1. How big is DNA?
© 2016 Paul Billiet ODWS

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

3. 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

4. E. coli chromosome
replicating
© 2016 Paul Billiet ODWS

5. 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

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

8. 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
21 000 23
Paris japonica ? 40

9. 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 = Mbp
3 billion base pairs x 0.3nm = 900 million nm = 0.9m
© 2016 Paul Billiet ODWS