 sets); produced by polyspermy; 100% fatal (spontaneous abortion after conception); few develop to term, but perish soon after birth |
| Partial hydatidiform mole | Developed from triploidies; egg fertilized by 2 sperm; develop from trophoblastic tissue (little fetal tissue); lack of vasculature, maternal fluid not drained from placenta, villi swell (resembling grapes) |
| Complete hydatidiform mole | Eggs that lose maternal nucleus and then fertilized by 2 sperm, resulting in all paternal genes; develops from trophoblastic tissue, but little fetal tissue; lack of vasculature = maternal fluids not drained from placenta = swollen villi = resemble grapes |
| Choriocarcinoma | Hydatidiform mole that has not aborted; mortality rate is 20% |
| Aneuploidy | Have the wrong number of chromosomes in parental set; one or more chromosomes added or removed |
| Trisomy | Have 3 copies of chromosome |
| Monosomy | Have 1 copy of chromosome |
| Nondisjunction | Failure of chromatids to separate during meiotic anaphase; what produces aneuploidies; older women increased rate of nondisjunctions (due to suspension of oocytes in prolonged meiotic prophase 1) |
| Aneuploidies in animals and humans | Lethal in animals (disrupt gene balance); humans can have 6 aneuploidies involving short chromosomes and survive (with developmental defects) |
| Prenatal screens | Fetal proteins (alpha-fetoprotein) secreted into amniotic cavity, pass through placenta, enter maternal blood stream; maternal levels of proteins used to screen for certain developmental defects |
| Prenatal screen tests | Low alpha-fetoprotein, unconjugated estriol, hCG, & serum dimeric inhibin A = Down syndrome; high alpha-fetoprotein, acetylcholinesterase = meningomyeloceles, gastroschisis |
| Down syndrome | Trisomy 21; incidence = 1/700 live births; 90% abort spontaneously; symptoms = short stature, epicanthal eyelid fold, broad skulls, large tongues, loose joints, stubby hands w/ simian creases, single crease of 5th digit, mental retradation |
| Edward syndrome | Trisomy 18; incidence: 1/6500 live births; most abort spontaneously; 95% perish w/i 1 yr; symptoms: clenched fist (2nd digit overlaps 3rd, 5th overlaps 4th); rocker bottom feet; prominent occiput; micrognathia; short sternum; mental retardation |
| Patau syndrome | Trisomy 13; incidence: 1/20000 live births; spontaneous abortion & postpartum mortality higher than Edward syndrome; symptoms: holoprosencephaly, cleft palate, prominent proboscis, polydactyly, rocker bottom feet, siezures |
| Turner syndrome | Monosomy (X chromosome - XO); incidence: 1/3000 live births; most abort spontaneously; symptoms: females - no ovaries, limited secondary sexual characteristics, webbed neck, broad shield-like chest, widely spaced nipples, no mental retardation) |
| Klinefelter syndrome | Extra X chromosome (XXY); incidence: 1/1000 live births; symptoms: males - some female secondary characteristics (gynomastia), underdeveloped male characteristics (small testes, little body hair), no mental retardation |
| Klinefelter syndrome with more than two X chromosomes | More severe phenotypes (mental retardation) - greater number of X's, more profound mental retardation |
| Extra sex chromosomes | XYY incidence: 1/1000 live births; symptoms: slightly reduced IQ (10-15 points), little/no physical abnormalities, minor learning disabilities (language skills); increased incidence in prison pops due to hyperactivity & ADD (not predisposed to violence) |
| Endogenous mutagenic processes | Occurring naturally within the cell |
| DNA ligase errors (endogenous) / ligation of strand breaks | Ligase automatically forms phosphodiester bonds between any free 3` -OH and 5` phosphate of DNA; strands cleaved by mutagen, may be rejoined incorrectly; DNA ligase has no way of determining original orientation; produces inversions, translocations, etc. |
| Unequal crossing over | Displaced exchange of strands during crossing over, so that sequence is deleted from one homolog and duplicated in another |
| DNA polymerase infidelity | Inherent error rate = 1 mismatch per 10^9-10^10 replicated base pairs |
| The cytochrome p-450 system | Natural liver function for removal of toxins; system oxidizes hydrophobic compounds (makes them water soluble to be excreted in urine); periodically make innocuous products mutagenic |
| Depurination | Release of purine (A / G) by cleavage of bond w/ 1` site of ribose; damage not repaired before next DNA replication, then any 4 bases incorporated into new strand |
| Deamination | Removal of amino group from base by oxidation of keto group; A / C = will result in transition mutation during next round of replication; deamination of G not mutagenic, T does not have amino group to remove |
| Tautomeric shifts | Transient changes in electron configuration of base = resemble another base; infrequent, but during replication can cause transition mutations |
| Exogenous mutagenic agents | Foreign factors affecting cell |
| Exogenous mutagenic agent: radiation | UV light, ionizing radiation, gamma rays |
| Exogenous mutagenic agent: UV light | Low energy form of electromagnetic radiation; electrons in atoms of DNA absorb energy of UV rays (chemically reactive); prevalent mutation induced by UV light crosslinks thymine bases = thymine dimers; cause point mutations, chromosomal aberrations |
| Exogenous mutagenic agent: ionizing radiation | Alpha & beta particles, x-rays; higher energy than UV; collide with molecules, excise electrons, produce highly reactive, ionic atoms; produces point mutations |
| Exogenous mutagenic agent: gamma rays | Extremely high energy; breaks DNA strands (penetrate deep into tissues); produce chromosomal aberrations |
| Chemical mutagens: alkylating agents (nitrogen mustard) | Add one or two carbons (methyls or ethyls) to DNA; interferes with DNA replication; causes point mutations, chromosomal aberrations |
| Chemical mutagens: strand cleavers (peroxides, sulfur compounds) | Sever phosphodiester bonds directly, inducing chromosomal aberrations |
| Chemical mutagens: base analogs (5-bromouracil) | Mimic nucleotides, inducing base pair substitutions; 5-BU (keto & enol conformations), keto - incorporated into DNA (in T spot), enol state - allow G where there should be A; result = G to A transitions |
| Chemical mutagens: intercalating agents (acridine orange, proflavin) | Multi-ring structures that intercalate/wedge between bases of DNA; creates tension in strands; results in chromosomal aberrations during replication |
| Insertion elements (viruses & transposons) | DNAs with ability to integrate into chromosome / excised from chromosome; integrate = disrupt function (insertional mutagenesis); excised = deletions / insertions left behind |
| DNA repair mechanisms | DNA polymerase proofreading, ligation of strand breaks, direct base repair, excision repair |
| DNA polymerase proofreading | Pol-delta has 3`-5` proofreading activity; allows it to double-check for base pair mismatches during replication; excise incorrect base; inherent error = one mistake occurs per cell division |
| Direct base repair | Some cellular processes can repair specific bases which have been covalently damaged; i.e. methylguanine methyltransferase (MGT) removes methyl groups added to carbonyl of guanosine by alkylating agent, methylmethane sulfonate |
| Excision repair | Utilizes specific enzymes that recognize mismatches/covalently damaged bp; UV specific endonuclease (repairs T-dimers), nicks phosphodiester bond (5` end), exonuclease removes region of strand w/ damaged base, pol-beta fills in gap & DNA ligase seals nick |
| Xeroderma pigmentosum | Product of defective UV specific endonuclease; results in extensive skin tumors after exposure to sunlight |
| Principles of teratology | Act on specific processes, produce spec. defects; defects = malformations, growth retardation, death; susceptibility infl. by fetal & maternal genetics; extent of malformation = dose & duration of exposure; susceptibility varies (most sensitive = 3-8 wks) |
Created by:
JaneO
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