13. Eukaryotic genome and regulation of gene expression.
Covers the organisation of the eukaryotic genome, from the non-coding majority of DNA and the unique, moderately repeated and highly repeated sequence classes to nucleolar organisers. It then explains how euchromatin and heterochromatin, including X-chromosome inactivation, affect transcription, followed by DNA methylation, histone modifications, and the stepwise assembly of the pre-initiation complex. The note closes with enhancers and silencers, homeobox and zinc finger DNA-binding motifs, and gene silencing by RNA interference. It includes a DNA sequence classification and worked examples of human satellite DNA units.
Topic 14 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 3 sections, about 630 words (4 min of reading), with 27 flashcards.
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Eukaryotic genome and regulation of gene expression.
CHROMATIN STRUCTURE AND TRANSCRIPTION
REGULATION OF GENE EXPRESSION
Eukaryotic genome and regulation of gene expression.
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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