Topic 3C.3 Controlling Gene Expression

transcription factor

protein that binds to the DNA in the nucleus and affects the process of transcribing DNA into RNA

promoter sequence

specific region on the DNA to which transcription factors bind to stimulate transcription

enhancer sequence

specific region of DNA to which transcription factors bind and regulate the activity of the DNA by changing the structure of the chromatin

exons

segments of a DNA or RNA molecule containing information coding for a protein or peptide sequence

introns

segments of a DNA or RNA molecule containing information which does not code for a protein or peptide sequence

pre-mRNA

mRNA that is transcribed directly from the DNA before it has been modified

spliceosomes

enzyme complexes that act on pre-mRNA, joining exons together after the removal of introns

DNA methylation

methylation of DNA (addition of a methyl -CH₃ group) to a cytosine in the DNA molecule next to a guanine in the DNA chain and prevents the transcription of a gene

DNA demethylation

removal of the methyl group from methylated DNA enabling genes to become active so they can be transcribed

heterochromatin

densely supercoiled and condensed chromatin where the genes are not available to be copied to make proteins

histone acetylation

addition of an acetyl group (COCH₃) to one of the lysines in the histone structure, which opens up the structure and activates the chromatin, allowing genes in that area to be transcribed

histone methylation

addition of a methyl group (CH₃) to a lysine in the histone, methylation may cause inactivation or activation of the region of DNA, depending on the position of the lysine

non-coding RNA (ncRNA)

98% of the RNA, which does not code for proteins but affects the transcription of the DNA code, modifies the chromatin structure or modifies the products of transcription