Explain its normal role and why scientists would regard it as the guardian of the genome

p53  or  Tumor protein (TP53 ) is the Guardian of  genome. located on locus 17p13.1  on chromosomes

It is  the gene that regulates  the protein that codes for process of cell cycle of ( mitosis and meiosis)' and cell death therefore suppresses the  uncontrollable   cells  growth which can  lead to tumor.

TP53 has relatively high molecular mass   of 53 kilodalton fractions in the cell ; this characteristics together with the ability to  conserve cell cycle stability  in  multicellular  organism  by stopping   mutation of  genetic materials by suppressing tumor  made it to be called the Guardian of genome.

ROLES

→ p53 functions by arresting the growth of cells to stop uncontrolled growth.

←it also  repair damage DNA to guide against mutation, by activation of protein involved in DNA  repair.

and  

←Promotes death of the cells (Apoptosis,) so that damaged or altered DNA would  not be transcript and translated  in the cell.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme