Santa Cruz Biotechnology offers an expansive library of transfected lysates that overexpress cell cycle proteins. The cell cycle, or cell-division cycle (CDC), refers to the series of events in a eukaryotic cell that occur between one cell division and the next. It consists of four distinct phases: G1, where the cell grows and prepares to duplicate its DNA; S, in which the cell duplicates its DNA; G2, where cell continues with growth and metabolism in preparation for mitosis; and M, in which the cell undergoes mitosis, segregating its chromosomes so that both daughter cells receive a total complement of 2N. Phosphorylation events regulate the cell cycle, which are ordered and directional such that it is impossible to "reverse" the cycle. There are two main classes of proteins that determine the progress through the cell cycle: cyclins and cyclin-dependent kinases (Cdks), but there are many other proteins involved. Transfected lysates that express cell cycle proteins offer a reliable means to evaluate antibody quality and serve as excellent positive controls for experiments involving antibodies.