1. Organization of the nuclear genome. Structure and function of genes. Expression of genetic information. Metabolism of mRNA
Covers how the nuclear genome is organised, from DNA wrapped around histones into nucleosomes and chromatin through to euchromatin and heterochromatin, then the functional elements of the genome. Goes on to define a gene and its components, outline transcription and the three steps of mRNA processing, and trace the cytoplasmic life of mRNA including decay pathways. Ends with a short section on clinical links such as splicing defects, altered mRNA decay and epigenetic silencing.
Topic 1 of 65 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 5 sections, about 546 words (4 min of reading), with 15 flashcards.
In this note
Organization of the Nuclear Genome, Structure and Function of Genes, Expression of Genetic Information, Metabolism of mRNA
I. Organization of the Nuclear Genome
II. Structure and Function of Genes
III. Expression of Genetic Information
IV. Metabolism of mRNA
I. Organization of the Nuclear Genome
The human nuclear genome is the complete set of DNA sequences located inside the cell nucleus. It contains around 3.2 billion base pairs, arranged into 46 chromosomes (22 pairs of autosomes and 2 sex chromosomes).
Levels of DNA packaging
At the most basic level, DNA is wrapped around histone proteins to form nucleosomes (147 bp of DNA + histone octamer).
These nucleosomes fold into a 30 nm chromatin fiber.
Chromatin can be of two main types:
Euchromatin → less condensed, transcriptionally active, contains most genes.
Heterochromatin → tightly packed, transcriptionally silent, usually repetitive DNA (e.g., centromeres, telomeres).
Further compaction leads to the chromosome structure seen during metaphase.
Functional elements of the genome
Exons → coding DNA, only ~1.5% of genome.
Introns → non-coding segments within genes, removed by splicing.
Regulatory DNA → promoters, enhancers, silencers that control expression.
