Questions

The two DNA strands are called polynucleotidesbecause they are composed of simpler monomer units called nucleotides. Eachnucleotideis composed of one of four nitrogen-containingnucleobases (cytosine, guanine, adenine or thymine), a sugar called deoxyribose, and a phosphate group.

AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus, which have an envelope enclosing the RNA genome. Transmission of HIV-infection generally occurs by (a) sexual contact with infected person, (b) by transfusion of contaminated blood and blood products, (c) by sharing infected needles as in the case of intravenous drug abusers and (d) from infected mother to her child through placenta.