Flashcards
Chromosome Biology
Flashcards do conjunto (22)
- 1Eukaryotic chromosomesPartitioned sections of genome, composed of DNA and proteins as chromatin
Contains functional element to ensure DNA efficiently replicated
DNA replication origins, telomeres to maintain integrity, centromere and kinetochore to facilitate chromosome separation
Heterochromatin = tightly packed, inaccessible to TF (junk)
Euchromatin = looser packaging (genes) - 2Human KaryotypeNumber and appearance of chromosomes
Staining techniques generate maps on banding pattern
G-bands through staining with Giemsa dye after treating mitotic chromosomes with protease
Dark staining contain DNA with low G+C and replicate in cell cycle
R bands contain G+C rich DNA and replicate early
Normal pattern of G and R banding gives reverence map- can help track disease - 3Translocationswapping bits of genetic information between chromosomes or within chromosomes
Visible selections of dNA
Characteristic binding patterns allow these to be visualised - 4Replication originsBacterial much simpler - one origin
Must have tight control - used once per cycle
Eukaryotic have multiple replication sites
Autonomously replicating sequences bind complex set of origin recognition complex proteins that control initiation
Many proteins in origins conserved throughout eukaryotes, though those in S.cerevisiae not found in other eukaryotic origins
More potential origins than used in S phase and which used depends on development
As cell cycle lengthens, number of origins declines- developmental modulation of origin activity
Different parts of chromosome replicated at different times - 5TelomeresOkazaki fragments use RNA primers - linear hence end of every cycle, more terminal DNA lost (~100bp)
Telomeres protect genetic integrity- arrays of short G rich repeats
Repeats provide multiple binding sites for several DNA sequence specific binding proteins, and formation T loop which tucks DNA end away
When too short, cell death or senescence triggered - 6TelomeraseTelomeres limit cell life span - some needed for many replications
Telomerase extend end by adding more G repeats on 3'-OH group of overhang (single strand)
Acts as template for lagging strand synthesis- buffer zone maintained at chromosomal end
Telomerase ribonucleoprotein - RNA dependent DNA polymerase and tops up ends in immortal cells - unicellular eukaryotes/ germ line/ stem cells/ unregulated in cancer cells - 7centromeresChromosomes need to be separated after DNA replication
Chromosomes coordinated with mitotic spindle via centromeres - specialised structures on each chromosome
Large numbers of proteins assemble e.g. CENP-A to form kinetochore
Kinetochore structure through which chromosomes interact with microtubules of mitotic spindle
Kinetochore mediated link allows sister chromatids to be pulled to opposite poles - 8Centromere characterisationbudding yeast - 125bp centromere with AT rich - very small with strict DNA sequence is unusual in eukaryotes
YAC don't function as chromosomes outside budding yeast cells, but good at cloning DNA with large repeats
Fission yeast - larger and more complex centromeres- error image on central core- large and repetitive DNA nature different from budding yeast - 9Vertebrate centromeresConsist of much repetitive sequence
Long tandem arrays
Human artificial chromosomes through introducing large stretches of cloned alpha satellite DNA into cultured human cells
Drosophila centromeres identified by selecting mitotically stable mini chromosomes and contain many transposon relics - 10Transposable elements - LINEsRepetitive DNA categories into various classes, dominated by types of transposable element and deletes derivatives - copies throughout human genome
LINEs ~20% genome. Retrotransposons ~6kb long. Intact have 2 ORF encoding RNA binding protein and protein in reverse transcriptase and endonuclease activities
Cellular RNA polymerase can transcribe full-length LINE elements in genome and transcript generated has 2 functions - translated alongside other mRNAs and proteins produced remain associated with LINE RNA (ribonucleoprotein complex)
RNP enters nucleus and LINE RNA template for own reverse transcriptase, generating DNA copy of LINE RNA which is randomly inserted back to genome
Most - 11SINEsSmall repeats transcribed by RNA polymerase III using LINE encoded enzymes to produce DNA copy of SINE RNA- inserted into genome
Most abundant are All repeats
LINE reversetranscriptase can mistakenly use mRNA originating from protein coding gene- cDNA inserted into genome as processed pseudogene (DNA copy of parental gene's mRNA - 12LTSResemble retrovirus
Encode reverse transcriptase but few active in human genome - 13Inactive relicsElements that move via DNA based cut and paste mechanism using DNA transposon encoded transposes protein- ~3% genome, no evidence active in past 40 million years
All of these - 14Simple Sequence RepeatsSatellite DNAs - tandem repeated non-coding DNAs ~6% genome
Microsatellites, mini satellites and satellite based in size of monomer and length of tandem
Repeated sequences written in repeated form e.g. ATATAT = (AT)3
Alpha-satellite DNA at human centromeres satellite DNA with clear function
0.1~20 kb arrant (TTAGGG)n forming telomeres are minisatellite - 15PolymorphicMost SSR are polymorphic - multiple alleles at each repeat locus
Means likely different alleles one acc chromosome hence tracking regions of genome by SSR is possible; and individuals likely different spectrum of SSR if different loci compares
Polymorphic useful for mapping diseases, DNA fingerprinting
Microsatellites can occur in genes - expansion of repeats disrupts expression and causes disease - 16Microsatellites and DNA fingerprintingDNA samples from individuals differ by 1 base per thousand hence 6 million differences in whole sequence. Identical twins similar, more closely related people more similar
Advantage of polymorphisms to fingerprint
Specific primers bind to unique polymorphic SSR, use in PCR to amplify
Different length SSR hence individual produce 2 fragments in PCR
Resolve on polyacrylamide gel
Each polymorphism shared by ~20% people, but look at loci and unique combinations of several polymorphisms allows use for identification - 17SGM+ profileEach pair of peaks represents genotype at locus on each chromosome
- 18Segmental duplicationsLarge blocks of genomic sequence sharing high degree of sequence identity that occur in 2 or more copies per haploid gene (though not loads)- 5% human genome
Within and between chromosomes
Species specific
Y chromosome has v.high density - 19Consequences of low copy repeatsevolution of new genes and functions
Small, compact gene duplication formed multigenerational families - provide increased level of gene productivity where needed
e.g. histone genes- duplication forms more as many needed every time DNA replicates - 20Gene duplicationDriving force behind generation of diversity- duplicated the freed from selection so can acquire new mutants and evolve new functions
Xq-linked Opsin formed red and greed opsin cluster- facilitate detection of larger spectrum of light, but near-identical gene duplication makes susceptible to rearrangement hence colourblindness - 21Global and Hox genesAlpha and beta globing duplicated in evolution and evolved different functions with specialised genes in embryo and foetus
Remnants fo evolutionary process seen in non-functional pseudogenes at both loci
Hox cluster encode proteins important in control of development
Set of related genes encoding proteins that regulate how sets of genes turned off and on - 22Gene numbersComplexity through increased sophistication in organisation and regulation of existing genes, not creating new genes
Unicellular e.g. simple eukaryotes or prokaryotes low gene numbers and densely packed hence rapid division as eliminated waste from genomes
Metazoans, genes more numerous and spaced out
Can compare genomic sequences for accurate annotation
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- Biology of Cells IA (Genetic Revolution) FlashCards sobre Chromosome Biology, criado por Alice Hathaway em 22-02-2019.
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- Alice Hathaway
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