A CASE FOR EVOLUTİONARY THİNKİNG: UNDERSTANDİNG HIV

Evolution unifies the biological sciences by serving as a conceptual framework. When presented with any biological phenomenon,one can ask, "How did that evolve?" As common descent connects present-day organisms with past organisms, evolution allows us to place biology in a historical context. Three other principles that unite biology are moleculer biology (organisms are made of molecules), genetics (an organism's traits are inherited and encoded on genes) and naturalism (biological phenomena are due to natural, as opposed to supernatural, causes). Evolutionary biology tries to understand 2 issues;

• How populations change through time following modifications in their environment.
• How new species come into being.

Definition: Descent with modification, or change in the characteristics of populations over time. Currently defined as changes in allele frequencies over time.

How Does the Immune System React to HIV?

• Dendritic cells capture the virus and present bits of its proteins to naive helper T cells. Once activated, naive cells divide to produce effector helper T cells.
• Effector helper T cells stimulate B cells displaying the same bits of viral protein to mature into plasma cells, which make antibodies that bind and in some cases inactivate the virus. Effector helper T cells also help activate killer T cells, which destroy host cells infected with the virus.
• Most effector T cells are short lived, but a few become long-lived memory helper T cells.

How AZT blocks reverse transcription

HIV's reverse transcriptase enzyme uses nucleotides from the host cell to build a DNA strand complementary to the virus's RNA strand. AZT mimics a normal nucleotide well enough to fool reverse transcriptase, but lacks the attachment site for the next nucleotide in the chain.



FİGURE 1.1 shows what reverse transcriptase does. The enzyme uses the virus's RNA as a template to construct a complementary strand of viral DNA. Reverse transcriptase makes the DNA with building blocks-nucleotides-stolen from the host cell.