describe structure of introns
non-coding DNA sequences, interrupt gene-coding sequence >
pre-mRNA undergoes RNA splicing, introns excised, exons spliced together, forms mature mRNA molecule
describe function of introns
enable alternative RNA splicing & subsequent production of multiple polypeptides from 1 gene
describe structure of centromeres
constricted region where 2 sister chromatids joined, spindle fibres attach to centromere during nuclear division >
found anywhere along length of chromosome but position is characteristic for specific chromosome >
centromeric region DNA include non-coding DNA(series of tandem repeats, heavily methylated) >
consist of specific DNA sequences where centromere-associated proteins bind, forms kinetochore
describe function of centromeres
important in ensuring proper nuclear division(mitosis/meiosis) by
holding sister chromatids together >
site where kinetochore assembles, spindle fibres attach; allows proper alignment, segregation of HC/SC to opp poles of cell
describe structure of telomeres
nucleoprotein complexes(telomeric DNA bound by telomere-specific binding proteins) found @ both ends of linear chromosome >
telomeric DNA non-coding, made up of series of tandem repeats >
have single-stranded region of DNA @ 3' ends; 3' end of telomeric DNA w/ aid of telomere-specific binding proteins, bend back on itself to form physical loop(t-loop) @ telomere
describe function of telomeres
ensures genes not lost/eroded due to end replication problem w/ each round of DNA replication, prevents loss of important genetic info >
telomeres protect, stabilise terminal ends of chromosomes; physical loop confers stability to linear chromosomes by preventing fusion of ss-end of 1 chromosome to ss-end of another via CBP >
telomeres protect, stabilise terminal ends of chromosomes; telomeric DNA binded to telomere-specific binding proteins, protects chromosomal ends from degradation by exonucleases >
critically short telomeres trigger apoptosis >
allow own extension by providing attachment site for correct positioning of telomerase
describe structure of promoters
specific segment of non-coding DNA, located upstream of transcription start site of gene >
includes core promoter, upstream promoter >
core promoter r&b by GTF, RNA pol; forms TIC, initiates transcription @ start site
describe function of promoters
binding site for GTF & RNA pol >
GTF r&b to TATA box of core promoter, recruits RNA pol to r&b to core promoter, forms TIC & initiates transcription @ start site; allows basal level transcription of gene
describe structure of enhancers
+ve regulatory elements, located far upstream/downstream from transcription start site
describe function of enhancers
binding site for activators(TF) >
binding of activators to enhancers accelerates assembly of TIC @ promoter, increases rate of transcription of gene
describe structure of silencers
-ve regulatory elements, located further upstream/downstream from transcription start site
describe function of silencers
binding site for repressors(TF) >
binding of repressors to silencers prevents assembly of TIC @ promoter, inhibits/decreases rate of transcription of gene