Enzyme inhibitors are often used as antiretroviral drugs in the treatment of HIV. Describe the structure of an enzyme and suggest how antiretroviral drugs would work in the treatment of HIV.

Enzymes are globular (globe-like) proteins, meaning they exist as 3D structures. As a protein, it is composed of a chain of amino acids which is able to fold into secondary structures such as alpha-helices and beta-pleated sheets, which subsequently interact and determine the tertiary (3D) structure of the protein. They are arranged so that the majority of residues on the outside of the protein are hydrophilic [charged, polar] (water-loving) and that the core of the protein contains hydrophobic residues. Enzymes possess active sites through which they can interact with substrates. These active sites contain specific amino acid residues which are able to catalyse reactions of the substrate, whether they be anabolic (synthesis) or catabolic (breakdown). A good suggestion as to how anti-retroviral drugs could be used to treat HIV would be as enzyme inhibitors [small molecules able to block/allosterically modify the active site of an enyme]. Certain enzymes such as integrase and reverse transcripitase are key to the integration of viral DNA into the host cell genome and for the replication of viral DNA, respectively. Inhibition of integrase would mean that the viral DNA could not be integrated into the host genome and would limit the production of viral DNA as a result. Inhibition of reverse transcriptase would mean that viral DNA could not be produced from viral RNA. Both of these actions would reduce the ability of the infected cell to replicate and the number of T-helper cells killed by HIV infection would be reduced [assumed knowledge that HIV infects T-helper cells via its gp-120 glycoprotein which interacts with the CD4 receptor of T-helper cells].