Which event Mark's the beginning of dna replication​

Replication fork

The formation of replication fork marks the event of the beginning of DNA replication. In the cell, the DNA replication begins in the genome where DNA unwinds and produces new strands. This then results into replication forks that grow apart in the process of cell division.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.