O

Fig. 9.4 The chemical composition of four bases found in DNA (After Gilmour and Sephton, 2003)

Fig. 9.5 The double helix of DNA. The bases can only associate in pairs: A-T and G-C. This property ensures identical replication of the double helix (After Gilmour and Sephton, 2003)

9 The Search for Life in Planetary Systems side view

9 The Search for Life in Planetary Systems side view

I cytosine, C

O phosphate group Q sugar

I cytosine, C

O phosphate group Q sugar

Another nucleic acid also plays an essential part: ribonucleic acid (RNA). RNA is similar to DNA, with a few differences: the sugar it contains is ribose, and not deoxyribose, and the base uracil replaces thymine.

RNA plays the role of transmitting the information contained within DNA. The transmission takes place as follows: the DNA unwinds its two chains and these, instead of reproducing themselves identically, use uracil instead of thymine to create a chain of RNA. The latter then separates from the original DNA to transmit its own version of the DNA sequence to another location.

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