Cell Biology Theme 3

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  • Created by: Splodge97
  • Created on: 14-05-17 15:42
What occurs in prophase?
Chromosomes are condensed, spindle is assembled (when microtubules grow out from the centrosome), nuclear envelope breaks down
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What occurs in metaphase?
Chromasomes align at the equator (attached to kinetochore protein surrounding centromere)
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What occurs in anaphase?
Paired chromosomes separate and migrate to opposite poles (using motor proteins kinesin and dynein)
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What occurs in telophase?
Nuclear envelope reassembles, actin contractile ring assembles, cytoplasm begins to separate
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What is cytokinesis?
Splitting of the cell into daughter cells after separation of the genome; the two sets of chromosomes decondense and the contractile ring tightens
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What occurs in the S phase of interphase?
DNA replication
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What occurs in the G1 phase of interphase?
Environment is termed favourable before S phase can begin
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What occurs in the G2 phase of interphase?
Determined DNA replication has occurred efficiently in the S phase (checks performed by independant DNA polymerase) before enters mitosis
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Other than in the G phases, name another cell cycle checkpoint?
Before anaphase, ensuring all chromosomes are correctly attached to the spindle
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Which cells are quiescent (constantly in G0)?
Mature nerve, cardiac and skeletal muscle cells
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What are mitogens?
Molecules which stimulate cell division (driving cells through the cell cycle). Similar to growth factors but have more functions. Often stimulate the accumulation of cyclins (by causing their gene transcription), activating cyclin dependant kinases.
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What are cyclin dependant kinases?
Enzymes activated by the binding of the protein cyclin - only activated at certain times in the cell cycle (so trigger its different stages by causing phosphorylation/dephosphorylation at the correct time)
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How are CDK's switched off?
Cyclin tagged with ubiquitin by proteasome and degraded by proteases
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What causes necrosis?
Acute physical/chemical injury, lack of oxygen or the influence of pathogens
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What occurs in necrosis?
Cells swelll and burst, releasing its contents and therefore causing an inflammatory response (which damages surrounding cells if prolonged)
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What occurs in apoptosis?
Cytoplasm is triggered to collapse by the flipping of phospholipids in the bilayer); this causes the whole cell to shrivel and collapse. Changes in the cell membrane then trigger phagocytosis.
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What are blebs?
Bulges of the membrane before collapse occurs in apoptosis
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What is a caspase cascade?
Intracellular amplification of the number of active caspase proteases (previously present as zymogens, activated by cleavage) when one caspase molecule activates many others. Cause apoptosis by cleaving the nuclear lamins and cytosilic proteins.
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Where and why is cytochrome C released?
Released from intermembrane space of mitochondria when they are damaged to instigate apoptosis (by activating caspases via IP3 and DAG)
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What is the role of the apoptosome?
Induces apoptosis by causing caspase activation (by cleavage)
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What are Bcl-2 proteins?
Promoters or inhibitors of apoptosis. Promoters = activate caspases or the formation of the apoptosome by initiating cytochrome C leakage. Inhibitors = Prevent action of promoter Bcl-2 proteins.
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What is the role of the p53 protein?
Activated by DNA damage - inhibits cyclin dependant kinases at G1 checkpoint so cell cycle blocked (before mitosis). If DNA damage too extensive it causes apoptosis by activating promoter Bcl-2 proteins.
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Why does mutated p-53 cause cancer?
Can't prevent progression into mitosis, so abnormal (malignant) daughter cells produced
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Which is the short arm of the chromosome?
p (q is long arm)
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What are the invasive methods of taking an embryo's karyotype?
Amiocentesis and chorionic villus sampling (non-invasive use mother's peripheral blood)
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What occurs in meiosis I?
Homologous chromosomes line up randomly at the equator by independant assortment; then re-combination (crossing-over) occurs. Spindle then separates the homologous pairs to form two diploid daughter cells.
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What occurs in meiosis II?
Sister chromatids separated to produce four gamete daughter cells (with novel gene assortments)
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What is a gene?
Locatable region corresponding to a unit of inheritance which is associated with regulatory, transcribed or other functional sequence regions
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What may unique genes code for?
Proteins or non-coding RNA's
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What are multi-gene families? How do they arise?
Genes with similar sequences (so which produce similar proteins). Arise through gene duplication and evolutionary divergence.
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What are gene superfamilies?
Genes with have limited sequence similarity but produce proteins with the same main domains (which have similar functions)
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Why aren't pseudogenes not expressed?
Mutation has made them silent or beacuse they have been inserted by a virus so have no promoter
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What are holomorphic alleles?
Caused by loss of function mutations; they have missense mutations which reduce their gene activity (so less gene product produced)
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What are null alleles?
Caused by loss of function mutations; don't produce a functional gene product as they are missing domains (through truncation) or have had amino acids deleted
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What is haploinsufficiency?
Caused by loss of function mutations; one allele of a gene is lost so only one functional allele which can't produce enough gene product to maintain the normal phenotype
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What can gain of function mutations cause?
Increase in gene activity, altered levels of gene expression (in different amounts, at different times or in different tissues)
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What are dominant-negative mutations?
Cause a loss of function as the mutant gene product interferes with the normal gene product
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What is a transition substitution?
When a single nucleotide susbtitution causes the same typer of base (purine or pyramidine) to be coded for
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What is a transversion substitution?
When a single nucleotide substitution causes a different type of base to be coded for
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What are non-conservative missense mutations
When the new amino acid caused by a single nucleotide substitution has different properties (conservative if same properties)
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What are nonsense mutations?
Cause a stop codon to be introduced early (shortening the polypeptide produced)
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What are splice sites?
Intron/exon boundaries; mutations here cause exon skipping or intron retention in mRNA
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What is trinucleotide repeat expansion?
Caused by looping of repeat sections during replication (when DNA polymerase 'slips'). Termed dynamic as instability increases with the number of repeats. Alter protein stability/function, causing trinucleotide repat disorders (Huntington's).
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What is aneuploidy?
Loss/gain of one/more chromosomes
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What is an example of monosomy?
Loss of X or Y chromosome in Turner's syndrome
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What is an example of trisomy?
Gain of chromosome 18 in Edward's syndrome
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What is the cause of Down's syndrome? What are its symptoms?
Trisomy 21, causes learning difficulties, growth delays, cardiac abnormalities, cleft lip, delayed eruption, macroglossia, periodontal disease and malocclusion
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What is polyploidy?
Addition of one or more complete haploid elements (triploidy when one extra chromosome per homologous pair causing miscarriage).
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What is non-dysjunction?
Abnormal spindle formation, causing unequal separation of chromosomes in meiosis to produce aneuploid germ cells
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What is reciprocal translocation?
When chromatin is unequally exchanged between homologous chromosomes during recombination - gives one very large chromosome and one very small chromosome
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What is robertsonian translocation?
Results from breakage of two chromosomes at the centromere, with fusion of their long arms to form one long chromosome (short arms are lost); therefore the chromosome number is reduced to 45
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What is pericentric inversion?
Reversal of chromosome segments on different sides of the centromere (between a p and q arm)
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What is paracentric inversion?
Reversal of chromosome segments on the same side of the centromere (between the p or q arms)
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What are blanced structural chromosome changes?
Result in no loss of DNA so harmless except when break points are in the middle of genes
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What are unbalanced structural chromosome changes?
Result in loss of DNA so almost always cause syndromes
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What are DNA abducts?
Mutations caused by the binding of chemicals to DNA; examples are depurination, deamination of cytosine (forming uracil) or methylation of cytosine (forming thymine)
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What is the result of ionising radiation?
Double strand breaks and chromosome abnormalities
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What is the result of UV radiation?
Forms thymine dimers (that arrest replication, causing nucleotide deletions)
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Describe nucleotide excision repair
Removal of thymine dimers and DNA abducts
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Describe non-homologous end joining
Sealing of a double strand break via processing by DNA nuclease and joining by DNA ligase - this shortens the strand
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Describe homologous recombination
Joining of double strand breaks by a special DNA nuclease whch uses an undamaged, homologous strand to repair the gap without loss of nucleotides
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How are SNP's inherited?
In haplotype blocks (groups of alleles inherited together as they are transferred as one in recombination)
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What are the functions of unique extragenic sequences?
Functions in gene regulation (promoters/enhancers)
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What are low copy repetitive sequences?
Extragenic sequences near centromeres and telomeres with 10-300kb repeated sections
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What are moderately repetitive sequences? Give examples
Extragenic sequences comprised of tandem repeats (1-200bp repeated sections). Includes satellites (longest, at centromeres/hetrochromatin), minisatellites (at teloomeres) and microsatellites (smallest, polymorphic, in euchromatin).
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What is assessed in DNA fingerprinting?
Minisatellites
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What is assessed in paternity testing?
Microsatellites (tandem repeats so small trinucleotide repeat expansions likely)
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What are highly repetitive sequences? Give examples
Caused by mobile DNA elements - either transposons (cut and paste themselves into different areas of the genome) or retroposons (inserted - usually from viruses - after being reverse transcribed from RNA). Examples are SINE's and LINE's.
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What is retrotransposition?
Transcription from the L1 promoter to produce hybrid RNA which is reverse transcribed to form cDNA. It is then inserted into existing genes to generate novel exons, regulatory regions and cause exon shuffling.
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What is penetrance?
Proportion (%) of inividuals carrying a geneotype which produces an associated phenotype
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What is expressivity?
Variation in the phenotype of individuals with a particular genotype
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What is a non-additive effect?
When the polygenes of a complex disorder don't act equally (so don't generate normal distrbution curves)
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How does the threshold model asses an individual's liability?
Overly normal distribution curve of whole population with familial liability - space between threshold lines (point at which anyone with higher expressivity has the disease) represents individual's liability
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What are linkage studies?
Previously used - mapped simple diseases by analysisng co-segregation (transmission together) and genetic markers
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What is disequilibrium mapping?
Overtaken linkage studies - fine mappping involving disease associated SNP's
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What are genome wide assocaition studies?
Preferred moodern genome study - involves genome-wide unbiased SNP genotyping to identify SNP's associated with diseases and their position (genes in these areas being studied as they are likely to cause the disease)
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What are pleitropic genes?
Genes with multiple functions (affected in syndromic disorders)
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What are the symptoms of Van der Woude syndrome?
Cleft lip, lip pits and hypodontia - caused by IRF6 mutation
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What are the symptoms of Treacher Collins syndrome?
Cleft lip, hypodontia, hypoplasia of mandible/zygoma, abnormal dentition and eyelid coloboma - caused by Tcof1 mutation (causing neural crest cells to undergo apoptosis)
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What is the cause of craniosynostosis?
FGFR2 mutations causing excessive receptor activation
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What are the symptoms of Apert's syndrome?
Coronal synostosis, hypoplasia and syndactily (fused digits)
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What are the symptoms of Crouzon syndrome?
Coronal synostosis, hypoplasia and overbite (caused by same mutation as Pfeiffer's syndrome which causes exorbitism - eyeball protrusion - instead of overbite)
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What are the symptoms of hypodroitic ectodermal dysplasia?
Oligodontia, sparse hair, few sweat glands and loss of alveolar bone - x linked and caused by EDA1 mutation
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What occurs in Reiger syndrome?
Oligodontia (maxillary incisors and molars lost) through PIX2 mutation
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What causes non-syndromic oligodontia?
PAX9 and MSX1 mutations - passed through autosomal dominant inheritance
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What are the symptoms of cleidocranial dysplasia?
Hyperdontia, scoliosis (abnormal spine twisting), small faces with broad noses, delayed eruption, malocclusion and enamel hypoplasia - all caused by RUNX2 mutation
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What are the late tooth defects?
Amelogensis imperfecta (enamel hypoplasia, hypomineralisation and hypomaturation), dentinogenesis imperfecta (soft dentine, bulbous amber crowns with short roots caused by DSPP mutation) and osteoperosis (increased alveolar bone density)
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What is Ehlers-Danlos syndrome?
Connective tissue disorder also resulting in small, fragile teeth with short roots - can't open mouth for long
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Card 2

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What occurs in metaphase?

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Chromasomes align at the equator (attached to kinetochore protein surrounding centromere)

Card 3

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What occurs in anaphase?

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Preview of the front of card 3

Card 4

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What occurs in telophase?

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Card 5

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What is cytokinesis?

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