Pre-Cell Division

• Each chromosome must be replicated; the two identical chromatids (replicates) are held together at the centromere, the chromatids must become supercoiled (from 30 nm thickness to 500 nm) and so form visible chromosomes
• Supercoiled chromosomes cannot perform their normal cell functions and so need to be in this state for as short a time as possible
• If the cell makes a mistake during DNA replication, it’s called a mutation and can happen around 50,000 to 500,000 times a day; most are repaired immediately by DNA polymerase, but occasionally they survive