Chloroplast DNA (ctDNA) The circular, superhelical double-strand DNA of the chloroplasts. The structure is two inverted repeats separating one small single copy and one large single copy. This structure is very similar in most plants, the size varies between 120 and 160 kb. The chloroplast genome consists of about 100 protein coding genes, 30 tRNAs genes and 4 rRNAs genes. Most chloroplast proteins are coded for by the nuclear genome, synthesised in the cytoplasm and transproted into the organelle.