DNA in Space

Scientists have evidence that some building blocks of DNA, the molecule that carries the genetic instructions for life, found in meteorites were most likely to have been created in space.
The DNA building blocks present in the meteorites are called nucleobases or nucleotide bases, a group of nitrogen-based molecules that are required in the formation of nucleotides, and nucleotides are the molecules that make up DNA. The primary nucleobases in DNA are cytosine, guanine, adenine and thymine.

For the first time, we have three lines of evidence that together give us confidence these DNA building blocks found in meteorites actually were created in space:

1. In two of the meteorites, trace amounts of three molecules related to nucleobases: purine, 2,6-diaminopurine, and 6,8-diaminopurine; were discovered for the first time. 2,6-diaminopurine, and 6,8-diaminopurine are almost never used in biology so these can't be due to contamination from terrestrial sources.
2. The amounts of the two nucleobases adenine and guanine found in DNA, plus hypoxanthine and xanthine which are similar to the nucleobases but not found in DNA, that were found in terrestrial ice samples from near the Antarctic meteorites were much lower, parts per trillion, than in the meteorites, where they were generally present at several parts per billion. This strongly suggests that terrestrial contamination was not responsible for the presence of these molecules in the meteorites.
3. The adenine, guanine, hypoxanthine and xanthine were produced in a completely non-biological reaction. In the lab, these same molecules were generated in non-biological chemical reactions containing hydrogen cyanide, ammonia, and water. This provides a plausible mechanism for their synthesis in the asteroid parent bodies, and supports the notion that they are extraterrestrial

Reference
NASA (2011, August 9). DNA building blocks can be made in space, NASA evidence suggests. ScienceDaily. Retrieved August 11, 2011, from http://www.sciencedaily.com­ /releases/2011/08/110808220659.htm

Further Reading
DNA
Functional Groups

Study Questions

1. What does the abbreviation DNA stand for?
2. Give the accepted abbreviations for each of the following nucleobases:
   • adenine
   • guanine
   • cytosine
   • thymine
3. Draw a structural formula for each of the nucleobases above.
4. On the structural formulae above, circle the functional groups present.
   
5. Below is the structural formula for hypoxanthine:
   
   Which nucleobase is it most similar to? Explain your answer.
6. Guanine can form 3 hydrogen bonds with cytosine. How many hydrogen bonds could be formed between hypoxanthine cytosine. Use a diagram to explain your answer.
7. The structure of 2,6-diaminopurine is shown below:
   
   Circle the two amine functional groups.
8. What functional groups would be found in a molecule of 6,8-diaminopurine?
9. Give the molecular formula for each of the following molecules:
   • hydrogen cyanide
   • ammonia
   • water
10. Why do you think scientists would try to make the nucleobases out of hydrogen cyanide, ammonia, and water in the laboratory?