Genome size increases as organisms become more complex. Amphibians and plants have genomes which are bigger than those of more recently evolved eucaryotes. BSL Lecture 1 – Procaryotic and eucaryotic genomes

Chromosome is ONE continuous strand of DNA without ends Human diploid DNA = 2meters Nucleus is mm. It is efficiently packaged! BSL Lecture 1 – Procaryotic and eucaryotic genomes

DNA packaging is studied by cleaving DNA with nucleases (DNAase1, micrococcocal nuclease) A ladder of fragments is seen, indicating that the DNA is being cut at discrete, regular intervals of about 200bp Nuclease cuts DNA at unprotected regions i.e. – those that are “naked” and do not have proteins associated with them BSL Lecture 1 – Procaryotic and eucaryotic genomes

EM of chromatin show the “beads On a string structure” Each bead is a barrel shaped nucleosome made up of 8 histone protein subunits H3,4,2A,2B. Linker histones may prevent coiled DNA from detaching from the nucleosome. 1 st Level of packing BSL Lecture 1 – Procaryotic and eucaryotic genomes

2 nd level of packing in which the nucleosomes condense into a helix with 6 nucleosomes per turn – the 30nm solenoid BSL Lecture 1 – Procaryotic and eucaryotic genomes

DNA + Histones = Nucleosome 6 nucleosomes = Solenoid Chromatin fibre Chromosomes. BSL Lecture 1 – Procaryotic and eucaryotic genomes

Chromatin structure has to be “opened up” to allow gene transcription, so that controlling proteins repressors / activators can bind to the gene promoter and modulate transcription Gene transcription relies on controlling proteins recognising specific sequences on the promoters and binding to them These controlling proteins cannot bind when DNA is in the chromatin form i.e. already associated with proteins which mask binding sites. BSL Lecture 1 – Procaryotic and eucaryotic genomes

Chicken erythroblasts at 14 days synthesise globin, cultured MSB cells do not. Nuclei from both types Of cell were treated With DNase1 and DNA cleaved with BamH1 BSL Lecture 1 – Procaryotic and eucaryotic genomes

The Borg link their brains to a collective consciousness via a unique subspace frequency emitted by each drone. This collective consciousness is experienced by the Borg as "thousands“ of voices — they are collectively aware, but not aware of themselves as separate individuals. BSL Lecture 1 – Procaryotic and eucaryotic genomes Cultured cells are analogous to a borg drone which has been separated from the collective… they lack essential factors…