The cell cycle allows living things to multiply, thrive, and heal wounds. There is a complicated process within the cycle.
There is one important activity that always happens in our body and may not be very conscious of us. Did you know that the cells inside us continue to grow. New cells are constantly popping up and there are cells that have to be sacrificed. This activity is called the term cell cycle.
Cell Cycle Definition
Simply put, a cell cycle is the life cycle of a cell. This cycle aims for the development and growth of the cell itself. The cell cycle begins with the division of a mother cell and ends with the formation of child cells (daughter cells) or the death of cells.
Cell Cycle History
In 2001, the three pioneers of cell biology: Leland Hartwell, Paul Nurse and Tim Hunt were awarded the Nobel Prize in Physiology of Medicine.
The prize was awarded for their success in discovering the regulatory mechanisms of cell cycles using a combination of genetic and molecular biology approaches. Helped by other researchers, they found that cyclin proteins and cyclin dependent kinases (CDKs) carry cells from a phase in the cell cycle into the next phase.
Before 1950, biologists and cell pathologists knew only 2 phases in the cell cycle that could be seen with a microscope, namely: Interphase and mitosis. Using long beans, Vicia faba, Howard and Pelc in 1953 said that interphase can be divided into 3 phases.
In late 1960, Hartwell recognized the genetic power to separate cell cycles. Through his research using yeast cells, he successfully identified 100 genes directly involved in the regulation of cell cycles, called CDC genes (cell division cycles). One of them is: CDC 28, which is a CDK that controls the first stage of G1 phase of the cell cycle and is therefore also called start.
In addition, Hartwell also found 3 checkpoint locations of the cell cycle.
While Paul Nurse also conducted a similar experiment with Hartwell, it was only using a different type of yeast.
In mid-1970, Nurse identified the CDC2 gene that played a role in the transition of phase G2 to M. Then Nurse isolated the gene in humans and discovered a CDK that was then called CDK1. He pointed out that CDK1 activation depends on reversible phosphorylation. After that, several different human CDK was found.
CDKs activity is formed through bonding with cyclin. Cyclin was first discovered by Tim Hunt while taking a physiology course at Marine Biological Laboratories in early 1980. He observed the presence of a specific protein that was destroyed in each cell division, but synthesized again in the next cycle.
The protein came to be known as cyclin.
His discovery was confirmed by Joan Ruderman, who found that in embryos that are splitting, there are many cyclins that interact with CDK molecules at different times of the cell cycle.
Cell Cycle Phase
The cell cycle is the stages that a cell must undergo to split or reproduce ase**xually. In general, the stages are as follows:
- Mitosis, subdivided into
- The interphase includes
- G1 Phase
- S Phase
- G2 Phase
This phase is actually outside of the cell cycle. Cells do not undergo division either rest or cells that have undergone maturation. Some cell types, such as nerve cells, go into G0 phase for good. Therefore, mature nerve cells no longer regenerate.
Some cell types can go into G0 phase and if under certain conditions can reenter the cell cycle. Examples are liver cells and intestinal cells. The epithelial cells are continuously in the phase of the cell cycle and do not enter the G0 phase. We know epithelial cells always do dividing to maintain barrier integrity between the internal milieu and the external milieu environment.
G1 Phase G1
G1 Phase is the first part of the interphase. This phase begins as soon as the cell undergoes cell division or mitosis. In this phase, the cells are metabolically active and experiencing growth.
Cell growth in G1 phase includes the formation of various proteins, the formation of various cell organelles, and the addition of cell volume. From this phase, cells can move on to S phase, stop the cell cycle from entering G0 phase, or stop in G1 phase. The regulation that determines this is the G1/S cyclin.
S stands for synthesis and the main feature in this phase is DNA synthesis. The cell genome in this phase will be replicated resulting in a new copy of the cell division process.
In G2 phase, cells again experience cell growth, including the synthesis of various proteins and organelles. In addition, microtubules also began to be composed and in this phase also carried out DNA damage checks. This damage is mainly carried out by the p53 protein.
After interphase (S G1, S, and G2 phase), the cell, then enters the mitosis phase or cell division. This mitosis phase is very short about 10% of the overall cycle phase (interphase covers 90% of the cell cycle time). Although brief, in this phase, the cells undergo a complex and a very regular process.