The cell cycle consists of stages involving the growth and division of eukaryotic cells. If there is a disruption in this process it could lead to cancer, which is when the cell cycle goes unchecked and results in tumors. The first stage of the cell cycle, interphase, which includes G1, S Phase, and G2, is where cells spend about 90% of their life. G1, or Gap 1, is when the cell grows, new proteins are made, organelles are developed, and DNA is checked for damage. Then, S Phase, or synthesis, is the stage when DNA replication occurs, making exact copies of genes. This happens when enzymes separate DNA to form two strands and nucleotides are added to the strands according to the base pairing rules of adenine with thymine and guanine with cytosine.
Helicase is the enzyme responsible for breaking down hydrogen bonds that hold the nucleotide bases together and DNA polymerase is the enzyme that synthesizes the DNA by adding the nucleotide bases and checking for errors. After S Phase, G2, or Gap 2, consists of the cell growing and preparing for mitosis by developing structures needed for cell division. Once the cell has been through interphase it can enter mitosis which is when the nucleus divides and results in two identical daughter cells. Mitosis consists of prophase, metaphase, anaphase, and telophase.
First, prophase is when the DNA compresses into chromosomes made of two sister chromatids connected at a centromere. Also, spindle fibers form from the centrioles causing the centrioles to move to opposite sides of the cell. Next, in metaphase, the nuclear envelope has degraded and the centromeres attach to spindle fibers so that chromosomes line up at the middle of the cell. Anaphase comes after and consists of sister chromatids separating at the centromeres and moving to opposite ends of the spindle fiber so the cell begins to lengthen. Then, telophase is when chromosomes uncoil to form chromatin, nuclear envelopes form around the chromatin, and spindle fiber deteriorates. The final stage of the cell cycle is cytokinesis, when cytoplasm pinches and divides to form two daughter cells.Cancer ConnectionIn normal cells, the cell grows and divides in a process known as the cell cycle, forming two identical daughter cells. In cancerous cells, however, the cell cycle goes unchecked and cells begin to grow uncontrollably which forms tumors.
At first tumors are benign and do not spread, but as they grow they become malignant and spread to healthy tissue. Cancer may then begin to spread through the bloodstream to other organs, and the more it spreads the more difficult it is to treat. One treatment is chemotherapy, which is strong drugs that target cells dividing very quickly, but it can affect healthy cells as well which causes it to have many side effects. When normal cells stop reproducing and start specializing they enter the G0 phase, and therefore cancer cells skip this phase and never enter it.