Cell Cycle Phases, Functions and Applications

The cell cycle is the process by which a cell undergoes growth and cell division.

Every living cell is in certain phases of the cell cycle.

This cell cycle is essential for the growth and multiplication of cells, thereby enabling the survival of the organisms.

Further, a faster cell cycle can speed up old age and decrease lifespan.

On the other hand, an irregular cell cycle can cause cancer.

Below, you will see the cell cycle’s details, its role in physiology effects on the body, and its applications in healthcare.

Cell cycle phases

Cell cycle
Cell cycle diagram showing ‘I’ and ‘M’ phases with regulators.

The cell cycle has two major phases as

  1. I phase
  2. M phase

The ‘I’ Phase is an “intermittent phase.” This is a phase where it grows and gets ready for division. This phase can be divided as

  1. G1 Phase
  2. S Phase
  3. G2 Phase and
  4. g0 phase.

‘M’ phase is the cell division phase and it has four subdivisions as

  • Prophase
  • Metaphase
  • Anaphase and
  • Telophase.

Let us see them in detail.

G1 (Gap Phase One)

  • It is the first phase of the ‘I’ phase.
  • Here the cell grows in size and volume.
  • For this, it takes up the nutrition from the available sources.
  • It is the longest phase of the cell cycle and the duration where is based on the cell type and other factors.
  • This phase leads to the ‘S’ phase, but some cells also go to the resting phase called the g0 phase.

G0 phase (resting phase)

  • This phase is not a distinct phase and not all the cells undergo this phase.
  • But some new cells immediately after formation from mitosis in the ‘M’ phase go for a brief resting phase.
  • Here, they have no activity and are almost inert.

‘S’ phase (DNA synthesis phase).

  • Due to this replication, the cell has 92 chromosomes instead of 46 chromosomes.
  • This set of 92 chromosomes is necessary to form two daughter cells having 46 chromosomes in each.

G2 phase

  • It is also called as second gap phase.
  • Here the cells grow further and get ready for cell division.

M phase is the mitosis phase.

This is the phase where the cell undergoes division to produce two daughter cells.

As mentioned before, it has four phases like

Prophase: Here, the chromatids are formed, mitotic spindle appears with centrioles. The centrioles move to each end of the cell and the nuclear envelope disappears.

Metaphase: The chromatids arrange at the center of the axis and are linked to centromeres.

Anaphase: Here each of the daughter chromatids moves towards one end of the cell.

Telophase. Here the mitotic spindle disappears, chromosomes uncoil and nuclear envelop forms.

M phase mitosis in cell cycle
Mitosis phases of cell division

Please go through our article on mitotic phases for more details.

Cell cycle regulators

The cell cycle has checkpoints that ensure DNA replication and other processes go healthily to form healthy daughter cells.

There are two types of checkpoint proteins: kinases and phosphorylases.

Proteins that regulate the cell cycle

Kinases check the newly formed DNA structure for abnormalities before letting it proceed to the next phase.

If there is any abnormality, stop the cell cycle so that the DNA gets repaired if the DNA cannot get fixed, it is left for autophagy or apoptosis.

The phosphorylases break down the kinases and enhance the
cell cycle.

Applications of cell cycle

In healthcare, the cell cycle is exploited for various targets to avail therapeutic benefits.

1. Antimicrobial action

  • Antibiotics and other antimicrobials act by explicitly targeting certain phases of the cell cycle and thereby inhibiting bacterial growth and multiplication.
  • For example, amino-glycoside antibiotics act in the G1 and G2 phases of the cell cycle and inhibit protein synthesis in bacterial cells.
  • Similarly, fluoroquinolone antibiotics act on the ‘S’ phase of cell division, targeting DNA replication and inhibiting the formation of chromosomes necessary for forming daughter bacterial cells.

2. Anti-cancer treatment

  • Anticancer drugs like 5-Fluorouracil inhibit the DNA synthesis of cancer cells and prevent their multiplication.
  • Similarly, vincristine binds to the tubulin protein and prevents the formation of microtubules. Microtubules are necessary to pull the chromosomes apart.

3. In rDNA technology

In industries, it is used for rDNA technology.

4. In the fermentation processes.

  • The recombinant E-coli cells in fermentation production are allowed to multiply profusely in fermentation.
  • During the G1 phase, they are stimulated to produce Insulin amino acid chains with external chemicals.
When during the cell cycle are chromosomes visible

In the mitotic phase of the cell cycle, the chromosomes are visible.

What is the longest stage of the cell cycle?

The G1 phase is the longest stage of the cell cycle.

Which phase occurs directly after g1

In most cases, it is the ‘S’ phase, but some cells opt for the G0 phase and rest.

Retinoblastoma (‘Rb’) function in cell cycle regulation and apoptosis

Retinoblastoma tumor suppressor protein interferes with the progression of the cell cycle at G1 to S-phase transition and tumor growth. It also regulates cell death by apoptosis with other factors.


  1. The cell cycle: a review
  2. The Role of Cell Cycle Regulators

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