The life and birth of a cell are commonly known as the cell cycle. It is observed to have a growth period and a reproducing period, and the former takes up most of the time. In the growth period, known as the interphase, there are three phases, namely G1, S, and G2. G2 is the last or second growth period after which mitosis or cell division happens. The cells can only enter S and the subsequent G2 phase if not pushed into the G0 phase. It is also the second of the gap phases between the S and M phases. When a cell grows in size, it is split into two. The growth of a eukaryote only means a larger number of cells than before. The natural growth of cells is essential to maintaining a healthy body, and when its growth is hindered, several diseases like cancer can take root. The mitosis for which G2 prepares the cell is also divided into five stages for completing the task of nuclei formation and cytokinesis or cell division.
The G2 Phase
The G2 phase of the cell cycle follows the synthesis where genes are multiplied and DNA is found as chromatins to form separate chromosomes again in the M phase. It is part of the preparation process that a cell undergoes before splitting into two and is the intermediate phase between the S phase where genetic materials multiply and the M phase where daughter nuclei are born.
G2/M CheckpointThere happen to be various proteins accumulated at the broken points of the DNA strands. When these are visible, the cell is not permitted to replicate. Another concern evaluated in the G2/M checkpoint is whether all DNA strands are doubled. This phase also checks if there are enough organelles in the right order. A cell’s growth can falter under stress. Using this notion, UV light is used to abort the functions of the cancer cells.
Functions of the G2 Phase
Spindle proteins that help arrange chromosomes in the right order are synthesised during the G2 phase of the cell cycle. Three different types of RNA formation are also carried out in this phase–mRNA, rRNA, and tRNA. The damaged DNA is repaired before entering the M phase to ensure no faulty genetic material is passed on. Further, the synthesis and storing of energy in ATP molecules happens in the G2 phase as in the G1 phase.
Duplication of various organelles is observed in this phase. Mitochondria, lysosomes, and plastids are some examples. Along with proteins, lipids are also synthesised in the G2 phase to provide enough for the membranes of the two daughter cells.
Before the G2 Phase
Before the G2 phase comes the synthesis or the S phase. One of two major steps for the cell cycle is performed here. The genetic material imbued in the DNA is replicated. The cyclins and cyclin-dependent-kinases (CDKs) are responsible for the transition from the S to G2 phase.
After the G2 Phase
After the G2 phase, mitosis-promoting factor or MPF is secreted, enabling the M phase to start. In the M phase, it starts to neutralise. The nucleus divides to form daughter nuclei. Around it, the cytokinesis supplies the protoplasm for the two daughter cells. The mitosis is divided into five sub-phases, namely prophase, prometaphase, metaphase, anaphase, and telophase. For the G2 phase and the beginning of the M phase before sister chromatids separate, 4N DNAs are found in the cells.
Differences Between the G1 and G2 phases
Both gap phases are also called growth phases. They prepare the cell for its ultimate work of duplication. However, this task is divided between the G1 and G2 phases. There are significant differences between the two. Let’s check them out:
|
Point of Difference |
G1 Phase |
G2 Phase |
|
Definition |
During a cell cycle the period from the end of the cell division to the beginning of DNA replication is known as G1 Phase. |
During a cell cycle the period just from the DNA replication completion to that of the beginning of cell division is known as G2 phase |
|
Sister Chromatids |
Sister chromatids are absent in the G1 phase. |
Sister chromatids are present in the G2 phase. |
|
Phase |
In interphase, the G1 phase is the first phase |
In case of G2, it is the last phase of interphase |
|
Requirement |
The G1 phase comprises growth as well as metabolism, which requires proteins as well as RNA. |
In the G2 phase, cell division preparation requires proteins as well as RNA. |
|
Number of Organelles |
The number of organelles remains the same in this phase |
The number of organelles increases in this phase |
|
Spindle Formation |
Spindle formation does not take place in this phase |
Spindle formation occurs in G2 phase |
Conclusion
The G2 phase is the second gap phase in the growing and preparatory period of a cell’s life. It helps and checks cell activities before cell division in the mitosis phase can begin. The growth period of the cell cycle or interphase is spread over three phases, G1, S, and G2. G2 is the last or second growth period after which mitosis or cell division happens. After that, the cell enters the M phase, where it engenders two cells by dividing itself. The new cells repeat the same behaviour provided they pass all intrinsic barriers set by the cell to ensure only the fittest are allowed to multiply.