Cell Cycle | Introduction , Phases & Checkpoints

Cell Cycle

Introduction to Cell Cycle: The cell cycle is the process by which a cell replicates its genetic material and synthesized the other elements of the cell and at the end divided into two daughter cells is known as Cell cycle

Cell Cycle

Cell Cycle Definition:

For the purpose of dividing eukaryote, the cells have to pass through a series of stages, which collectively known as the cell cycle. The cell cycle consists of Interphase:� G1 (Gap 1), S (for synthesis), G2 (Gap 2), in these phases genetic material replicates; and an M phase; in this phased process of mitosis occurs to partitioning the genetic material and divides the cells.

A German researcher in 1855 Rudolf Virchow made an essential observation about living creatures that all cells originate from another cell or in the Latin form known as Omnis cellula e cellula,�.

Cell Cycle Diagram

Cell Cycle

Cell Cycle Introduction Activity

Cells duplicate by dividing themselves into two daughter cells. After division, every parent cell is divide by producing two daughter cells. Furthermore, these newly formed daughter cells can grow itself by giving two other cells at that time this cell act as parent cell and give rise to the two daughter cells. By this new population of the cells formed by the division of a single cell by progeny from it. In other words, by these cycles of cells growth as well as the division of a single cell is done into millions of cells. Growth and reproduction are basically the main characteristics of cells and essential need of all living organisms.

Cell Cycle

Cell Division:

Cell division is a very noteworthy process in all living organisms. During the division of each cell, DNA of the cell replicate and after this growth of the cell takes place. In the cell, all these processes must be performed in a well-harmonized way by ensuring correct division and formation of the progeny of the cells containing unchanged genomes.

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Phases of the Cell Cycle

The Cell Cycle is divided into two main phases.

  1. Interphase
  2. Mitotic Phase

Cell Cycle Diagram

Cell Cycle Diagram

After the cell division, the growth of the cell is a continuous process. In this �DNA synthesis occurred only during one precise stage in the cell cycle. The replicated genetic material the chromosomes (DNA) are then disseminated to daughter nuclei by a multifaceted series of procedure in the cell division. All these events are furthermore controlled by genetic material. �The chromosome is basically a thread-like structure composed of nucleic acids and protein that are present in the nucleus of all living cells. Chromosomes are the materials which carried genetic information in the form of genes.

Stages of the Cell Cycle

Cell Cycle comprised of two stages whose description is described below:

Interphase Stages:

Stages of Interphase: Interphase has three different stages to prepare for cell division. These stages are Gap 1, Synthesis, and Gap 2. These distinct stages perform different functions. Cell Cycle Interphase is described below:

Gap 1:

Gap 1 or G1 is the first stage or sub-phase of interphase. In Gap 1, the chromosomes in the nucleus have not replicated or reproduce, and the cell grows up. The cell becomes increases in size because it has to divide. If the cell not grows increase, after division its size ultimately becomes too small. After the division, again and again, it became smaller and smaller until there was nothing will left. Gap 1 can be different in the time to perform its function because it depends on the type of cell.

In the G1 Phase of Cell Cycle, different cells take a different length of time to grow up and for replicated. Healthy cells which have the ability to perform their work properly stay in this stage for weeks or years. If they stay in this sub-phase for a long period of time, they enter in �Gap 0 or G 0� phase, which is suspended the animation. Some special internal and external signals needed to get out from G 0. There is a transition sub-phase between G1 and S, known as restriction point. Synthesis:


Synthesis or, S stage is the second stage of interphase. The cells enter this sub-phase when the genetic material of cells is duplicated. Each chromosome replicated, and a pair of sister chromosomes produce. A chromosome is a strand of DNA covered around protein. Chromosome divides when DNA strand unwrap and separated from each other.

In S Phase of Cell Cycle, these strands serve as templates new strand of DNA that is formed. In the nucleus, free-floating nucleotides attach themselves with nitrogen bases of the template strand. Newborn chromosome becomes half of the new strand and half of the original parent strand. If the cell is a somatic cell, it enters in mitosis after interphase, and sister chromatids will be separated and create two similar copies of the genome. It will entre in meiosis if cell rose the gamete. In meiosis, chromosomes separately divide, and sister chromatid creates a cell with half of the full genome. After synthesis, the cell must prepare for cell division.

Gap 2:

G2 Phase of Cell Cycle: When DNA replicated during synthetic sub-phase, the cell enters into Gap2 or G2 sub-phase. In Gap2, cell given rise to the cytoplasm, and ready to replicate many important organs. In plants, both chloroplasts and mitochondria must be replicated or have the same copies to provide the ability to produce energy to the daughter cells. In animals, the mitochondria are replicated to provide the ability to produce enough energy to daughter cells. Gap2 perform function until cell enters into cell division stage �M�. In mitosis, the cell divides and the phase starts again. And if the cell divides in the meiosis, before entering into interphase and repeat the phase, gamete fertilizes with DNA.

Cell Cycle

M Phase ( Mitotic Phase )

M phase is the mitotic phase in which multi-steps perform to duplicated chromosomes, separate and move into new similar daughter cells. There are two parts of being� phase first part is called karyokinesis, or nuclear division, and the second part is known as cytokinesis, in which physical separation of cytoplasm occurs into two daughter cells. Cell Cycle Mitosis is described below :

Mitosis is divided into five phases: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.

Half of the mitosis occupied over prophase. This is the longest phase of mitosis. In this phase, the nuclear membrane breaks down. Centrosome duplicates itself in order to form two daughter cells. The centrosomes organize the microtubules production to form spindle fibers. Each chromosome replicated and consists of sister chromatids held together by a centromere.

In this phase, replicated chromosomes migrate to the equatorial plane in the midline of the cell. The mitosis spindle region is called the metaphase plate. The structure associated with centromere bind with spindle fibers, known as kinetochore. The individuals of spindle fibers bind to kinetochore structure on each side of the centromere, so chromosomes condense continue.

The chromosomes arrange themselves in a straight line along with the metaphase plate of the spindle fiber apparatus.

Anaphase is the shortest phase of mitosis. The sister chromatids of chromosomes re pulled apart, and move to the opposite ends of the cell. The separated sister chromatids are now daughter chromosomes.

Telophase is the final phase of mitosis. It reverses many processes observe by prophase. The nuclear membranes do some changes to improve the chromosomes grouped. The chromosomes uncoil and became diffuse in this stage. And the spindle fibers disappear.


Cytokinesis is the final division of cells to produce new cells. In plants, the metaphase plate forms a cell plate. In animals, cytoplasm has a constriction. Then the cell enters in interphase, which is the interval between mitosis division.

Cell Cycle Checkpoints:

Cell Cycle Regulation: The cell cycle is a complicated process. There are some checkpoints in the cycle, to check that everything goes right. The cell cycle has variable time length, even also for cells of a single organism. �The timing of events of the cell cycle of different organisms is controlled by both internal and external mechanism of the cell.

The cell cycle consists of three main checkpoints.

  • Phase G1 (for DNA integrity and cell size)
  • Phase G2 (for DNA damage and chromosomes duplication)
  • Phase M (for attachment of a spindle fiber and kinetochore)

The functions of checkpoints are to detect DNA damage and send the signal to delay cell cycle in advance till damaged chromosomes repaired.