P53 is a tumor protein. It is often referred to as the "guardian of the genome". It can stop the cell from growing, repairs DNA and controls cell death, which is called apoptosis. As the cell is cycle goes on, p53 stops the growth of the cell when there is an error or damage in the DNA. This action prevents the defective cell from replicating. The p53 then signals the production of proteins that repair DNA. If the DNA is not fixable, it programs apoptisis.
If by some chance that the p53 gene are mutated, then it cannot do those functions, which may result in cancer or the uncontrolled replication of defective cells.
Though some cells are bigger than others, they do not scale with size. For example if you look at skin cells on a dog they would be similar in size to a skin cell from a human. When an animal or species is bigger it is usually just made from more cells.
All proteins are composed of amino acids. Each amino acid in a protein is linked by chemical bonds. Enzymes are composed of chains of amino acids. Enzymes are a type proteins that turn a cell into a highly developed miniature factory carrying out chemical reactions very fast.
