How big is DNA? © 2016 Paul Billiet ODWS

DNA is a big molecule Ruptured viral particle (bacteriophage) X95 000 DNA about 1.7µm © 2016 Paul Billiet ODWS

How do you measure a piece of DNA? John Cairns 1963 Inhibit thymine synthesis in the cells Add 3H-thymidine and incubate Burst cells - very gently Remove surplus 3H-thymidine Filter to trap DNA Digest proteins using a protease Dry filter with DNA attached then autoradiograph for 1-4 months © 2016 Paul Billiet ODWS

E. coli chromosome replicating © 2016 Paul Billiet ODWS

The Genome The total DNA found in a single copy of its chromosomes (haploid set) Known as the C-value b/c cells of the same species have a constant amount of DNA Only a small proportion codes for proteins e.g. Humans 1.5% We do not know what the rest does. © 2016 Paul Billiet ODWS

Measuring the genome today Densitometry Flow cytometry Nuclei of a newt cells Feulgen stain Human melanoma cells

Some DNA molecules Organism Genome / Mbp Genes n T2 phage (virus) 0.164 300 Prokaryote Escherichia coli 4.6 4300 1 Eukaryotes Saccharomyces cerevisiae 12.5 5770 16 Drosophila melanogaster 120.0 32 122 4 Homo sapiens 3 000.0 21 000 23 Paris japonica 149 000.0 ? 40

Calculating the physical length of DNA in a genome 1 Mbp = base pairs x 106 The distance between two base pairs = 0.3nm Example Human C-value = 3 000 Mbp 3 billion base pairs x 0.3nm = 900 million nm = 0.9m © 2016 Paul Billiet ODWS