Cell Cycle Resting Phase | Interphase | G1, G0, S and G2 phases

Cell Cycle Resting Phase

The cell cycle resting phase is also known as the interphase. As the name indicates it is a phase or period of the cell cycle between two consecutive cell divisions when the chromosome is not visible in the cell. “Resting” word for interphase is used to indicate that the cell is not dividing. However, this phase is associated with active metabolic activities preparing the cell for mitosis.

The resting phase or interphase is further divided into:

1. G1 phase
2. G0 phase
3. S phase
4. G2 phase

Cell Cycle Resting Phase or Interphase

1. G1 phase

G1 phase is also known as Gap 1 or growth 1 phase. In this phase, extensive metabolic activities take place such as:

1. Specific enzymes are produced
2. DNA base units i.e., adenine, cytosine, guanine, and thymine are accumulated.
3. Cell organelles are replicated.
4. Other raw materials are prepared that will be required in the coming steps.
5. The cell grows in size to accommodate all the synthesized products.

The length of the G1 phase is the longest of all other interphases. Cells decide in the G1 phase whether to pass the restriction point and enter the S phase or move on to G0. These choices are based on the integrity of the signaling apparatus that detects extracellular signals and the extracellular signals that the cell receives. 

If the cell decides to divide then the G1 phase will move into the S phase and if the cell will not divide then the G1 phase will move into the G0 phase. Any mistake in the regulation of G1 progress leads to the occurrence of cancer.

2. G0 phase

G0 (zero) phase is the resting phase or a checkpoint phase. In this phase, the cell performs its basic and regulatory functions. No metabolic activities related to the preparation of cells for division or cell division will take place in this phase. The cell will remain in this phase until it receives a signal to enter the S phase.

3. S phase

S phase is the synthesis phase. In this phase, the machinery required for cell division is prepared by using the raw material prepared during the G1 phase. The main processes taking place during this phase include:

1. DNA is replicated using base units i.e., adenine, cytosine, guanine, and thymine.
2. Histone proteins are synthesized.
3. Nucleosomes are prepared by joining histones and DNA.
4. Chromosome number is doubled

Since precise genome duplication is essential for effective cell division, the S-phase mechanisms are strictly regulated and highly conserved.

4. G2 phase

The G2 phase is called Gap 2 or the growth 2 phase. It is the pre-mitotic phase preparing the cell to enter the cell division phase (mitosis). This phase is associated with protein synthesis and cell growth. The length of G2 is the smallest compared to G1 and S phases. The main process that takes place during the G2 phase include:

1. Storage of energy for the movement of chromosomes during mitosis
2. Mitotic-specific proteins are synthesized
3. Microtubule and RNA subunits are prepared.

After the G2 phase, cells enter the cell division phase called mitosis. During mitosis, cells utilize the machinery prepared during interphase to divide the nucleus through karyokinesis and then divided the cytoplasm into two cells by cytokinesis.

Cell Cycle Resting Phase: Differenet phases of interphase and their functions

How long does interphase last in minutes?

The length of each phase of the interphase is different and depends on the functions performed by them. For example, in the case of a mammalian cell, the average cell cycle is of approximately 24 hours, out of which G1 takes 10 hours, the S phase takes 5-6 hours, the G2 phase takes only 3-4 hours, and M phase takes 2 hours only.

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Some Questions and Answers

1. What is the resting phase of the cell cycle?

A. Resting phase of the cell cycle is a period of the cell cycle between two consecutive cell divisions when the chromosome is not visible in the cell. It is also known as interphase.

2. How much of the cell cycle is spent in interphase?

A. Length of each phase of interphase is different and depends on the functions performed by them. In the case of a mammalian cell, the average cell cycle is of approximately 24 hours, out of which G1 takes 10 hours, the S phase takes 5-6 hours, and the G2 phase takes only 3-4 hours.

3. is interphase a resting stage of mitosis?

A. Yes, it is a period of the cell cycle between two consecutive cell divisions. It prepares the cell for division.

4. What is the longest and shortest phase of the interphase?

A. The G1 phase is the longest while the G2 phase is the shortest phase of the interphase.

5. What are the 4 stages of interphase?

A. The four stages of interphase are the G1 (Gap 1 or growth 1) phase, G0 (Gap zero) phase, S (synthesis) phase, and G2 (Gap 2 or growth 2) phase.

6. Why interphase is called the resting phase?

A. “Resting” word for interphase is used to indicate that cell is not dividing. However, this phase is associated with active metabolic activities preparing the cell for mitosis.