Final answer:
Antigens are not required to generate a cDNA library; they are part of the immune system and unrelated to the process of constructing a library that represents the expressed genes in an organism's tissues.
Step-by-step explanation:
To generate a cDNA library, the following components are generally required: mRNA, reverse transcriptase, restriction enzymes, and a vector. Among the options provided, the component that is not required to generate a cDNA library is antigens.
The purpose of a cDNA library is to focus on the expressed genes of an organism or tissue, represented by its mRNA. The mRNA is used as a template by reverse transcriptase to make cDNA, which is double-stranded by DNA polymerase and then ligated into a vector, such as a plasmid or bacteriophage.
An antigen is a molecule or molecular structure that may be recognized by the immune system, specifically by antibodies, B cells, or T cells. It is not involved in the process of creating a cDNA library, which is focused on the genetic expression rather than immune response.