First off it would 'attack' the immune system, the virus would attach itself to healthy cells, then continue to move through your body - your bodies first response is always going to be your immune system - it's going to fight the foreign visitor aka the virus. The virus will then move down towards your respiratory system. And given the symptoms that you may experience whilst your body is fighting the virus is how it may work with other systems (these two being the main ones) for example; diarrhea, nausea/vomiting, headaches, sore throat, etc. And it will also depend on the patients history. Hope this helps.
A purine is a nitrogenous base found in nucleic acids, and contains a 6-membered pyrimidine ring fused to the 5-membered imidazole ring. The most common examples of purine bases are adenine and guanine.
Thus, the nitrogen base pictured is adenine, and the nucleotide considered is a purine
