Cell Cycle Overview

Key Questions

  • The cell cycle is the replication and reproduction of cells, whether in eukaryotes or prokaryotes.

    It is important to organisms in different ways, but overall it allows them to survive.

    For prokaryotes, the cell cycle, called Binary Fission, allows for them to live on by dividing into two new daughter cells.

    For eukaryotes, consider an animal such as a cat, if a cat were to have a severe injury, it would need the cell cycle to replicate cells to replace those that were damaged in the injury and hence needs the cell cycle to heal itself.

    Zygotes also depend on the cell cycle to form its many cells in order to produce a baby organism at the end of its process.

    Plants require the cell cycle to grow and provide life for every other organism on earth. and therefore the cell cycle is highly important to organisms as if it were not present or if it were to stop suddenly, life would completely end.

  • Answer:

    Cell cycle is a series of events operating towards cell division.


    The cell cycle is divided into following phases:
    1. #G_1# phase (Cell prepares for DNA replication)
    2. #S# phase (Replication of DNA is achieved)
    3. #G_2# phase (Cell prepares for division)
    4. #M# phase (Cell actually divides and makes daughter cells)

    Figure 1 A summary figure to describe the cell cycle

    Each of the phases is described below in details:

    #G_1# phase
    It is the first step of the cells to start preparing for division. It is also called growth phase as cells start preparation for division. In this phase, the cell starts accumulating all the proteins required for its division and grows in size. The duration of this phase in the cell cycle is variable.

    #G_1# phase also acts as the crossroads for the cells where it chooses any one of the following:
    1. whether it wants to proceed to cell cycle S phase
    2. enters a resting phase #G_0#
    3. Stops replication and enters into differentiation to carry a specific role.

    Once the decision is made to proceeds in the cell cycle, cell makes a transition to #S# phase. If the cell decides to exit the cell cycle and enters in a resting phase the cells enters into #G_0# phase. In #G_0# phase, cell has the capability to enter into cell cycle later as when it is required.

    #S# phase
    It is the second phase in the cell cycle where whole genome of the cell is replicated into two copies. There are proteins which do DNA replication for the cell. IT is a relatively longer phase of the cell cycle as whole genome present in the cell is replicated.
    A point to remember here is that cell makes sure that the whole genome is replicated once and only for one time.

    During this phase itself the c ell scans the gemone for any abbreations or damages and corrects it , if possible, by staying in #S# phase. Once the DNA replication is complete, the cell enters into #G_2# phase.

    #G_2# phase
    In this second Growth phase the cell prepares itself to undergo mitosis in #M# phase. The cell starts to rearrange its microtubules, which play crucial role in #M# phase. After the preparation for entering into #M# phase is complete the cell enters into next phase of the cell cycle.

    #M# phase
    It is a very brief part of the cell cycle and in which the cell divides and makes two daughter cells. It is the phase where nuclear division happens (Karyokinesis). It has very strict regulation and very crisp phases.

    Mitosis cycle is divided into following phases
    1. All of the DNA condenses into Chromosomes and this pahse is called Prophase. Here cells nuclear membrane starts to disintergate.
    2. During Metaphase using microtubules the cell aligns all its chromosomes in a common plane called metaphase plate.
    3. As cell proceeds in Anaphase, cells separate sister chromatids present in the chromosomes and moves towards two opposite poles.
    4. At Telophase, nuclear membrane starts to reappear and ingulf the nuclear material.
    5. Finally during Cytokinesis, cell divides and forms daughter cells.