the human body blueprint The Replication of Cells

Author: Sanalan Kumar Editors: Benetta Wang and Saniya Chaudhari

G1, S, G2, and M are the four phases of the cell cycle Cells in the G1 stage tend to grow in size, generate protein, and create RNA. This is the most important phase since it prepares the cells for the following phases and ensures that they perform properly. The S stage occurs during the interphase when the cell duplicates its chromosomes by DNA synthesis The G2 phase encourages cells to grow larger and create more proteins In the G2 phase, there is also a checkpoint to see if the cell is ready to divide, which leads to the Mitosis stage (M). Mitosis causes cells to split into daughter cells, which perform a cell's life role. This is necessary because multicellular organisms must expand and repair themselves. After mitosis, some cells go into a resting phase, which is also known as G0 G0 is when the cell is neither dividing or preparing to divide, it is usually checking or maintaining its proper functions But this is not forever, as the cells can “wake up” and start to divide again, which is the case in stem cells. This is why stem cells are gathered from umbilical cords which are donated for research, as they can become any type of cell. Yet, nerve and heart cells never exit the G0 phase as they can never divide after reaching maturity, this is why if you suffer severe burns to a limb and lose your nerve endings, you can never feel anything in that limb ever again. Some cells also stop developing at the G1 phase. This is called “growth arrest” and it occurs when a cell’s DNA is damaged, after which it will repair the damaged DNA Growth arrest occurs so that the damaged DNA does not replicate itself uncontrollably in the S phase, which will affect the other phases as well. There is also the instance where growth arrest can occur at the G2 phase, right before Mitosis, which is crucial as you do not want 2 new daughter cells that may be defective and start dividing out of control Thankfully, there is a 3rd checkpoint where if a cell has an unrepairable error in its DNA, it will undergo apoptosis, meaning that it self destructs The remains of the dead cell will be consumed by a macrophage, which is a type of white blood cell. This is good news as if these damaged cells did not undergo apoptosis, they would have started to replicate uncontrollably This is the case for many malignant cancer tumours Apoptosis protects the body through removing such damaged cells, as they may affect the developing human embryo and cause birth defects.