Final answer:
The amount of DNA per cell increases due to replication before cell division and decreases over time as telomeres shorten with each division, eventually leading to the cessation of cell division.
Step-by-step explanation:
The DNA per cell trend increases when cells are preparing to divide, where each cell will replicate its DNA, doubling the amount of DNA it contains. This is important because during cell division, each new daughter cell needs an exact copy of the parental DNA. However, the DNA amount decreases over time due to structures called telomeres, which are repetitive nucleotide sequences at the ends of chromosomes that shorten each time a cell divides, eventually causing the cell to stop dividing or die.
Cells are genetically programmed to divide only a certain number of times, and each round of replication carries a risk of DNA damage and mutations. Over time, as mutations accumulate, cells may reach a point where they can no longer divide effectively. Furthermore, the presence of telomerase is essential for maintaining the telomeres. Without sufficient telomerase activity, telomeres become too short, which can also halt cell division or lead to cell death.
The DNA per cell trend increases and then decreases in a repeating pattern because of the process of cell division. During cell division, the DNA in a dividing cell must be copied through replication. This replication process involves the synthesis of a new complementary DNA chain using each chain of the double helix as a template.
As cells continue to divide, the telomeres at the ends of the chromosomes become shorter. Telomeres have repetitive sequences that protect the genes from getting deleted. In humans, a six base pair sequence, TTAGGG, is repeated 100 to 1000 times. The discovery of the enzyme telomerase helped in understanding how chromosome ends are maintained, as it adds complementary bases to the RNA template at the end of the chromosome.