NEL Molecular Genetics 661
Figure 1
DNA sequences are represented by the letters A, T, C, and G.
Exploration The Size of the Genome
All organisms, no matter how simple they may seem to us,
require DNA in each cell to encode the instructions necessary
to live and reproduce. The total DNA of an organism is referred
to as its genome. In bacteria, the genomic DNA is circular,
accounts for 2 % to 3 % of the cell’s mass, and occupies about
10 % of its volume. In this activity, you will make a model of an
Escherichia colicell that will be 10 000 times bigger than actual
size. You will also gain an appreciation for how compactly DNA
is packed within a cell.
Materials:2 cm gelatin capsule, 10 m of white thread, 10 m of
coloured thread- Try to construct the bacterium by placing the long lengths of
thread inside the gelatin capsule. Good luck! It’s not easy!
(a) Why does it take two lengths of thread to represent the
chromosome?
(b) Is the thread that you tried to place in the capsule too
thick to represent the actual thickness of the DNA?
(What percentage of bacterial cell volume does your
thread fill, and what is the actual volume that the DNA
occupies in the bacteria?)
(c) If the human genome is 1000 times bigger than the E. coli
genome, how many metres of thread would it take to
represent the human genome?
(d) What size container would you need to hold the thread
representing the human genome?