What is the Difference Between G1 and G2 Phase of Cell Cycle

The main difference between G₁ and G₂ phase of the cell cycle is that G₁ phase is the first phase of the cell cycle, and it follows the cell division whereas G₂ phase is the third phase of the cell cycle, and it follows the S phase. Furthermore, G₁ phase is responsible for the determination of the fate of the cell or the entry of the G₀ phase while G₂ phase prepares the cell for division.

G₁ and G₂ phase of the cell cycle are the first and the last phase of interphase. Synthesis of RNA and proteins are major events of both phases. Moreover, the G₂ phase is responsible for the increase in the number of organelles in the cell.

Key Areas Covered

1. What is the G1 Phase of Cell Cycle
     – Definition, Events, Importance
2. What is the G2 Phase of Cell Cycle
     – Definition, Events, Importance
3. What are the Similarities Between G1 and G2 phase of Cell Cycle
     – Outline of Common Features
4. What is the Difference Between G1 and G2 Phase of Cell Cycle
     – Comparison of Key Differences

Key Terms

Cell Cycle, Cell Division, G₀ Phase, G₁ Phase, G₂ Phase, Interphase, S Phase

What is the G1 Phase of Cell Cycle

G₁ phase or Gap 1 phase of the cell cycle is the first phase of the interphase. Generally, interphase is the phase between two subsequent cell divisions. Also, it is responsible for the growth of the cell. During G₁ phase, the cell is more active in terms of metabolism. Also, one of the main important events that occurs during G1 phase is the determination of the fate of the cell. Some cells differentiate into a special type of cell found in tissue after undergoing cell division. Usually, differentiated cells lack the ability to undergo further divisions. Another set of cells may enter into the G₀ phase, which is a temporary resting period in the division. Other cells may remain in the regular cell cycle by continuously undergoing cell division.

Figure 1: Cell Cycle Phases

Furthermore, the G₁ phase is followed by the S phase of the interphase. DNA replication is the major event of the S phase. Therefore, the G₁ phase is responsible for preparing the cell for undergoing DNA replication by synthesizing proteins and accumulating building blocks of DNA. The cell has to accumulate DNA associated proteins as well as sufficient energy to complete DNA replication. Also, the G₁ checkpoint at the end of the G₁ phase ensures the integrity of DNA prior to replication.

What is the G2 Phase of Cell Cycle

G₂ phase or Gap 2 phase of the cell cycle is the final phase of the interphase. It occurs after the S phase of the interphase. Therefore, the nucleus of a cell in the G₂ phase contains replicated DNA; hence, the nucleus is prominent. Also, the G₂ phase is followed by the mitotic phase. Therefore, the G₂ phase is responsible for preparing the cell to cell division. Thus, the number of cell organelles is increased by replicating them. Moreover, the cytoskeleton prepares for the formation of the mitotic spindle.

Figure 2: Eukaryotic Replication Cycle

Moreover, the proteins and RNA synthesized during the G₂ phase are responsible for the preparation of the cell for division. Ultimately, the G₂ checkpoint at the end of the G2 phase checks the proper duplication of DNA before entering the nuclear division phase.

Similarities Between G1 and G2 phase of Cell Cycle

• G₁ and G₂ phase of the cell cycle are the first and the last phase of the interphase.
• The main function of both phases is cell growth and preparation for their function.
• Furthermore, the synthesis of RNA and proteins are two major events of both phases.
• Also, no increase in the number of cells occurs in both phases.
• At the end of each phase, the cell has to pass cell cycle checkpoints to assess the events of each phase.

Difference Between G1 and G2 Phase of Cell Cycle

Definition

G₁ phase of the cell cycle refers to the period in the cell cycle from the end of cell division to the beginning of DNA replication while G₂ phase of the cell cycle refers to the period in the cell cycle from the completion of DNA replication to the beginning of cell division. Thus, this is the main difference between G₁ and G₂ phase of cell cycle.

Consequence

Moreover, G₁ phase is the first phase of the interphase while G₂ phase is the last phase of the interphase.

Follows

Another difference between G₁ and G₂ phase of cell cycle is that the G₁ Phase occurs just after the cell division while the G₂ phase occurs after the S phase.

Followed by

Furthermore, G₁ phase is followed by the S phase of the interphase while G₂ phase is followed by the nuclear division.

Length

Also, one other difference between G₁ and G₂ phase is that G₁ phase is lengthier than G₂ phase.

Function

Functionally, the difference between G₁ and G₂ phase is that while G₁ phase is responsible for the determination of the fate of the cell of the entry of the G₀ phase, G₂ phase is responsible for the preparation of the cell for the next cell division event.

Synthesis of RNA and Proteins

Besides, the RNA and proteins synthesized during the G₁ phase are required for the growth and the metabolism of the cell while the RNA and proteins synthesized in the G₂ phase are required for the preparation of the cell for division.

Nucleus

The nucleus of the G₁ phase does not contain sister chromatids while the nucleus of the G₂ phase contains sister chromatids. Hence, this is also a difference between G₁ and G₂ phase.

Organelle Number

The number of organelles remains the same during the G₁ phase while organelles replicate to increase in number during the G₂ phase.

Spindle Formation

No spindle formation occurs during the G₁ phase while the mitotic spindle begins to form during the G₂ phase. Thus, this is also an important difference between G₁ and G₂ phase.

Cell Cycle Checkpoints

Moreover, G₁ checkpoint at the end of the G₁ phase assesses the integrity of DNA while G₂ checkpoint at the end of the G₂ phase assesses the proper chromosome duplication.

Conclusion

The G₁ phase of the cell cycle is the first phase of the interphase followed by the cell division. It is responsible for cell growth and the RNA and proteins synthesized in this phase are used for the growth and the metabolism of the cell. The main function of the G₁ phase is to determine the fate of the cell. Moreover, G₁ phase is followed by the S phase, which undergoes DNA replication. On the other hand, G₂ phase is the final phase of the interphase, which occurs after the S phase, leading to another cell division phase. Therefore, the main function of the G₂ phase is to prepare the cell for division by synthesizing RNA and proteins. Also, organelles replicate to increase the number during the G₂ phase. Therefore, the main difference between G₁ and G₂ phase is their role in the cell cycle.

References:

1. “The Cell Cycle|Biology I.” Lumen, Available Here.

Image Courtesy:

1. “Cell Cycle 3-3” By Cell_Cycle_3.png (CC BY-SA 3.0) via Commons Wikimedia   
2. “Eukaryotic replication cycle” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia