Pairs of coloured letters c and g , as well as a and t on the bridge which are lit up at night in red and green represent cytosine , guanine , adenine and thymine , the four bases of DNA .
Pairs of coloured letters ( `` c '' and `` g '' , as well as `` a '' and `` t '' ) on the bridge which are lit up in red and green . They represent cytosine , guanine , adenine and thymine , the four bases of DNA .