11.Transcription control in eukaryotes. Levels of gene expression regulation.
Covers how eukaryotic DNA is organised, from unique and repeated sequence classes to satellite DNA and nucleolar organisers, then how euchromatin and heterochromatin, including X-chromosome inactivation, affect expression. It goes on to DNA methylation, histone modifications, the steps of transcription initiation with the pre-initiation complex, enhancers and silencers, developmental regulatory cascades with homeobox genes, DNA-binding motifs, and finally gene silencing and RNA interference. Human satellite DNA examples and the Barr and Davidson body structures are named.
Topic 11 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 10 sections, about 630 words (5 min of reading), with 27 flashcards.
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Transcription control in eukaryotes. Levels of gene expression regulation.
Eukaryotic DNA Organization
Types of DNA Sequences
Chromatin Structure and Transcription
Regulation of Gene Expression
Transcription Initiation
Enhancers and Silencers
Regulatory Cascades and Development
DNA Binding Motifs
Gene Silencing
Eukaryotic DNA Organization
Most of the DNA in eukaryotic cells is stored inside the nucleus.
Chromatin is a mix of DNA and proteins that helps organize and compact the genome.
Around 90 percent of eukaryotic DNA is non-coding, meaning it does not directly code for proteins.
Types of DNA Sequences
Unique sequences
Found in only one or two copies
Include nearly all structural and regulatory genes
Moderately repeated DNA
Found in tens to thousands of copies
Includes histone and rRNA genes
Some have regulatory roles, but many have unknown functions
Highly repeated DNA (Satellite DNA)
Short sequences repeated many times in tandem
Found in centromeres and telomeres
Mostly structural; function often unclear
Examples in humans:
Alpha (alphoid) DNA: 171 bp units, present on all chromosomes
Beta satellite DNA: 68 bp, found on certain centromeres
Satellite 1, 2, 3: 5 to 48 bp, found in heterochromatin and centromeres
Nucleolar organizers
Chromosome regions that contain rRNA gene repeats
Located on the short arms of chromosomes 13, 14, 15, 21, and 22
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