Cellular junctions: by connecting cells to their neighbors
Receptors: allowing cells to respond to chemical messages
concentration of the enzyme, concentration of the substrate, and temperature. However there are more than three. A lock and key analogy is used when explaining the specific action of an enzyme with a single substrate.
Not sure what "new people" are. But, it could be possible from cloning (not possible yet) or just from parent's DNA created to be your own DNA. It is just natural for us to be young, then as grow older we age.
~Hoped this helped.
~Bob Ross®