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WVSOM - Molecular-3

Mutations

QuestionAnswer
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 on 2011-09-30



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