Suppose you could measure the amount of DNA within a single cell...?

Question

Let's say a cell in the G1 stage of the cell cycle contains one unit of DNA. Discuss how this quantity of DNA changes as the cell goes through the cell cycle and the phases of mitosis until it reenters a G1 stage. Be sure to identify the cellular processes that result in any changes in the quantities of DNA within the cell.

Homeowrk help!! I am no good with Biology, and I really don't understand this entire section! Help!

Answer 1

In the G1 phase, often called the G0/G1 phase, the cell has a normal DNA complement, exactly the amount of DNA that cells of that species normally have when they are not undergoing cell division. This is sometimes called the "resting phase", however the cell is at rest only from the viewpoint of replication. It may be carrying on thousands of other biochemical processes.

At some point the cell receives a signal that it is going to divide into two new cells. Shortly thereafter the cell enters S-phase (which means synthesis phase). The DNA complement of the cell begins to increase as each base pair of the original DNA replicates itself. This process continues until all the base pairs have replicated themselves, so at the end of S-phase the DNA complement is exactly twice what it was during G0/G1 phase. The cell is then said to be in G2 phase. This phase is sometimes combined with the mitosis phase and referred to as G2/M phase.

During most of this phase the amount of DNA remains constant, but its configuration changes. The chromatin threads contract into chromosomes (prophase of mitosis), and line up across the equator of the cell (metaphase of mitosis). Then, in the anaphase period of mitosis the pairs of identical chromosomes separate and move into opposite halves of the cell. And finally, in telophase of mitosis, a new cell membrane forms, separating the old cell into two new cells, each having exactly the same DNA configuration that the original cell had before the whole process began. These two new cells are then in G0/G1 phase, completing the cycle.