What is the Longest Phase of the Cell Cycle

The longest phase of the cell cycle is the G1 phase. It is the first phase of the interphase. During the G1 phase, the cell prepares for division. Cells are highly metabolically active during the G1 phase. The building blocks required for DNA replication are accumulated during this phase. The associated proteins in DNA replication, as well as the energy for DNA replication, are also produced during this phase. The G1 phase is followed by the S phase of the interphase. DNA is replicated during the S phase with the use of acquired building blocks, proteins, and energy.

Key areas Covered

1. What is Cell Cycle
     – Definition, Stages, Function
2. What is the Longest Phase of the Cell Cycle
     – Role of G1 Phase

Key Terms: Cell Cycle, G1 Phase, Interphase, Protein Synthesis, S phase 

What is the Longest Phase of the Cell Cycle - Infographic

What is Cell Cycle

The cell cycle is the series of events that takes place within the cell, leading to the division of a parent cell into two identical daughter cells. The two daughter cells consist of the same amount of genetic material, organelles, and other molecules as the parent cell. The three stages of the cell cycle are interphase, mitotic phase, and cytokinesis.

  1. Interphase – Interphase is the first stage of cell cycle, which prepares the cell for the upcoming nuclear division. The three phases of interphase are the G1 phase, S phase, and G2
  2. Mitotic phase – Mitotic phase is the second stage of cell division. The replicated genetic material is divided into two daughter nuclei through mitosis. The four stages of mitosis are prophase, metaphase, anaphase, and telophase.
  3. Cytokinesis – The cytoplasm of the parent cell divides into to by cytokinesis.

The stages of Cell cycle are shown in figure 1.

What is the Longest Phase of the Cell Cycle

Figure 1: Cell Cycle

The increase of the number of cells by the cell cycle allows the growth of tissues in the body. It is also important during the embryonic development.

What is the Longest Phase of the Cell Cycle

The longest phase of cell cycle is the G1 phase, which occurs during the interphase. G1 phase is followed by the S phase in which DNA is replicated. Therefore, before entering the S phase, the cell must fulfill several requirements for DNA replication such as associated proteins, and energy. The cell fulfills these requirements during the G1 phase. The metabolism is high during the G1 phase when compared to the other phases of the cell cycle. Protein synthesis occurs at higher rates during this phase. Somatic cells in the body are specialized to perform a specific function in the body. In specialized cells, the regular metabolism occurs during the G1 phase. Hence, the cells spend most of the cell cycle in G1 phase.

Regulation of G1 Phase

The G1 phase is regulated by two components: biochemical regulators and cell cycle checkpoints. Biochemical regulators involved in the regulation of G1 phase are the G1/S cyclins. The cyclin activity significantly rises at the end of the G1 phase. It promotes the transition from G1 phase to the S phase. The G1 checkpoint found at the G1/S transition ensures the fulfillment of the requirements of DNA replication during the G1 phase.

Transition into G0 Phase

G1 phase also consists of a restriction point by which the cells that do not fulfill the above requirements are transformed into a dormant phase called G0 phase. The cells in the G0 phase can enter the cell cycle after fulfilling the requirements of the G1 phase.


The longest phase is the G1 phase, which is the first phase of interphase. During G1 phase, cell fulfills the requirements for DNA replication, which occurs in the next phase of the cell cycle.


1. “The Cell Cycle.” Lumen, Available here.

Image Courtesy:

1.”Cell Cycle 2-2″ By Cell_Cycle_2.svg: *Cell_Cycle_2.png: Original uploader was Zephyris at en.wikipediaderivative work: Beaoderivative work: Histidine (talk) – Cell_Cycle_2.svg (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology and Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things. She has a keen interest in writing articles regarding science.

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